Skin exposure to isocyanates: reasons for concern

"Isocyanates and isocyanides - life-threatening toxins or essential compounds?"

Isocyanides and isocyanates are some of the most reactive compounds in organic chemistry, making them perceived as compounds with high potential for use in both the laboratory and industry. With their high reactivity also comes several disadvantages, most notably their potentially high toxicity. The following article is a collection of information on the toxic effects of the isocyanide group on the human body and the environment. Information on the mechanism of how these harmful substances affect living tissues and the environment, worldwide information on how to protect against these chemicals, current regulations, and exposure limits for specific countries is compiled. The latest research on the application uses of isocyanates and isocyanides is also outlined, as well as the latest safer and greener methods and techniques to work with these compounds. Additionally, the presented article can serve as a brief guide to the organic toxicity of a group of isocyanates and isocyanates.

Polymer chain extenders induce significant toxicity through DAF-16 and SKN-1 pathways in Caenorhabditis elegans: A comparative analysis

Polymer chain extenders, commonly used in plastic production, have garnered increasing attention due to their potential environmental impacts. However, a comprehensive understanding of their ecological risks remains largely unknown. In this study, we employed the model organism Caenorhabditis elegans to investigate toxicological profiles of ten commonly-used chain extenders. Exposure to environmentally relevant concentrations of these chain extenders (ranging from 0.1 µg L-1 to 10 mg L-1) caused significant variations in toxicity. Lethality assays demonstrated the LC50 values ranged from 92.42 µg L-1 to 1553.65 mg L-1, indicating marked differences in acute toxicity. Sublethal exposures could inhibit nematodes' growth, shorten lifespan, and induce locomotor deficits, neuronal damage, and reproductive toxicity. Molecular analyses further elucidated the involvement of the DAF-16 and SKN-1 signaling pathways, as evidenced by upregulated expression of genes including ctl-1,2,3, sod-3, gcs-1, and gst-4. It implicates these pathways in mediating oxidative stress and toxicities induced by chain extenders. Particularly, hexamethylene diisocyanate and diallyl maleate exhibited markedly high toxicity among the chain extenders, as revealed through a comparative analysis of multiple endpoints. These findings demonstrate the potential ecotoxicological risks of polymer chain extenders, and suggest the need for more rigorous environmental safety assessments.

Fragrances as a trigger of immune responses in different environments

Fragrances can cause allergic skin reactions, expressed as allergic contact dermatitis and reactions in the respiratory tract that range from acute temporary upper airway irritation to obstructive lung disease. These adverse health effects may result from the stimulation of a specific (adaptive) immune response. Th1 cells, which essentially produce interleukin-2 (IL-2) and interferon-γ (IFN-γ), play a key role in allergic contact dermatitis and also on allergic sensitization to common allergens (e.g., nickel and fragrance). It has been shown that fragrance allergy leads to Th2/Th22 production of IL-4, IL-5 and IL-13, controlling the development of IgE and mediating hypersensitivity reactions in the lung, such as asthma. Cytokines released during immune response modulate the expression of cytochrome P450 (CYPs) proteins, which can result in alterations of the pharmacological effects of substances in inflammatory diseases. The mechanisms linking environment and immunity are still not completely understood but it is known that aryl hydrocarbon receptor (AhR) is a sensor with conserved ligand-activated transcription factor, highly expressed in cells that controls complex transcriptional programs which are ligand and cell type specific, with CYPs as targeted genes. This review focuses on these important aspects of immune responses of the skin and respiratory tract cells, describing some in vitro models applied to evaluate the mechanisms involved in fragrance-induced allergy.

Recycled Waste as Polyurethane Additives or Fillers: Mini-Review

The intensive development of the polyurethanes industry and limited resources (also due to the current geopolitical situation) of the raw materials used so far force the search for new solutions to maintain high economic development. Implementing the principles of a circular economy is an approach aimed at reducing the consumption of natural resources in PU production. This is understood as a method of recovery, including recycling, in which waste is processed into PU, and then re-used and placed on the market in the form of finished sustainable products. The effective use of waste is one of the attributes of the modern economy. Around the world, new ways to process or use recycled materials for polyurethane production are investigated. That is why innovative research is so important, in which development may change the existing thinking about the form of waste recovery. The paper presents the possibilities of recycling waste (such as biochar, bagasse, waste lignin, residual algal cellulose, residual pineapple cellulose, walnut shells, silanized walnut shells, basalt waste, eggshells, chicken feathers, turkey feathers, fiber, fly ash, wood flour, buffing dust, thermoplastic elastomers, thermoplastic polyurethane, ground corncake, Tetra Pak®, coffee grounds, pine seed shells, yerba mate, the bark of Western Red Cedar, coconut husk ash, cuttlebone, glass fibers and mussel shell) as additives or fillers in the formulation of polyurethanes, which can partially or completely replace petrochemical raw materials. Numerous examples of waste applications of one-component polyurethanes have been given. A new unexplored niche for the research on waste recycling for the production of two components has been identified.

Identification of true chemical respiratory allergens: Current status, limitations and recommendations

Asthma in the workplace is an important occupational health issue. It comprises various subtypes: occupational asthma (OA; both allergic asthma and irritant-induced asthma) and work-exacerbated asthma (WEA). Current regulatory paradigms for the management of OA are not fit for purpose. There is therefore an important unmet need, for the purposes of both effective human health protection and appropriate and proportionate regulation, that sub-types of work-related asthma can be accurately identified and classified, and that chemical respiratory allergens that drive allergic asthma can be differentiated according to potency. In this article presently available strategies for the diagnosis and characterisation of asthma in the workplace are described and critically evaluated. These include human health studies, clinical investigations and experimental approaches (structure-activity relationships, assessments of chemical reactivity, experimental animal studies and in vitro methods). Each of these approaches has limitations with respect to providing a clear discrimination between OA and WEA, and between allergen-induced and irritant-induced asthma. Against this background the needs for improved characterisation of work-related asthma, in the context of more appropriate regulation is discussed.

Cascade Exotherms for Rapidly Producing Hybrid Nonisocyanate Polyurethane Foams from Room Temperature Formulations

For decades, self-blown polyurethane foams─found in an impressive range of materials─are produced by the toxic isocyanate chemistry and are difficult to recycle. Producing them in existing production plants by a rapid isocyanate-free self-blowing process from room temperature (RT) formulations is a long-lasting challenge. The recent water-induced self-blowing of nonisocyanate polyurethane (NIPU) formulations composed of a CO2-based tricyclic carbonate, diamine, water, and a catalyst successfully addressed the isocyanate issue, however failed to provide foams at RT. Herein, we elaborate a practical solution to empower the NIPU foam formation in record timeframes from RT formulations. We generate cascade exotherms by the addition of a highly reactive triamine and an epoxide to the formulation of the water-induced self-foaming process. These exotherms, combined to a fast cross-linking imparted by the triamine and epoxide, rapidly raise the temperature to the foaming threshold and deliver hybrid NIPU foams in 5 min with KOH as a catalyst. Careful selection of the monomers enables producing foams with a wide range of properties, as well as with an unprecedented high biobased content up to 90 wt %. Moreover, foams can be upcycled into polymer films by hot pressing, offering them a facile reuse scenario. This robust cheap process opens huge perspectives for greener foams of high biobased contents, expectedly responding to the sustainability demands of the foam sector. It is potentially compatible to the retrofitting of industrial foaming infrastructures, which is of paramount importance to accommodate existing foam production plants and address the huge foam market demands.

Club Cells-A Guardian against Occupational Hazards

Club cells have a distinct role in the epithelial repair and defense mechanisms of the lung. After exposure to environmental pollutants, during chronic exposure, the secretion of club cells secretory protein (CCSP) decreases. Exposure to occupational hazards certainly has a role in a large number of interstitial lung diseases. According to the American Thoracic Society and the European Respiratory Society, around 40% of the all interstitial lung disease is attributed to occupational hazards. Some of them are very well characterized (pneumoconiosis, hypersensitivity pneumonitis), whereas others are consequences of acute exposure (e.g., paraquat) or persistent exposure (e.g., isocyanate). The category of vapors, gases, dusts, and fumes (VGDF) has been proven to produce subclinical modifications. The inflammation and altered repair process resulting from the exposure to occupational respiratory hazards create vicious loops of cooperation between epithelial cells, mesenchymal cells, innate defense mechanisms, and immune cells. The secretions of club cells modulate the communication between macrophages, epithelial cells, and fibroblasts mitigating the inflammation and/or reducing the fibrotic process. In this review, we describe the mechanisms by which club cells contribute to the development of interstitial lung diseases and the potential role for club cells as biomarkers for occupational-related fibrosis.

Reduced Isocyanate Release Using a Waterproof, Resin-Based Cast Alternative Relative to Fiberglass Casts

The effects of occupational isocyanate exposure range from asthma and contact dermatitis to neurotoxicity and cancer. Respiratory sensitization due to orthopedic cast application has been well documented. This study aims to compare the safety of standard-of-care fiberglass casts and a novel waterproof cast alternative by measuring the amount of isocyanate released during off-gassing over time. A 3D-printed arm simulator with comparable casing material amounts was placed in a sealed chamber. An isocyanate-sensing color-changing (SafeAir) tag was used to measure the levels of toxic exposure. Triplicate trials were conducted across all time periods (15 min, 1 h, and 24 h) and conditions. The bare arm simulator and freshly opened tags served as negative controls. Normalized pixel intensity indexes and isocyanate release estimates in ppb were derived from ImageJ-analyzed SafeAir tag photos. Fiberglass casts exhibited greater isocyanate release than both the waterproof alternative (p = 0.0002) and no-cast controls (p = 0.0006), particularly at 24 h. The waterproof alternative and no-cast control did not statistically differ (p = 0.1603). Therefore, the waterproof alternative released less isocyanate than the fiberglass casts. Waterproof cast alternatives may be safer than fiberglass by limiting medical professionals' exposure to toxic isocyanates and, thus, decreasing their risk of suffering occupational asthma.

Reconstruction of exposure to methylene diphenyl-4,4'-diisocyanate (MDI) aerosol using computational fluid dynamics, physiologically based toxicokinetics and statistical modeling

OBJECTIVES

This study employed computational fluid dynamics (CFD), physiologically based toxicokinetics (PBTK), and statistical modeling to reconstruct exposure to methylene diphenyl-4,4'-diisocyanate (MDI) aerosol. By utilizing a validated CFD model, human respiratory deposition of MDI aerosol in different workload conditions was investigated, while a PBTK model was calibrated using experimental rat data. Biomonitoring data and Markov Chain Monte Carlo (MCMC) simulation were utilized for exposure assessment.

RESULTS

Deposition fraction of MDI in the respiratory tract at the light, moderate, and heavy activity were 0.038, 0.079, and 0.153, respectively. Converged MCMC results as the posterior means and prior values were obtained for several PBTK model parameters. In our study, we calibrated a rat model to investigate the transport, absorption, and elimination of 4,4'-MDI via inhalation exposure. The calibration process successfully captured experimental data in the lungs, liver, blood, and kidneys, allowing for a reasonable representation of MDI distribution within the rat model. Our calibrated model also represents MDI dynamics in the bloodstream, facilitating the assessment of bioavailability. For human exposure, we validated the model for recent and long-term MDI exposure using data from relevant studies.

CONCLUSION

Our computational models provide reasonable insights into MDI exposure, contributing to informed risk assessment and the development of effective exposure reduction strategies.

Dynamic PEG-PLA/Hydroxyurethane Networks Based on Imine Bonds as Reprocessable Elastomeric Biomaterials

The development of dynamic covalent chemistry opens the way to the design of materials able to be reprocessed by an internal exchange reaction under thermal stimulus. Imine exchange differs from other exchange reactions by its relatively low temperature of activation. In this study, amine-functionalized star-shaped PEG-PLA and an aldehyde-functionalized hydroxyurethane modifier were combined to produce PEG-PLA/hydroxyurethane networks incorporating imine bonds. The thermal and mechanical properties of these new materials were evaluated as a function of the initial ratio of amine/aldehyde used during synthesis. Rheological analyses highlighted the dynamic behavior of these vitrimers at moderate temperature (60-85 °C) and provided the flow activation energies. Additionally, the reprocessability of these PEG-PLA/hydroxyurethane vitrimers was assessed by comparing the material properties before reshaping and after three reprocessing cycles (1 ton, 1 h, 70 °C). Hence, these materials can easily be designed to satisfy a specific medical application without properties loss. This work opens the way to the development of a new generation of dynamic materials combining degradable PEG-PLA copolymers and hydroxyurethane modifiers, which could find applications in the shape of medical devices on-demand under mild conditions.

Importance of and Approach to Taking a History of Exposures to Occupational Respiratory Hazards

Occupational respiratory diseases are caused by exposure to respiratory hazards at work. It is important to document those exposures and whether they are causing or exacerbating disease because these determinations can have important impacts on diagnosis, treatment, job restrictions, and eligibility for benefits. Without investigation, it is easy to miss clinically relevant exposures, especially in those with chronic diseases that can have work and nonwork causes. The first and most important step in identifying exposures to respiratory hazards at work is to take an appropriate history. For efficiency, this is a two-step process. An initial quick screening history is done by asking only a few questions. Follow-up questions are asked if there are positive responses to the screening questions or if an occupational etiology is suspected based on the clinical presentation. Electronic health records have promise for facilitating this process. Follow-up to the screening history may include additional questions, evaluating additional sources of information about workplace exposures, and medical testing. Radiographic findings or tests conducted on noninvasive samples or lung tissue can be used as biomarkers. Online resources can be used to learn more about exposures associated with occupations and industries and to see if investigations evaluating exposures were performed in the patient's own workplace. It is important to adhere to the patient's wishes about contacting the employer. With patient consent, the employer can be an important source of information about exposures and, if a problem exists, has an important role in taking corrective action. Consultation for challenging cases is available from a variety of professional and governmental entities. If a clinician identifies a significant public health issue, such as an occupational disease outbreak, it is important to notify relevant public health authorities so that steps can be taken to prevent additional exposures and appropriately care for those already exposed.

A physiologically-based kinetic (PBK) model for work-related diisocyanate exposure: Relevance for the design and reporting of biomonitoring studies

Diisocyanates are highly reactive substances and known causes of occupational asthma. Exposure occurs mainly in the occupational setting and can be assessed through biomonitoring which accounts for inhalation and dermal exposure and potential effects of protective equipment. However the interpretation of biomonitoring data can be challenging for chemicals with complex kinetic behavior and multiple exposure routes, as is the case for diisocyanates. To better understand the relation between external exposure and urinary concentrations of metabolites of diisocyanates, we developed a physiologically based kinetic (PBK) model for methylene bisphenyl isocyanate (MDI) and toluene di-isocyanate (TDI). The PBK model covers both inhalation and dermal exposure, and can be used to estimate biomarker levels after either single or chronic exposures. Key parameters such as absorption and elimination rates of diisocyanates were based on results from human controlled exposure studies. A global sensitivity analysis was performed on model predictions after assigning distributions reflecting a mixture of parameter uncertainty and population variability. Although model-based predictions of urinary concentrations of the degradation products of MDI and TDI for longer-term exposure scenarios compared relatively well to empirical results for a limited set of biomonitoring studies in the peer-reviewed literature, validation of model predictions was difficult because of the many uncertainties regarding the precise exposure scenarios that were used. Sensitivity analyses indicated that parameters with a relatively large impact on model estimates included the fraction of diisocyanates absorbed and the binding rate of diisocyanates to albumin relative to other macro molecules.We additionally investigated the effects of timing of exposure and intermittent urination, and found that both had a considerable impact on estimated urinary biomarker levels. This suggests that these factors should be taken into account when interpreting biomonitoring data and included in the standard reporting of isocyanate biomonitoring studies.

Occupational Exposure and Health Impact Assessment of Diisocyanates in Finland

Diisocyanates are a group of chemicals widely used in different industrial applications. The critical health effects related to diisocyanate exposure are isocyanate sensitisation, occupational asthma and bronchial hyperresponsiveness (BHR). Industrial air measurements and human biomonitoring (HBM) samples were gathered in specific occupational sectors to examine MDI, TDI, HDI and IPDI and the respective metabolites from Finnish screening studies. HBM data can give a more accurate picture of diisocyanate exposure, especially if workers have been exposed dermally or used respiratory protection. The HBM data were used for conducting a health impact assessment (HIA) in specific Finnish occupational sectors. For this purpose, exposure reconstruction was performed on the basis of HBM measurements of TDI and MDI exposures using a PBPK model, and a correlation equation was made for HDI exposure. Subsequently, the exposure estimates were compared to a previously published dose-response curve for excess BHR risk. The results showed that the mean and median diisocyanate exposure levels and HBM concentrations were low for all diisocyanates. In HIA, the excess risk of BHR from MDI exposure over a working life period was highest in the construction and motor and vehicle industries and repair sectors, resulting in estimated excess risks of BHR of 2.0% and 2.6%, and 113 and 244 extra BHR cases in Finland, respectively. Occupational exposure to diisocyanates must be monitored because a clear threshold for DI sensitisation cannot be established.

Isocyanate induces cytotoxicity via activation of phosphorylated alpha synuclein protein, nitrosative stress, and apoptotic pathway in Parkinson's Disease model-SHSY-5Y cells

BACKGROUND

Neurotoxic disorders account for a significant portion of the diseases that influence the worldwide disease burden. Parkinson's disease is one such disease that is linked with environmental toxin exposure. Isocyanates are a highly reactive industrial intermediate used widely in manufacturing plastic products, paints, etc. This study aims to delineate the neurotoxic potential of isocyanate in Parkinson's cell model-SHSY-5Y cells.

METHODOLOGY

SHSY-5Y cells were treated with isocyanate analogue (N succinimidyl N methyl carbamate) in time and dose dependant manner. Different parameters were assessed like protein expression, nitrosative stress level, antioxidant enzymes level and apoptosis.

RESULTS

Our findings demonstrate that dose- and time-dependent isocyanate exposure increases reactive nitrogen species and decreases the glutathione, SOD, and catalase levels. Further, increased phosphorylated alpha-synuclein protein and activation of caspase 3 exert cytotoxicity in SHSY-5Y cells.

CONCLUSION

Our research reveals that widely used isocyanate induces cytotoxicity, apoptosis, nitrosative stress, and protein dysfunction, which might constitute a potential mechanism of neurodegeneration in Parkinsonism.

Recent Advancements in Polyurethane-based Tissue Engineering

In tissue engineering, polyurethane-based implants have gained significant traction because of their high compatibility and inertness. The implants therefore show fewer side effects and lasts longer. Also, the mechanical properties can be tuned and morphed into a particular shape, owing to which polyurethanes show immense versatility. In the last 3 years, scientists have devised methods to enhance the strength of and induce dynamic properties in polyurethanes, and these developments offer an immense opportunity to use them in tissue engineering. The focus of this review is on applications of polyurethane implants for biomedical application with detailed analysis of hard tissue implants like bone tissues and soft tissues like cartilage, muscles, skeletal tissues, and blood vessels. The synthetic routes for the preparation of scaffolds have been discussed to gain a better understanding of the issues that arise regarding toxicity. The focus here is also on concerns regarding the biocompatibility of the implants, given that the precursors and byproducts are poisonous.

Mechanically Robust and Chemically Recyclable Polyhydroxyurethanes from CO2-Derived Six-Membered Cyclic Carbonates

In the current context of sustainable chemistry development and new regulations, aminolysis of cyclic carbonate is one of the most promising routes to nonisocyanate polyurethanes, also called polyhydroxyurethanes (PHU). In this study, a new kind of shape memory PHU vitrimers with outstanding mechanical properties and chemical recyclability is prepared. The monomer employed for aminolysis to form the PHUs is bis(six-membered cyclic carbonate) of 4,4'-biphenol (BCC-BP), which is synthesized by bi(1,3-diol) precursors and CO₂. The synthetic strategy, isocyanate-free and employing CO₂ as a building block, is environmentally friendly and suits the concept of carbon neutrality. The thermal properties, mechanical properties, and dynamic behaviors of the PHUs are explored. The maximum breaking strength and elongation at break of the resultant PHUs reach 65 MPa and 452%, respectively, exceeding other reported PHU-based materials in combined performance. Such a PHU material can also lift up a load 4700 times heavier than its own weight by a shape recovery process. Finally, the bi(1,3-diol) can be regenerated through the alcoholysis of PHUs to realize chemical recycling. This work provides a feasibility study for a green synthetic approach and for designing a novel PHU material with outstanding properties.

New Method to Biomonitor Workers Exposed to 1,6-Hexamethylene Diisocyanate

Isocyanates such as 1,6-hexamethylene diisocyanate (HDI), 4,4'-methylenediphenyl diisocyanate, and toluene diisocyanate are highly reactive compounds that have a variety of commercial applications, including manufacturing polyurethane foam, elastomers, paints, adhesives, coatings, insecticides, and many other products. Their primary route of occupational exposure is through inhalation. Due to their high chemical reactivity, they are toxic and have adverse effects at the cellular and subcellular levels, leading to irritative and immunological reactions associated with lung disease. High concentrations of isocyanates are strong respiratory irritants. Bronchial sensitization and asthma are among the major adverse clinical reactions associated with low-level chronic exposure to isocyanates. Albumin adducts have been linked to the mechanism of occupational asthma caused by isocyanates. Isocyanates react in vivo with albumin, which is recognized by the immune system. Albumin adducts of isocyanates trigger immune responses and are probably the antigenic basis for isocyanate asthma. Sensitization to isocyanates is the main pathway for adverse health effects. Therefore, markers for the biologically effective dose such as albumin adducts of HDI are needed. A new isocyanate adduct of HDI with lysine─N^ε-[(6-amino-hexyl-amino)carbonyl]-lysine (HDI-Lys)─was synthesized and characterized by ¹H-NMR, ¹³C-NMR, and mass spectrometry (MS). Appropriate internal standards─HDI-Lys-4,4'-5,5'-d₄ (HDI-d₄-Lys) and N^ε-[(7-amino-heptyl-amino)carbonyl]-lysine (Hep-Lys)─were synthesized to establish a LC-MS/MS method for the analysis of HDI adducts in in vitro modified albumin and in workers. The presence of HDI-Lys was found after pronase digestion of albumin and confirmed by two independent chromatographic approaches: with a C8 reversed-phase column and with a hydrophilic interaction liquid chromatography column. Quantification was performed with positive electrospray ionization (ESI)-MS. The adduct peak found in vivo was confirmed with the less sensitive negative ESI-MS. In summary, these are new compounds and methods to determine isocyanate-specific adducts with albumin in workers exposed to HDI.

Accelerating the Curing of Hybrid Poly(Hydroxy Urethane)-Epoxy Adhesives by the Thiol-Epoxy Chemistry

The polyaddition between dicyclic carbonates and diamines leading to poly(hydroxy urethane)s (PHUs) has emerged as the preferred method for the synthesis of green, non-isocyanate polyurethanes. However, when proposed for use as structural adhesives, the long times for completion of aminolysis of the 5-membered cyclic carbonates under ambient conditions force the use of complementary chemistries to accelerate the curing process. In this work, a system that combines an amino-terminated PHU (NH₂-PHU-NH₂), an epoxy resin, and a thiol compound was employed to develop high-shear strength PHU-epoxy hybrid adhesives able to cure at room temperature in short times. A NH₂-PHU-NH₂ prepolymer synthesized by using a sub-stoichiometric quantity of dicyclic carbonates was mixed with a bisphenol A-based epoxy resin for the preparation of the structural adhesive. While this adhesive showed good lap-shear strength and shear resistance under static load and temperature, the curing process was slow. In order to speed up the curing process, a thiol (trimethylolpropane tris(3-mercapto propionate)) was added and its impact on the curing process as well as on the adhesive properties was evaluated. The trifunctional thiol additive allowed for faster curing in the presence of the 1,1,3,3-tetramethylguanidine basic catalyst. Moreover, a combination of NH₂-PHU-NH₂ and the thiol as curing agents for the epoxy resin resulted in adhesives with superior toughness, without any deterioration of the ultimate lap-shear strength or shear resistance under load and temperature, making these adhesives suitable for high-demand applications in the automotive industry.

Non-Isocyanate Polyurethane Bio-Foam with Inherent Heat and Fire Resistance

Polyurethanes (PUs) are versatile and widespread, particularly as flexible and rigid foams. To avoid isocyanates and other toxic reagents required for synthesis, such as phosgene, alternative synthetic routes have been utilized to produce non-isocyanate polyurethanes (NIPUs). A thermally and flame-resistant rigid NIPU was produced from environmentally benign and bio-sourced ingredients, requiring no catalyst or solvents. A foamed structure was obtained by the addition of glutaraldehyde and four different carboxylic acids: malic acid, maleic acid, citric acid, and aconitic acid. The resulting morphology, thermal degradation, and flame resistance of each foam were compared. The properties vary with each carboxylic acid used, but in each case, peak thermal degradation and peak heat release are postponed by >100 °C compared to commercial rigid PU foam. Furthermore, in a butane torch test, NIPU foams exhibit an 80% higher remaining mass and a 75% reduction in afterburn time, compared to commercial polyurethane. This bio-based polyurethane eliminates the hazards of traditional PUs, while imparting inherent thermal stability and flame resistance uncharacteristic of conventional foams.

Lignin as a Renewable Building Block for Sustainable Polyurethanes

Currently, the pulp and paper industry generates around 50-70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed.

Development of a new SPE UPLC-MS/MS method for extraction and quantitation of toluene diamine on gloves following toluene diisocyanate exposure

RATIONALE

Toluene diisocyanate (TDI) is a highly reactive isocyanate commonly used as a mixture of 2,4- and 2,6- isomers in the production of flexible foams. Exposure to TDI occurs primarily through vapour inhalation in workplaces where TDI is produced or used, but dermal exposure is also possible during some tasks. To ensure workplace safety, accurate monitoring of TDI and toluene diamine (TDA) levels is required. Methods of quantifying field effectiveness of gloves in preventing dermal exposure have not been established. Therefore, there is a need to develop a new practical method for assessing glove effectiveness for TDI/TDA.

METHOD

A new offline SPE UPLC-MS/MS method for the quantitation of TDA isomers from TDI-exposed gloves was developed. Gloves were dipped in a solution of 1% acetic acid leading to a full conversion to TDA. TDA-free amine compounds were derivatized with acetic anhydride to increase chromatographic retention and signal intensity.

RESULTS

2,4-Diaminotoluene-α, α, α-d3 (2,4-d₃ -TDA) was selected as a surrogate standard to minimise the variability in sample preparation and instrumental sensitivity. The choice of UPLC-MS/MS operated in multiple reaction monitoring (MRM) mode allowed to reach much lower limits of detection (LOD). The LOD of the method was 6.86 and 2.83 ng/mL (0.03 and 0.01 μg) for 2,6-TDA and 2,4-TDA, respectively. The limit of quantitation (LOQ) was 22.85 and 9.42 ng/mL (0.11 and 0.05 μg) for 2,6-TDA and 2,4-TDA, respectively.

CONCLUSION

A new UPLC-MS/MS analytical method has been developed to determine field effectiveness of gloves for preventing dermal exposure to TDI/TDA. The new technique overcomes some limitations for measuring putative dermal exposure to isocyanates and may be useful in exposure monitoring and future research on isocyanate health risks.

Toluene diisocyanate occupational exposure data in the polyurethane industry (2005-2020): A descriptive summary from an industrial hygiene perspective

This article provides an overview of toluene diisocyanate (TDI) workplace air concentration data. Data were collected between 2005-2020 in workplaces across the United States, Canada, and the European Union by a number of different organizations, primarily using the sampling procedures published in OSHA Methods 42 and 5002. The data were then collated and organized by the International Isocyanate Institute. Air samples were collected from several market segments, with a large portion of the data (87%) from the flexible foam industry. The air samples (2534 in total) were categorized into "area" or "personal," and the personal samples were subcategorized into "task," "short term," and "long term." Most of the air sample concentrations (87%) were less than 5 ppb. However, the presence of airborne TDI greater than 5 ppb indicated the importance of respiratory protection in some situations; therefore, respirator use patterns were studied and summarized. Additionally, this article provides a summary of air sample concentrations at different flexible foam manufacturing job roles. The information on air sampling concentrations and respiratory protection during TDI applications collected in this paper could be useful for product stewardship and industrial hygiene purposes in the industries studied.

Choline Chloride/Urea Deep Eutectic Solvents: A Promising Reaction Medium for the Synthesis of Bio-Based Poly(hydroxyurethane)s

The development of more sustainable and eco-friendly polymers has attracted much attention from researchers over the past decades. Among the different strategies that can be implemented towards this goal, the substitution of the toxic reagents/monomers often used in polyurethane chemistry has stimulated much innovation leading to the development of the hydroxylated version of PURs, namely, the poly(hydroxyurethane)s (PHURs). However, some PHURs remain far from being sustainable as their synthesis may involve monomers and/or solvents displaying poor environmental impacts. Herein, we report on the use of more sustainable conditions to synthesize the biobased polycarbonates involved in the aminolysis reaction. In addition, we demonstrate that the use of renewable deep eutectic solvents (DESs) can act both as excellent solvents and organocatalysts to promote the aminolysis reaction.

Assessment of personal inhalation and skin exposures to polymeric methylene diphenyl diisocyanate during polyurethane fabric coating

Methylene diphenyl diisocyanate (MDI) monomers and polymeric MDI (pMDI) are aromatic isocyanates widely used in the production of polyurethanes. These isocyanates can cause occupational asthma, hypersensitivity pneumonitis, as well as contact dermatitis. Skin exposure likely contributes toward initial sensitization but is challenging to monitor and quantitate. In this work, we characterized workers' personal inhalation and skin exposures to pMDI in a polyurethane fabric coating factory for subsequent health effect studies. Full-shift personal and area air samples were collected from eleven workers in representative job areas daily for 1-2 weeks. Skin exposure to hands was evaluated concomitantly with a newly developed reagent-impregnated cotton glove dosimeter. Samples were analyzed for pMDI by liquid chromatography-tandem mass spectrometry. In personal airborne samples, the concentration of 4,4^'-MDI isomer, expressed as total NCO, had a geometric mean (GM) and geometric standard deviation (GSD) of 5.1 and 3.3 ng NCO/m³, respectively (range: 0.5-1862 ng NCO/m³). Other MDI isomers were found at much lower concentrations. Analysis of 4,4^'-MDI in the glove dosimeters exhibited much greater exposures (GM: 10 ng/cm²) and substantial variability (GSD: 20 ng NCO/cm²; range: 0-295 ng NCO/cm²). MDI inhalation exposure was well below occupational limits for MDI for all the job areas. However, MDI skin exposure to hands was substantial. These findings demonstrated the potential for substantial isocyanate skin exposure in work settings with very low airborne levels. This exposure characterization should inform future studies that aim to assess the health effects of work exposures to MDI and the effectiveness of protective measures.

Synthesis and properties of foams from a blend of vegetable oil based polyhydroxyurethane and epoxy resin

This article aims to highlight the synthesis of foams from a blend of hydroxyurethane of castor oil and epoxy resin. An epoxidized castor oil of 4% oxirane oxygen was first converted to cyclic carbonate of castor oil at 120°C, 1 atm CO2 pressure and then it was reacted with three different aliphatic diamines to yield amine terminated Polyhydroxyurethane (PHU). Foams were prepared in a metal mould from the blend of PHU, epoxy resin, epoxy hardener and polymethylhydrogensiloxane blowing agent which releases hydrogen gas upon reaction with amine. FTIR and 1H NMR of cyclic carbonate of castor oil and PHU of castor oil were done to confirm their chemical structures. Optical microscopy and scanning electron microscopy of foams was done to assess their cellular morphology along with DSC and TGA to evaluate their thermal properties. Both flexible and rigid type of foams were synthesised in this study. Resilience of flexible foams was inspected using a ball rebound test and compression-recovery test while thermal insulation property was checked by measuring thermal conductivity, thermal diffusivity and R-values of rigid foams from heat transfer study using a heat transfer apparatus.

Absorption, distribution, metabolism, and excretion of methylene diphenyl diisocyanate and toluene diisocyanate: Many similarities and few differences

Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are high production volume chemicals used for the manufacture of polyurethanes. For both substances, the most relevant adverse health effects after overexposure in the workplace are isocyanate-induced asthma, lung function decrement and, to a much lesser extent, skin effects. Over the last two decades many articles have addressed the reactivity of MDI and TDI in biological media and the associated biochemistry, which increased the understanding of their biochemical and physiological behavior. In this review, these new insights with respect to similarities and differences concerning the adsorption, distribution, metabolism, and excretion (ADME) of these two diisocyanates and the implications on their toxicities are summarized. Both TDI and MDI show very similar behavior in reactivity to biological macromolecules, distribution, metabolism, and excretion. Evidence suggests that the isocyanate (NCO) group is scavenged at the portal-of-entry and is not systemically available in unbound reactive form. This explains the lack of other than portal-of-entry toxicity observed in repeated-dose inhalation tests.

Cascade (Dithio)Carbonate Ring Opening Reactions for Self-Blowing Polyhydroxythiourethane Foams

Polyurethane (PU) foams are very common materials that have found many applications over the years. Their use is constantly improving due to their unique physical properties and easy blowing which does not require the addition of a blowing agent. Greener routes have been explored in the recent years to replace isocyanates. One of the most promising routes is leading to Polyhydroxyurethanes (PHU). However, with PHUs, external blowing agent are usually required to obtain a foam. Thus, our work focuses on PHU foam synthesis using in situ reaction to produce NIPU foam. Hence, the aminolysis of thiocyclic carbonate triggers Pearson reaction between released thiols and cyclic carbonates which serves as a chemical blowing agent. This article is protected by copyright. All rights reserved.

Enhanced and Reusable Poly(hydroxy urethane)-Based Low Temperature Hot-Melt Adhesives

Poly(hydroxy urethane)s (PHUs) based on 5-membered cyclic carbonates have emerged as sustainable alternatives to conventional isocyanate-based polyurethanes. However, while from the point of view of sustainability they represent an improvement, their properties are still not competitive with conventional polyurethanes. In this work, the potential of PHUs as reversible hot-melt adhesives is discussed. We found that with a judicious choice of reagents (i.e., the dicyclic carbonate and diamine), the detrimental hydrogen bonding between the soft segment of the chains and the pendant hydroxyl groups was partially avoided, thus imparting PHUs with hot-melt adhesion properties (i.e., adhesion at elevated temperatures and cohesiveness at a temperature lower than T_g/T_m). The importance of a balanced hard to soft segment ratio, along with the relevance of the chain extender in the final properties, is highlighted. Addition of aliphatic diamines (HMDA, 1,12-DAD) resulted in rubbery materials, while the employment of cycloaliphatic (CBMA) or aromatic ones (MXDA, PXDA) led to materials with hot-melt adhesive properties. The thermoreversibility of all compositions was assessed by rebonding specimens after lap-shear tests. Lap-shear strength values that were comparable to the virgin adhesives were observed. The breaking and reformation of hydrogen bonding interactions was demonstrated by FTIR measurements at different temperatures, as well as by rheological frequency sweep experiments. In order to mitigate the negative impact of the low molar mass PHUs and to enhance the service temperature of the adhesives, a hybrid PHU was prepared by adding a small amount of an epoxy resin, which acts as a cross-linker. These hybrid PHUs maintain the thermoreversibility displayed by thermoplastic PHUs while providing better adhesion at elevated temperatures. We believe that this work provides some important insights into the design of PHU-based hot-melt adhesives.

Enzymes and sensitization via skin exposure: A critical analysis

Some proteins, including enzymes, can induce allergic sensitization of various types, including allergic sensitization of the respiratory tract. There is now an increased understanding of the role that the skin plays in the development of IgE-mediated allergy and this prompts the question whether topical exposure to enzymes used widely in consumer cleaning products could result in allergic sensitization. Here, the evidence that proteins can interact with the skin immune system and the way they do so is reviewed, together with a consideration of the experience gained over decades of the use of enzymes in laundry and cleaning products. The conclusion drawn is that although transcutaneous sensitization to proteins can occur (typically through compromised skin) resulting in IgE antibody-mediated allergy, in practice such skin contact with enzymes used in laundry and cleaning products does not appear to pose a significant risk of allergic disease. Further, the evidence summarized in this publication support the view that proteins do not pose a risk of allergic contact dermatitis.

Is Isocyanate Exposure and Occupational Asthma Still a Major Occupational Health Concern? Systematic Literature Review

Isocyanate, whose disease-inducing mechanism is poorly understood, with poor prognosis, is widely used. Asthma is the most frequent manifestation of prolonged exposure. We assessed the evolution of the incidence of isocyanate-induced occupational asthma over time. PubMed and Cochrane databases were systematically searched for studies published since 1990 that assessed the relationship between occupational exposure to isocyanates and asthma. We identified 39 studies: five retrospective cohort studies, seven prospective cohort studies, three of which were inception cohorts), seven observational cross-sectional studies, five literature reviews, two case series, and 13 registry studies. The incidence of occupational asthma secondary to isocyanate exposure has decreased from more than 5% in the early 1990s to 0.9% in 2017 in the United States. Despite the wide use of optimal collective and individual protection measures, the risk of occupational asthma has stabilized. Occupational asthma risk can be assessed with good sensitivity using self-questionnaires and pulmonary function tests. Occupational avoidance should be implemented as soon as possible after the first symptoms appear because the prognosis becomes increasingly poor with the persistence of exposure. It is now necessary to study specifically cutaneous sensitization to isocyanates and to define what protective equipment is effective against this mode of exposure.

Trends in non-isocyanate polyurethane (NIPU) development

The transition towards safer and more sustainable production of polymers has led to a growing body of academic research into non-isocyanate polyurethanes (NIPUs) as potential replacements for conventional, isocyanate-based polyurethane materials. This perspective article focuses on the opportunities and current limitations of NIPUs produced by the reaction between biobased cyclic carbonates with amines, which offers an interesting pathway to renewable NIPUs. While it was initially thought that due to the similarities in the chemical structure, NIPUs could be used to directly replace conventional polyurethanes (PU), this has proven to be more challenging to achieve in practice. As a result, and in spite of the vast amount of academic research into this topic, the market size of NIPUs remains negligible. In this perspective, we will emphasize the main limitations of NIPUs in comparison to conventional PUs and the most significant advances made by others and us to overcome these limitations. Finally, we provide our personal view of where research should be directed to promote the transition from the academic to the industrial sector.

A Brief Introduction to the Polyurethanes According to the Principles of Green Chemistry

Polyurethanes are most often called “green” when they contain natural, renewable additives in their network or chemical structure, such as mono- and polysaccharides, oils (mainly vegetable oils), polyphenols (e.g., lignins, tannins), or various compounds derived from agro-waste white biotechnology (Principle 7). This usually results in these polyurethanes obtained from less hazardous substrates (Principle 4). Appropriate modification of polyurethanes makes them susceptible to degradation, and the use of appropriate processes allows for their recycling (Principle 10). However, this fulfilment of other principles also predisposes them to be green. As in the production of other polymer materials, the synthesis of polyurethanes is carried out with the use of catalysts (such as biocatalysts) (Principle 9) with full control of the course of the reaction (Principle 11), which allows maximization of the atomic economy (Principle 2) and an increase in energy efficiency (Principle 6) while minimizing the risk of production waste (Principle 1). Moreover, traditional substrates in the synthesis of polyurethanes can be replaced with less toxic ones (e.g., in non-isocyanate polyurethanes), which, at the same time, leads to a non-toxic product (Principle 3, Principle 5). In general, there is no need for blocking compounds to provide intermediates in the synthesis of polyurethanes (Principle 8). Reasonable storage of substrates, their transport, and the synthesis of polyurethanes guarantee the safety and the prevention of uncontrolled reactions (Principle 12). This publication is a summary of the achievements of scientists and technologists who are constantly working to create ideal polyurethanes that do not pollute the environment, and their synthesis and use are consistent with the principles of sustainable economy.

Poly(hydroxyurethane) Adhesives and Coatings: State-of-the-Art and Future Directions

Polyurethane (PU) adhesives and coatings are widely used to fabricate high-quality materials due to their excellent properties and their versatile nature, which stems from the wide range of commercially available polyisocyanate and polyol precursors. This polymer family has traditionally been used in a wide range of adhesive applications including the bonding of footwear soles, bonding of wood (flooring) to concrete (subflooring), in the automotive industry for adhering different car parts, and in rotor blades, in which large surfaces are required to be adhered. Moreover, PUs are also frequently applied as coatings/paints for automotive finishes and can be applied over a wide range of substrates such as wood, metal, plastic, and textiles. One of the major drawbacks of this polymer family lies in the use of toxic isocyanate-based starting materials. In the context of the REACH regulation, which places restrictions on the use of substances containing free isocyanates, it is now urgent to find greener routes to PUs. While non-isocyanate polyurethanes (NIPUs) based on the polyaddition of poly(cyclic carbonate)s to polyamines have emerged in the past decade as greener alternatives to conventional PUs, their industrial implementation is at an early stage of development. In this review article, recent advances in the application of NIPUs in the field of adhesives and coatings are summarized. The article also draws attention to the opportunities and challenges of implementing NIPUs at the industrial scale.

Potential classification of chemical immunologic response based on gene expression profiles

Occupational immune diseases are a serious public health burden and are often a result of exposure to low molecular weight (LMW) chemicals. The complete immunological mechanisms driving these responses are not fully understood which has made the classification of chemical allergens difficult. Antimicrobials are a large group of immunologically-diverse LMW agents. In these studies, mice were dermally exposed to representative antimicrobial chemicals (sensitizers: didecyldimethylammonium chloride (DDAC), ortho-phthalaldehyde (OPA), irritants: benzal-konium chloride (BAC), and adjuvant: triclosan (TCS)) and the mRNA expression of cytokines and cellular mediators was evaluated using real-time qPCR in various tissues over a 7-days period. All antimicrobials caused increases in the mRNA expression of the danger signals Tslp (skin), and S100a8 (skin, blood, lung). Expression of the T_H2 cytokine Il4 peaked at different timepoints for the chemicals based on exposure duration. Unique expression profiles were identified for OPA (Il10 in lymph node, Il4 and Il13 in lung) and TCS (Tlr4 in skin). Additionally, all chemicals except OPA induced decreased expression of the cellular adhesion molecule Ecad. Overall, the results from these studies suggest that unique gene expression profiles are implicated following dermal exposure to various antimicrobial agents, warranting the need for additional studies. In order to advance the development of preventative and therapeutic strategies to combat immunological disease, underlying mechanisms of antimicrobial-induced immunomodulation must be fully understood. This understanding will aid in the development of more effective methods to screen for chemical toxicity, and may potentially lead to more effective treatment strategies for those suffering from immune diseases.

Risk Assessment for Toluene Diisocyanate and Respiratory Disease Human Studies

BACKGROUND

Toluene diisocyanate (TDI) is a highly reactive chemical that causes sensitization and has also been associated with increased lung cancer. A risk assessment was conducted based on occupational epidemiologic estimates for several health outcomes.

METHODS

Exposure and outcome details were extracted from published studies and a NIOSH Health Hazard Evaluation for new onset asthma, pulmonary function measurements, symptom prevalence, and mortality from lung cancer and respiratory disease. Summary exposure-response estimates were calculated taking into account relative precision and possible survivor selection effects. Attributable incidence of sensitization was estimated as were annual proportional losses of pulmonary function. Excess lifetime risks and benchmark doses were calculated.

RESULTS

Respiratory outcomes exhibited strong survivor bias. Asthma/sensitization exposure response decreased with increasing facility-average TDI air concentration as did TDI-associated pulmonary impairment. In a mortality cohort where mean employment duration was less than 1 year, survivor bias pre-empted estimation of lung cancer and respiratory disease exposure response.

CONCLUSION

Controlling for survivor bias and assuming a linear dose-response with facility-average TDI concentrations, excess lifetime risks exceeding one per thousand occurred at about 2 ppt TDI for sensitization and respiratory impairment. Under alternate assumptions regarding stationary and cumulative effects, one per thousand excess risks were estimated at TDI concentrations of 10 - 30 ppt. The unexplained reported excess mortality from lung cancer and other lung diseases, if attributable to TDI or associated emissions, could represent a lifetime risk comparable to that of sensitization.

Occupational Exposure to Diisocyanates in the European Union

Objectives

Diisocyanates are a chemical group that are widely used at workplaces in many sectors. They are also potent skin- and respiratory sensitizers. Exposure to diisocyanates is a main cause of occupational asthma in the European Union. To reduce occupational exposure to diisocyanates and consequently the cases of diisocyanate-induced asthma, a restriction on diisocyanates was recently adopted under the REACH Regulation in the European Union.

Methods

A comprehensive evaluation of the data on occupational exposure to the most important diisocyanates at workplaces was made and is reported here. The diisocyanates considered are methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI), accounting for more than 95% of the market volume in the EU. The exposure assessment is based on data from Chemical Safety Reports (CSRs) of REACH Registration Dossiers, workplace air monitoring data from Germany, from the UK Health and Safety Executive (HSE), and literature data relevant for the EU, and the USA.

Results

Occupational exposure to diisocyanates is particularly relevant in: (i) C.A.S.E. applications (Coatings, Adhesives, Sealants, Elastomers), (ii) production of polyurethanes (PUs) (e.g. slab-stock foam), (iii) handling of partly uncured PU products (e.g. cutting, demoulding, spray application of foam), and (iv) when diisocyanates/PUs are heated (e.g. hot lamination, foundry applications/casting forms). Ranking of the reported data on inhalation to diisocyanate exposure at workplaces (maximum values) leads to following order: (i) HDI and its oligomers in coatings, (ii) MDI in spray foam applications, (iii) TDI in manufacture of foam, (iv) TDI in manufacture of PUs and PU composite materials, (v) TDI in adhesives, (vi) MDI in adhesives, (vii) MDI in manufacture of PUs and PU composite materials, (viii) TDI in coatings, (ix) MDI in manufacture of foam, and (x) HDI in adhesives.

Classification of chemicals as respiratory allergens based on human data: Requirements and practical considerations

Occupational asthma is an important health problem that can include exacerbation of existing asthma, or induce new asthma either through allergic sensitisation, or non-immunological mechanisms. While allergic sensitisation of the respiratory tract can be acquired to proteins, or to low molecular weight chemicals (chemical respiratory allergens) this article is on the latter exclusively. Chemical respiratory allergy resulting in occupational asthma is associated with high levels of morbidity and there is a need, therefore, that chemicals which can cause sensitisation of the respiratory tract are identified accurately. However, there are available no validated, or even widely accepted, predictive test methods (in vivo, in vitro or in silico) that have achieved regulatory acceptance for identifying respiratory sensitising hazards. For this reason there is an important reliance on human data for the identification of chemical respiratory allergens, and for distinguishing these from chemicals that cause occupational asthma through non-immunological mechanisms. In this article the reasons why it is important that care is taken in designating chemicals as respiratory allergens are reviewed. The value and limitations of human data that can aid the accurate identification of chemical respiratory allergens are explored, including exposure conditions, response characteristics in specific inhalation challenge tests, and immunological investigations.

Biobased polyurethanes for biomedical applications

Polyurethanes (PUs) are a major family of polymers displaying a wide spectrum of physico-chemical, mechanical and structural properties for a large range of fields. They have shown suitable for biomedical applications and are used in this domain since decades. The current variety of biomass available has extended the diversity of starting materials for the elaboration of new biobased macromolecular architectures, allowing the development of biobased PUs with advanced properties such as controlled biotic and abiotic degradation. In this frame, new tunable biomedical devices have been successfully designed. PU structures with precise tissue biomimicking can be obtained and are adequate for adhesion, proliferation and differentiation of many cell's types. Moreover, new smart shape-memory PUs with adjustable shape-recovery properties have demonstrated promising results for biomedical applications such as wound healing. The fossil-based starting materials substitution for biomedical implants is slowly improving, nonetheless better renewable contents need to be achieved for most PUs to obtain biobased certifications. After a presentation of some PU generalities and an understanding of a biomaterial structure-biocompatibility relationship, recent developments of biobased PUs for non-implantable devices as well as short- and long-term implants are described in detail in this review and compared to more conventional PU structures.