Upgrading Sustainable Polyurethane Foam Based on Greener Polyols: Succinic-Based Polyol and Mannich-Based Polyol

Synthesis of bio-polyol-functionalized nanocrystalline celluloses as reactive/reinforcing components in bio-based polyurethane foams by homogeneous environment modification

Nanocrystalline Cellulose (NCC or CNC) is widely used as a filler in polymer composites due to its high specific strength, tensile modulus, aspect ratio, and sustainability. However, CNC hydrophilicity complicates its dispersion in hydrophobic polymeric matrices giving rise to aggregate structures and thus compromising its reinforcing action. CNC functionalization in a homogeneous environment, through silanization with trichloro(butyl)silane as a coupling agent and subsequent grafting with bio-based polyols, is herein investigated aiming to enhance CNC dispersibility improving the filler-matrix interaction between the hydrophobic PU and hydrophilic CNC. The modified CNCs (m_Ci) have been studied by XRD, SEM, and TGA analyses. The TGA results show that the amount of grafted polyol is strongly influenced by both its molar mass and OH number and the maximum amount of grafted polyol reaches up to 0.32 mmol per grams of functionalized CNC, within the explored conditions. The effect of different concentrations (1-3 wt%) of m_Ci on the physical, morphological, and mechanical properties of the resulting bio-based composite polyurethane foams is evaluated. Composite PU foams present compressive modulus up to 4.81 MPa and strength up to 255 kPa more than five times higher than those reinforced with unmodified CNC or with modified CNC in heterogeneous chemical environment. The improvement of mechanical properties of the examined PU foams, as a consequence of the incorporation of bio-polyols modified CNCs where polyol's OH groups interact with polyurethane precursors, could further broaden the use of these materials in building applications.

The Role of Superabsorbent Polymers and Polymer Composites in Water Resource Treatment and Management

In the last century, the issue of "water reserves" has become a remarkably strategic topic in modern science and technology. In this context, water resource treatment and management systems are being developed in both agricultural and urban area scenarios. This can be achieved using superabsorbent polymers (SAPs), highly cross-linked hydrogels with three-dimensional, hydrophilic polymer structures capable of absorbing, swelling and retaining huge amounts of aqueous solutions. SAPs are able to respond to several external stimuli, such as temperature, pH, electric field, and solution composition and concentration. They can be used in many areas, from sensor technology to drug delivery, agriculture, firefighting applications, food, and the biomedical industry. In addition, new categories of functional SAP-based materials, mainly superabsorbent polymer composites, can also encapsulate fertilizers to efficiently provide the controlled release of both water and active compounds. Moreover, SAPs have great potential in wastewater treatment for the removal of harmful elements. In this respect, in the following review, the most promising and recent advances in the use of SAPs and composite SAPs as tools for the sustainable management and remediation of water resource are reviewed and discussed by identifying opportunities and drawbacks and highlighting new challenges and aims to inspire the research community.

Efficient recycling pathway of bio-based composite polyurethane foams via sustainable diamine

Aminolysis is widely recognized as a valuable chemical route for depolymerizing polymeric materials containing ester, amide, or urethane functional groups, including polyurethane foams. Bio-based polyurethane foams, pristine and reinforced with 40 wt% of sustainable fillers, were depolymerized in the presence of bio-derived butane-1,4-diamine, BDA. A process comparison was made using fossil-derived ethane-1,2-diamine, EDA, by varying amine/polyurethane ratio (F/A, 1:1 and 1:0.6). The obtained depolymerized systems were analyzed by FTIR and NMR characterizations to understand the effect of both diamines on the degradation pathway. The use of bio-based BDA seemed to be more effective with respect to conventional EDA, owing to its stronger basicity (and thus higher nucleophilicity), corresponding to faster depolymerization rates. BDA-based depolymerized systems were then employed to prepare second-generation bio-based composite polyurethane foams by partial replacement of isocyanate components (20 wt%). The morphological, mechanical, and thermal conductivity properties of the second-generation polyurethane foams were evaluated. The best performances (σ10 %=71 ± 9 kPa, λ = 0.042 ± 0.015 W∙ m-1 ∙K-1) were attained by employing the lowest F/A ratio (1:0.6); this demonstrates their potential application in different sectors such as packaging or construction, fulfilling the paradigm of the circular economy.

Effect of Different Methods to Synthesize Polyol-Grafted-Cellulose Nanocrystals as Inter-Active Filler in Bio-Based Polyurethane Foams

Currently, the scientific community has spent a lot of effort in developing "green" and environmentally friendly processes and products, due the contemporary problems connected to pollution and climate change. Cellulose nanocrystals (CNCs) are at the forefront of current research due to their multifunctional characteristics of biocompatibility, high mechanical properties, specific surface area, tunable surface chemistry and renewability. However, despite these many advantages, their inherent hydrophilicity poses a substantial challenge for the application of CNCs as a reinforcing filler in polymers, as it complicates their dispersion in hydrophobic polymeric matrices, such as polyurethane foams, often resulting in aggregate structures that compromise their properties. The manipulation and fine-tuning of the interfacial properties of CNCs is a crucial step to exploit their full potential in the development of new materials. In this respect, starting from an aqueous dispersion of CNCs, two different strategies were used to properly functionalize fillers: (i) freeze drying, solubilization in DMA/LiCl media and subsequent grafting with bio-based polyols; (ii) solvent exchange and subsequent grafting with bio-based polyols. The influence of the two functionalization methods on the chemical and thermal properties of CNCs was examined. In both cases, the role of the two bio-based polyols on filler functionalization was elucidated. Afterwards, the functionalized CNCs were used at 5 wt% to produce bio-based composite polyurethane foams and their effect on the morphological, thermal and mechanical properties was examined. It was found that CNCs modified through freeze drying, solubilization and bio-polyols grafting exhibited remarkably higher thermal stability (i.e., degradation stages > 100 °C) with respect to the unmodified freeze dried-CNCs. In addition, the use of the two grafting bio-polyols influenced the functionalization process, corresponding to different amount of grafted-silane-polyol and leading to different chemico-physical characteristics of the obtained CNCs. This was translated to higher thermal stability as well as improved functional and mechanical performances of the produced bio-based composite PUR foams with respect of the unmodified CNCs-composite ones (the best case attained compressive strength values three times more). Solvent exchange route slightly improved the thermal stability of the obtained CNCs; however; the so-obtained CNCs could not be properly dispersed within the polyurethane matrix, due to filler aggregation.

Enhancement of Anticorrosive Performance of Cardanol Based Polyurethane Coatings by Incorporating Magnetic Hydroxyapatite Nanoparticles

The present investigation demonstrates renewable cardanol-based polyol for the formulation of nanocomposite polyurethane (PU) coatings. The functional and structural features of cardanol polyol and nanoparticles were studied using FT-IR and 1H NMR spectroscopic techniques. The magnetic hydroxyapatite nanoparticles (MHAPs) were dispersed 1–5% in PU formulations to develop nanocomposite anticorrosive coatings. An increase in the strength of MHAP increased the anticorrosive performance as examined by immersion and electrochemical methods. The nanocomposite PU coatings showed good coating properties, viz., gloss, pencil hardness, flexibility, cross-cut adhesion, and chemical resistance. Additionally, the coatings were also studied for surface morphology, wetting, and thermal properties by scanning electron microscope (SEM), contact angle, and thermogravimetric analysis (TGA), respectively. The hydrophobic nature of PU coatings increased by the addition of MHAP, and an optimum result (105°) was observed in 3% loading. The developed coatings revealed its hydrophobic nature with excellent anticorrosive performance.

Recent Advances in Development of Waste-Based Polymer Materials: A Review

Limited petroleum sources, suitable law regulations, and higher awareness within society has caused sustainable development of manufacturing and recycling of polymer blends and composites to be gaining increasing attention. This work aims to report recent advances in the manufacturing of environmentally friendly and low-cost polymer materials based on post-production and post-consumer wastes. Sustainable development of three groups of materials: wood polymer composites, polyurethane foams, and rubber recycling products were comprehensively described. Special attention was focused on examples of industrially applicable technologies developed in Poland over the last five years. Moreover, current trends and limitations in the future “green” development of waste-based polymer materials were also discussed.

Development and Characterization of Tailored Polyurethane Foams for Shock Absorption

In this paper, different types of polyurethane foams (PUR) having various chemical compositions have been produced with a specific density to monitor the microstructure as much as possible. The foam may have a preferential orientation in the cell structure. The cellular polyurethane tends to have stubborn, typical cellular systems with strong overlap reversibility. Free expansion under atmospheric pressure enables formulas to grow until they are refined. Moreover, the physicochemical characterization of the developed foams was carried out. They later are described by apparent density, Shore hardness, Raman spectroscopy analysis, X-ray diffraction analysis, FTIR, TGA, DSC, and compression tests. The detailed structural characterization was used by scanning electron microscope (SEM) and an optical microscope (MO) to visualize the alveolar polymer’s semi-opened cells, highlighting the opened-cell morphology and chemical irregularities. Polyurethane foams with different structural variables have a spectrum characterization that influences the phase separation and topography of polyurethane foam areas because their bonding capability with hydrogen depends on chain extender nature. These studies may aid in shock absorption production; a methodology of elaboration and characterization of filled polyurethane foams is proposed.

Production of Rigid Polyurethane Foams Using Polyol from Liquefied Oil Palm Biomass: Variation of Isocyanate Indexes

Development of polyurethane foam (PUF) containing bio-based components is a complex process that requires extensive studies. This work reports on the production of rigid PUFs from polyol obtained via liquefaction of oil palm empty fruit bunch (EFB) biomass with different isocyanate (NCO) indexes. The effect of the NCO index on the physical, chemical and compressive properties of the liquefied EFB-based PUF (EFBPUF) was evaluated. The EFBPUFs showed a unique set of properties at each NCO index. Foaming properties had affected the apparent density and cellular morphology of the EFBPUFs. Increasing NCO index had increased the crosslink density and dimensional stability of the EFBPUFs via formation of isocyanurates, which had also increased their thermal stability. Combination of both foaming properties and crosslink density of the EFBPUFs had influenced their respective compressive properties. The EFBPUF produced at the NCO index of 120 showed the optimum compressive strength and released the least toxic hydrogen cyanide (HCN) gas under thermal degradation. The normalized compressive strength of the EFBPUF at the NCO index of 120 is also comparable with the strength of the PUF produced using petrochemical polyol.

Fully Renewable Non-Isocyanate Polyurethanes via the Lossen Rearrangement

In this work, a straightforward and efficient synthesis approach to renewable non-isocyanate polyurethanes (NIPUs) is described. For this purpose, suitable and renewable carbamate monomers, possessing two double bonds, are synthesized from hydroxamic fatty acid derivatives via the Lossen rearrangement in a one-step synthesis, and sustainable dithiols are synthesized from dialkenes derived from renewable feedstock (i.e., limonene and 1,4-cyclohexadiene). Subsequently, the comonomers are polymerized with the highly efficient thiol-ene reaction to produce NIPUs with M_n values up to 26 kg mol^-1 bearing thioether linkages. The main side product of the Lossen rearrangement, a symmetric urea, can also be polymerized in the same fashion. Important in the view of sustainability, the monomer mixture can also be used directly, without separation. The obtained polymers are characterized by NMR, attenuated total reflection-infrared spectroscopy, differential scanning calorimetry, and size exclusion chromatography.

Recent Progress in Processing Functionally Graded Polymer Foams

Polymer foams are an important class of engineering material that are finding diverse applications, including as structural parts in automotive industry, insulation in construction, core materials for sandwich composites, and cushioning in mattresses. The vast majority of these manufactured foams are homogeneous with respect to porosity and structural properties. In contrast, while cellular materials are also ubiquitous in nature, nature mostly fabricates heterogeneous foams, e.g., cellulosic plant stems like bamboo, or a human femur bone. Foams with such engineered porosity distribution (graded density structure) have useful property gradients and are referred to as functionally graded foams. Functionally graded polymer foams are one of the key emerging innovations in polymer foam technology. They allow enhancement in properties such as energy absorption, more efficient use of material, and better design for specific applications, such as helmets and tissue restorative scaffolds. Here, following an overview of key processing parameters for polymer foams, we explore recent developments in processing functionally graded polymer foams and their emerging structures and properties. Processes can be as simple as utilizing different surface materials from which the foam forms, to as complex as using microfluidics. We also highlight principal challenges that need addressing in future research, the key one being development of viable generic processes that allow (complete) control and tailoring of porosity distribution on an application-by-application basis.