Thermally stable, transparent, pressure-sensitive adhesives from epoxidized and dihydroxyl soybean oil

Fabrication of well-dispersed cellulose nanocrystal reinforced biobased epoxy composites using reversibility of covalent adaptable network

Cellulose nanocrystal (CNC) shows great potential in reinforced composites but it is difficult to disperse in epoxy thermosets due to its poor dispersity in epoxy monomers. Herein, we reported a novel approach to disperse CNC in epoxidized soybean oil (ESO)-derived epoxy thermosets uniformly by using the reversibility of dynamic imine-containing ESO-derived covalent adaptable network (CAN). The crosslinked CAN was deconstructed by an exchange reaction with ethylenediamine (EDA) in dimethyl formamide (DMF), leading to a solution of deconstructed CAN with plenty of hydroxyl and amino groups, which could form strong hydrogen bonds with hydroxyl groups of CNC and thus facilitated and stabilized dispersion of CNC in the deconstructed CAN solution. Epoxy composite with well-dispersed CNC was finally achieved by a reformation of CAN through the removal of DMF and EDA. In this way, the epoxy composites with CNC content up to 30 wt% were successfully prepared and showed drastically reinforced mechanical properties. The tensile strength and Young's modulus of the CAN were improved by up to ~70 % and ~45 times with the incorporation of 20 and 30 wt% CNC, respectively. The composites showed excellent reprocessability without significant loss in mechanical properties after reprocessing.

Adhesive Interfaces toward a Zero-Waste Industry

This Feature Article evaluates ongoing efforts to adapt adhesives toward the goal of zero-waste living and suggests the most promising future directions. Adhesives are not always considered in zero-waste manufacturing because they represent only a small fraction of a product and offer no additional functionality. However, their presence restricts the reintegration of constituent parts into a circular economy, so a new generation of adhesives is required. Furthermore, their production often leads to harmful pollutants. Here, two main approaches toward addressing these problems are considered: first, the use of natural materials that replace petroleum-based polymers from which conventional adhesives are made and second, the production of dismantlable adhesives capable of debonding on demand with the application of an external stimulus. These approaches, either individually or combined, offer a new paradigm in zero-waste industrial production and consumer applications.

Valorization of camelina oil to biobased materials and biofuels for new industrial uses: a review

Global environmental pollution is a growing concern, especially the release of carbon dioxide from the use of petroleum derived materials which negatively impacts our environment's natural greenhouse gas level. Extensive efforts have been made to explore the conversion of renewable raw materials (vegetable oils) into bio-based products with similar or enhanced properties to those derived from petroleum. However, these edible plant oils, commonly used for human food consumption, are often not suitable raw materials for industrial applications. Hence, there is an increasing interest in exploring the use of non-edible plant oils for industrial applications. One such emerging oil seed crop is Camelina sativa, generally known as camelina, which has limited use as a food oil and so is currently being explored as a feedstock for various industrial applications in both Europe and North America. Camelina oil is highly unsaturated, making it an ideal potential AGH feedstock for the manufacture of lower carbon footprint, biobased products that reduce our dependency on petroleum resources and thus help to combat climate change. This review presents a brief description of camelina highlighting its composition and its production in comparison with traditional plant oils. The main focus is to summarize recent data on valorization of camelina oil by various chemical means, with specific emphasis on their industrial applications in biofuels, adhesives and coatings, biopolymers and bio-composites, alkyd resins, cosmetics, and agriculture. The review concludes with a discussion on current challenges and future opportunities of camelina oil valorization into various industrial products.

Biobased Approach for Synthesis of Polymers and Sustainable Formulation of Industrial Hardeners

The adhesive manufacturing industry needs more eco-sustainable processes. In this regard, the main road is to replace raw fossil materials with renewable resources or waste biomass, and simultaneously improve synthetic steps by using clean and greener reagents under mild conditions. In this paper, a synthetic pathway for producing biobased succinyl peroxide (SP) from waste biomass is reported, and then the application range of this polymerization agent to methacrylates and styrene-free resins is extended. At the same time, new formulations of pastes based on benzoyl or succinyl peroxide, displaying an almost complete biobased carbon content, are investigated and tested as cross-linking agents for mastic marble and unsaturated polyester resins. Physicochemical characterization of the final products and polymers is carried out with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance (NMR) and peak exothermic curve analyses.

Sustainable UV-Crosslinkable Acrylic Pressure-Sensitive Adhesives for Medical Application

This study aimed to investigate the potential of photoreactive acrylate patches as systems for transdermal drug delivery, in particular, using more renewable alternatives and more environmentally friendly synthesis routes of transdermal patches. Therefore, the aim of this study was to develop a transdermal patch containing ibuprofen and investigate its performance in vitro through the pigskin. Transparent patches were prepared using four acrylate copolymers with an incorporated photoinitiator. Two types of transdermal patches based on the photocrosslinking acrylic prepolymers with isobornyl methacrylate as biocomponent and monomer increasing Tg ("hard") were manufactured. The obtained patches were characterized for their adhesive properties and tested for permeability of the active substance. It turns out that patches whose adhesive matrix is photoreactive polyacrylate copolymers have a higher cohesion than patches from commercial adhesives, while the modification of the copolymers with isobornyl methacrylate resulted in an improvement in adhesion and tack. This study demonstrates the feasibility of developing photoreactive acrylic-based transdermal patches that contain biocomponents that can deliver a therapeutically relevant dose of ibuprofen.

Effect of flame retardants on mechanical and thermal properties of bio-based polyurethane rigid foams

A soy oil-based polyol (HSBP) was synthesized from epoxidized soy oil through a ring-opening reaction with distilled water. A phosphorus-containing flame retardant (DOPO–HSBP) was synthesized through the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and HSBP. A nitrogen-containing flame retardant (T–D) was prepared by the reaction of diethanolamine with glycol diglycidyl ether. The structures of HSBP, DOPO–HSBP, and T–D were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (¹H NMR). The flame-retardant rigid polyurethane foam (PPUFs and NPUFs) was prepared successfully by mixing HSBP, DOPO–HSBP, and T–D. The effects of DOPO–HSBP content on the mechanical, thermal, and flame-retardant properties of PPUFs and NPUFs were investigated by tensile tests, thermogravimetric analyses (TGA), limiting oxygen index (LOI), and UL-94 vertical burning level. The morphology of PPUFs and NPUFs was studied via scanning electron microscopy (SEM). With the increase in the percentage of DOPO–HSBP added, the flame retardant property of rigid polyurethane foam (RPUF) was greatly improved. When the phosphorus-containing flame retardant DOPO–HSBP was added to 50% of the RPUF with the nitrogen-containing flame retardant T–D, the LOI value of the foam increased from 18.3 to 25.5, and the UL-94 result was classified as “V-0” with almost no effect on the mechanical properties of the RPUF. The results showed that the phosphorus and nitrogen synergistic flame retardants of DOPO–HSBP and T–D can endow excellent flame retardant properties to RPUF without affecting its mechanical properties.

A vegetable oil-based polyurethane rigid foam containing a phosphorus–nitrogen dualflame retardant system was prepared, and the foam exhibited not only excellent flame retardant properties but also good mechanical properties.

Bio-based and Degradable Block Polyester Pressure-Sensitive Adhesives

A new class of bio-based fully degradable block polyesters are pressure-sensitive adhesives. Bio-derived monomers are efficiently polymerized to make block polyesters with controlled compositions. They show moderate to high peel adhesions (4-13 N cm-1 ) and controllable storage and loss moduli, and they are removed by adhesive failure. Their properties compare favorably with commercial adhesives or bio-based polyester formulations but without the need for tackifier or additives.

High-performance water-borne fluorescent acrylic-based adhesive: synthesis and application

Water-borne adhesives have immense importance in cellulose-based materials, where their durability, handling, and strength remain to be a major concern. The present work demonstrates the development of three water-borne adhesives, namely, poly(1-vinyl-2-pyrrolidone-co-acrylic acid), poly(acrylonitrile-co-acrylic acid), and poly(1-vinyl-2-pyrrolidone-co-acrylonitrile-co-acrylic acid) applicable for cellulose-based materials. These acrylic-acid based adhesives were characterized by Fourier-transform infra-red spectroscopy, thermogravimetric analysis, X-ray diffraction, gel permeation chromatography, and universal testing machine. The synthesized polymer adhesives can be stored in the powder form for a longer period, thus utilizing less space. In order to use as adhesives, suitable formulations can be prepared in water. The adhesives show thermal stability up to 300 °C. Our studies show that poly(1-vinyl-2-pyrrolidone-co-acrylonitrile-co-acrylic acid) showed higher lap shear strength (ASTM D-906) than commercially available adhesives. In addition, these adhesives, being fluorescent in nature, can be detected under UV light and thus are applicable for the detection of fractured joints of any specimen. This property also helps in anti-counterfeiting applications, thus adding further to their utility.

Synthesis and application of a water-borne fluorescent acrylic adhesive, which can be stored as a powder for long-term use.

Synthesis and Antimicrobial Activity of Metal-Containing Linseed Oil-Based Waterborne Urethane Oil Wood Coatings

In this study, the antimicrobial agents of mono(hydroxyethoxyethyl)phthalate (M(HEEP)₂) with different metal of M = Zn, Mn, Pb, and Ca were synthesized from diethylene glycol (DEG), phthalic anhydride (PA), and divalent metal acetates including calcium acetate, zinc acetate, manganese acetate, and lead acetate, respectively. The waterborne urethane oil (WUO) dispersions synthesized from linseed oil, diisocyanates (hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI)), dimethylolpropionic acid at NCO/OH molars of 0.9, by acetone processing method were described as in our previous report. The M(HEEP)₂ antimicrobial agents as well as the commercial nanosilver powder were added into WUO dispersions as the antimicrobial coatings. The effects of various antimicrobial agents and dosages (0.0, 0.2, 0.6, 0.8, 1.0, 2.0, and 4.0 phr) on antimicrobial activity of WUO films against gram-negative bacterium of Escherichia coli, gram-positive bacterium of Staphylococcus aureus, brown-rot fungus of Gloeophyllum trabeum, and white-rot fungus of Lenzites betulina were assessed. In addition, the film properties of the best antimicrobial WUO coatings were also examined. The results showed that the antimicrobial agents of mono(hydroxyethoxyethyl) phthalate M(HEEP)₂ (M = Zn, Mn, Pb, and Ca) powders should certainly be synthesized by FTIR, ¹H-NMR, ¹³C-NMR, and energy-dispersive X-ray spectroscopy (EDS) identifications and the yields of them were 43–55%. The results also revealed that the WUO film synthesizing with HDI films containing Zn(HEEP)₂ of 2.0 phr and Pb(HEEP)₂ of 0.4 phr had the best antibacterial activity for E. coli and S. aureus, respectively. The IPDI films containing Zn(HEEP)₂ of 1.0 phr had the best antibacterial activity for both E. coli and S. aureus. For antifungal activity, the WUO film synthesizing with HDI films containing Pb(HEEP)₂ of 0.8 phr and Zn(HEEP)₂ of 2.0 phr as well as IPDI films containing Mn(HEEP)₂ of 0.2 phr and Zn(HEEP)₂ of 4.0 phr had the best performances against G. trabeum and L. betulina, respectively. Comparing with commercial nanoAg powder, the Zn(HEEP)₂ and Pb(HEEP)₂ had a superior antifungal efficiency for G. trabeum and L. betulina, while it had a slightly inferior efficiency in the antibacterial activity for E. coli and S. aureus. On the properties of WUO films, adding metal-containing antimicrobial agents could slightly enhance the thermal stability, but lowered the gloss of all films, however, the T_g value increased for HDI film and decreased for IPDI film. In addition to this, they had no significant difference in the film properties including hardness, impact resistance, bending resistance, adhesion, mass retention, and light-fastness between the WUO films with and without adding antimicrobial agents.

Monitoring the structure–reactivity relationship in epoxidized perilla and safflower oil thermosetting resins

The reactivity of epoxidized perilla oil and epoxidized safflower oil with two aromatic dicarboxylic acids was studied. The presence of S–S bonding at the β position of the carboxylic group increases the reactivity of the acidic proton toward epoxy ring opening.

A Review on Styrene Substitutes in Thermosets and Their Composites

In recent decades, tremendous interest and technological development have been poured into thermosets and their composites. The thermosets and composites with unsaturated double bonds curing system are especially concerned due to their versatility. To further exploit such resins, reactive diluents (RDs) with unsaturated sites are usually incorporated to improve their processability and mechanical properties. Traditional RD, styrene, is a toxic volatile organic compound and one of the anticipated carcinogens warned by the National Institute of Health, USA. Most efforts have been conducted on reducing the usage of styrene in the production of thermosets and their composites, while very few works have systematically summarized these literatures. Herein, recent developments regarding styrene substitutes in thermosets and their composites are reviewed. Potential styrene alternatives, such as vinyl derivatives of benzene and (methyl)acrylates are discussed in details. Emphasis is focused on the strategies on developing novel RD monomers through grafting unsaturated functional groups on renewable feedstocks such as carbohydrates, lignin, and fatty acids. This review also highlights the development and characteristics of RD monomers and their influence on processability and mechanical performance of the resulting thermosets and composites.

Effect of an Anhydride Excess on the Curing Kinetics and Dynamic Mechanical Properties of Synthetic and Biogenic Epoxy Resins

This work analyzes the effect of the anhydride excess on the nonisothermal curing kinetics and on the final properties of synthetic and biobased epoxy resins. Diglycidyl ether of bisphenol A (DGEBA) and epoxidized soybean oil (ESO) were crosslinked using methyltetrahydrophthalic anhydride (MTHPA) as a curing agent and 1-methylimidazole (1MI) as an initiator. It was shown that the ESO/MTHPA/1MI system reacts slower than the DGEBA/MTHPA/1MI system, giving place to a more significant evaporation of the curing agent during the reaction. As a result, an excess of anhydride improves the final thermal properties of the ESO/MTHPA/1MI network, contrary to the behavior observed for DGEBA/MTHPA/1MI. The knowledge of the kinetics of the curing process and the optimal amount of the curing agent for each system is of critical importance for a more efficient processing of these materials.

Contribution of Surface Energy to pH-Dependent Underwater Adhesion of an Acrylic Pressure-Sensitive Adhesive

Maintaining the underwater adhesive performance over a broad range of solution pH is challenging but necessary for many biomedical applications. Therefore, understanding how environmental conditions influence the mechanisms of bonding and debonding of pressure-sensitive adhesives (PSAs) can provide guidelines for materials design. We investigate how the presence of acrylic acid as a co-monomer impacts the adhesion of a model PSA in aqueous environments of varying pH. The adhesives under investigation are poly(2-ethylhexyl acrylate), or poly(2-EHA), and poly(2-EHA) co-polymerized with 5 wt % acrylic acid, or poly(2-EHA- co-AA). We characterize bonding and debonding (adhesion) of the adhesives using probe tack measurements with a spherical hydrophobic glass probe. We analyze the performance of the two PSAs in air and in low-ionic-strength buffered aqueous solutions of pH 3- 11. We find that the presence of the acrylic acid co-monomer increases the cohesiveness of the PSA and leads to stronger adhesion under all conditions investigated. We also observe that the presence of the acrylic acid co-monomer imparts the PSA with a strong dependence of adhesion on the solution pH. Dynamic contact angle and  ζ potential measurements support the hypothesis that deprotonation of the acrylic acid groups at higher pH causes the decrease in adhesion at higher pH. Rheological measurements do not show changes in the dynamic mechanical properties of the PSAs after exposure to solutions of pH 3- 11. Our measurements allow us to isolate the effect of the solution pH on the surface and bulk properties of the PSA. In the absence of the acrylic acid co-monomer, the bulk dissipation and the surface properties of the PSA are independent of the solution's pH.

Reinforcement of Castor Oil-Based Polyurethane with Surface Modification of Attapulgite

Polyurethane/attapulgite (PU/ATT) nanocomposites derived from castor oil were prepared by incorporation of 8 wt % ATT, acid-treated ATT, and KH560-treated ATT. The effects of three ATTs (ATT, acid-ATT, and KH560-ATT) on the comprehensive properties of PU/ATT nanocomposites were systematically investigated. The results showed that the incorporation of 8 wt % of three ATTs could produce an obvious reinforcement on the castor oil-based PU and that the silane modification treatment, rather than the acid treatment, has the more effective reinforcement effect. SEM images revealed the uniform dispersion of ATT in the PU matrix. DMA confirmed that the storage modulus and glass transition temperature (Tg) of PU/ATT nanocomposites were significantly increased after blending with different ATTs. For PU/KH560-ATT8 nanocomposites, the thermal stability of the PU was obviously enhanced by the addition of KH560-ATT. In particular, 8 wt % KH560-ATT loaded castor oil-based PU nanocomposites exhibit an obvious improvement in tensile strength (255%), Young's modulus (200%), Tg (5.1 °C), the storage modulus at 25 °C (104%), and the initial decomposition temperature (7.7 °C). The prepared bio-based PU materials could be a potential candidate to replace petroleum-based PU products in practical applications.

Synthesis of Linseed Oil-Based Waterborne Urethane Oil Wood Coatings

The linseed oil glyceride (LOG) was synthesized by using a transesterification process with a glycerol/linseed oil molar ratio of 1.0. The waterborne urethane oil (WUO) wood coating was prepared by acetone process. First, dimethylolpropionic acid was reacted with hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), followed by adding LOG at various NCO/OH molars of 0.7, 0.8, and 0.9, respectively, and the COOH-containing prepolymer was obtained. Then, the ionomer which was prepared by neutralizing prepolymer with trimethylamine, was dispersed by adding deionized water, and the water⁻acetone dispersion was obtained. Finally, the acetone was removed by vacuum distillation. In the whole synthesized process, the LOG and COOH-containing prepolymer could be steadily synthesized by FTIR analysis, and the weight-average molecular weight and polydispersity of COOH-containing prepolymer increased with an increase of NCO/OH molar ratios. During the water dispersion process of the ionomer acetone solution, the point of phase inversion was prolonged, meaning the solid content decreased with an increase of NCO/OH molar ratios. After acetone was removed, the color of WUO was milky-white, and it was weakly alkaline and possessed a pseudoplastic fluid behavior. The particle size of WUO increased with increasing of NCO/OH molar ratios, however, the storage stability was extended for HDI and shortened for IPDI synthesized with increasing of NCO/OH molar ratios.

Influence of Phase Separation on Performance of Graft Acrylic Pressure-Sensitive Adhesives with Various Copolyester Side Chains

Acrylic pressure-sensitive adhesives with various polyester side-chain lengths were synthesized to investigate the effect of branching on phase separation and polymer mechanical performance. The polyester macromonomers (MMs) were produced through ring-opening co-polymerizations of l-lactide (l-LA) and ε-caprolactone (ε-CL) initiated with 2-hydroxyethyl methacrylate (HEMA), which provides the polyester chains with terminal vinyl groups. By varying the HEMA content, a range of MM chain lengths constructed from L₁₀C₄ (five l-LA and four ε-CL units) to L₁₀₀C₄₀ were obtained at a constant monomer mole ratio. Copolymerization of 2-ethylhexyl acrylate and acrylic acid with these MMs at constant mass composition provided a series of comb copolymers consisting of acrylic backbones with polyester branches of various chain lengths. Characterization of thin films cast from the polymers using thermal analysis and scanning probe microscopy showed a transition from a homogeneous phase to the formation of distinct microphases with increasing branching chain lengths. Rheological analysis of the linear viscoelastic responses was also used through small-amplitude oscillatory shear, and dynamic master curves were constructed by time-temperature superposition. The rheological data were also consistent with phase separation for the longer side-chain lengths of L₅₀C₂₀ and L₁₀₀C₄₀. The extra elastic contribution at low frequency and the temperature dependence of a _T both show obviously effect of separated phases. Performance testing of polymer films showed that the chain extension resulted in a significant increase in both peel strength and shear resistance, which was accompanied by a modest decrease in film tackiness. The results demonstrate that tailoring branch chain structures provide a promising means for controlling the properties of the high-biomass content adhesive polymers.

Importance of Substrate Functionality on the Adhesion and Debonding of a Pressure-Sensitive Adhesive under Water

We investigate the effect of an aqueous environment on the adhesion of a model acrylic pressure-sensitive adhesive (PSA) composed of 2-ethylhexyl acrylate-co-acrylic acid. We use probe-tack adhesion measurements accompanied by in situ imaging of the contact region during bonding and debonding. Within the probe-tack tests, we use both hydrophilic (piranha and plasma treatment) and hydrophobic (C₁₈-silanization) surface treatments to investigate the contribution of the probe's surface energy on the underwater adhesion. In examining contact formation in air and underwater, we find that the presence of water when contact is made leads to different modes of PSA relaxation and contact formation. For all probes investigated, the adhesive strength between the PSA and the probe decreases when measured underwater. Additionally, we observe that the presence of water during debonding has a more pronounced effect on the adhesive strength of the PSA when probed by a hydrophilic surface as opposed to a hydrophobic surface. Using fingering wavelength analysis, we estimate the surface energy of the PSA in situ and find that when submerged in water, the PSA has a significantly higher surface energy compared to in air. Therefore, combining the observation of different modes of contact formation, the increase in surface energy, and the importance of the surface energy of the probe, we suggest that the decrease in adhesive strength in water can be explained by the hydration of the PSA and by trapped water defects between the PSA and the probe.

Thermoplastic Polyurethanes Stemming from Castor Oil: Green Synthesis and Their Application in Wood Bonding

We report an efficient and green approach to synthesize a linear castor oil-based polyurethane (CPU) without using any solvent or catalyst. Diol monomers were first synthesized by the aminolysis reaction between castor oil and diamines; this was accomplished within 6 h at 130 °C. Polymerization of the diols and isocyanate was further confirmed by Fourier transform infrared (FTIR), 1H-nuclear magnetic resonance (1H-NMR), and gel permeation chromatography analyses. The resultant CPUs showed a good thermal stability with an initial degradation temperature higher than 300 °C, and their mechanical and wood bonding property can be modulated by the structures of diamine. In addition, the CPUs possessed a satisfying water resistance property with the water absorption amount lower than 2%. The green conversion of castor oil to thermoplastic polyurethane affords new opportunities in bio-based industries.

Copolymers from epoxidized soybean oil and lactic acid oligomers for pressure-sensitive adhesives

Corn based lactic acid oligomers and soybean based epoxidized oil were copolymerized under UV irradiation for biobased pressure-sensitive adhesives (PSA).

Synthesis and characterization of acrylic polyols and polymers from soybean oils for pressure-sensitive adhesives

Soybean oil based acrylic polyol with modulated acrylate and hydroxyl functionalities was polymerized under UV radiation for biobased pressure-sensitive adhesives (PSA).

Surface-initiated self-healing of polymers in aqueous media

Polymeric materials that intrinsically heal at damage sites under wet or moist conditions are urgently needed for biomedical and environmental applications. Although hydrogels with self-mending properties have been engineered by means of mussel-inspired metal-chelating catechol-functionalized polymer networks, biological self-healing in wet conditions, as occurs in self-assembled holdfast proteins in mussels and other marine organisms, is generally thought to involve more than reversible metal chelates. Here we demonstrate self-mending in metal-free water of synthetic polyacrylate and polymethacrylate materials that are surface-functionalized with mussel-inspired catechols. Wet self-mending of scission in these polymers is initiated and accelerated by hydrogen bonding between interfacial catechol moieties, and consolidated by the recruitment of other non-covalent interactions contributed by subsurface moieties. The repaired and pristine samples show similar mechanical properties, suggesting that the triggering of complete self-healing is enabled underwater by the formation of extensive catechol-mediated interfacial hydrogen bonds.

High capacity, easy release adhesives from renewable materials

Reversible adhesives composed of renewable materials are presented which achieve high force capacities (810 N) while maintaining easy release (∼ 0.25 N) and reusability. These simple, non-tacky adhesives consist of natural rubber impregnated into stiff natural fiber fabrics, including cotton, hemp, and jute. This versatile approach enables a clear method for designs of environmentally-responsible, reversible adhesives for a wide variety of applications.