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1. Latex Adhesives from Plant Oils for Multisubstrate Applications

   Iryna Bon, Vasylyna Kirianchuk ( April 2021 , ACS Spring 2021)

   ACS (Ed.)

   High functionality of new adhesives based on vinyl monomers from plant oils (POBMs) can be controlled by physico-chemical properties of latexes synthesized from POBMs. This research aims to improve the performance and sustainability of POBM-based latex adhesives. Elaborating on this concept, camelina (CMM) and high oleic soybean oil-based (HOSBM) monomers were incorporated into latex copolymers to evaluate adhesives performance on multiple substrates. Life Cycle Assessment (LCA) method was used as a tool to evaluate the environmental performance of the synthesized biobased latex adhesives. Latex adhesives were synthesized from combination of methyl methacrylate (MMA), butyl acrylate (BA) and POBMs at various monomer ratios. The MMA content in monomer mixture was kept at 55 wt%, while BA (within remaining 45 wt% of the feed) has been gradually replaced by POBM in monomer feed, yielding feasible latex adhesive formulations. Latex adhesives performance was evaluated using peel testing (ASTM D 1876-08) on the multiple substrates. Presence of HOSBM and CMM fragments in latex copolymers improves adhesives peel strength on most substrates. It was found that performance of POBM-based adhesives can be improved by varying adhesive consumption. It was shown that the incorporation of POBMs into latex copolymers enhances hardness of the latex films upon formation of latex networks. LCA results demonstrated a positive environmental impact when BA was replaced with POBM leading to a lower toxicity for latex adhesives overall. To address the hotspots pinpointed by conducting the initial LCA a number of strategies were implemented. The environmental performance of the biobased adhesive was improved by synthesizing POBM using 2-Methyl-tetrahydrofuran – an environmentally friendly alternative of widely used solvent tetrahydrofuran. Additionally, monomer washing step was improved by replacing dichloromethane with hexane, a solvent with a relatively lower environmental impact. Finally, comparison of the several monomers used for synthesis of the adhesive showed that POBM had the lowest negative impact on the environment as well as human health in various categories. In summary, the obtained experimental data demonstrate plant-oil based latexes environmental benefits and potential as adhesives as well as their utility for usage on multiple substrates. 

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2. Sustainable glucose-based block copolymers exhibit elastomeric and adhesive behavior

   https://doi.org/10.1039/c6py00700g  

   Nasiri, Mohammadreza ; Reineke, Theresa M. ( January 2016 , Polymer Chemistry)

   Herein, we present the direct modification of glucose, an abundant and inexpensive sugar molecule, to produce new sustainable and functional polymers. Glucose-6-acrylate-1,2,3,4-tetraacetate (GATA) has been synthesized and shown to provide a useful glassy component for developing an innovative family of elastomeric and adhesive materials. A series of diblock and triblock copolymers of GATA and n -butyl acrylate (n-BA) were created via Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. Initially, poly(GATA)- b -poly(n-BA) copolymers were prepared using 4-cyano-4-[(ethylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CEP) as a chain transfer agent (CTA). These diblock copolymers demonstrated decomposition temperatures of 275 °C or greater and two glass transition temperatures ( T g ) around −45 °C and 100 °C corresponding to the PnBA and PGATA domains, respectively, as measured by differential scanning calorimetry (DSC). Triblock copolymers of GATA and n-BA, with moderate dispersities ( Đ = 1.15–1.29), were successfully synthesized when S , S -dibenzyl trithiocarbonate (DTC) was employed as the CTA. Poly(GATA)- b -poly(nBA)- b -poly(GATA) copolymers with 14–58 wt% GATA were prepared and demonstrated excellent thermomechanical properties ( T d ≥ 279 °C). Two well-separated glass transitions near the values for homopolymers of n-BA and GATA (∼−45 °C and ∼100 °C, respectively) were measured by DSC. The triblock with 14% GATA exhibited peel adhesion of 2.31 N cm −1 (when mixed with 30 wt% tackifier) that is superior to many commercial pressure sensitive adhesives (PSAs). Use of 3,5-bis(2-dodecylthiocarbonothioylthio-1oxopropoxy)benzoic acid (BTCBA) as the CTA provided a more efficient route to copolymerize GATA and n-BA. Using BTCBA, poly(GATA)- b -poly(nBA)- b -poly(GATA) triblock copolymers containing 12–25 wt% GATA, with very narrow molar mass distributions ( Đ ≤ 1.08), were prepared. The latter series of triblock copolymers showed excellent thermal stability with T d ≥ 275 °C. Only the T g for the PnBA block was observed by DSC (∼−45 °C), however, phase-separation was confirmed by small-angle X-ray scattering (SAXS) for all of these triblock copolymers. The mechanical behavior of the polymers was investigated by tensile experiments and the triblock with 25% GATA content demonstrated moderate elastomeric properties, 573 kPa stress at break and 171% elongation. This study introduces a new family of glucose-based ABA-type copolymers and demonstrates functionality of a glucose-based feedstock for developing green polymeric materials. 

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3. Mechanical reinforcement of waterborne latex pressure‐sensitive adhesives with polymer‐grafted nanoparticles

   https://doi.org/10.1002/pol.20230355  

   Desroches, Griffen J. ; Gatenil, Perapat P. ; Nagao, Keisuke ; Macfarlane, Robert J. ( August 2023 , Journal of Polymer Science)

   Waterborne pressure sensitive adhesives (PSAs) consisting of polymer microparticle emulsions (i.e. latex) are more commonly used in commercial applications than solvent‐borne alternatives, as the use of water as a suspension medium provides better consumer safety and reduces environmental impact. However, the lower mechanical performance of waterborne PSAs prevents their use in applications requiring permanent adhesion or strong bonding between substrates. This reduction in mechanical strength is often attributed to void spaces that form during water evaporation and coalescence of the latex particles, and thus a potential strategy to improve PSA strength would be to add filler materials to occupy these voids. Fundamental studies investigating how interfacial interactions between the latex and fillers affect the collective strength of the films would enable better design of adhesive compositions to tailor PSA mechanical properties. Here we report the use of polymer brush‐grafted nanoparticles (PGNPs) as a means of mechanically reinforcing the PSAs, and determine how different aspects of the particle and polymer brush designs enable this improvement in adhesive performance. The PGNPs investigated here are intentionally designed to phase segregate into the aqueous phase of the initial latex suspension, which allows them to both fill free pore volume and also form multivalent supramolecular interactions with the latex particles to form polymer bridges that improve the interconnectivity of the final film. These studies provide insight into potential design strategies for tuning PSA properties with PGNPs, and enable up to 32% improvements to the cohesive strength of the PSAs without the typical deterioration of adhesive strength observed in PSAs using non‐brush‐coated particle fillers.

    

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4. Allyl Sulfides in Garlic Oil Initiate the Formation of Renewable Adhesives

   https://doi.org/10.1039/D3PY00390F  

   Sayer, Kyler B. ; Miller, Veronica L. ; Merrill, Zackery ; Davis, Anthony E. ; Jenkins, Courtney L. ( January 2023 , Polymer Chemistry)

   The development of inverse vulcanization has provided a simple method to create sulfur-based materials. The low cost, ease of synthesis, and variety of applications has led to a rapid expansion of the field. These polysulfides can be synthesized with a wide range of sulfur contents (20-90% S) depending on the desired properties. Garlic essential oil (GEO) has a high sulfur content, which offers the opportunity to replace sulfur, a petroleum byproduct, with a renewable monomer to make materials with moderate sulfur contents. Using a one-pot, solvent-free synthesis, comparable to inverse vulcanization, GEO can be polymerized to create renewable adhesives at temperatures as low as 120 °C with reaction times decreasing at higher temperatures. Here we have explored the composition of garlic oil from a variety of commercial suppliers by NMR. Through simple 1H NMR analysis, the major sulfur-containing compounds of GEO can be identified and differentiated by sulfur rank. These data were used to select garlic oils with varied compositions to examine the impact on the poly(GEO) properties using solubility, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis as well as adhesive performance. GEO was then subjected to different reaction times and temperatures and the degree of polymerization was monitored by 1H NMR. The polysulfides were then evaluated as adhesives at different extents of polymerization to better understand how the reaction conditions impact adhesive performance. The failure mode and mechanical properties of the polymers were analyzed using measurements of maximum adhesion strength and work of adhesion. This study has provided a better understanding of polymers formed from GEO, providing a viable route to developing renewable, S-based materials. 

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5. A comparison of adhesive polysulfides initiated by garlic essential oil and elemental sulfur to create recyclable adhesives

   https://doi.org/10.1039/D2PY00418F  

   Davis, Anthony E. ; Sayer, Kyler B. ; Jenkins, Courtney L. ( August 2022 , Polymer Chemistry)

   Despite adhesives having their origins in natural materials, most glues are formed from petroleum-based products. However, many natural adhesives lack the strength to compete with synthetic glues. Therefore, strong, sustainable alternatives are needed. Data presented here build on prior work that combines elemental sulfur, a petroleum byproduct, and garlic essential oil (GEO) which is composed of allyl sulfides, to make adhesives. Here, we have demonstrated that both sulfur and GEO can initiate polymerization at 160 °C with another petroleum byproduct, dicyclopentadiene, and a variety of natural monomers through the formation of sulfur radicals. In addition to using natural monomers and petroleum byproducts, these processes are solvent free and have high atom economy, limiting waste formation, and meeting many principles of green chemistry. Much of this work has focused on determining the effect of each sulfur source on polymerization and adhesion. A family of polymers were created with varied S : GEO : monomer ratios and characterized to determine differences in their chemical and materials properties. Despite similarities in the reaction mechanism, sulfur tends to polymerize more rapidly and create materials that are more ductile and more easily reprocessed. GEO is slower to react causing more polymerization to take place on the adherend surface yielding a more brittle polymer with higher maximum adhesion strength but lower work of adhesion. Both polymers exhibited effective adhesive recyclability. Overall, a combination of natural oils and petroleum byproducts were combined to make inexpensive, sustainable, recyclable adhesives. 

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