• Employing a novel bioelastomer to toughen polylactide

      Kang, H.; Qiao, B.; Wang, R.; Wang, Z.; Zhang, L.; Ma, J.; Coates, Philip D. (2013)
      Biodegradable, biocompatible polylactide (PLA) synthesized from renewable resources has attracted extensive interests over the past decades and holds great potential to replace many petroleum-derived plastics. With no loss of biodegradability and biocompatibility, we highly toughened PLA using a novel bioelastomer (BE)–synthesized from biomass diols and diacids. Although PLA and BE are immiscible, BE particles of ∼1 μm in diameter are uniformly dispersed in the matrix, and this indicates some compatibility between PLA and BE. BE significantly increased the cold crystallization ability of PLA, which was valuable for practical processing and performance. SEM micrographs of fracture surface showed a brittle-to-ductile transition owing to addition of BE. At 11.5 vol%, notched Izod impact strength improved from 2.4 to 10.3 kJ/m2, 330% increment; the increase is superior to previous toughening effect by using petroleum-based tougheners.
    • Highly toughened polylactide with novel sliding graft copolymer by in situ reactive compatibilization, crosslinking and chain extension

      Li, X.; Kang, H.; Shen, J.; Zhang, L.; Nishi, T.; Ito, K.; Zhao, C.; Coates, Philip D. (2014-08-05)
      The “sliding graft copolymer” (SGC), in which many linear poly-ε-caprolactone (PCL) side chains are bound to cyclodextrin rings of a polyrotaxane (PR), was prepared and employed to toughen brittle polylactide (PLA) with methylene diphenyl diisocyanate (MDI) by reactive blending. The SGC was in situ crosslinked and therefore transformed from a crystallized plastic into a totally amorphous elastomer during reactive blending. Meanwhile, PLA-co-SGC copolymer was formed at interface to greatly improve the compatibility between PLA and SGC, and the chain extension of PLA also occurred, were confirmed by FTIR, GPC, SEM, and TEM. The resulting PLA/SGC/MDI blends displayed super impact toughness, elongation at break and nice biocompatibility. It was inferred from these results the crosslinked SGC (c-SGC) elastomeric particles with sliding crosslinking points performed as stress concentrators and absorbed considerable energy under impact and tension process.
    • Tough bio-based elastomer nanocomposites with high performance for engineering applications

      Wei, T.; Lei, L.; Kang, H.; Qiao, B.; Wang, Z.; Zhang, L.; Coates, Philip D.; Hua, K-C.; Kulig, J. (2012)
      Biomass feedstock is a viable alternative to finite fossil fuel resources to provide many of the same—plus others that petrochemicals cannot—chemical building blocks required to fabricate durable and high-performance materials. We demonstrate here for the first time a new generation of synthesized elastomers, namely bio-based engineering elastomers (BEE). These are of particular significance because they are synthesized from monomers derived from biomass, by routes which are suitable for large scale production, and they exhibit thermo-mechanical properties at least equivalent to current commercial petrochemical-derived elastomers. Bio-based monomers in large scale production, such as sebacic acid, itaconic acid, succinate acid, 1,3-propanediol, and 1,4 butanediol are chosen to generate the first synthetic BEE matrix through melting polycondensation—a comparatively simple reaction scheme offering good control and the potential for low cost, large-scale production. A novel linear BEE, an almost non-crystalline copolyester elastomer with low glass transition temperature (Tg) containing double bonds is designed and synthesized using multiple monomers (to help suppress crystallization). Silica nanoparticles are then introduced into the BEE matrix to achieve significant strengthening and improved environmental stability. Chemical crosslinks formed by peroxide and the pendant double bonds in the copolyester macromolecules endow the BEE with both the necessary high elasticity and required environmental stability. The BEE nanocomposites obtained exhibit excellent thermomechanical properties, such as an ultimate tensile strength of 20 MPa.