Chemical advances are increasing the proportion of polymer waste that can be recycled

Vegetable oils are an attractive source for polymers due to their low cost, abundance, annual renewability, and ease of functionalization. Stearyl and lauryl acrylate, derived from vegetable oils such as soybean, coconut, and palm kernel oil, have been polymerized through reversible addition−fragmentation chain transfer polymerization, resulting in poly(styrene-b-(lauryl acrylate-co-stearyl acrylate)-b-styrene) (SAS) triblock copolymers. Varying the length of the side chain on the polyacrylate midblock (C18 and C12 in stearyl and lauryl acrylate repeat units, respectively) is a convenient tool for tuning the physical properties of the triblock copolymers. The SAS triblock copolymers exhibit properties appropriate for thermoplastic elastomer (TPE) applications. Small-angle X-ray scattering and transmission electron microscopy experiments have elucidated the microphase-separated morphology of the SAS triblock copolymers, consistent with a spherical morphology lacking long-range order. The physical properties of the polymers can be readily tuned by varying the acrylate midblock composition, including the melting temperature, viscosity, and triblock copolymer tensile properties. Tensile testing reveals elastomeric behavior with high elongation at break. Surprisingly, the order−disorder transition temperature of the triblock copolymer is not dependent on the acrylate composition in the midblock. This indicates that the acrylate composition can be used as a tool to manipulate the physical properties of the triblock copolymers without affecting the order−disorder transition temperature, or processing temperature, of the TPEs.

Polymerized soybean oil (polySOY) and isotactic poly(L-lactide) (PLLA) were melt blended to increase the toughness of PLLA in an all renewable blend. The polySOY samples were prepared by crosslinking soybean oil by the addition of a free radical crosslinking agent or by heating the oil in the presence of oxygen. Soybean oil is relatively nonreactive compared to other vegetable oils, and conjugation of the double bonds within the fatty acid chains of the soybean oil triglyceride prior to crosslinking led to significantly increased reactivity. Poly(isoprene-b-L-lactide) block copolymers were used to compatibilize the blends due to the high degree of immiscibility between PLLA and polySOY. The blending of polySOY and PLLA resulted in significant improvements in the tensile toughness of the blend compared to neat PLLA. The blend morphology was dependent on the polySOY gel fraction or weight-average molar mass; the polySOY characteristics were key indicators of the tensile toughness.

Ring-opening bulk polymerization of L-lactide using N-2-hydroxyethylmaleimide (HEMI) as the initiator and tin(II) 2-ethylhexanoate as the catalyst produced a reactive end-functionalized poly-(L-lactide) (HEMI-PLLA). Melt blends of HEMI-PLLA and conjugated soybean oil (CS) were prepared. HEMI-PLLA underwent a Diels-Alder reaction with the CS to high conversion, coupling the two immiscible components. Up to three HEMI-PLLA molecules reacted with one CS molecule to create products with varying architecture that acted as compatibilizers for the melt blend. Blends of HEMI-PLLA and 5 wt % CS resulted in a greater than 17-fold increase in elongation to break compared to PLLA homopolymer and more than doubled the elongation to break compared to a 5 wt % CS blend with unreactive PLLA. Analysis of the blend morphology indicated that the in situ formation of the compatibilizer decreased the CS droplet diameter compared to unreactive binary blends and that an optimum droplet diameter exists for toughening PLLA with CS.

Polylactide (PLA), a commercially available thermoplastic derived from plant sugars, finds applications in consumer products, disposable packaging, and textiles, among others. The widespread application of this material is limited by its brittleness, as evidenced by low tensile elongation at break, impact strength, and fracture toughness. Herein, a multifunctional vegetable oil, acrylated epoxidized soybean oil (AESO), was investigated as a biodegradable, renewable additive to improve the toughness of PLA. AESO was found to be a highly reactive oil, providing a dispersed phase with tunable properties in which the acrylate groups underwent cross-linking at the elevated temperatures required for processing the blends. Additionally, the presence of hydroxyl groups on AESO provided two routes for compatibilization of PLA/AESO blends:(1) reactive compatibilization through the transesterification of AESO and PLA and (2) synthesis of a PLA star polymer with an AESO core. The morphological, thermal, and mechanical behaviors of PLA/oil blends were investigated, in which the dispersed oil phase consisted of AESO, soybean oil (SYBO), or a 50/50 mixture of AESO/SYBO. The oil additives were found to toughen the PLA matrix, with significant enhancements in the elongation at break and tensile toughness values, while maintaining the glass transition temperature of neat PLA. In particular, the blend containing PLA, AESO, SYBO, and the PLA star polymer was found to exhibit a uniform oil droplet size distribution with small average droplet size and interparticle distance, resulting in the greatest enhancements of PLA tensile properties with no observable plasticization.