Unexpected Toughening of Poly(lactic acid) by Microwave-Assisted Devulcanization of Waste Latex Rubber

Abstract

Vulcanized, foamed latex rubber features high density of intercommunicated cells and controlled elastomeric properties, rendering wide applications from elastic sponges to rubbery coatings. This provides an emergent incentive for properly recycling, devulcanizing and reusing the waste latex rubber (WLR). Here, a microwave-assisted devulcanization (MAD) approach was disclosed to cleave the cross-links without severe rupture of backbone rubber chains, strategically involving the use of a microwave-assisted hydrothermal reaction at 180 °C for several minutes and incorporation of graphene nanosheets serving as the nanoabsorbers of microwave irradiation. The MAD processing duration was examined to be a vital parameter controlling the macromolecular characteristics: a high devulcanization degree of 83.6% was obtained with 8 min MAD, whereas the soluble content was undesirably increased to 76.2% after 16 min. The devulcanization efficacy was examined by melt compounding with poly(lactic acid) (PLA), displaying extensive interfacial interactions and thereby, creating strong and resilient interfacial adhesion within the PLA composites. With the addition of 10 wt % devulcanized WLR by 8 min MAD, the tensile strength and elongation at break of PLA composites were largely promoted to 58.2 MPa and 16.6%, increasing nearly 62% and 240% compared to those of pure PLA, respectively. The proposed MAD approach may open an environment-respecting and reliable pathway to sustainable recycling of waste rubber, yielding useful components to toughen PLA without sacrificing the strength.

Biodegradable MOFilters for Effective Air Filtration and Sterilization by Coupling MOF Functionalization and Mechanical Polarization of Fibrous Poly(lactic acid)

“…As revealed by the XRD profiles in Figure 4e, the prominent diffraction peak of pure PLA membranes was located at 2θ = 16.4°, attributed to the lattice planes (200)/(110), and crystallization exhibited α′ crystalline phase. 38 After MOF functionalization, slight right shifts were observed for all the prominent diffraction peaks, with the largest shift (2θ = 16.7°) in PLA@ZIF8-6 membranes. The addition of ZIF-8 crystals transformed the α′ crystalline phase to α crystalline phase, which increased the degree of order and decreased the crystal plane spacing.…”

“…The above results confirmed the formation of ZIF-8 crystals on the surface of PLA@ZIF8 membranes. As revealed by the XRD profiles in Figure e, the prominent diffraction peak of pure PLA membranes was located at 2θ = 16.4°, attributed to the lattice planes (200)/(110), and crystallization exhibited α′ crystalline phase . After MOF functionalization, slight right shifts were observed for all the prominent diffraction peaks, with the largest shift (2θ = 16.7°) in PLA@ZIF8-6 membranes.…”

A comprehensive review on polystyrene/waste rubber blends: Effective parameters on mechanical properties

“…14,15 In this process, the size of rubber particles is reduced, and their surface area is increased. The produced ground tire rubbers (GTRs) are used to improve some properties of polymers, for example, toughening brittle polymers like PS, poly(lactic acid), PLA, [16][17][18] and epoxy. [19][20][21] However, apart from the positive effects on the toughness, the addition of waste rubbers may result in some negative influences on other properties, such as the biodegradability and biocompatibility of PLA and the mechanical strength of epoxy.…”