Influence of agro-industrial wastes over the abiotic and composting degradation of polylactic acid biocomposites

Abstract

Combining polylactic acid (PLA) with waste fibers to produce reinforced biocomposites is of top interest to replace conventional polymers for environmentally friendlier materials. Natural fibers have a remarkable effect on the mechanical and thermal properties of the biocomposites. This reinforcing effect strongly depends on the chemical compositions of fibers, which will also influence the susceptibility of the biocomposites to abiotic and biotic degradation processes. This study evaluated the effect of agave and coir waste fibers over the abiotic and composting degradation of PLA-based biocomposites. Compression-molded PLA/agave and PLA/coir biocomposites using GMA-g-PLA as compatibilizer were subjected to accelerated weathering. Weathered and unweathered samples were further submitted to water absorption to analyze their hydrolytic degradation and composting for biotic degradation. Both fibers showed significant influence on biocomposites degradation. The role of the fibers in UV and hydrolytic degradation was positive for impact properties since the biocomposites were less affected than PLA. Water uptake was increased with fiber addition, while hydrolytic degradation was decreased. The weathering (abiotic degradation) accelerated the PLA biodegradation rate. In general, the results showed that adding both fibers to PLA could help its outdoor performance, maintaining the biodegradable characteristics of these materials.

Mechanical recycling of PLA: Effect of weathering, extrusion cycles, and chain extender

“…The higher disintegration occurred after 20 days, which agrees with the results obtained by Arrieta et al and Ghorpade et al, which mention that PLA presents more significant degradation after 2 weeks of composting 44,45 . This behavior is because, during the first days of composting, the microorganisms adapt to the environment, and the high molecular weight PLA chains begin to hydrolyze to form lower molecular weight chains to be later metabolized by the microorganisms 30,46 . The samples subjected to weathering (PLAW and PLAEW) showed faster disintegration with each reprocessing cycle; combined hydrolysis and UV light start the degradation of PLA, causing shorter polymeric chains that microorganisms can easily consume.…”

“…The initial carbonyl index for PLA was 3.43, and the values corresponding to the samples reprocessed by extrusion showed slight increases in the intensity of this signal which occurred by the oxidation reactions that induce the formation of carboxylic acids. The samples exposed to weathering and extrusion presented higher increases in carbonyl groups; this is due to photo‐oxidation, which occurs mainly by the Norrish II mechanism, which has as its final stage the formation of chains with carbonyl terminal groups, which causes an increase in this index 30 . Similar results are obtained with the PLAEJW samples.…”

“…The samples exposed to weathering and extrusion presented higher increases in carbonyl groups; this is due to photo-oxidation, which occurs mainly by the Norrish II mechanism, which has as its final stage the formation of chains with carbonyl terminal groups, which causes an increase in this index. 30 Similar results are obtained with the PLAEJW samples. The samples exposed to weathering without extrusion presented decreases in the carbonyl groups.…”

“…44,45 This behavior is because, during the first days of composting, the microorganisms adapt to the environment, and the high molecular weight PLA chains begin to hydrolyze to form lower molecular weight chains to be later metabolized by the microorganisms. 30,46 The samples subjected to weathering (PLAW and PLAEW) showed faster disintegration with each reprocessing cycle; combined hydrolysis and UV light start the degradation of PLA, causing shorter polymeric chains that microorganisms can easily consume. In this sense, the addition of Joncryl was a concern for the composting of PLA since it was expected that longer chains would be more difficult to disintegrate.…”

On the Production of Poly(Lactic Acid) (PLA) Compounds with Metallic Stearates Based on Zinc, Magnesium and Cobalt. Investigation of Torque Rheometry and Thermal Properties

“…20,21 From the point of view of technical characteristics, PLA has high tensile strength, high elastic modulus, good transparency, biocompatibility, and good processability, generating potential for applications in packaging and the biomedical area. [22][23][24] Thus, PLA is considered a bioplastic with all the characteristics to replace traditional plastic. 25 However, the main drawback of PLA is its low impact strength, which limits its application in parts that require high impact.…”