Rigid and film bioplastics degradation under suboptimal composting conditions: A kinetic study

Mature compost promotes biodegradable plastic degradation and reduces greenhouse gas emission during food waste composting

Mature compost can promote the transformation of organic matter (OM) and reduce the emission of polluting gases during composting, which provides a viable approach to reduce the environmental impacts of biodegradable plastics (BPs). This study investigated the impact of mature compost on polybutylene adipate terephthalate (PBAT) degradation, greenhouse gas (GHG) emission, and microbial community structure during composting under two treatments with mature compost (MC) and without (CK). Under MC, visible plastic rupture was advanced from day 14 to day 10, and a more pronounced rupture was observed at the end of composting. Compared with CK, the degradation rate of PBAT in MC was increased by 4.44 % during 21 days of composting. Thermobifida, Ureibacillus, and Bacillus, as indicator species under MC treatment, played an important role in PBAT decomposition. Mature compost reduced the total global warming potential (GWP) by 25.91 % via inhibiting the activity of bacteria related to the production of CH4 and N2O. Functional Annotation of Prokaryotic Taxa (FAPROTAX) further revealed that mature compost addition increased relative abundance of bacteria related to multiple carbon (C) cycle functions such as methylotrophy, hydrocarbon degradation and cellulolysis, inhibited nitrite denitrification and denitrification, thus alleviating the emission of GHGs. Overall, mature compost, as an effective additive, exhibits great potential to simultaneously mitigate BP and GHG secondary pollution in co-composting of food waste and PBAT.

Short- and long-term toxicity of nano-sized polyhydroxybutyrate to the freshwater cnidarian Hydra viridissima

The accumulation of increasingly smaller plastic particles in aquatic ecosystems is a prominent environmental issue and is causing a significant impact on aquatic biota. In response to this challenge, biodegradable plastics have emerged as a potential ecological alternative. Nevertheless, despite recent progress in polymer toxicology, there is still limited understanding of the ecological implications of biodegradable plastics in freshwater ecosystems. This study evaluated the toxicity of polyhydroxybutyrate nano-sized particles (PHB-NPLs) on the freshwater cnidarian Hydra viridissima assessing individual and population-level effects. Data revealed low toxicity of PHB-NPLs to H. viridissima in the short-term, as evidenced by the absence of significant malformations and mortality after the 96-h assays. In addition, hydras exhibited rapid and complete regeneration after 96 h of exposure to PHB-NPLs. Feeding assays revealed no significant alterations in prey consumption behavior in the 96-h mortality and malformations assay and the regeneration assay. However, significantly increased feeding rates were observed after long-term exposure, across all tested concentrations of PHB-NPLs. This increase may be attributed to the organisms' heightened energetic demand, stemming from prolonged activation of detoxification mechanisms. These changes may have a cascading effect within the food web, influencing community dynamics and ecosystem stability. Furthermore, a dose-dependent response on the hydras' populational growth was found, with an estimated 20 % effect concentration (EC20,8d) on this endpoint of 10.9 mg PHB-NPLs/L that suggests potential long-term impacts on the population's reproductive output and potential depression and local extinction upon long-term exposure to PHB-NPLs on H. viridissima. The obtained data emphasizes the importance of evaluating sublethal effects and supports the adoption of long-term assays when assessing the toxicity of novel polymers, providing crucial data for informed regulation to safeguard freshwater ecosystems. Future research should aim to unravel the underlying mechanisms behind these sublethal effects, as well as the impact of the generated degradation products.

Morphology and Performance Relationship Studies on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Poly(butylene adipate-co-terephthalate)-Based Biodegradable Blends

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly(butylene adipate-co-terephthalate) (PBAT) blends hold great potential for use in sustainable packaging applications for their advanced performance. Understanding the structure-property relationship in the blends at various proportions is significantly important for their future application, which is addressed in this work. The study found that the inherent brittleness of PHBV can only be modified with the addition of 50 wt % PBAT, where co-continuous structures formed in the blend as revealed by scanning electron microscopy (SEM) analysis. The elongation at break (%) of the blends increased from 3.81 (30% PBAT) to 138.5% (50% PBAT) and 345.3% (70 wt % PBAT), respectively. The fibrous structures of the PBAT formed during breaking are beneficial for energy dissipation, which greatly increased the toughness of the blends. Both the SEM observation and glass-transition temperature study by dynamic mechanical analysis indicated that the PHBV and PBAT are naturally immiscible. However, by simply mixing the two polymers with different composition ratios, the properties including melt flow index, heat deflection temperature, and mechanical properties can be tailored for different processing methods and applications. Our research work herein illustrates the fundamental structure-property relationship in this popular blend of PHBV/PBAT, aiming to guide the future modification direction in improving their properties and realizing their commercial applications in different scenarios.

Use of Ricinus communis shredded material as filler in rotational molded parts to improve the bio-disintegration behavior

This paper focuses on the use of castor oil plant (Ricinus communis) as filler in rotomolded parts using polyethylene (PE) and polylactic acid (PLA) as polymer matrixes. The vegetable shredded material was used in 5 and 10% weight following a dry blending procedure and then rotomolded to obtain cube test parts. This material was characterized to determine its chemical composition, thermal stability, and structure. The NaOH-treated material shows reduced hemicellulose content and higher thermal stability. Obtained composite materials were characterized in terms of mechanical (tensile, flexural, and impact) and thermal properties, morphology, and bio-disintegration behavior. The use of Ricinus as filler in rotomolded PE composite decreases, in general terms, mechanical properties of neat PE, while no significant changes in thermal or bio-disintegration properties are found. On the contrary, PLA composites show higher tensile strength and similar Young's modulus than the matrix, although with reduced flexural and impact properties. Alkali-treated Ricinus material produces parts with higher porosity and thus, lower mechanical properties than composites with untreated material. Finally, the incorporation of this vegetal material modifies to a great extent the thermal properties of the PLA matrix. The bio-disintegration rate increases due to the use of fibers, probably because of the higher moisture absorption of composites.