We used dynamic mechanical analysis (DMA) to evaluate soy flour adhesives made with and without a conventional crosslinking agent, polyamideamine-epichlorohydrin (PAE). Fixed-frequency and constant strain rate studies revealed that PAE contributes to a decrease in glass transition temperature (T_g), an increase in toughness, and a decrease in both the rubbery plateau modulus and onset temperature, consistent with plasticization. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) studies of water-soluble extracts from pre-cured soy flour revealed the presence of polypeptides with exchangeable protons, carbohydrates, citric acid and lactic acid. Deuterium exchange studies showed that the protonated peptides were no longer water-soluble after cure. Instead, post-cure extracts contained heat-modified carbohydrates and carboxylic acids, together with adipic acid when PAE was employed. These results are consistent with a mechanism whereby PAE not only undergoes hydrolysis and chain scission, but also competitively co-reacts with peptides and carboxylic acids to yield a plasticized chain-extended network with decreased crosslink density, counter to its anticipated function. The implications of these findings as they pertain to moisture resistance and wood adhesion will be discussed.

Biocomposites have recently received more attention because of raising environmental awareness and the drive toward sustainable technologies. The most common biodegradable polymer is poly(lactic acid) (PLA), which has an excellent balance of physical and rheological properties, but there is some limit to its usage. PLA properties can be improved by adding different types of fibers or fillers that come from agricultural waste. In this study, corn cob and lavender stem were used to reinforce PLA without any coupling agent, and the properties of the composites were investigated. The melt flow rate (MFR) values decreased with the corn cob content and increased with the addition of lavender stem. Mechanical tests showed that the tensile and flexural modulus of the composites increased and the strengths decreased with the reinforcement material content. The rigidness of PLA slightly decreased with the addition of fillers. There was no significant effect on the thermal properties. The unremarkable improvement of the reinforcement was due to the lack of appropriate adhesion of the two phases. The structure of the compounds was found to be homogenous on the scanning electron microscopy (SEM) micrographs. The incorporation of corn cob and lavender stem can reduce the production cost of materials.

Biodegradable biopolymers like polyhydroxybutyrate (PHB) hold promise for sustainable packaging, but their inherent degradability reduces material stability. Synthetic stabilizers, though effective, raise environmental and potential toxicity concerns. This study explores a multifunctional natural anti-aging agent: a hemp extract rich in cannabidiol (CBD) and cannabichromene (CBC). PHB composites with varying hemp extract concentrations were prepared and subjected to thermooxidative and weathering aging. Characterization employed FTIR-ATR, carbonyl index, and spectrophotometry. Static mechanical properties, DSC, and surface free energy (SFE) were also assessed. Notably, the hemp extract exhibited stability under ambient conditions but showed migration with time and aging. The results suggest a plasticizing effect on PHB and highlight the contrasting roles of the extract: inhibiting thermooxidative aging while potentially accelerating aging under atmospheric conditions. This opens avenues for tailoring material durability, further evaluated by life cycle analysis (LCA). This work represents one of the first investigations into hemp extract as an anti-aging agent for eco-friendly polymers, expanding the knowledge base of natural multifunctional additives.

This is an editorial article. It has no abstract.

The augmented demand for sustainable nanocomposites has paved the way to explore naturally derived materials. Nanocellulose, with its bountiful sources and inherent properties, ranks top in the list of biofillers with a perspective of reducing the carbon footprint. A systematic study is required to understand the reinforcing effect of various types of nanocellulose. In the present work, we selected three types of nanocellulose, i.e., cellulose nanocrystal (CNC), cellulose nanofiber (CNF) and microfibrillated cellulose (MFC), to investigate the effect of geometrical structure on the properties of unvulcanized natural rubber (NR). Incorporating these fillers improved the tensile strength and modulus of natural rubber films significantly through reinforcement via filler network structure. The reinforcing effect of CNF was found to be higher compared to CNC and MFC, where an increase of 3.85 MPa in tensile strength from the neat sample was obtained. More uniform dispersion was evident through transmission electron microscopy, atomic force microscopy and Raman imaging for CNF in the rubber matrix. The structural properties were determined using Raman spectra and X-ray diffraction. The rheological studies revealed a good interaction between filler and NR. The work presented comprehensively compares different types of nanocellulose as reinforcing filler in NR matrix, which will help the researchers select an ideal type for their specific application and, thus, the proper usage of renewable resources, leading to sustainability and a circular economy.