Abstract
Lactic acid oligomers (OLAs) were in situ synthesized from lactic acid (LAc) and grafted onto chokeberry pomace (CP) particleboards by direct condensation. Biocomposites of poly (lactic acid) (PLA) and modified/unmodified CP particles containing different size fractions were obtained using a mini-extruder. To confirm the results of the grafting process, the FTIR spectra of filler particles were obtained. Performing 1HNMR spectroscopy allowed us to determine the chemical structure of synthesized OLAs. The thermal degradation of modified CP and biocomposites were studied using TGA, and the thermal characteristics of biocomposites were investigated using DSC. In order to analyse the adhesion between filler particles and PLA in biocomposites, SEM images of brittle fracture surfaces were registered. The mechanical properties of biocomposites were studied using a tensile testing machine. FTIR and 1HNMR analysis confirmed the successful grafting process of OLAs. The modified filler particles exhibited a better connection with hydrophobic PLA matrix alongside improved mechanical properties than the biocomposites with unmodified filler particles. Moreover, a DSC analysis of the biocomposites with modified CP showed a reduction in glass temperature on average by 9 °C compared to neat PLA. It confirms the plasticizing effect of grafted and ungrafted OLAs. The results are promising, and can contribute to increasing the use of agri-food lignocellulosic residue in manufacturing biodegradable packaging.
Highlights
These days, environmental issues are becoming key when designing plastic materials.Following the EU Strategy for Plastics in the Circular Economy [1], the goal is to achieve the sustainable management of the product at every stage of its life
Analyzing the chokeberry pomace (CP)-g-OLA-pure filler spectrum shows a peak at around 3200 cm−1 assigned to the OH stretching vibration decreased compared to ungrafted CP filler
It is a result of the esterification of the hydroxyl group by lactic acid (LAc), which results in a reduction in OH group concentration
Summary
Tg dueslight to thedecrease limitationinofTthe .mobility of chains by natural fibers embedded in the m1 This phenomenon is related to the plasticizing effect of OLAs matrix [54]. In this case, the Tg of neat PLA was found at 60 ± 0 °C; it decreased 2–3 °C and increasing PLA chain mobility [35]. Except for the unfilled PLA matrix, samples were after introducing unmodified CP filler This behavior can be caused by the presence of characterized by a double melting peak (Tm1 and Tm2 ). OLAs have an increasing impact on the degree of crystallinity [35]
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