On the performance of biodegradable self-reinforced composites (SRCs) based on poly(lactic acid) (PLA)

FRERKING, MARÍA EMILIA; ROUYER, ARTHUR; BUTTO, MARTÍN; BOVI, JIMENA; MELAJ, MARIANA; BERNAL, CELINA

Merseburg

Conferencia; Internationale wissenschaftliche Tagung Polymertec 2021digital; 2021

Hochschule Merseburg

The growing concern of society on the limited availability of fossil fuel resources has aroused much interest in bio-based materials. At the same time, the extensive use and non-biodegradable character of traditional plastics derived from fossil fuels leading to significant waste accumulation have triggered extensive research on biodegradable polymers which under appropriate conditions will break down far more quickly. Among them, poly(lactic acid) (PLA) is one of the best candidates as a result of its good combination of mechanical properties, renewable origin, biodegradability in compost and relatively low cost. Thus, PLA is an excellent substitute to commodity polymers in different applications such as packaging, textiles, bottles, bags and automotive parts. However, its relatively brittle nature and low thermal stability still limit its use in a great number of applications. Hence, PLA is commonly combined with other polymers, different types of particles or fibres. On the other side, natu-ral fibre-reinforced polymer composites have attracted significant interest in the last dec-ades due to their outstanding environmental-friendly characteristics such as non-toxicity, low density, biodegradability and cheap production cost, being considered as good alterna-tives to fossil fuel-based polymers. Among natural fibres, the refined form of wood pulp: microcrystalline cellulose (MCC), appears as an appealing reinforcing filler for polymers due to its remarkable properties such as fire resistance, anti-abrasiveness, and biocompatibility [1]. In addition, self-reinforced composites (SRCs) or all-polymer composites have been de-veloped to overcome the difficulty of traditional composites to be recycled. In SRCs, the rein-forcement is composed of highly oriented strong fibres or tapes, while the matrix is a poly-mer of the same chemical nature but with lower melting or softening point. In this way, fully recyclable light composites having excellent adhesion between phases can be obtained. Ex-tensive literature exists regarding the preparation and characterization of self-reinforced composites based on synthetic polymers as well as on bio-based ones [2–5]. Self-reinforced composites compete with traditional composites in many applications depending on their performance/cost ratio. In the present work, biodegradable self-reinforced composites based in a PLA matrix reinforced with high strength PLA fibres were obtained by film-stacking followed by compression molding. PLA was also compounded in an intensive mixer with different contents of microcrystalline cellulose fibres to be used in the form of com-pression moulded films as the matrix of the SRCs. The morphology-processing-properties relationship of the different developed composites was investigated. The effect of the self-reinforced composites consolidation temperature was also studied. The morphology of the matrix films was analyzed by scanning electron microscopy (SEM) on cryo-fractured surfaces obtained at liquid nitrogen temperature. While the PLA film exhibited a smooth fracture sur-face, matrix films containing MCC presented increased roughness with significant evidence of cellulose fibres aggregation. In addition, some gaps between the aggregates and the ma-trix were clearly observed suggesting a weak interaction between the hydrophilic MCC and the hydrophobic PLA. Differential scanning calorimetry (DSC) analysis indicated that MCC acted as nucleating agent for PLA crystallisation and that, irrespectively of the SRCs consoli-dation temperature, the PLA fibres maintained their structure after moulding. Uniaxial ten-sile tests were also carried out for both the matrix films and the self-reinforced composites. The results for the matrix films indicated that the incorporation of MCC was detrimental to tensile strength, ductility and toughness, whereas stiffness values remained practically invar-iable. These results can be attributed to the above mentioned incompatibility between MCC and PLA and the subsequent fibres aggregation. In the SRCs, the increase in the consolida-tion temperature led to improvements in most of the tensile properties, especially in tough-ness, while the addition of MCC in the matrix films had a negative effect on these properties. Finally, disintegration tests in composting conditions at 58 °C were carried out for the differ-ent SRCs. These tests showed that the material with the highest content of MCC (20 wt.%) was visibly disintegrated after 30 days, while the other composites did not present signifi-cant morphological changes after the same burial time. Further work is still needed to obtain SRCs based on PLA which exhibit simultaneous improvements in tensile properties and disin-tegration ability with respect to neat PLA.