TOUGHNESS MODIFICATION OF PLA BIOCOMPOSITES

Abstract: High brittleness of polylactic acid (PLA) is the main drawback for the use of this material in the packaging sector. To overcome this drawback, there are many PLA blends with other thermoplastic tough materials. To maintain the biodegradable properties of PLA blends, the preparation of blends with other biodegradable materials is preferred. The most commonly used are poly(3-hydroxybutyrate) (PHB) and polybutylene adipate terephthalate (PBAT). The disadvantage of PHB is its high price, and the disadvantage of PBAT is the incompatibility of PLA and PBAT. For PLA-PBAT blends, multifunctional reactive polymers are used as reactive compatibilizers. For packaging applications, epoxy oligomers can be used as reactive compatibilizers. To reduce the price of PLA blend, biomass can be added as filler. In the present work, the PLA matrix was mixed with 15 wt.% and 20 wt.% PBAT in the presence of a multifunctional reactive polymer with epoxy groups. As biomass, 5 wt.% and 10 wt.% of hops were added along with compatibilizer. The mechanical, thermal and impact properties were tested and evaluated. The presence of hops keeps the thermal properties of biocomposites at the level of pure PLA. The addition of PBAT lowers the stiffness and strength, but dramatically increases the toughness of the biocomposites. In biocomposites, cold crystallization of PLA occurs at lower temperatures compared to neat PLA. From the results, we can conclude that hops increases the stiffness and decreases the glass transition temperature, while the addition of PBAT decreases the stiffness and glass transition temperatures, but both together act as nucleating agents for the crystallization of PLA matrix. Reactive compatibilization was successful as the biocomposite exhibited over 200 % higher impact strength and over 240 % higher elongation at break compared to the neat PLA matrix. The biocomposites are cheaper alternative and can be used in the packaging sector due to their good stiffness, strength, toughness and low price compared to the petroleum-based materials currently used in the packaging sector. Another advantage is that biomass can be used as a filler in biocomposites without the need for surface treatment as a suitable compatibilizer is used.