Balázs Imre

Adhesion and micromechanical deformation processes in PLA/CaSO4 composites

PLA/CaSO4 composites were prepared from uncoated and stearic acid coated filler particles in a wide composition range. The strength of interfacial adhesion was estimated quantitatively with three independent methods. Structure was characterized by DSC, XRD and SEM measurements, while mechanical properties by tensile and instrumented impact tests. The results proved that adhesion is twice as strong in composites prepared with the uncoated particles than in those containing the coated filler. Coating changes also local deformation processes around the particles. Although debonding is the dominating micromechanical deformation process in all composites, local plastic deformation is larger around coated particles. The extent of this deformation depends very much also on the local distribution of particles. The final properties and performance of the composites depend unambiguously on the micromechanical deformation processes occurring during loading, on debonding and the subsequent plastic deformation. Stearic acid used for the coating of the filler seems to dissolve in the polymer and locally change its properties.

Physical ageing and molecular mobility in PLA blends and composites

Poly(lactic acid) (PLA) blends and composites were prepared from thermoplastic starch, poly(butylene-adipate-co-terephtalate), polycarbonate, wood flour and CaSO4 in a wide range of compositions. The thermal transitions of PLA were studied by differential scanning calorimetry. The detailed analysis of the transitions of PLA/thermoplastic starch blends indicated that they all are determined by the molecular mobility of PLA chains. Blending changes molecular mobility, and thus it often decreases glass transition temperature and modifies the extent of enthalpy relaxation. All other transitions and characteristics, i.e. cold crystallization, melting and the corresponding enthalpies, change accordingly. Increased molecular mobility accelerates also the physical ageing of the polymer. The interaction between PLA and the various components used for modification changed in a wide range, but no direct correlation was found between the strength of interaction and molecular mobility.