PLA composites were prepared using six lignocellulosic fibers with widely varying particle characteristics.The composites were characterized by tensile testing, scanning electron (SEM) and polarization optical (POM) microscopy. Micromechanical deformation processes during loading were followed by acoustic emission measurements. Interfacial adhesion was estimated by three independent methods. Contrary to most claims published in the literature, interfacial adhesion between PLA and natural fibers was found to be rather strong, a result confirmed by the quantitative estimation of adhesion strength, acoustic emission measurements and SEM study. Strong interfacial adhesion results in weak dependence of the extent of reinforcement on the particle characteristics of the reinforcing fibers. Both acoustic emission measurements and microscopy indicated that the dominating micromechanical deformation process is 2 the fracture of the fibers and close correlation was found between the initiation stress of fiber fracture, reinforcement and the ultimate strength of the composites.

Two reactive coupling agents, N,N-(1,3-phenylene dimaleiimide) (BMI) and 1,1-(methylenedi-4,1-phenylene)bismaleimide (DBMI) were used to improve interfacial adhesion in PLA/wood composites. First the effect of the coupling agents was established in a series of experiments in which the amount of coupling agent changed at constant wood content, and then the effect of coupling was determined at various wood loadings (0-60 vol%). Composites were homogenized in an internal mixer and compression molded to plates. Tensile properties were determined and micromechanical deformations were studied by acoustic emission measurements. The two compounds improved the properties of the composites. Stiffness, strength and deformability increased simultaneously supplying sufficient proof for coupling. Because of the flexibility of the molecule, DBMI is a more efficient coupling agent in the studied composites than BMI. However, the effect of coupling is small, because only a few very large particles debond under the effect of external load. Smaller particles adhere strongly to the matrix even without coupling proving that interfacial adhesion is strong in PLA/wood composites.

PLA biocomposites were prepared using three corncob fractions and a wood fiber as reference. The composites were characterized by tensile testing, scanning electron (SEM) and polarization optical (POM) microscopy. Micromechanical deformation processes were followed by acoustic emission measurements. The different strength of the components was proved by direct measurements. Two consecutive micromechanical deformation processes were detected in composites containing the heavy fraction of corncob, which were assigned to the fracture of soft and hard particles, respectively.The fracture of soft particles does not result in the failure of the composites that is initiated either by the fracture of hard particles or by matrix cracking. Very large particles debond easily from the matrix resulting in catastrophic failure at very low stresses. At sufficiently large shear stresses large particles break easily during compounding, thus reinforcement depending on interfacial adhesion was practically the same in all composites irrespectively of initial fiber characteristics.

Crystallization kinetics of β-nucleated isotactic polypropylene (β-iPP) under isothermal conditions were investigated by differential scanning calorimetry (DSC). iPP was nucleated by a trisamide derivative, namely tris-2,3-dimethyl-hexylamide of trimesic acid (TATA). In the presence of TATA possessing dual nucleating ability, the formation of the α-and β-form occurs simultaneously. An isothermal stepwise crystallization (ISC) method is suggested in this work, which can separate the crystallization process of β-and α-iPP and consequently their crystallization kinetics can be evaluated separately. The results indicated that the mechanism of crystallization changes in temperature especially in the vicinity of the upper critical temperature of the formation of the β-phase. In addition, it was found that the ratio of the growth rates of β-and α-modification determines the characteristics of crystallization and influences the apparent rate constant of crystallization of both polymorphs.