Acetyl tri-n-butyl citrate (ATBC) and poly-(ethyleneglycol)s (PEGs) with different molecular weights (from 400 to 10000) were used in this study to plasticize poly(L-lactic acid) (PLA). The thermal and mechanical properties of the plasticized polymer are reported. Both ATBC and PEG are effective in lowering the glass transition (T g ) of PLA up to a given concentration, where the plasticizer reaches its solubility limit in the polymer (50 wt % in the case of ATBC; 15-30 wt %, depending on molecular weight, in the case of PEG). The range of applicability of PEGs as PLA plasticizers is given in terms of PEG molecular weight and concentration. The mechanical properties of plasticized PLA change with increasing plasticizer concentration. In all PLA/plasticizer systems investigated, when the blend T g approaches room temperature, a stepwise change in the mechanical properties of the system is observed. The elongation at break drastically increases, whereas tensile strength and modulus decrease. This behavior occurs at a plasticizer concentration that depends on the T g -depressing efficiency of the plasticizer.

Simple esterification and etherification reactions were applied to steamexploded Flax (Linum usitatissimum) with the aim of changing the surface properties through modification of fiber surface chemistry. Native and chemically modified cellulose fibers were characterized in terms of thermal stability, surface chemistry, morphology, and crystal structure. Independent of the substituent nature, chemically modified fibers exhibited a thermal stability comparable to that of native cellulose. Introduction of the desired chemical groups at the fiber surface was demonstrated by TOF-SIMS analysis, whereas FTIR showed that the substitution reaction involved only a small fraction of the cellulose hydroxyls. No change of the native crystalline structure of cellulose fibers was caused by chemical modification, except in the case where ether substitution was carried out in water-isopropanol medium. Cellulose fibers with unchanged structure and morphology and carrying at the surface the desired chemical groups were obtained for reinforcing applications in polymer composites.

The kinetics of the enzymatic degradation of bacterial poly(3-hydroxybutyrate) (PHB) is studied using PHB-depolymerase A from Pseudomonas lemoignei (Tris−HCl buffer, pH = 8, T = 37 °C). Biodegradation experiments are performed on PHB in the form of both compression-molded films and powder suspension. From WAXS and DSC measurements the two substrates show the same crystalline fraction. The rate of hydrolysis of PHB films is determined by gravimetry and also through spectrophotometric quantification of the hydrolysis products at λ = 210 nm. For the suspension of PHB particles, a turbidimetric determination of the biodegradation rate is applied. A simple two-step kinetic model is proposed, which predicts that the hydrolysis rate per unit substrate surface area reaches a plateau at high enzyme concentrations. The model satisfactorily describes the enzymatic degradation results of PHB film and PHB powder suspension, provided that the remarkable changes of exposed area caused by enzymatic attack to the latter substrate are taken into account. Analysis of the enzymatic degradation results yields analogous hydrolysis rate constants for film (1.48 μg cm-2 min-1) and powder suspension (1.42 μg cm-2 min-1).