Wood fiber-reinforced composites were prepared from poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB/HV) copolymers containing 9 and 24% valerate. The effects of fibers on crystallization were investigated. Thermomechanical pulp, bleached Kraft fibers, and microcrystalline cellulose filler were used as the reinforcing phase. The crystallization of PHB/HV in composite materials was examined using Modulated Differential Scanning Calorimetry (MDSC) and hotstage microscopy. Hot-stage microscopy showed that polymer crystallites are nucleated on the fiber surface and that the density of nuclei was greater in fiber-reinforced composites than in unfilled material. Dynamic crystallization experiments showed that bleached Kraft, thermomechanical pulp, and microcrystalline cellulose increased the crystallization rate of PHB and PHB/HV both from the glass and melt. However, ultimate crystallinity determined from the heat of crystallization was the same in unreinforced and reinforced materials. The kinetics of PHB/HV crystallization were examined using nonisothermal Avrami-type analysis. Unreinforced and Kraft-reinforced PHB were characterized and compared with unreinforced PHB/9%HV. The Avrami exponent of crystallization, related to nucleation mechanism and growth morphology, is 2.0 for unreinforced PHB, 2.8 for kraft-reinforced PHB, and 3.0 for unreinforced PHB/9%HV.

SYNOPSISThe effect of fiber reinforcement on the crystallization kinetics of poly (ethylene terephthalate) , or PET, was investigated using differential scanning calorimetry. The objective of the study was to determine how the effects of fiber reinforcement on P E T crystallization are modified by the presence of polymer nucleating and plasticizing additives. Unidirectional fiber composites were prepared using aramid and glass fibers in PET. The rate of crystallization of PET, as reflected by crystallization half-time, is seen to depend on reinforcing fiber type, crystallization temperature, and presence of nucleant or plasticizer. However, degree of crystallinity of P E T is largely unaffected by the presence of additives and reinforcing fibers. Crystallization kinetics are analyzed using the Avrami model for P E T volume crystallized as a function of time. Avrami plots for P E T and fiber-reinforced PET exhibit two linear regions, possibly corresponding to primary and secondary crystallization. The crystalline morphology of fiber-reinforced P E T was also studied using polarized light microscopy. Results concerning nucleation density and growth morphology are used in explaining differences seen in crystallization kinetics in fiber-reinforced systems. 0 1994 John

No abstract

The crystallization and transition temperatures of poly(ethy1ene terephthalate) (PET) in blends with polycarbonate (PC) is considered using thermal analysis. Additives typically used in commercial polyester blends, transesterification inhibitor and antioxidant, are found to enhance the crystallization rate of PET. Differential scanning calorimetry (DSC) reveals two glass transition temperatures in PET/PC blends, consistent with an immiscible blend. Optical microscopy observations are also consistent with an immiscible blend. Small shifts observed in the TB of each component may be due to interactions between the phases. The degree of crystallinity of PET in PET/PC blends is significantly depressed for high PC contents. Also, in blends with PC content greater than 60 w t %, two distinct crystallization exotherms are observed in dynamic crystallization from the melt. The isothermal crystallization kinetics of PET, PET modified with blend additives, and PET in PET/PC blends have been evaluated using DSC and the data analyzed using the Avrami model. The crystallization of PET in these systems is found to deviate from the Avrami prediction in the later stages of crystallization. Isothermal crystallization data are found to superimpose when plotted as a function of time divided by crystallization half-time. A weighted series Avrami model is found to describe the crystallization of PET and PET/PC blends during all stages of crystallization.

No abstract