PBT sheets were extruded from T-die using a single extruder and were winded by a take-up roller controlled at 50°C and with speed at 1.2 m/min. Oriented PBT sheets were prepared with various winding roll speeds at 3.6, 4.8 and 6.0 m/min. Fine structure and physical properties of PBT sheets thus obtained were investigated by measuring the molecular orientation, crystal structure, dynamic visco-elasticity, thermal and mechanical properties, sonic modulus, etc. PBT melts were found to be readily crystallizable in the sheet. In the case of roll drawing, the DRmax of PBT sheet was 5. The PBT sheets prepared from winding speed at 6 m/min showed polymorphism of both α- and β-form crystallites with crystallinity of about 24%. In the tri-directional WAXD patterns, the PBT sheets by the roll drawing method turned out to be oriented in the uniplanar-axial form. For the roll drawn PBT sheets with various winding speeds, large orientation effects were observed in the winding direction together with improved thermal and mechanical properties.
Poly(hexano-6-lactone) (PCL*) fibers were enzymatically degraded by a hydrolase in vitro. The extent of degradation of PCL fibers was examined by weight loss, mechanical properties loss such as tensile strength and ultimate elongation decreases, and visual observations by scanning electron microscopy. The in vitro degradation of PCL fibers was carried out using a lipoprotein lipase
(Lipase-PS) as a hydrolase. The kinetic study on the weight loss of PCL fiber accompanying the enzymatic degradation suggested that the degradation of PCL fibers gradually takes place from the surface, not bulk degradation. The rate of degradation was found to depend on draw ratio and crystallinity of the PCL fibers. The strength loss of PCL fibers in the course of degradation took place faster than the weight loss of PCL fibers. Sonic velocity measurements as well as dynamic mechanical properties of PCL fibers were also examined as a function of weight loss of sample fibers with Lipase-PS treatments. It was shown that sonic velocity and value of loss tangent d changed steeply for undrawn PCL fiber in the first step with enzymatic digestion.
Objectives: To assess risk factors for the growth and development of small-for-gestational age (SGA) infants whose birth weight was less than the 10th percentile.
Patients and methods: SGA infants who were admitted to the neonatal intensive care unit from 1995 to 1998 were enrolled in the study. Fifty-six SGA infants, having no chromosomal abnormalities, inherited diseases, TORCH infections, major anomaly and/or multiple birth, were divided into 34 asymmetrical and 22 symmetrical SGA infants by ≥ or <10th percentile head circumference (HC) at birth. The physical growth including HC, and the developmental quotient (DQ) and intelligent quotient (IQ) scores were evaluated up to 6 years of age.
Results: Symmetrical SGA infants had lower levels of weight, height and HC, but not of total DQ at 3 years or IQ scores at 6 years of age than asymmetrical SGA infants. The 21 SGA infants who had a HC less than the 10th percentile at 1 year of age (non-catch-up group) showed lower total DQ (mean 96 vs. 105) and IQ (82 vs. 102) scores than 34 SGA infants who had not (catch-up group).
Conclusions: These results suggested that psychomotor development of SGA infants depended on the HC at 1 year of age rather than that at birth.