The influence of formation temperatures on the crystal structure and mechanical properties of ultrahigh-molecular-weight polyethylene/high-density polyethylene-blend fibers prepared by melt spinning

The influence of spinning temperature on ultrahigh-molecular-weight polyethylene/high-density polyethylene as-spun blend filaments and the influence of drawing temperature on ultrahigh-molecular-weight polyethylene/high-density polyethylene-blend fibers were investigated. The results showed that the optimum spinning and hot-drawing temperatures were 310℃ and 85℃, respectively, and blending with high-density polyethylene improved the orienting ability of the molecular chains and the crystallization ability. The blend filaments spun at 310℃ had the best molecular chain orientation, crystallinity and crystal orientation of the filaments examined; both lower and higher spinning temperatures were detrimental to the crystal structure growth of the as-spun blend filaments. The optimum drawing temperature of the blend fibers was 85℃, which resulted in blend fibers with the best molecular chain orientation, crystallization, and crystal orientation as well as the thinnest grains of the fibers examined. The highest tensile strength and initial modulus were 1204 MPa and 20.4 GPa, respectively; these high values can be attributed to the fibrillar structure, which consisted of extended molecular chains and thin grains. The results in this paper can help disclose the effect mechanism of formation temperature on the melt spinning method used to produce high-strength ultrahigh-molecular-weight polyethylene fibers.

Thin-wall injection molding of high-density polyethylene for infrared radiation system lenses

High-density polyethylene (HDPE) lenses are used for infrared radiation (IR) systems, such as radiation thermometers to transmit the IR of the 10 μm region. High IR transmittance and low visible ray (VR) transmittance are necessary for IR system lenses. This experimental investigation of thin-wall injection molding was conducted using 0.5 mm cavity thickness with a disk shape, finished to a mirror-like surface. As factors affecting transmittance, we evaluated the thickness, surface roughness, crystallinity, internal structure, and molecular chain orientation of molded parts, which were produced using four HDPE melt flow rates (MFRs). The changed molding conditions were mold temperature and holding pressure. Results showed that the thin-molded parts had higher IR transmittance. The thin-molded part was obtained with the smallest MFR of 5. Furthermore, the VR transmittance decreased when the molecular chain orientation in the molded parts was small and the crystallinity was high. The small orientation and high crystallinity were obtained simultaneously with the largest MFR of 42. Therefore, it was impossible to obtain high IR transmittance and low VR transmittance simultaneously by a change of MFR. This study confirmed that surface roughness and crystallinity do not affect transmittance.

Crystallization by thermal processing of Poly(lactide) stereocomplex thin films

Various properties of polymers such as optical, barrier and mechanical properties are substantially anisotropic, since molecular orientations of polymer chains strongly affect the physical properties. Controlling the chain orientation in the semicrystalline polymers can thus lead us to valuable technological breakthroughs. Polymer ultrathin films have attracted great attention due to their vast applications. In thin films, the molecular chain orientation depends on the method of processing, thickness and substrate interactions. In the present study, we report on the crystallization condition dependent molecular chain orientation and crystallinity peculiar to the ultrathin films of biodegradable Poly(lactide) (PLA) stereocomplex (SC) with thicknesses ranging from several nm to several hundred nm. Equimolar solution of two enantiomers of PLA, poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) has attracted great attention because of the formation of SC which shows decent physical properties better than PLLA and PDLA. Combination of surface sensitive X-ray diffraction and scattering techniques, including grazing incidence wide angle X-ray diffraction (GIWAXD), X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) measured at synchrotron radiation facility (SPring-8, Japan) and infrared reflection absorption spectroscopy (IR-RAS) were used to characterize the film structures. In the SC films, two different polymer chain configurations, i.e., lying molecules and standing molecules revealed to be controlled by simple thermal processes.