Continuously extruded micro‐textured polypropylene films

The continuous extrusion of micro‐textured isotactic polypropylene (i‐PP) film and its tribological properties are reported. As analyzed by scanning electron microscopy, a rectangular‐semicircular micro‐patterned die successfully produced extruded cast‐films with hill‐like micro‐texture. Such films displayed static and kinetic coefficients of friction (COF_s and COF_k) values of 0.247 ± 0.028 and 0.245 ± 0.003, respectively, for a steel fixture sliding along the micro‐texture of the film. The equivalent COF_s and COF_k values for non‐textured (NT) films were 0.369 ± 0.036 and 0.340 ± 0.024, respectively, confirming that textured films displayed a reduction in COF of about 30%. For textured and NT films sliding on textured films, the COF_k values were even lower at 0.161 ± 0.013 and 0.113 ± 0.004, which represents about 20–40% reduction as compared with that for the NT‐NT counterparts. Films coated with a silicone lubricant displayed COF_s and COF_k values of 0.334 ± 0.042 and 0.099 ± 0.012, respectively, for NT films sliding over lubricated NT films, and 0.426 ± 0.031 and 0.063 ± 0.006, respectively, for textured films sliding over lubricated textured films. The COF_k values for textured/non‐lubricated films approach those of NT/lubricated films, indicating that micro‐textured polypropylene films may be used in environmentally sensitive applications where lubricants and fluorinated additives may not be used for reducing friction. POLYM. ENG. SCI., 54:2147–2154, 2014. © 2013 Society of Plastics Engineers     

Calendered linear low‐density polyethylene consolidated meat and bone meal composites

Bioplastics produced from meat and bone meal (MBM) suffer from rapid and drastic mechanical property deterioration because of their hydrophilic nature. This study investigates mechanical and water stability of composites produced from introduction of a minor component of a synthetic polyethylene as a binder phase to consolidate MBM. The milled and sieved MBM was compounded with 5–60 wt % linear low‐density polyethylene (LLDPE) and formed into composite sheets by calendering, which is an industrially relevant process. Results indicated that a minimum of 15 wt % LLDPE content was required to form a nominally continuous binder phase that allowed for good processability and environment stability of the composites. As expected, the water vapor permeability (WVP) and water absorption characteristics of the composites were intermediate between those of MBM and LLDPE. Sheets containing 15 wt % LLDPE absorbed up to 35 wt % water. Composites tested after being soaked in water showed an initial decrease in TS of about 30% for the first hour but then remained fairly unchanged in the next 72 hours, confirming their moderate environment stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41145.     

Carbon fibers derived from UV‐assisted stabilization of wet‐spun polyacrylonitrile fibers

A rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40623.     

Thermal processing and properties of bioplastic sheets derived from meat and bone meal

Chemical modification of plasticized meat and bone meal (MBM) and its thermal processing into bioplastic sheets is reported. Specifically, MBM plasticized with 30 wt% glycerol and modified with calcium hydroxide (CH) (0, 3, 7, and 10 wt%) was batch compounded at 100°C, 15–30 min, and 60 rpm followed by thermal compaction at 140°C to produce sheets. The effect of CH content on the chemical structure, processability, and tensile properties (static and dynamic) of modified MBM sheets were studied. Fine particle size of MBM and moderate environment humidity produced well‐consolidated sheets. Increase in CH content to about 7 wt% was found to increase tensile strength and modulus, whereas the strain to failure decreased. Fourier transform infrared spectroscopy analysis of modified MBM sheets showed that the changes in mechanical properties could be attributed to increased interactions between protein chains, which were further aided by the precipitation of the fat portion of MBM. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polarized wave electromagnetic shielding of anisotropic carbon nanomodifier‐based LLDPE composites

The polarized wave electromagnetic shielding (EM SE) of nanocomposites containing 10 vol% of carbon nanomodifiers in a semicrystalline matrix is reported. Heat‐treated carbon nanofibers, Pyrograf^® III PR‐19 heat treatment (HT) and multiwalled carbon nanotubes (MWNT) HT were dispersed in a linear low‐density polyethylene matrix to produce flow‐induced orientation of the nanomodifiers in the spun microfilaments. Consequently, the electrical conductivity of the resulting nanocomposites exhibited anisotropic behavior due to the nanomodifier orientation. The in‐plane conductivity in the longitudinal direction (PR‐19 HT comp.: ～0.02 S/m; MWNT HT comp.: ～3 S/m) was at least an order of magnitude higher than that along the transverse direction. As measured with a rectangular waveguide (WR510, 1.45–2.2 GHz), the PR‐19 HT‐ and MWNT HT‐oriented nanocomposites (1‐mm thick) displayed EM SE values of 0.7 dB and 3.0 dB, respectively, when the nanomodifiers were transversely oriented with the polarized electric field. In contrast, when the orientation of the nanomodifiers was parallel with the field, EM SE values of 3.2 and 9.0 dB were obtained, respectively. The higher EM SE values are consistent with high conductivities observed in the direction of preferred orientation of the modifiers. POLYM. ENG. SCI., 55:299–307, 2015. © 2014 Society of Plastics Engineers     

Transient shear rheology and rheo‐optical microstructural characterization of a thermotropic liquid crystalline polymer

The shear rheology and the corresponding microstructure evolution during transient flow of a thermotropic liquid crystalline polymer (LCP; Vectran V400P) are reported; the polymer does not display a crystalline melting phenomenon. The steady shear viscosity displays three regions that are typical of LCPs. However, the transient shear stress displays a local stress maximum at a strain of ≈ 2, a local minimum at a strain of ≈ 20, and then a stress overshoot at a strain of ≈ 100 before attaining a steady state value. The transient first normal stress difference exhibits a distinct overshoot at ≈ 100 strain units. The steady‐state first normal stress difference is always positive in the tested shear rate range 0.1–10 s^–1. In situ rheo‐optical characterization revealed that the melt shows a threaded texture at rest. Upon start up of shear flow, this threaded texture becomes deformed, and the domains initially appear to stretch and align in the shearing direction. Next, the domains break up, and a significant drop in the optical intensity is observed. These microstructural features are used to explain the presence of the first maximum and the minimum observed in the transient shear stress. Polym. Eng. Sci. 45:187–197, 2005. © 2005 Society of Plastics Engineers.     

Influence of drapability by using stitching technology to reduce fabric deformation and shear during thermoforming

Forming of woven fabric into a complex shape involves shear deformation of the fabric elements (warp and weft). Various researchers investigated the shear deformation during the manufacturing of thermoplastic composites (TPC) based on the hemispherical geometry, where the highly deformed edges and corners are considered as a waste. In many applications the complete formed geometry including areas around the curvature has to be used. A new idea to influence the deformation behavior of woven fabric by incorporated seams at localized sections is presented in this paper. The study is based on the photographic analysis of dry sewn preforms and thermoplastic matrix (PA12) impregnated laminates, before and after the deformation. The seams applied at the highly deformable and predefined zones help to reduce fabric shearing or to transfer the shear forces into the unsheared areas during the thermoforming process. The intensity of reduction in the fabric shear depends on the type of the sewn geometry. The results obtained can be applied in the part design, the preform engineering, and the positioning of stitches.