Shear-induced crystallization of isotactic polypropylene within the oriented scaffold of noncrystalline ultrahigh molecular weight polyethylene

Fundamental studies on shear-induced nucleation and beta-phase formation in the isotactic polypropylene—effect of the temperature

The complex and incompletely understood phenomenon of shear-induced crystallization of polymers may be nowadays analysed via the in situ POM-shear stage methodology. In this research, the two main issues were investigated with the use of the Linkam CCS450 shear stage connected with POM microscope. It was found that the secondary nucleation in the tree well-known temperature regimes plays the greater role in the overall crystallization kinetics than the shear induced primary nucleation. Furthermore, it was found that the tendency towards β-phase formation in shear conditions is dependent on the temperature value during shear treatment. It may be concluded that the temperature is the key parameter in the primary and secondary nucleation process and beta-phase formation in the iPP melts.

UHMWPE-Based Glass-Fiber Composites Fabricated by FDM. Multiscaling Aspects of Design, Manufacturing and Performance

The aim of the paper was to improve the functional properties of composites based on ultra-high molecular weight polyethylene (UHMWPE) by loading with reinforcing fibers. It was achieved by designing the optimal composition for its subsequent use as a feedstock for 3D-printing of guides for roller and plate chains, conveyors, etc. As a result, it was experimentally determined that loading UHMWPE with 17% high density polyethylene grafted with VinylTriMethoxySilane (HDPE-g-VTMS) was able to bind 5% glass fillers of different aspect ratios, thereby determining the optimal mechanical and tribological properties of the composites. Further increasing the content of the glass fillers caused a deterioration in their tribological properties due to insufficient adhesion of the extrudable matrix due to the excessive filler loading. A multi-level approach was implemented to design the high-strength anti-friction ‘UHMWPE+17%HDPE-g-VTMS+12%PP’-based composites using computer-aided algorithms. This resulted in the determination of the main parameters that provided their predefined mechanical and tribological properties and enabled the assessment of the possible load-speed conditions for their operation in friction units. The uniform distribution of the fillers in the matrix, the pattern of the formed supermolecular structure and, as a consequence, the mechanical and tribological properties of the composites were achieved by optimizing the values of the main control parameters (the number of processing passes in the extruder and the aspect ratio of the glass fillers).

Role of Melt Plasticizing Temperature in Morphology and Properties of PE100 Pipes Prepared by a Rotational Shear System

To increase the maximum internal pressure that a polyethylene (PE) pipe can withstand, a novel rotational shear system (RSS) was constructed in this study to fabricate PE pipes with enhanced hoop strength by applying hoop shear on the pipes using a rotational mandrel. The microstructure and morphology with the influences of melt plasticizing temperature on PE pipes processing under rotational shear were investigated indirectly using small-angle X-ray scattering and wide-angle X-ray diffraction (SAXS/WAXD) measurements. In the SAXS patterns, equatorial streaks and meridional scattering peaks were clearly observed in all three samples prepared at different melt plasticizing temperatures, 215, 235, and 255 °C. Their presence indicated that shish-kebab crystals form in rotational shear. Compared to those at the low melt temperature, the increase in the melt temperature enhanced the amount and the dimensions of shish formed. However, the shish also relaxed faster at the high melt temperature. This behavior was attributed to the enhancement of the molecular chain's athletic ability. The hoop tensile strength and the heat resistance of the pipes peaked at the melt plasticizing temperature of 235 °C, 75.2 MPa, 102.4 °C, up 1 MPa, 0.2 °C (compared to the 215 °C) and 7.8 MPa, 3.2 °C (compared to the 255 °C). The axial strength increased with an increase of melt plasticizing temperature. However, the increase of melt plasticizing temperature worsens the inherent good tensile toughness of PE100 pipes as the axial elongation at break decreases.

In Situ Time-Resolved X-ray Scattering Study of Isotactic Polypropylene in Additive Manufacturing

Using a specially designed apparatus, which collects simultaneous temperature and X-ray scattering data, we performed in situ measurements of the filament during MatEx 3D printing. The data show that the MatEx 3D printing extrusion process provides sufficient shear to form shish-kebab structures, which initially nucleate at the filament surface and spread into the filament core. Time-resolved measurements show that the kebab component near the surface relaxes after deposition of the second filament and enhances chain diffusion across the interface. SEM images indicate near complete interfacial merging of the filaments, which results in excellent mechanical properties.

A portable extruder for in situ wide angle x-ray scattering study on multi-dimensional flow field induced crystallization of polymer

We have designed and constructed a portable extruder with a rotatable mandrel, which can be employed to study the multi-dimensional flow field (MDFF) induced crystallization of polymer combined with in situ wide angle x-ray scattering (WAXS). With the piston driving the melt sample to flow along the channel, a direct axial shear field is achieved. At the same time, the central mandrel keeps rotating under a stable speed, providing the sample with an additional circumferential shear field. By presetting different proportions of the two shear fields, namely, axial and circumferential, various flow states of the sample can be obtained, which makes it capable of investigating the effects of MDFF on polymer crystallization. We have performed an in situ WAXS experiment of MDFF induced crystallization of isotactic polypropylene based on the portable extruder at the beam line BL16B in Shanghai Synchrotron Radiation Facility. The rheological and structural information is collected simultaneously, which manifests the viability of the portable extruder on regulating MDFF and can provide guidance for polymer processing.

Extensional rheometer for in situ x-ray scattering study on flow-induced crystallization of polymer

We designed and constructed an extensional rheometer for in situ small and wide angle x-ray study on flow-induced crystallization of polymer. Two rotating drums with an axis distance of 20 mm are employed to impose extensional deformation on the samples. With a constant angular velocity, the two drums generate a constant Henkcy strain rate as sample length for testing keeps constant during deformation. An ionic liquid is used as heating medium to prevent polymer melt from bending downward due to gravity, which is excellent in terms of high thermal stability, low viscosity, and relative low adsorption on x-ray. Flow-induced crystallization experiments are conducted with this apparatus on x-ray scattering station in Shanghai Synchrotron Radiation Facility (SSRF), which allows us to collect rheological and structural data simultaneously and may lead to a better understanding on flow-induced crystallization of polymer.