Control over β-form hybrid shish-kebab crystals in polypropylene pipe via coupled effect of self-assembly β nucleating agent and rotation extrusion

Surface Roughening of Irradiation-Activated Basalt Fiber through In Situ Growth of SiO2: Effects on Crystallization and Properties of PP Composites

Basalt fiber (BF) is deemed a new environmentally friendly and high-performance fiber material due to its high strength, electrical insulation, corrosion resistance and high temperature resistance. Yet, the surface inertness restricts its practical application. In this work, the BF was irradiated and activated by electron beam, followed by in situ growth of SiO2 using a hydrothermal method, then composites with polypropylene (PP) were prepared by microinjection molding. According to the results of scanning electron microscopy (SEM) and Fourier transform infrared (FTIR), more active sites can be formed after irradiation, thus more SiO2 nanoparticles were generated on the surface of BF. Consequently, the rough surface of modified BF could provide stronger shear force during melt processing and resulted in a higher orientation of the molecular chains, increasing the lamellar thickness and generating more highly ordered β crystals in the composites. I400BF-gSiO2 exhibited the highest content of β crystals with the crystallinity of 53.62% and orientation of β (300) crystal plane of 0.91, which were 8.66% and 0.04 higher than those of the composite with pristine BF. Furthermore, due to the perfection of crystals, increased interfaces and interfacial interlocking between PP molecules and modified BF, I400BF-gSiO2 showed good overall performance, with storage modulus of 8000 MPa at -100 °C, glass transition temperature of 23.03 °C and tensile strength of 62.2 MPa, which was 1900 MPa, 1.23 °C and 29.6 MPa higher than neat PP. Hence, the surface roughing strategy proposed in this work is expected to provide some insight and promote the application of BF reinforced thermoplastic composites.

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

The rare earth nucleating agent was used to modify block copolymerized polypropylene (PPB) in foaming process. The results show that the crystallization of PPB and the melting temperature of β-crystal increased gradually with increased β-crystal nucleating agent content. The total crystallinity decreased with amount of addition increasing, and the relative content of β-crystal increased first and then decreased. When β-crystal nucleating agent content was 0.4 wt%, the relative β-crystal content reached the maximum value of 95.27%, and the final crystal grain refinement significantly. The addition of rare earth β-crystal nucleating agent has a good effect on improving the uniformity of foam cells. Under the same content of β-crystal nucleating agent and pressure, the average cell diameter and expansion ratio increased with the saturation temperature increasing. After the foaming temperature reaches 155°C, the expansion ratio began to decrease, which was also consistent with the changed trend of relative β-crystal content. At the same content of temperature and relative β-crystal, as the foaming pressure increased, the cell diameter decreased gradually, and the expansion ratio increased first, and then decreased.

Crystalline Modification of Isotactic Polypropylene with a Rare Earth Nucleating Agent Based on Ultrasonic Vibration

In this paper, the crystalline modification of isotactic polypropylene (PP) with a rare earth β nucleating agent (WBG) with different ultrasound conditions was investigated by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The relationship between the ultrasound conditions and the crystalline structure, as well as the mechanism for the behavior, were revealed. SEM showed that the dispersion of the nucleating agent in the PP matrix was better at shorter ultrasound distances. In addition, the higher the water cooling temperature, the better the nucleating agent was dispersed in the PP matrix. The results of XRD and DSC showed that the crystallinity and the relative content of the β-crystal were increased with nearer ultrasound distance, as well as increased in higher water cooling temperatures. In particular, under the same conditions, the crystallinity and the relative content of the β-crystal after ultrasonic treatment were much higher than those without ultrasound.

Facile Fabrication of Electrically Conductive Low-Density Polyethylene/Carbon Fiber Tubes for Novel Smart Materials via Multiaxial Orientation

Electromechanical sensors are indispensable components in functional devices and robotics application. However, the fabrication of the sensors still maintains a challenging issue that high percolation threshold and easy failure of conductive network are derived from uniaxial orientation of conductive fillers in practical melt processing. Herein, we reported a facile fabrication method to prepare a multiaxial low-density polyethylene (LDPE)/carbon fibers (CFs) tube with bidirectional controllable electrical conductivity and sensitive strain-responsive performance via rotation extrusion technology. The multidimensional helical flow is confirmed in the reverse rotation extrusion, and the CFs readily respond to the flow field leading to a multiaxial orientation in the LDPE matrix. In contrast to uniaxial LDPE/CF composites, which perform a "head to head" conjunction, multiaxial-orientated CF networks exhibit a unique multilayer structure in which the CFs with distinct orientation direction intersect in the interface, endowing the LDPE/CF composites with a low percolation threshold (15 wt %) to those of the uniaxial ones (∼35 wt %). The angles between two axes play a vital role in determining the density of the conductive networks in the interface, which is predominant in tuning the bending-responsive behaviors with a gauge factor range from 12.5 to 56.3 and the corresponding linear respond region from ∼15 to ∼1%. Such a superior performance of conductive LDPE/CF tube confirms that the design of multiaxial orientation paves a novel way to facile fabrication of advanced cost-effective CF-based smart materials, shedding light on promising applications such as smart materials and intelligent engineering monitoring.

Influence of different β-nucleation agents on poly(l-lactic acid): structure, morphology, and dynamic mechanical behavior

The WBG-II and TMB-5000 are both effective nucleating agents, which not only can enhance the crystallization rate, but also alter the packing structure of PLLA chain in the crystals.