Shibing Bai

Morphology, mechanical and thermal oxidative aging properties of HDPE composites reinforced by nonmetals recycled from waste printed circuit boards

In this study nonmetals recycled from waste printed circuit boards (NPCB) is used as reinforce fillers in high-density polyethylene (HDPE) composites. The morphology, mechanical and thermal oxidative aging properties of NPCB reinforced HDPE composites are assessed and it compared with two other commercial functional filler for the first time. Mechanical test results showed that NPCB could be used as reinforcing fillers in the HDPE composites and mechanical properties especially for stiffness is better than other two commercial fillers. The improved mechanical property was confirmed by the higher aspect ratio and strong interfacial adhesion in scanning electron microscopy (SEM) studies. The heat deflection temperature (HDT) test showed the presence of fiberglass in NPCB can improve the heat resistance of composite for their potential applications. Meanwhile, the oxidation induction time (OIT) and the Fourier transform infrared (FTIR) spectroscopy results showed that NPCB has a near resistance to oxidation as two other commercial fillers used in this paper. The above results show the reuse of NPCB in the HDPE composites represents a promising way for resolving both the environmental pollution and the high-value reuse of resources.

Control over crystalline form in polypropylene pipe via mandrel rotation extrusion

In this paper, isotactic polypropylene pipes were prepared via mandrel rotation extrusion and the effects of mandrel rotation speed on crystalline form of Polypropylene (PP) pipes were investigated. The results indicated that properly high mandrel rotation speed could promote the growth of β crystal markedly in the inner surface of PP pipes, while too high mandrel rotation speed could induce the formation of α column crystal and suppress the formation of β crystal. However, only similar α spherulites appeared in the outer layer of PP pipes prepared by different mandrel rotation speed. This implied there should be different key factors impacting the crystalline form along thickness direction of PP pipes: for external layer, its “cooling rate controlled” and for internal layer, its “mandrel rotation speed controlled”. As a result, gradient crystalline structure was obtained by the compounding effects of cooling rate and mandrel rotation speed.

Influence of Shearing on Crystallization Behavior of Polyoxymethylene/Poly(Ethylene Oxide) Crystalline/Crystalline Blends

The effect of shearing on crystallization behavior of a crystalline/crystalline blend, polyoxymethylene [POM]/poly(ethylene oxide) [PEO], was investigated using polarized light microscopy connected with a CSS450 shearing hot-stage, scanning electron microscopy, differential scanning calorimetry [DSC], and x-ray diffraction [XRD]. The experimental results indicated that the shearing made POM and PEO disperse more evenly and increased the inclusion and entanglement effects between the molecular chains of POM and PEO and therefore enhanced the influence of PEO on the crystallization of POM. As a result, the blend sheared at a shear rate of 20 s−1 for 10 min at 160°C formed shish–kebab crystals and produced more interlamellar structures compared with the formation of perforated spherulites in the unsheared blend. Moreover, a more obvious shoulder melting peak of POM appeared in the DSC heating trace and a new diffraction peak occurred at 2θ = 31.7° in the XRD pattern for the sheared POM/PEO [50/50] blend.

Effect of blend composition on crystallization behavior of polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

The influence of blend composition on crystallization behavior of a typical crystalline/crystalline blend, polyoxymethylene (POM)/poly(ethylene oxide) (PEO), during slow non-isothermal crystallization was investigated by polarized light microscope (PLM) connected with a THMS600 hot-stage, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The experimental results indicated that with increasing PEO content in the blend, the crystallization temperature of POM of the blends reduced and the multiple crystalline morphologies or structures including two kinds of interfibrillar or interlamellar structures were produced. The melting point of each component decreased with raising the content of the other constituent due to the inclusion and entanglement between POM and PEO molecules. The shoulder melting peak of POM appeared in DSC heating traces of the PEO-rich blend because the stronger inclusion and entanglement induced the imperfect crystallization of POM.

The Effect of Cooling Mode on Slow Crack Growth Resistance of Polyethylene Pipe

High-density polyethylene (HDPE) pipes have been widely used as gas or water transport pipes owing to their comprehensive advantages. One of the principal failure modes determining pipe service lifetime is slow crack growth (SCG) with the crack occurring first at the inner surface due to the slow cooling rate of the pipes inner wall during polyethylene (PE) pipe extrusion. In order to change the conventional cooling mode and increase the cooling rate in the inner wall of PE pipe during extrusion, a novel extrusion equipment was designed and manufactured by our research team. For this paper, compressed air as a cooling medium was introduced through the interior of the hot extruded pipe during its extrusion to realize the quick inner wall cooling, and the effects of the inner walls cooling rate on the microstructure and mechanical properties of the PE pipe were investigated. The experimental results showed that simultaneously cooling of both the outer and inner walls could decrease the difference in the solidification rate across the pipe and reduce the residual internal stresses in PE pipe. The quick cooling of the inner wall of the extruded pipe could also decrease the PE crystal thickness, and increase the number of tie molecules in the inner wall, which is a key parameter determining the resistance to SCG. As a result, compared to the PE pipe produced by the conventional extrusion, the crack initiation time of the PE pipe manufactured by the novel method increased from 27 h to 45 h and the crack growth rate was slower.

Influence of Solid-state Shear Milling on Structure and Mechanical Properties of Polypropylene/Polyethylene Blends

ABSTRACT A polypropylene/polyethylene (50/50) blend was prepared at ambient temperature through a solid-phase mechanochemical reactor and is shown to have potential for development as an effective way of recycling mixed plastic waste. The changes of structure and properties of the prepared blend were systematically investigated. It was found that polypropylene and polyethylene phase dimensions significantly reduced and compatibility between phases was enhanced after co-milling. The excellent impact toughness is mainly attributed to the uniform dispersion of the polypropylene and polyethylene phases in the blend and the compatibilization effect of the PP/PE-grafted copolymers produced by the three-dimensional shearing force. GRAPHICAL ABSTRACT

High-performance Thermal and Electrical Conductive Composites from Multilayer Plastic Packaging Waste and Expanded Graphite

Plastic film packaging waste is an important environmental concern worldwide, and finding effective ways to reuse multilayer plastic packaging waste (MPW) presents major challenges. However, current recycling technologies for multilayer plastic packaging often lead to low-quality products. Herein, we reported a facile route to produce value-added MPW composites with high isotropic thermal conductivity and efficient electromagnetic interference shielding effectiveness (EMI SE) for the first time. Using solid-state shear milling (S3M) technology, flaky MPW powder is successfully fabricated, which is followed by a powder mixing (PM) and compression molding process to produce a continuous expanded graphite (EG) network. As a result, the MPW/EG-PM composites (31.6 vol%) exhibit a superb through-plane thermal conductivity of 9.7 W m−1 K−1 and an anisotropy of 1.1. The Agari model fitting coefficient revealed the effective fabrication of a continuous 3D network and the finite element simulation visually confirmed the excellent heat-transfer capabilities of the filler network in the MPW/EG-PM composites. Moreover, such a 3D network also led a low electrical conductivity percolation threshold of 2.6 vol%, a high EMI SE of 44.8 dB and satisfactory mechanical strength. Such materials not only remove environmental pollution but also have potential applications in the cooling electronics and electromagnetic interference shielding areas.