Wei Gong

Preparation of a Novel Inorganic–Organic Nucleating Agent and Its Effect on the Foaming Behavior of Polypropylene

In this study, a supramolecular compound (Zn@Q[6]) was synthesized by cucurbit[6]uril (Q[6]) and zinc acetate [Zn(Ac)2] through a chemical method. Powder X-ray diffraction and X-ray crystallography analyses were conducted to confirm the crystallographic structure of Zn@Q[6]. Results showed that the four-coordinated Zn(II) centre coordinated with four chloride ions, and each [ZnCl4]2− anion interacted with three Q[6] molecules through hydrogen bonds between Q[6] and the chloridion of [ZnCl4]2−. Subsequently, Zn@Q[6], Zn(Ac)2 and the mixture of Zn(Ac)2 and Q[6] were introduced respectively as nucleating agents into polypropylene (PP) microcellular injection using azodicarbonamide (ADC) as a chemical blowing agent. Compared with Zn(Ac)2 and the mixture of Zn(Ac)2 and Q[6], improved cell morphology was obtained with addition of Zn@Q[6] obviously at relatively high injection temperatures, except 175u2009°C, at which no obvious improvement in Zn@Q[6] was observed. The underlying mechanisms were then discussed by thermal and rheological analyses. Zn@Q[6] could be a novel inorganic–organic nucleating agent that can suppress the catalysis activity of Zn(II) for the decomposition of ADC and PP.

Study on Foaming Behavior of Microcellular PP/Inorganic Powder Composites

The modified inorganic powder material (one-dimensional MgSO4 whisker, two-dimensional Mica, zero-dimensional SiO2 ) was added into polypropylene with 5% wt. The microcellular foam PP composite was prepared under the condition of twice-open mold. According to the principle of interfacial adhesion，Liquid-solid interface free energy of PP composite system was calculated by means of the contact angle. Based on heterogeneous nucleation theory, foaming behavior of microcellular foam material was characterized quantitatively by interfacial behavior. The effects of different inorganic powder material on foaming behavior were analyzed in microcellular foam polypropylene. The results indicated that the minimum nucleation energy barrier of PP/Mica composite system is 46.94N.mwith the nucleation rate in 5.53×1011. After foaming, the cell diameter of the composite is 22.1μm and the cell density is 6.92×108 months/cm3.

Effects of Process Conditions on Mechanics Properties of Micro-Foaming PP/GF Composites

The microcellular foaming PP/GF composites was made under the condition of twice-open mold by using chemical foaming injection method, according to glass fiber reinforced mechanism, the effect rule of GF on mechanics properties was studied in microcellular foam PP composites. The results showed that tensile and impact strength of Micro-foam PP/GF composites by one-step method were higher than that of micro-foam PP/GF composites by two-step method, when the content of GF is 30%, the tensile and impact strength of micro-foam PP/GF composites by one-step method can reach 55.72MPa and 7.5kJ/m2 respectively，one-step method can get higher strength and higher toughness micro-foam PP/GF composites.

Effects of Annealing Process on Crystallization and Low Temperature Resistance Properties of PP-R Composites

The effects of the annealing process on the mechanical properties and crystallization behaviors of polypropylene random copolymer (PP-R) composites were investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The experimental results indicated that the annealing process significantly influenced the comprehensive properties of PP-R composites. At temperatures below 23 °C, the impact strength of the PP-R composites annealed at 120 °C for 6 h was relatively high at 74.73 kJ/m2, which was 16.8% higher than that of the samples annealed at 80 °C for 6 h. At low temperatures (-30-0 °C), the impact strength ranged from approximately 13.31 kJ/m2 to 54.4 kJ/m2. In addition, the annealing process conducted at 120 °C for 6 h improved the crystalline structure and low-temperature toughness of the PP-R composites and induced α-form to β-form crystal transformation. The work provides a possible method to reinforce and toughen the semicrystalline polymer at low temperatures (-30-0 °C) by annealing.

Study on thermal insulation performance of EVA foaming materials

ABSTRACT Foaming EVA was prepared with molding method in this paper, the effect of the cell size, cell wall thickness and filling gas type on thermal insulation performance of foaming EVA were analysed by the mechanism of insulation. The results show that the cell size, cell wall thickness and filling gas type have a significant influences on the insulation performance. When the cell size is 71.3 μm, the thermal conductivity is the smallest at low frequency 1000 Hz, which is 0.042 W/ (m.k). When the cell wall thickness is 8.2 μm, thermal conductivity of foaming EVA is minimal, which is 0.045 W / (m.K), the insulation effect is ideal. When the filling gas is hydrogen, the thermal insulation performance of foaming EVA is poor, but when the filling gas is nitrogen, the result is opposite.

Effects of zinc acetate and cucurbit[6]uril on PP composites: crystallization behavior, foaming performance and mechanical properties

Abstract In this study, polypropylene (PP) foams were prepared with 1.0 wt% of cucurbit[6]uril (Q[6]), zinc acetate (Zn(Ac)2), Zn@Q[6] (a supramolecular compound synthesized from Q[6] and Zn(Ac)2), or a mixture of Zn(Ac)2 and Q[6] (weight ratio of 1:1) through injection molding in the presence of a chemical blowing agent, azodicarbonamide. The effect of the additions on the crystallization behavior and foaming performance of PP and the mechanical characterizations of the foaming samples were determined. The results showed that the additions can change the crystallization type from homogeneous to heterogeneous, increase the crystallization rate and shrink the size but increase the density of spherulites. Among the additions, Q[6] most significantly altered the crystallization properties. Scanning electron microscopy (SEM) images revealed that the PP foaming performance can be improved by Zn(Ac)2 addition at a lower temperature (175°C); however, further increasing the temperature had an undesirable effect. Q[6] exhibited the optimum foaming improvement effect on PP in a wide temperature range (175–195°C). Adding nanoparticles also enhanced the tensile properties, flexural strength and impact strength of foaming PP at low temperatures. However, with increasing temperature, the poor cell structure demonstrated undesirable effects in terms of tensile strength, flexural strength and impact strength.

Preparation of Microcellular Epoxy Foams through a Limited‐Foaming Process: A Contradiction with the Time–Temperature–Transformation Cure Diagram

3D cross-linking networks are generated through chemical reactions between thermosetting epoxy resin and hardener during curing. The curing degree of epoxy material can be increased by increasing curing temperature and/or time. The epoxy material must then be fully cured through a postcuring process to optimize its material characteristics. Here, a limited-foaming method is introduced for the preparation of microcellular epoxy foams (Lim-foams) with improved cell morphology, high thermal expansion coefficient, and good compressive properties. Lim-foams exhibit a lower glass transition temperature (Tg ) and curing degree than epoxy foams fabricated through free-foaming process (Fre-foams). Surprisingly, however, the Tg of Lim-foams is unaffected by postcuring temperature and time. This phenomenon, which is related to high gas pressure in the bubbles, contradicts that indicated by the time-temperature-transformation cure diagram. High bubble pressure promotes the movement of molecular chains under heating at low temperature and simultaneously suppresses the etherification cross-linking reaction during post-curing.

Injection processing and foaming behaviors of polypropylene composite foams

A volume-adjustable cavity of molding machine for polymer foaming was fabricated with renovation of an ordinary injection molding machine. Polypropylene (PP) composite foams were prepared by chemical foaming method via the volume-adjustable cavity of the molding machine. The decompressing and short shot processes in preparing the samples were carried out to adjust the cell structure of the foamed samples. The structures that foamed insufficiently, moderately, and excessively were observed in these two foaming processes. The foamed PP composite samples generated in decompressing process have more desirable cell structure than those generated by short shot process, specifically, the cell structure with the cell size of 46.97 μm, cell density of 3.18×106 cell/cm3, and cell size dispersion of 10.76 μm was achieved in the decompressing process. A controlled foaming process was realized through the decompressing process using the injection foaming equipment with a volume-adjustable cavity. The foamed PP composite has the insufficient, moderate, and excessive foamed structures in these two foaming processes.

Numerical Simulation of the Effects of Cell Size on the Mechanical Property of Microcellular Polypropylene

The tensile model of foams is built using UG software and the tensile deformation processes of microcellular polypropylene foams with different cell sizes are simulated using finite element method (FEM). The effect of cell size on mechanical property is evaluated based on the microstructure of the foams. The cells with small and uniform size are in a state of plane stress, which improved effectively mechanical property of the foams. Whereas the cells with large and nonuniform size are in a state of plane strain, which leads to low mechanical property. The simulation results coincide well with experimental results.