Volume 40, Issue 3

When the semi-crystalline polymers undergo shearing during flow, the orientation of the molecular chains are induced. In order to study the effect of polypropylene orientation on foaming, we designed an injection mold with a long flow ratio. The samples were prepared by different process conditions and characterized by polarized Fourier transform infrared spectroscopy (FTIR). The degree of orientation was calculated by infrared dichroism. It was found that the orientation of the amorphous region has the greatest influence, and the subsurface layer in the cross section along the flow direction had the largest degree of orientation. The samples were foaming in a self-made sealed cavity under the same condition. The foamed samples were observed by scanning electron microscopy, and it was found that the shish-kebab crystal structure was induced in the surface layer and the subsurface layer under strong shear force. The shish-kebab crystal structure restricted the space for bubble nucleation and growth, and a large number of sub-micron and nano-scale cells appeared in the space of nucleation and growth. Along the flow orientation direction, the longitudinal and transverse sections of each foamed sample with the degree of orientation decreases, the density of cells and the average diameter of cells increases gradually, and the expansion of the foams have an advantage in the direction of flow orientation. The degree of orientation corresponding to the amorphous ribbon (1153 cm −1 ) of all the samples were arranged from small to large, and it was found that the expansion ratio decreased when the degree of orientation increased. The effect of orientation on foaming properties of polypropylene provides a new strategy for designing other polymer foams.

The objective of this work is to investigate the thermomechanical, electrical, and shape-memory properties of bisphenol A-type cyanate ester (BACE)/polybutadiene epoxy (PBEP)/carbon black (CB) composite and assess its feasibility applied for deployable structure. Using a BACE/PBEP polymer as matrix and superconducting carbon black (CB) and short carbon fibers (SCFs) as reinforcing material, the shape memory composite was prepared by compression molding. The effects of CB and SCF content on the shape memory properties of the composites were investigated. The results demonstrate that the glass transition temperature ( T g ) and the storage modulus of the composites increases as SCFs content increase. Because of the synergic effect of CB and SCFs, the shape memory composites exhibit excellent shape memory performance, and the shape recovery ratio is about 100%. With the increase in SCF content, the recovery time decreased, and the volume electrical resistivity of the composite could decrease by adding a small amount of SCFs. According to the above results, a shape memory polymer composite deployable structure was prepared.

The green synthesis of nanoparticles is of considerable interest because it is eco-friendly, cost-effective, biocompatible, and non-toxic. Split pulse extract was used as a reducing/capping agent for the synthesis of titanium dioxide (TiO 2 ) nanoparticles. Green synthesized nanoparticles were embedded in the polydimethylsiloxane (PDMS) membrane by using a solution casting technique to develop a nanocomposite. This thin film was characterized using Fourier transform infrared spectroscopy, scanning probe microscopy, high-resolution scanning electron microscopy, ultraviolet-visible spectroscopy, and contact angle analysis. The antibacterial property of the TiO 2 /PDMS nanocomposite was examined, and the results showed excellent antibacterial activity of TiO 2 /PDMS compared to PDMS without nanoparticles. The nanocomposite film exhibited antibacterial activity against Gram-positive and Gram-negative bacteria in the presence of TiO 2 nanoparticles in the polymer. Here, different weight percentages of TiO 2 nanoparticles, i.e. 0%, 7%, 10%, and 13%, were loaded on the PDMS surface to enhance its antibacterial activity. The green synthesis of TiO 2 nanoparticles embedded in PDMS and their suitability for antibacterial activity are reported for the first time.

Conductive hydrogels without adhesiveness and durability characteristics face great challenges in practical applications, such as inconvenient use, unstable contact voltage, and difficult to store. Herein, we present sodium polyacrylate (PAANa) hydrogels with binary solvent systems composed of water and an alcohol [ethylene glycol (EG), glycerol (GLY), or poly(ethylene glycol) (PEG)] as solvent instead of traditional water to research their self-adhesiveness, durability, conductivity, and mechanical properties. PAANa hydrogels exhibited higher self-adhesive properties and durability after alcohol content increased, and GLY/water hydrogels showed the best self-adhesive and stable properties. With more alcohols added, the weaker conductivity became, and EG/water hydrogels showed the highest conductivity. It was observed the long carbon chain length of alcohol could help improve the rheological properties of hydrogels. Thus, PEG/water hydrogels had the highest storage modulus, loss modulus, and consistency. The results demonstrated that the GLY/water binary solvent could provide good self-adhesiveness and durability, but EG/water and PEG/water showed better conductivity and mechanical properties, respectively. Therefore, our work may provide novel physical insights into the long-term usage of self-adhesive conductive hydrogels to practical requirements.

Ultra-high-molecular-weight polyethylene (UHMWPE) has been widely used in industry; however, the applications for UHMWPE are limited because of low hydrophilic and adhesive properties. Herein, we developed the surface properties of UHMWPE by using side-chain crystalline block copolymers (SCCBCs), which consist of a side-chain crystalline unit and a functional unit. This process only required immersing the UHMWPE film in the diluted SCCBC solution, which enabled the UHMWPE surface to be coated homogeneously. The results of the contact angle and tensile shear test showed that the surface of UHMWPE modified with SCCBC was improved in hydrophilicity and adhesive properties. In addition, high adhesion strength was measured on UHMWPE surfaces dipped in a SCCBC solution at high temperature with the UHMWPE film becoming elongated at all parts other than the adhesion contact area.

Conventional acrylamide hydrogel exhibits a slow swelling rate which limits its potential for novel applications. It is a formidable challenge to increase the rate of swelling and if addressed successfully, this paves new paths for significant advanced applications. Fast responding polyacrylamide hydrogels with microporous structures and an interconnected network of capillary channels have been successfully synthesized by free radical emulsion-templated polymerization (a 2.5 m acrylamide monomer solution was crosslinked with 1% N,N-methylenebisacrylamide using 5% potassium persulfate as the initiator). Virgin coconut oil (70% v/v) was used as the pore forming agent, which was dispersed in the aqueous monomer solution by using 5% non-ionic surfactant (Tween 80 ® ). Developed porous acrylamide hydrogel displayed approximately 600 wt% water absorptivity compared to the dry weight of the sample in 15 s at 30°C. Swelling ratio and scanning electron microscopy studies uncovered the characteristic microporous structure of the hydrogel. Pores of the hydrogel are interconnected to form capillary channels and thus they are responsible for the higher swelling rate of the hydrogel.

The eccentric rotor extruder is a new kind of extrusion equipment with novel structure and outstanding engineering performance. As the structure of the eccentric rotor extruder is different from that of the traditional screw extruder, the control of the barrel temperature becomes important, including avoiding the influence of heating coupling and achieving high control accuracy. A neuron proportional-integral-derivative (neuron-PID) control algorithm of barrel temperature for the eccentric rotor extruder is introduced. The neural self-learning algorithm is able to tune PID parameters online, and the particle swarm optimization (PSO) algorithm is adopted to optimize the initial weight coefficients of the neuron. The experimental results show that the PSO-neuron-PID controller has the advantages of low overshoot and high control accuracy, and the influence of heat coupling can be counteracted effectively.

A new process, called thermoset in-mold forming, for combining thermoset master forming and thermoset forming in one mold is in development. A pre-impregnated continuous-fiber reinforced sheet based on epoxy (prepreg) is formed in the injection molding machine, followed by instantaneous overmolding of a short-fiber reinforced epoxy compound in one step. Compared with conventional processes in which thermoset injection molding, prepreg compression molding, and hence curing of the materials are separated, the new process allows for the combination in one step and simultaneous curing of both components. The result is a hybrid component, which features a continuous-fiber reinforced part for higher mechanical performance and a short-fiber reinforced part with high design freedom for integration of additional functions. For a successful combination of both materials in one process, it is essential to investigate the bond strength between them in relation to the processing parameters and their influence on the degree of cure. This paper analyzes the influence of the mold temperature in this process on curing degree, bond strength, and the processing viscosity.

Waste tire rubber was comparatively devulcanized by using two-roll mill mechano-chemical and microwave techniques at room temperature. The former technique was performed utilizing tetramethylthiuram disulfide and mercaptobenzothiazole disulfide. The developed devulcanized elastomer was characterized by scanning electron microscopy, chemical soluble fraction indication, and cross-link density determination. The blend was mixed in two roll mills by replacing a portion of virgin styrene-butadiene rubber (SBR) in a common formulation with the devulcanized waste rubber (DWR) product at various ratios, namely 10, 20 and 50 wt%. The morphological micrographs confirmed marked improvement in compatibility between both rubbery materials. The tensile strength and elastic modulus examinations of the fabricated blends ensured successful substitution of the virgin SBR with DWR. The abrasion resistance of SBR proved unaffected by blending with DWR. The compounded blends were subjected to γ rays at different radiation doses elevated up to 200 kGy and comparatively mechanically investigated.

In this paper, self-reinforced samples with different mechanical properties were obtained by adjusting the molding parameters by co-injection molding technology, and the micro-morphology of these samples was observed. Then, using structured statistical methods, the analysis of variance and response surface methodology were used to study the effects of various molding variables on the morphology and properties of the materials, and to determine the most important molding variables and their interaction relationships. Finally, the associated experimental data were fitted by the least square minimization program, and the parameters in the fitting equation were dimensionless to obtain the correlative dimensionless equation. The purpose was to establish the mechanism model of the influence of the molding parameters on the co-injection self-reinforced sample and to objectively analyze its mechanism. It was found that the melt temperature is the most important factor affecting the morphology and mechanical properties. The highly oriented skin thickness is the most important factor in determining the tensile properties of the sample. The change in crystallinity is the most important factor in relation to the elastic modulus. Through the establishment of the relevant dimensionless equations, the theoretical study on the tensile strength and elastic modulus of the co-injection self-reinforced samples of the molding parameters was preliminarily realized.