Volume 40, Issue 4 -

This study focuses on the influence of cryogenic temperature on the interface of carbon fiber reinforced plastics (CFRPs). Results of interfacial shear strength ( IFSS ) and mode II interlaminar fracture toughness ( G IIC ) at −196°C increased by 15.3% and 27.6% compared to the condition at room temperature (RT). By measuring the IFSS at −196°C, a new experimental method was designed based on microbond test. The layer shear fracture morphologies of CFRP were observed by atomic force microscopy and scanning electron microscopy, respectively. In order to study the interlaminar fracture mechanism, the interface and resin fracture hybrid model was built, and the shear-lag theory of interfacial toughness was adopted to analyze the energy release rate ( G dc ) of microbond. The results showed that the G dc value was increased by 11.5% from RT to −196°C temperature. A higher G IIC of CFRP was dominated by the higher IFSS and resin energy absorption at −196°C.

Haze ( H ) is not an accumulative property based on the addition of internal haze ( H i ) and surface haze ( H s ) parameters, though the relation ( H s  =  H  −  H i ) is widely accepted and used nowadays in research and development of plastic films. To evaluate the correct relation, the analytical relation between the total haze ( H ) and the haze of a single film ( h i ) in the film superposition model was firstly concluded, which is 1 −  H is equal to the product of 1 −  h i of every single film. This relation was validated by the experimental results using thin films of different kinds of polymers with different hazes. Based on this relation, the expression of surface haze was concluded. When the two surfaces of a film were the same, the haze of the single surface Hs¯=1−(1−H)/(1−Hi).$\overline {{H_{\rm{s}}}} = 1 - \sqrt {(1 - H)/(1 - {H_{\rm{i}}})} .$ The mathematical relation between haze and thickness was also obtained.

To obtain uniform and controllable material removal on hard and brittle materials, a novel processing technology with functionally graded lapping and polishing plate (FG-LPP) was proposed. Taking application of particles/rubber composites and adjustable contact stress of workpiece as key point, the abrasive particles and rubber were mixed with different mass ratios; then the FG-LPP was formed with characteristics of required quasi-continuous distribution of Young’s modulus in the radial direction by two-step processing technique. The properties of Young’s modulus, loss factor, and glass transition temperature of different particles/rubber composites were tested and calculated. Through comparison and analysis, silicon carbide (SiC)/chloroprene rubber (CR) composites are the suitable application object of FG-LPP. Moreover, by laser particle size analyzer, scanning electron microscope, and X-ray diffraction, the size distribution of abrasive particles, micromorphology of particles/rubber composites and their phase composition were tested respectively to better reveal the structure and properties. The test results indicate that under the action of ZnO and MgO, CR undergoes a vulcanization reaction gently and forms a spatial three-dimensional structure. Thus, it helps to increase the intermolecular distance and weaken the intermolecular forces because the NO is easy to enter the CR molecules, which improves the intermiscibility between SiC and CR.

The adhesive properties of a self-prepared bio-based epoxy resin with native cellulose nanocrystals (CNCs) are evaluated in this article. The porosity of actual CNCs is high. The most promising finding is the acquisition of high tensile modulus. The addition of CNC composites significantly increased the tensile modulus at lower wt.%, and the maximum crystallinity of CNCs was obtained. Bearing in mind the advantages of CNCs, scanning electron microscopy (SEM) showed a uniform distribution of concentrated CNCs. Clusters were formed at higher CNCs ratios, and the composite matrix content with high CNCs produced good expansion, low crystallinity, and increased elongation. Our analysis showed that the original CNCs were more evenly distributed in the self-prepared bio-based epoxy resin, which enhanced transformation, supported by improved dispersion of native CNCs. The presence of native CNCs greatly improved and enhanced the bonding performance of the bio-based epoxy resin in the interface area. Enhancing the mechanical properties of native CNCs has broad application prospects in environmental areas. This suggests that the widespread use of native CNCs in environmental engineering applications is feasible, especially in terms of adhesives properties.

Exfoliated organo-montmorillonite (O-Mt) layers were successfully encapsulated in a terpolymer microsphere (PAAA) of acrylamide (AM)/acrylic acid (AA)/2-acrylamido-2-methylpropanesulfonic acid (AMPS) via in situ inverse suspension polymerization, with the aid of the organic modification by cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfonate (SLS). The chemical structure and properties of the Mt were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), which showed that SLS molecules successfully intercalated Mt interlayers and enhanced the thermostability of Mt. The microsphere morphologies of the polymer and its nanocomposites were detected by scanning electron microscopy (SEM). The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the exfoliated O-Mt dispersed in the polymer matrix. The introduction of well-dispersed O-Mt layers significantly enhanced the comprehensive performance of these microspheres, including thermostability and plugging properties. The T max of PAAA/1.5 wt.% O-Mt nanocomposite is increased by 46°C compared to the pure terpolymer. The plugging rate of PAAA/2.0 wt.% O-Mt reached up to 85.8%. Therefore, these selected nanocomposite microspheres can provide an effective plugging in the high-permeability layers.

Polymer composites offer a great advantage in biomedical field over the traditional materials used like, metal, ceramics, or polymer alone. Polymer composites provide tailor-made facilities to design required physiological and mechanical properties in biomedical products. Poly(lactic acid) (PLA) is a popular aliphatic polyester used in various biomedical products because they have a renewable source and after resorption they enter well into the Krebs cycle of the human body. However, PLA suffers from hydrolysis and subsequent weight loss in aqueous environment. To improve the hydrolytic properties of hydrophobic PLA and to incorporate the biocompatibility from chitosan (CS) into it, in this study CS has been grafted onto PLA film. CS with 78% of degree of deacetylation and viscosity average molecular weight of about 8,31,760 Da was grafted onto hydrolyzed PLA film surface. Kjeldahl analysis confirmed the attachment of CS onto the PLA films. From thermal stability analysis, it was observed that percentage of weight retention at 600°C of the CS-g-PLA was around 15% higher than that of pure PLA. The mechanical properties of final CS-grafted-PLA composites showed more resistance to hydrolytic degradation than that of pure PLA film.

Cobalt ferrite functionalized chitosan graphene oxide (CoFe 2 O 4 @CS@GO) was inserted successfully in polyvinylpyrrolidone (PVP), and its distribution was distinguished through scanning electron microscope (SEM) analysis. Furthermore, the thermal and structural characterizations of the CoFe 2 O 4 @CS@GO-PVP nanocomposite were accomplished via the TGA, DSC, FT-IR, and XRD methods. The magnetic characterization of the synthesized nanocomposite was specified by vibrating sample magnetometer (VSM). Results demonstrated the improved thermal stability of pure PVP with the addition of CoFe 2 O 4 @CS@GO. The DSC analysis results also showed that the glass transition temperature of 158.9°C–164.8°C was obtained for the CoFe 2 O 4 @CS@GO-PVP nanocomposites. The FT-IR spectra indicated that an interaction occurred between CoFe 2 O 4 @CS@GO and PVP. Due to a good distribution of CoFe 2 O 4 @CS@GO in the PVP matrix, the strong interaction shown by the ~18 cm −1 red shift with good complexation of the carbonyl functional group of PVP with CoFe 2 O 4 @CS@GO was observed for the CoFe 2 O 4 @CS@GO-PVP (5% w/w) nanocomposite.

In this study we report on the preparation and characterization of biocomposites based on a sodium montmorillonite-ibuprofen (MtIb) hybrid and neat poly(ethylene glycol), neat sodium carboxymethylcellulose or poly(ethylene glycol)-carboxymethylcellulose blend 50/50 biocomposites as drug carriers. Ib, a poorly soluble drug, was first intercalated into sodium Mt and then the resulting hybrid was compounded with the different polymeric matrices. Ib incorporation efficiency in Mt was determined by UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermal analysis. Both X-ray diffraction and differential scanning calorimetric studies revealed that the intercalation of Ib between the clay layers induced amorphization of the drug. Differential scanning calorimetry and Fourier transform infrared spectroscopy revealed the development of strong interactions between Ib and the polymer matrix. A study of the release of Ib from the synthesized biocomposites in simulated intestinal fluid (pH 7.4) was investigated. To better understand the release mechanism of drug molecules from the different carriers, several kinetic models have been applied.

The qualities of injection-molded parts are affected by process parameters. Warpage and volume shrinkage are two typical defects. Moreover, insufficient or excessively large clamping force also affects the quality of parts and the cost of the process. An experiment based on the orthogonal design was conducted to minimize the above defects. Moldflow software was used to simulate the injection process of each experiment. The entropy weight was used to determine the weight of each index, the comprehensive evaluation value was calculated, and multi-objective optimization was transformed into single-objective optimization. A regression model was established by the random forest (RF) algorithm. To further illustrate the reliability and accuracy of the model, back-propagation neural network and kriging models were taken as comparative algorithms. The results showed that the error of RF was the smallest and its performance was the best. Finally, genetic algorithm was used to search for the minimum of the regression model established by RF. The optimal parameters were found to improve the quality of plastic parts and reduce the energy consumption. The plastic parts manufactured by the optimal process parameters showed good quality and met the requirements of production.