Volume 28, Issue 2

Polymer grafting of carbon black (CB) has been intensely researched as polymer modification is one of the effective means for improving the solubility and compatibility of carbon black. Recent advances in the polymer grafting methods allow the introduction of polymers with well controlled composition, structure and molecular weight onto the surface of CB. In addition, modification by functional polymers provides a powerful impetus to extend the applications of polymer-CB composites such as sensitive materials. This review focuses on the development of these grafting polymerization methods and some novel applications of polymer grafted CB.

In recent years, production of nano-sized wound dressing materials from biopolymers by electrospinning method has attracted great attention. In this study, chitosan that is an inherently antimicrobial polymer and chitosan (CS)/poly(ethylene oxide) (PEO) blend solutions were electrospun to obtain nanofiber webs for wound-dressing applications. Although electrospinning of chitosan with PEO was previously studied, this study emphasized the effect of molecular weight of polymer used, total polymer concentration and electrical conductivity of polymer solution on fiber formation. Results show that selection of suitable solvent and determination of optimum process parameters were key factors for obtaining uniform nanofibers. Antimicrobial activities of these nanofiber webs against S.aureus, E.coli, and C.albicans were tested according to AATCC 100–2004. Over 99% reduction in the number of microorganisms with pure chitosan nanofibers and over 50% reduction with CS/PEO blend nanofibers were obtained.

The effect of nano-particle geometry on flow and recovery of polymer melts based on ethylene vinyl acetate (EVA) was investigated. Two nano-particles, calcium carbonate (CaCO 3 ) and montmorillonite clay, were used with concentrations between 2.5 and 15% by weight. First, by using small amplitude oscillatory shear and transient step shear tests, the linear and non-linear response of the nano-composites was studied. Then, to examine the structure recovery, the same behavior was studied on pre-sheared samples. The linear and non-linear data revealed that the effect of nano-particles in material flow is more important for anisometric particles which can be attributed to their ability to form a fractal structure controlling the rheological properties while spherical particles are not able to form such networks. Recovery experiments revealed that while nano-composites containing spherical particles have relatively similar response in subsequent tests, the rheological properties decreased significantly for platelet particles. The recovery results were also interpreted based on a filler-network mechanism and the reduction of the nano effect for anisometric particles was related to the breakdown of the filler network. These observations were validated by morphological investigations.

A differential molding system for micro injection molding of thermoplastics was designed and fabricated. As the core part, a planetary gear pump was integrated into the molding module and used for metering, delivering and supercharging. The molding system was installed in the stationary platen beside which a servo motor was connected to the transmission shaft of the pump through a coupling. A traditional injection molding machine which was equipped with this module could be upgraded to a precise micro injection molding machine and realized the function of multiple micro injection molding machines. A process study was first performed to verify the machine performance and to determine the influence of the main process parameters. It has been proved by experiments that the differential molding system could realize the manufacture of fine and precision parts with micro structures in one step with high efficiency at low cost.

Fiber-reinforced elastomeric isolators (FREIs) are a new generation of seismic isolation devices in which steel plates are replaced by fibers. FREIs have a number of advantages over SREIs including; superior energy dissipation capability, potentially low manufacturing cost, light weight, and the possibility of being produced in long rectangular strips or large sheets and being modified to the required size locally. The main purpose of this work was to investigate the effect of shear strain amplitude and loading cycles on the horizontal characteristics of fiber reinforced nanocomposite elastomeric isolators (FRNEIs) which were manufactured based on nanocomposite rubber compounds. The results of typical isolator horizontal test showed that by increasing the number of cycles of loading and shear strain, the values of effective horizontal stiffness and shear modulus of FRNEI decrease and the viscous damping increases. This stress softening is known as the “Mullins effect”, which occurs in filled rubbers.

The role of feeding method, as an important parameter in competition with thermodynamic parameters, on determining the nanoclay partitioning and its impact on microfibril formation in PP/PBT blend nanocomposite fibers were investigated. In the direct feeding method in which all components were fed into the extruder simultaneously, the major part of nanoclay with almost unchanged interlayer d-spacing was located in the PP matrix and the rest of the nanoclay partitioned into the PBT dispersed phase. However in the PBT based masterbatch method nanoclay, due to much greater melt intercalation occurred, remained in PBT droplets in the form of tactoids and/or platelets. In the masterbatch feeding method, incorporation of compatibilizer assisted more fraction tactiods and/or platelets to be transferred from PBT to the PP matrix while in the direct method it enhanced the extent of melt intercalation in the PP matrix. It was demonstrated that the nanoclay concentration in PBT droplets plays an important role in the extent of the microfibril formation during the melt spinning process. While at low organoclay loading (1 wt%) fine microfibrils could be formed in the fibers prepared by both methods of feeding, at higher organoclay loading (3,5 wt%) uniform microfibrils could hardly be developed in the fibers, particularly, in the masterbatch feeding method due to high melt elasticity of the PBT droplets and uneven distribution of platelets and/or tactoids in the droplets.

The influence of hot water and the water-carrying agent aluminum potassium sulfate dodecahydrate (alum) on the mechanical and thermal properties of the silane-water crosslinked linear low density polyethylene (LLDPE) was investigated. LLDPE was melt-grafted with various content of vinyl trimethoxysilane (VTMS) using dicumyl peroxide (DCP) as initiator. The results show that the contribution of hot water to gel content is poor, about 2 to 16%, compared with that of the silane grafted LLDPE. Is feasible to achieve silane-water crosslinking reaction with alum for self-crosslinked LLDPE; furthermore, the self-crosslinked LLDPE has lower crosslink density (ν). It was found that alum could not only conduct silane-water crosslinking reaction effectively, but also improve the mechanical properties, especially the elongation behavior. The heat of fusion (ΔHm), the melting temperature (Tm), and the degree of crystallinity (Xc) of the hot water crosslinked LLDPE decreased with the advancement of VTMS. The Avrami exponent n of self-crosslinked sample was larger than that of hot water crosslinked sample. This means that the alum could contribute to the growth of crystallization.

Melamine-urea-formaldehyde (MUF) foam was prepared using melamine modified urea formaldehyde resin. The effects of blowing agent, curing agent and surfactant on the properties of MUF foam such as apparent densities, compression strength, microstructure, fragility, limited oxygen index, thermal conductivity and formaldehyde emission were investigated. The best performance of MUF was obtained as the composition of blowing agent, curing agent and surfactant were 2.5%, 18% and 12% respectively. The water resistance of MUF foam, contents of foam's burning gas, curing mechanism and physical properties were also studied by Contact angle analyzer, TGA-FT-IR, FT-IR and 13 C NMR.

The main objective of the present work was to study the role of organoclay on the microfibrillation process of epoxy phase in Poly(butylene terephtalate), PBT, matrix both in presence and absence of epoxy curing agent. The PBT/epoxy blend samples with constant blend ratio (60/40) were prepared by melt mixing in a twin screw extruder. The elongational flow imposed by drawing the extrudate at the die exit permitted controlled generation of fibrile morphology of the dispersed epoxy phase, with a fiber diameter of 0.8 μm and an aspect ratio greater than 100. It was shown that when the curing agent was added into the extruder, its reactivity with epoxy at high temperature was high enough and selectively affected on the epoxy phase. The SEM results showed smaller epoxy droplet size for samples containing nanoclay compared to simple blends. This could be explained in terms of hindrance effect of nanoclay in reducing the coalescence as a dominating parameter due to presence of nanoclay in both phases. These results were supported by the melt linear viscoelastic results which showed enhanced low frequency viscosity and storage modulus for these samples. Addition of nanoclay was found to have little effect on extent of fibrillation epoxy droplet in stretched samples. The rheological results obtained for stretched samples showed very strong increase in low frequency solid body response whose extent was increase with increasing draw ratio. This mainly attributed to special 3-D network formed between microfibrils whose shape was stabilized by either presence of nanoclay or accelerated curing process of fibrillated epoxy. From SEM micrographs and linear viscoelastic measurements it can be deduced that curing process has small changes on the extent of fibrillation epoxy droplet in stretched samples. But it leads to improvement of interfacial interaction between two phases in the nanocomposites.

The paper presents the processing and mechanical characterization of chopped carbon fibre reinforced homogenous and functionally graded vinyl ester composites and also reports on their sliding wear characteristics respectively. The sliding wear characteristics are studied with the help of POD test employing the design of experiments approach based on Taguchi's orthogonal arrays. Dynamic mechanical analysis is carried out of the investigated homogenous/FGMs composites to investigate the overall stiffness/flexibility, so as to improve the specific wear rate. Present study reveals that graded composite possess good mechanical and wear characteristics compared to homogenous composites. SEM confirms the graded dispersion of carbon fibre in the matrix.

This report studied, both experimentally and numerically, the factors affecting the warpage in in-mold decoration (IMD) injection molded parts. All experiments were conducted on an 80-ton injection-molding machine. The materials used in the experiments included poly(ethylene terephthalate) (PET) films and 30 % glass fiber-filled PET resins. U-shaped plate parts with three different angles (90°, 135°, and 150°) at the corners were molded. The influence of various processing parameters on part warpage was investigated using an experimental matrix, with its design based on the experimental-parameter-design method developed by Taguchi. The experimental results suggested that all molded parts warped toward the side of the decoration film. For the parameters selected in the experiments, the corner angle and the melt injection pressure were found to be the principal factors affecting the warpage of IMD injection molded parts. The 90° angled parts exhibited the greatest amount of warpage, while the 150° angled parts showed the least amount of warpage. Additionally, a commercially available code (Moldex ® 3-D) was used to simulate the temperature distribution during the filling process and the molded part warpage. Calculated warpage satisfactorily matched with the experimental data. It has been shown that the warpage of IMD injection molded parts is mainly caused by the imbalanced temperature distribution during cooling, due to the part geometry and the decoration films.

Calcium carbonate (CaCO 3 ) with various shapes and size was prepared using CaCl 2 and Na 2 CO 3 aqueous solutions containing various additives. High density polyethylene (HDPE)/4 wt% CaCO 3 composites were prepared using a Haake Rotational Rheometer. The effects of the CaCO 3 particle shapes and size on the thermal and mechanical properties were investigated and characterized by differential scanning calorimetry (DSC) and universal testing machine. The results show the addition of CaCO 3 to HDPE can increase the crystallization and decrease the melting temperature and crystallization temperature. The tensile yield strength of the composites was higher than that of HDPE. Sphere-like CaCO 3 is the best form in improving the thermal stability and cubic CaCO 3 can cause negative effect to the toughness. The impact strength of the composites is significantly increased with decreasing CaCO 3 particle size. SEM examination of the fractured surfaces of the composites shows that CaCO 3 reacted in cavitations and “lance” functions which increase the impact strength of the HDPE/CaCO 3 composites.

In recent years, many replication methods of microstructures on large-area substrates have been reported. The plate-to-plate hot embossing process is a low cost, fast, high throughput and the most possibility of mass production method for replication of micro/nano structures with high precision and high quality. However, micro hot embossing is not practical to use in mass production due to the many difficulties. This paper reports a innovative non-uniform heating hot embossing system for fabrication of large-size, high precise and high brightness light guide plate. Steam is used as heating medium, and water of 12°C is used for cooling. The v-groove patterns in the stamper have been replicated to the light guide plates (LGPs) with an area of 488 mm by 277 mm. The experimental results show that the non-uniform heating system could achieve a transcription rate of over 99%, compared with 95% using conventional uniform heating system. Furthermore, less warpage, the less thickness variation, the higher average luminance and the higher brightness field distribution have been found. The results indicate that non-uniform heating system is likely to be a promising technique for the fabrication of optical elements.

In this article two polymer/nanocomposite films with 5 and 10% silicate particles based on Poly(amide-imide) (PAI) from N-trimellitylimido-L-phenyl alanine were prepared via solution intercalation method through blending of organoclay with the PAI solution. Poly(amide-imide) was synthesized by the direct polycondensation reaction of N-trimellitylimido-L-phenyl alanine with 4,4′-diamino diphenyl ether in the presence of triphenyl phosphite (TPP), CaCl 2 and pyridine (Py). Morphology and structure of the resulting PAI-nanocomposite films were characterized by FTIR spectroscopy, X-ray diffraction and scanning electron microscopy (SEM). The effect of clay dispersion and the interaction between clay and polymeric chains on the properties of nanocomposites films were investigated by using Uv-vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements.