Volume 29, Issue 3

This article reported on finite element simulation to predict the creep responses of wood/poly (vinyl chloride) (WPVC) composite members before and after strengthening by using high carbon steel (HCS) flat bar strips bonded to the tension side of composite members. The short-term properties and creep characteristics, in accordance with power law models of WPVC composites and HCS flat bar materials, were determined individually by extensive experimental investigations. The experimental results indicated that strengthening of WPVC composites with HCS flat bar strips could increase the flexural and creep performances of the WPVC composite members both in flat-wise and edge-wise directions. The improvement in the edge-wise direction was relatively greater than that in the flat-wise direction, representing the loading direction dependence for this composite member. Abaqus finite element analysis (FEA) software was applied to predict the creep responses of WPVC composite members based on the characteristics of the individual component material; these results were then verified by the experimental results. Good correlations between FEA and experimental results were found in all cases, indicating that Abaqus software with the power law creep model can be used as an alternative tool for determining the creep responses of WPVC composites.

A study of reinforcement mechanism of multi-walled carbon nanotubes (MWCNT) in nitrile rubber (NBR) matrix was carried out. Attempts to enhance the dispersion degree of MWCNT and the NBR-MWCNT interaction were conducted using numerous approaches, namely, sonication and chemical treatments of MWCNT with nitric acid (HNO 3 ), nitric-sulfuric acid mixture (HNO 3 /H 2 SO 4 ) and potassium permanganate (KMnO 4 ). Rheological behavior, dynamic properties and electrical properties of MWCNT/NBR vulcanizates were monitored. Results gained reveal the magnitude of Payne effect increases with MWCNT content and mixing time. The expanded MWCNT and continuous-network formation are observed with an increase in mixing time, yielding enhanced mechanical properties and electrical properties. With MWCNT modification, a significant reduction in the state-of-mix of MWCNT composites is exhibited. SEM results demonstrate the highest magnitude of MWCNT dispersion in the system with HNO 3 , but relatively poor interaction with NBR. The HNO 3 /H 2 SO 4 or KMnO 4 system demonstrates poor MWCNT dispersion after treatment which is probably due to the compaction of MWCNT during the drying stage after the chemical treatment process, giving the detrimental effect to mechanical and electrical properties of vulcanizates.

The influence of material data input towards the mold filling behavior of a natural rubber compound during an injection molding process was investigated. A commercial injection molding software (Cadmould) was utilized in evaluating the effect of using experimentally obtained material data on the mold filling progression in comparison to the actual injection molding procedure. The experimental rheological data were measured using a capillary rheometer and subsequently, the Carreau and Cross models were used to acquire the rheological parameters by curve fitting and extrapolation procedures. The cure kinetics data were obtained by employing a cure rheometer technique along with utilization of empirical approach through application of mathematical models proposed by Claxton–Liska and Deng–Isayev. It was discovered that the acquired data were able to function as reliable material data input as they were comparable with related data available in the software materials' database. Verification of the simulated filling profiles by experimental short shots specimens showed that the software Rubber Package was able to predict the realistic filling behavior of the formulated natural rubber compound inside the mold cavity when the measured material data were utilized. Whereas, the usage of available material data from the software database failed to model the mold filling progression of the prepared natural rubber compound.

Thermoplastic vulcanizate (TPV) nanocomposites based on 60/40 (%wt) natural rubber (NR)/polypropylene (PP) blends were prepared by melt blending in an internal mixer. Sodium montmorillonite (Na-MMT) was first added in natural rubber latex to obtain natural rubber/clay masterbatch, which was subsequently dynamically crosslinked while mixing with molten PP. The effect of Na-MMT content were examined concerning elastomeric properties of NR/PP blends dynamically vulcanized using phenolic resin as a curing agent. Morphology characterization observed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and 3D microfocus X-ray computerized tomography showed that the dynamic vulcanization with nanoclay addition changed the blend morphology from a co-continuous-like structure to droplet-like phase one, and the clay remained within NR phase in intercalated and aggregated forms. Furthermore, the presence of clay induced the decrease in crosslinking of NR, but promoted the mixing between NR and PP during dynamic vulcanization. This suggested that nanoclay worked as a kind of morphology modifier during dynamic vulcanization. The addition of clay marginally enhanced the 100 % modulus and tensile strength, but led to the decrease of the elongation at break. The optimal level of tensile strength improvement was obtained with loading of 5 phr clay. The permanent set of the NR/PP/Clay TPV nanocomposites was well maintained at the acceptable level as elastomer. The resistances to oil and heat were improved with incorporation of clay, proportional to clay loading. The experimental results indicated that the nanoclay had a positive effect on improving the 60/40 NR/PP blend morphology, which provided a little benefit to strength of the TPVs. However, the addition of nanoclay offered an improvement in oil and thermal resistances due to a combined effect of the clay dispersion and improved morphology of NR and PP blends.

Brominated tert octyl phenol formaldehyde resin (PR) is an important cross linker for chlorinated butyl rubber (CIIR). There are two competitive reactions in the vulcanization process of CIIR, the cross-linking reaction and the self-poly-condensation reaction of PR. The cross-linking density was measured by the equilibrium swelling method. The results showed: with the increasing of PR content, the cross-linking density increased when it was less than 10 phr, and decreased when the PR content exceeded 10 phr. The kinetics equation of cross-linking reaction and the self-poly-condensation reaction was obtained by non-isothermal DSC method. The results showed that the concentration index n 2 of PR in the cross-linking reaction was far less than the concentration index n 3 of PR in the self-poly-condensation reaction. The self-poly-condensation reaction was more sensitive to the concentration of PR. This explained that the cross-linking density was out of proportion with the cross linker PR content. The mechanical properties and the dynamic mechanical properties were investigated by the universal testing machine and the dynamic mechanical performance analysis (DMA), respectively. The results showed that the cross-linking density had a great impact on the mechanical properties and the dynamic mechanical properties, and the variation trend of the cross-linking density was further confirmed by the corresponding variation of the properties. When the PR content was 5 phr, the CIIR vulcanizates had better mechanical properties.

Nowadays there is a widespread phenomenon of dairy residue, which causes a great deal of waste. To solve this problem, the copolymer of fluorinated acrylate resin was synthesized and the resisting fluid film was prepared. The proprieties of the fluorinated acrylate resin coatings were characterized by scanning electron microscope (SEM), measuring the contact angle of the droplet liquid on the surface of the coating, the influence of acidic environment, the adhesion to substrate material, and analyzing thermogravimetry (TG) and Gas Chromatography (GC). It was found that the fluorinated acrylate resin film is a kind of resisting fluid film with excellent property and it is safe, nontoxic and readily biodegradable. So it was said a very potential dairy packaging material.

Now-a-days, natural fiber based composites are emerging as a supplement to the synthetic fiber composites. The aim of the present work is to investigate the three-body abrasive wear behavior of needle-punch nonwoven jute fiber reinforced epoxy (NJFE) composites in an abrasive environment. Three-body abrasion studies have been done on composites using rubber wheel abrasion tester. The design of experiments approach using Taguchi methodology is employed for the parametric analysis of abrasive wear process. The effect of the factors such as sliding velocity, fiber loading, applied load, sliding distance and abrasive size on the specific wear rate and coefficient of friction of composite has been studied. Experimental results reveal the improvement of abrasive wear behavior of the composites with the addition of fiber as compared to neat epoxy. At steady state condition, it has been observed that composites with 36 wt% fiber loading shows minimum specific wear rate. From the statistical analysis it has been concluded that the factor combination with sliding velocity of 120 cm/s, fiber loading of 36 wt%, normal load of 10 N, sliding distance of 50 m and abrasive size of 400 μm gives minimum specific wear rate whereas sliding velocity of 144 cm/s, fiber loading of 36 wt%, normal load of 10 N, sliding distance of 70 m and abrasive size of 300 μm gives minimum coefficient of friction. Finally, the worn surfaces are examined by using scanning electron microscopy (SEM) and possible abrasion wear mechanisms are discussed.

Hot embossing is widely used to replicate micro-structures on polymer plate surfaces. The polymer parts of curved surfaces with micro-structures have important functions in various optoelectronic components. However, due to the high precision needed for embossing machines and mold manufacturing, achieving uniform pressure on curved surfaces during the embossing process is difficult. This study modified conventional hot embossing processes to develop an elastic bag embossing system (EBES) for replicating micro-structures on curved surfaces. The pressure equalizing properties of the elastic bag enabled uniform application of pressure on curved surfaces embossed with a general hot compression machine. For the EBES-assisted hot embossing process, a nickel stamper was attached to the elastic bag to compress and replicate micro-structures on the PC film covering the mold surface with single direction curve. This study also developed an EBES-assisted UV exposure process that used a PDMS soft-mold attached to the elastic bag surface to compress the UV curable photoresist covering the surface of the convex lens. Micro-structures were then formed by exposing the photoresist. Experimental results showed that the EBES with Ni stamper could successfully replicated micro-structures onto a 200 mm × 200 mm curved PC film and that the EBES-assisted UV exposure could successfully produced a 50 mm diameter fresnel lens on a convex profile with material of UV photoresist. Experimental tests of pressure-sensitive film showed that EBES enables uniform application of pressure on curved surfaces during the embossing process on standard hot compression machines. The experimental results confirm that the EBES developed in this study is an efficient and economical method for replicating micro-structures on curved surface.

In this paper, ultrasound was applied in extrusion reaction processing to graft an Elastomer (DE) with maleic anhydride (MAH), in order to improve the non-polarity of DE. Two types of DE-g-MAH were prepared by different methods and had similar grafting degree about 0.2 % and then they were added into the polyamide-6/elastomer (PA6/DE) blends, respectively. The effect of DE-g-MAH on the interfacial properties of PA6/DE blends was studied. The experimental results showed that, compared to the DE-g-MAH initiated by peroxide, DE-g-MAH initiated by ultrasound had better effect on refining the particle size of the dispersion phase and keeping the stability of the phase in the blends, which could be confirmed through SEM and Molau tests. When 5 % DE-g-MAH initiated by peroxide was added, the particle size of dispersion phase was 3.90 μm, however, when 5 % DE-g-MAH initiated by ultrasound was added, the particle size of dispersion phase was 2.82 μm. The results of TGA and mechanical tests showed the improved interfacial interaction and enhanced interfacial adhesion of the blend by adding DE-g-MAH, respectively.

In this study, vetiver grass fiber was used as a natural filler in natural rubber (NR) and polylactic acid (PLA) composite. Glycidyl methacrylate grafted natural rubber (NR-g-GMA) was used as a compatibilizer. The main objective of this research is to study the degradability of PLA and PLA composites under soil burial test. It was shown that vetiver grass fiber showed a significant role in the degradability of PLA composites under soil burial condition. Mechanical properties of PLA composites dramatically decreased after burial in soil compared to those of pure PLA. Moreover, addition of vetiver grass fiber at 20 and 30 % (w/w) content led to a significant increase in weight loss of the specimens with increasing burial time. From SEM micrographs, better interfacial adhesion between PLA, vetiver grass fiber, and NR particles was observed with the addition of NR-g-GMA. This indicated that the compatibility of PLA/vetiver/NR can be improved by using NR-g-GMA. Furthermore, mechanical properties of injection molded PLA and PLA composites were compared with those of compression molded samples. Injection molded specimens of neat PLA and PLA composites showed higher tensile strength than compression molded specimens. This may be due to the result of higher fiber orientation along flow direction in injection molding.

Polyamide66 (PA66) is being widely used for automobile part and other applications. In many cases, PA66 is reinforced with glass fiber to enhance its mechanical properties. In this study, the mechanical properties and glass fiber distributions in injection molded part have been investigated for glass fiber reinforced PA66. Two shapes of glass fibers, circular and flat, were used for the glass fiber reinforced PA66. X-ray microtomography (micro-CT) was used to observe the glass fiber distributions in the PA66 composites. Micro-CT photos were taken in three directions to observe the three-dimensional glass fiber distributions in the injection molded specimens. Investigation of the mechanical properties in relation to the glass fiber orientation revealed that the orientation of the fibers enhanced the mechanical properties. Glass fibers with smaller diameters resulted in better mechanical properties. Circular glass fiber reinforced PA66 exhibited better mechanical properties than flat glass fiber reinforced PA66. The skin layer showed that the glass fibers strongly orientated to the flow direction while glass fibers in the core layer orientated perpendicular to the flow direction because of fountain flows. Glass fibers in the core layer also oriented to the width direction of the flow. Consequently, glass fibers in this core region oriented three dimensionally. Full three-dimensional model of glass fiber orientation was proposed in this paper.

It is shown that at unprecedented (high) temperatures an extremely slow long lasting shear treatment, which requires almost an hour for its unwinding, can produce a highly oriented structure in the melt of a crystallizing polypropylene. It seems that a convection process, which is characteristic for shear flow, furthers intimate contacts between parts of passing by macromolecular coils. In this respect an inspection of the broad spectrum of crystallization speeds of quiescent melts of a variety of polymers is instructive. The conception, which is defended in the present paper, is that thread-like nuclei are the result of the straightening of assemblages of already loosely connected macromolecules. At the high temperature applied the melt must immediately be quenched after the cessation of the flow in order to preserve the obtained thread-like nuclei. Apparently, only the number of successful encounters is relevant and not the frequency of their occurrence. For a lower frequency more time is required. It is evident that even mild touches can cause permanent adhesions, if the mutual local conformations just fit. One is reminded of the click of a slot. A new apparatus for unlimited shearing is described. This apparatus uses polymer samples, which are ring-shaped, being cut from molded plates of reasonable thickness. These rings possess an unusually large radius of 18 cm, in order to keep the curvature of the flow lines low. Rectilinear unlimited shearing is approached in this way.

The extrusion process is greatly affected by both feed zone geometry and dimensions of pellets fed into the hopper. The paper presents the results of studies undertaken to investigate the effect of both the dimensions of a feed pocket made in the barrel below the feed opening and pellet length on the single-screw extrusion process for plasticized poly(vinyl chloride). The dependencies of the extrudate temperature, extruder screw torque, polymer mass flow rate and unit energy consumption supplied to the extruder on the above mentioned variable factors were determined. It has been found that the most advantageous solution for the investigated screw speed range is to run the extrusion process at the highest screw speeds possible, feed the extruder with pellets whose length is similar to their diameter, and use the feed pocket in the barrel.

In this paper, we report a chemical way to resolve longer motions units in the glass-rubber transition region of poly (ethyl acrylate) (PEA), so called internal plasticization. The ethyl acrylate (EA) monomers were copolymerized with little amount of isoprene (IP) monomers. We propose that the single bonds adjunct to double bonds would have better flexible activity than usual single bonds, so the motion units located between two adjunct double bonds would be enhanced. The dynamic mechanical spectra of internally plasticized PEA (IPPEA) and PEA show that the tan δ of IPPEA is asymmetric, while the tan δ of PEA is symmetric. Furthermore, the results of 2D-DMAS show that the LSM, SRM and RM of IPPEA are located at 7 °C, 12 °C and 36 °C. The shoulder peak of tan δ of IPPEA at higher temperature side was confirmed that it contains sub-rouse mode (SRM) and rouse mode (RM). Thus, internal plasticization is an effective way to resolve modes above T g .