Volume 37, Issue 3

Crumb rubber (CR), as a final product from end-of-life tires through size reduction process, has proved an appropriate end product for accumulated discard waste tires all around the world. Unlike pre-existing pulverization methods, such as ambient or cryogenic grinding and solid-state shear extrusion, an entire cool pulverization process utilizing ultra-high pressure water jet (UHPWJ) was proposed in this paper. Pulverization experiments under various processing parameters were designed and conducted. The particle size distributions of produced CR were obtained using laser particle analyzer. Microscopic morphologies of CR and rubber fracture surface were observed under scanning electron microscopy. The crosslink density and gel fraction of produced CR were experimentally determined. Influence of four main processing parameters as pump pressure, transverse velocity, standoff distance and impacting angle was discussed in detail, and the most suitable processing parameters were recommended. The results show that the particle size distribution of produced CR with UHPWJ is between 45 μm and 200 μm, and the surface of CR is coarse and porous. High compressive shear effect and erosion are the main mechanisms in UHPWJ pulverization. Besides, the produced CR has already been partly devulcanized after UHPWJ pulverization, and polymer degradation occurred in the meanwhile.

The friction and wear properties of polyoxymethylene/polytetrafluoroethylene (POM/PTFE) composites were investigated by using a block-on-ring friction tester and special focus was paid to the effect of weight average molar mass ( M w ) of POM. To study the thermodynamic characteristics and wear mechanism of composites, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used. Results showed that friction and wear properties of the composite blends were strongly affected by the M w of POM and the loading fractions of PTFE. POM/PTFE composites with lower M w of POM owned better wear resistance abilities under a high-speed sliding regime, which resulted from the effective lubrication of transferred wear debris under a relatively high sliding speed. However, the transfer layer on the counterface could be easily peeled off under the low sliding speed, resulting in higher wear rate of POM/PTFE composites with lower M w of POM. POM and its composites with high M w showed comparative high friction levels, related to the strong adhesion between the resin and the steel counterpart. DSC analysis showed that POM with lower M w had higher crystallinity, which was beneficial to the improvement of wear resistance in a high-speed sliding condition.

Acrylonitrile-butadiene-styrene (ABS) grafted copolymer prepared by emulsion polymerization was used to modify different molecular weight poly (vinyl chloride) (PVC) resins. The effects of the molecular weight of the PVC resins on dynamic mechanical analyses (DMA) of PVC/ABS blends and matrix plasticizing behavior on the impact mechanical properties and the morphology were investigated. The tan δ peaks of PVC/ABS blends occurred at the same temperature obtained by DMA, indicating that miscibility of PVC/ABS blends was independent of the molecular weight of PVC. The notched Izod impact test results indicated that the amount of polybutadiene (PB) rubber needed for the brittle-ductile transition (BDT) increases together with the molecular weight of PVC when milled at 165°C. Increasing the operation temperature and adding the plasticizer dioctyl phthalate (DOP) could change the matrix plasticizing extent and the BDT. At a milling temperature of 165°C, the BDT was reached only with 3.6 wt% PB when DOP was added, in contrast to the addition of 7.2 wt% PB in the absence of DOP. The morphology of different plasticized degree of PVC/ABS blends was studied by transmission electron microscopy (TEM) showing that the PVC-1/ABS blends milled at 165°C showed a larger unstained area than the other series of PVC blends.

The correlation between cure properties and structure of nanoclay filled composite laminate has not been studied extensively. Most of the cure studies were preferably done using small samples through a calorimetric method. In this study, the effect of varying weight ratio of nanoclay (1–5 wt%) on bulk cure properties of epoxy glass fiber reinforced composite (GFRC) laminates was studied. Bulk cure of unfilled and clay filled GFRC laminates was determined using the dynamic mechanical analysis-reheat method (DMA-RM). DMA-RM cure properties gave a better coordinate method, with better cure efficiency achieved in clay filled GFRC laminates when compared to unfilled GFRC laminates. The correlation between nanoclay and DMA-RM degree of cure was coordinated with compressive and in-plane shear strength properties. The degree of cure value of 78% by DMA-RM at 1 wt% clay filled GFRC corresponds with the compressive modulus and in-plane shear strength highest values, which are 20% and 14% increase, respectively, also at 1 wt% clay filled GFRC. The structures of the unfilled and clay filled epoxy were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Clay filled epoxy up to 3 wt% showed no distinct diffraction peak, which suggested that nanoclay is randomly dispersed in the matrix.

In this study, the short-cut web interlayer and three-dimensional (3D) needle-punched technique were used to improve the interlaminar shear strength (ILSS) of 2.5D fabric laminated composites. The ILSS was measured by the short beam testing method, and the tensile and bending tests were carried out to investigate the in-plane mechanical properties. Observations on microstructure and crack propagation were carried out. The damage mechanisms of different 2.5D fabric laminated composites were analyzed. The results showed that the short-cut web interlayer and 3D needle-punched technique resulted in the improvement of ILSS, and they affected the tensile and bending properties of 2.5D fabric laminated composites.

Blending of recycled poly(ethylene terephthalate) (RPET) and polycarbonate (PC) was performed by melt compounding. The blends were subsequently fabricated to dumbbell specimens by vented injection molding. The mechanical properties, thermal characteristic and morphology of RPET/PC blends were investigated as a function of PC contents. Vented injection molding presented an advantage for superior mechanical properties of RPET/PC blends. The addition of PC enhanced impact strength and fracture toughness with remaining tensile properties. The glass transition temperatures of PET and PC shifted toward each other, which indicated their partial miscibility of RPET and PC in the blends. The toughness mechanism of RPET and PC was related to core-shell structure and good interfacial adhesion at higher contents of PC.

The main purpose of this work was to evaluate the long term performance of butt welded polyethylene (PE) pipes in comparison to non-welded counterparts. Therefore, old welded PE pipes with different ages that had been used in Algerian gas distribution systems for up to 30 years were investigated. Samples prepared by butt welding of unaged pipes were used as reference. Crystallinity, melt rheology and thermal stability of pipes materials were examined at the weld zone and at the pipe wall. In order to assess the mechanical strength of welds, tensile test was conducted on both welded and unwelded specimens and the results of the strain to failure were considered for the determination of the weld factor. Compared to the reference, the results revealed that the crystallinity of PE materials at the weld zone was not affected by ageing as at the pipe wall. However, a slight decrease of the melt viscosity was observed for both welded and non-welded samples. The welds were found to be more sensitive to thermal and oxidative degradation than the parent pipes while the remaining amount of antioxidants was sufficient for service continuation. The tensile results indicate that welds strength were almost unaffected by ageing.

Potential of using powder coating recyclates as filler material for polyethylene compounds was investigated. Due to their strong adhesion to the metal surface during compounding at extrusion temperatures higher than 100°C, the coating powder recyclates were chemically modified to facilitate its processing by extrusion and injection molding at higher temperatures. For this purpose, the coating powder recyclates were first hydrolyzed with addition of an alcohol as swelling agent. The deactivated recyclates were mixed at different ratios with the matrix polymer, a linear low-density polyethylene (LLDPE). The mixtures obtained were then compounded by extrusion and subsequently injection molded to plates to produce specimens for testing. The resulting samples were characterized mechanically by tensile, bending, and impact strength tests. In summary, the powder coatings recyclates can be processed as filler for thermoplastic material, without any adhesion problems up to 160°C and 180°C in the extruder and in the injection molding machine, respectively.

The adhesion between rubber and the reinforcing textile plays an important role in ensuring the serviceability of composites. The present study aims to develop an enzyme based surface roughening process for nylon 6,6 fabric to improve its adhesion strength to rubber. Polyamide (nylon 6,6) fabric was micro-roughened through catalysed hydrolytic degradation of the surface chains, using a protease enzyme treatment. The concentration of the enzyme was optimized in terms of surface roughness measured by a KES-FB4 surface tester. Scanning electron microscopy (SEM) images of the protease treated fabric showed a heterogeneous rough appearance with cracks and pits. Fourier transform infrared (FTIR) analysis confirmed the surface hydrolysis of polyamide-6,6 due to the enzymatic treatment. Protease enzyme treated fabrics were then subjected to resorcinol formaldehyde latex (RFL) treatment, followed by a rubber moulding. Micro-roughening of nylon 6,6 fibre with an optimum surface roughness (SMD) of 20.3 μm was obtained for 3% enzyme concentration. Physicochemical mechanisms of the optimum effect and enzyme assisted hydrolysis were proposed. In line with surface roughness, peel strength also increased up to an enzyme concentration of 3% and then it decreased, however, the enzyme treated fabric showed higher peel strength than the control fabric.

This work demonstrates a novel simple method to study the accurate real time optical transparency of a crosslinked polymer blend during its swelling in good solvent. Heterogeneous natural rubber (NR) and poly (ethylene-co-vinyl acetate) (EVA) blends were used for this experiment. Aromatic solvents such as benzene, toluene and xylene were used as the probe molecules. Optical transparency of the samples increases with increase in EVA content in the blends during swelling. The penetrant solvent molecular size also affects the optical transparency of the blends. This new method can effectively measure the optical transparency of polymer gels during their swelling. Also, these blends can be a promising material for optical switching.

Poly(vinylidene fluoride) (PVDF)/chitin (CH) blend membranes were prepared via the method of immersion-precipitation phase transformation with the solvent system N,N-dimethylacetamide (DMAc)/lithium chloride (LiCl) as solvent and water as coagulant. The effect of CH on membrane structure and performance was investigated. Owing to the strong hydrophilicity, CH chains enriched on the blend membrane surface and improved the hydrophilicity of the membrane. The addition of CH also led to the formation of finger-like pores and the increase of pore size and porosity. The flux and the flux recovery ratio (FRR) of the blend membrane were higher than that of pure PVDF membrane. The fouling resistance of the blend membrane was lower than that of PVDF original membrane. In a word, the addition of CH to PVDF membrane improved the hydrophilicity and the anti-fouling ability of PVDF membrane.