Volume 27, Issue 2

The rheology and processing of tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers and TFE/HFP/per-fluoro(alkyl vinyl ether) (TFE/HFP/PAVE) terpolymers, also known as FEP polymers, are reviewed in this paper. Dynamic linear viscoelasticity and other fundamental rheological properties such as the critical molecular weight for the onset of entanglements, M c , the zero-shear viscosity versus molecular weight relationship, dependence of rheology on thermal history and aspects of shear-induced crystallization are presented. The melt fracture and wall slip behavior of FEP resins is also discussed. Finally, possible processing aids that can be used in the extrusion of FEP resins in order to postpone melt fracture phenomena to higher flow rates are also discussed thoroughly.

Microcellular foamed polypropylene (PP)/SiO 2 composites were prepared by using micro-SiO 2 and nano-SiO 2 particles. The effects of the particle size of SiO 2 on the foaming behavior and mechanical properties of the composites were studied based on heterogeneous nucleation theory. The results showed that the silica facilitated the cell nucleation to some extent. The average cell size of 16.3 μm and the cell density of 4.46 × 10 7 cells/cm 3 were achieved for the composite foam at the silica content of 4 wt.%. The plastic deformation of the PP was strongly constrained due to the presence of the nano-silica. The tensile and impact strength of the nano-SiO 2 composite foam are larger than those of the micro-SiO 2 composite foam due to the high crack propagation resistance in the microcellular PP/nano-SiO 2 composite.

In this research work, three different types of nano-composites based on EPDM/NBR blend (70/30 wt.%) have been prepared: one type including Cloisite 20A in EPDM phase, the other one containing Cloisite 30B in NBR phase and the third type consisting of Cloisite 20A in EPDM and Cloisite 30B in NBR phases simultaneously (called EN-xAB). XRD and TEM techniques showed intercalated or exfoliated structures for all types of nano-composites. According to SEM results, the most roughness of the surface was observed at EN-xAB nano-composites. Cure characteristics of the samples showed that the lowest scorch and cure time and highest crosslink density was devoted to EN-xAB samples. Comparison of mechanical properties of the nano-composites showed that the best properties were found in the samples consisted of both types of organo-clays simultaneously.

In this work, the mechanical and morphological properties of high density polyethylene (HDPE)/flax fiber composites are reported. In particular, the effect of adding a rubber phase (SBR) in terms of recycled ground tire rubber (GTR) is determined. Samples with different concentrations of flax fibers and rubber powders were prepared. Also, the addition of a coupling agent (SEBS) on both matrix-fiber and matrix-rubber surface adhesion and composite morphology is investigated. The results show an improvement in both matrix-rubber and matrix-fiber surface adhesion after incorporation of the coupling agent leading to improved tensile and flexural properties. Also, impact strength results showed a toughening effect of the HDPE matrix by flax and SBR addition.

Injection mold filling process was analyzed for a rectangular plate with micro patterns on the surface. For products with micro patterns whose dimensions are much larger than the dimensions of the micro patterns, numerical analysis may require a prohibitively large number of numerical grids. In order to solve this problem, anlaysis was done by separating the global flow through the base plate from the filling of the micro patterns. Global flow was analyzed using the generalized Hele-Shaw (GHS) model, while local flow for micro patterns was simulated by the Navier-Stokes equation. The boundary conditions, such as pressure and temperature, for the local analysis were obtained using the results of the global analysis. The proposed method was validated by experiments. Experimental observation showed good agreement with the numerical results. Effect of process parameters on the transcription fidelity was further examined. The numerical approach presented in this paper would enable a more efficient analysis and provide better understanding of filling behavior during injection molding of parts with micro patterns on the surface.

The cooling process in polymer injection molding is of great importance as it has a direct impact on both productivity and product quality. In this paper a Multi-objective Optimization Genetic Algorithm, denoted as Reduced Pareto Set Genetic Algorithm with Elitism (RPSGAe), was applied to optimize both the position and the layout of the cooling channels in the injection molding process. The optimization model proposed in this paper is an integration of genetic algorithms and Computer-Aided Engineering, CAE, technology applied to polymer process simulations. The main goal is to implement an automatic optimization scheme capable of defining the best position and layout of the cooling channels and/or setting the processing conditions of injection moldings. In this work the methodology is applied to an L-shape molding with the aim of minimizing the part warpage quantified by two different conflicting measures. The results produced have physical meaning and correspond to a successful process optimization.

Ink wash-off has been one of the problems that has confounded the overall success of the in-mold decoration (IMD) process for injection molded parts. In this report, an experimental matrix design based on the Taguchi method was conducted to examine the influence of processing parameters on the ink washoff of molded parts. The resins used in the study were 20% glass fiber filled poly(ethylene terephthalate) (PET). A commercially available PET film pre-printed with grids was employed to prepare the parts. Specimens of three different thicknesses were molded using a pin injection gate on an injection molding machine with a reciprocating screw system. After molding, the severity of ink washoff was determined by an image analysis program. The experimental results suggested that molded composite parts of smaller thicknesses exhibited more severe ink washoff. For the parameters selected in the experiments, the melt temperature and mold temperature were found to be the principal factors affecting the ink failure of IMD injection molded composites. Furthermore, numerical simulations using a commercially available code were completed to better understand the mechanism of the ink washoff problem. The calculated results suggested that the ink was mainly washed off by the high shear stress of hot polymer melts. It is shown that the formation mechanisms of ink washoff can be explained, and, this being done, steps can be taken to ensure that the washoff is minimized. This provides significant advantages in terms of improved product quality.

Melt extrusion of polyvinyl alcohol (PVOH) is desirable over commonly practiced solution film casting due to reduced energy input, environmental footprint, and processing cost, however, melt extrusion processing of plasticized polyvinyl alcohol (PVOH) presents a significant processing challenge due to inherent adhension issues of extruded PVOH film to the surface of equipment. This paper reports a method using inorganic fillers such as CaCO 3 and talc to facilitate the plasticized PVOH processing for blown films. Parameters are also identified for additional process studies to optimize the mechanical properties of blown films. It was found that the preferred inorganic filler is CaCO 3 for the PVOH stickiness reduction. The filled PVOH films were found to have delayed or reduced water solubility. It takes about 7 to 10 minutes for the filled PVOH films to dissolve in water whereas the neat PVOH films are soluble in water instantly. The delayed water solubility may be desirable for certain specialty applications such as packaging of pesticides during shipping and storage. With improved processability by incorporating filler, the melt extrusion produced PVOH film should cost less than the solution-cast PVOH films.

In-situ molecular orientation behavior of isotactic polypropylene films prepared by quenching at 0°C was investigated under uniaxial and biaxial extension at elevated temperatures. Both the retardation value of film and the stress were simultaneously measured during stretching. The stress required to deform films depended on the stretching temperature, but the retardation was nearly independent of temperature.

This paper is devoted to the study of fiber breakage during compounding with a polyamide matrix in a Buss kneader. Results showed a drastic decrease of glass fiber length during compounding, typically from 3500 to 350 μm. Fiber breakage depended on processing conditions: it increased with screw speed, but the effect of feed rate was less clear. Fiber breakage increased also with the severity of the screw profile. Characterizations of fiber length evolution along the screw profile have also been performed after dead-stop experiments. Generally speaking, fiber length evolution can be described using a modified Shon-Liu-White model, in which either the number of turns or the specific energy is considered.

Peel adhesive strengths of multi-layered laminates composed of two polypropylene (PP) sheets and an inserted polyethylene (PE) layer (the middle layer) between the PP layers were evaluated. PE-glycidyl methacrylate (GMA) copolymers and a maleic-anhydride grafted PP (MAPP) were compared to the PE homopolymer and the PP homopolymer. The peel adhesive strength of PE-GMA/MAPP laminates was much higher than that of PE homopolymer/PP homopolymer laminates. Meanwhile, the blends composed of the PE-GMA and three types of PE homopolymer (PE-GMA+LDPE, PE-GMA+MDPE, PE-GMA+HDPE) were formulated as the PE middle layer of the multi-layered laminates. The PE blends had the same amount of glycidyl groups, and the deformation capacity was different in each. Namely, the PE blend of LDPE had higher elongation to break than the PE blend of HDPE. The peel adhesive strength of the multi-layered laminates with the middle layer of the LDPE blend was highest among the three types of laminates with the middle layer of the PE blends. Scanning electron microscopy on the fractured surfaces revealed that the large plastic deformation of the LDPE blended middle layer was responsible for the high energy absorption, and resulted in the high peel strength.

The tubing extrusion-forming process of a fluoropolymer (FEP) melt was studied both experimentally and numerically. The flow behaviour of a FEP resin was determined by using a tubular die used in industrial-scale operations and these data were compared with simulation results using (i) a viscous model (Cross) and (ii) a viscoelastic one (the Kaye–Bernstein, Kearsley, Zapas / Papanastasiou, Scriven, Macosko or K-BKZ/PSM model) in order to assess the viscoelastic effects. In all simulations, compressibility, thermal and pressure effects on viscosity were taken into account. It was found that the viscoelastic results for the pressure, and hence the stresses at the wall, were always higher than the viscous results. Both were higher than the experimental results. A quadratic slip model plus viscoelasticity was found necessary to reproduce the experiments. The smooth flow curves resulting from this industrial tubular-coating die are a further manifestation that this is an appropriate design for coating fluoropolymers at very high apparent shear rates, exceeding 5000 s −1 .

Polystyrene (PS) has been chemically modified with cyclic anhydrides such as glutaric anhydride (GA), citraconic anhydride (CA) and phthalic anhydride (PA) in the presence of BF 3 ·O(C 2 H 5 ) 2 in chloroform and succinic anhydride (SA) in 1,2-dichloroethane. Some important reaction parameters were determined in order to optimize the acylation process. ATR FT-IR and 1 H NMR studies indicate that the acylation reaction can introduce both carboxyl group and double bond (for only citraconic anhydride) onto pendant aromatic groups of the polymer. The adhesion properties and corrosion resistance of the acylated PS on metal surface under various conditions have been investigated.