The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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We have developed a novel microbubble inflation method to measure the viscoelastic properties of ultrathin polymer films over a range of stresses and temperatures. The method is capable of measuring the biaxial creep compliance response of films as thin as 13 nm. We summarize some prior experiments that show a dramatic stiffening of both poly(vinyl acetate) (PVAc) and polystyrene (PS) in the rubbery regime at the reduced thickness but a material specific degree of reduction in the glass transition temperature. In addition, we show preliminary results of creep recovery experiments and thin film rupture images that suggest that the method can be used for a broader range of mechanical measurements than originally anticipated.
The objective of this work was to evaluate nano and micro size fillers on shape memory (SM) properties of polyurethane nanocomposites. The matrix material was synthesized from diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD), and polycaprolactonediol (PCL). Organoclay, carbon nanofiber, carbon black, and silicon carbide were selected as fillers. Our results indicate that exfoliated organoclay augments SM performance significantly, while other fillers diminish it by interfering with the soft segment crystallinity and/or hard segment phase separation. Better SM properties with organoclay can be attributed to mechanical reinforcement without interfering with crystallinity and phase separation.
Both experiments and numerical studies were conducted to investigate the PS foam screw characteristics with R22 blowing agent in a single screw extruder. Five thermocouples and pressure transducers are equipped in this extruder. R22 is the blowing agent for this study, which is injected into the extruder at 18.4D with temperature around 200°C. Without the blowing agent, it is found that the pressure monotonously increases along the screw axis after the distance of 24D. However, the pressure profile changes after the blowing agent is injected. A hybrid FEM/FDM was applied to predict the Q-P characteristic curves for PS and PS foam extrusion.
Dimensionless analysis is a powerful tool in analyzing the transient heat transfer and flow processes accompanying melt flow in an injection mold or cooling in blown film,to quote a couple of examples. However, because of the nature of non-Newtonian polymer melt flow the dimensionless numbers used to describe flow and heat transfer processes of Newtonian fluids have to be modified for polymer melts. This paper describes how an easily applicable equation for the cooling of melt in a spiral flow in injection molds has been derived on the basis of modified dimensionless numbers and verified by experiments. Analyzing the air gap dynamics in extrusion coating is another application of dimensional analysis.
The difference in thermoforming processability of three STYRON* high-impact polystyrene (HIPS) resins was investigated. Experiments were performed on a moldbottle thermoformer as well as a step-case tool thermoformer. Disparities observed were analyzed in terms of differences in rheological properties of the resins. Conclusions were drawn as to which rheological characteristics the resins should possess in order to give the largest temperature processing window coupled with high quality thermoformed parts.
We describe results for experiments in which a novel rheological technique is applied to a styrene-isoprene-styrene triblock copolymer in the vicinity of the order-disorder transition. Mechanical Hole Burning Spectroscopy (MSHB) was developed to probe dynamic heterogeneity in polymers. In this technique, a large amplitude oscillatory strain (LAOS) is imposed on a sample as a perturbation, and is followed by a small step strain. The relaxation response is then compared with that without the LAOS perturbation. It has been assumed that mechanical holes for heterogeneous systems. For homogeneous systems no hole would result. Here the heterogeneity of a tri-block copolymer was investigated in the vicinity of its order-disorder transition and it was found that the mechanical hole intensity gradually decreases as the phase boundary is approached from the ordered regime. At the one-phase or the disordered region, no apparent holes were observed.
Cationic nanoclays were treated with various novel modifiers based on ionic liquids of different structure and/or molecular weight. Initial experiments with short chain dialkyl imidazolium and monoalkyl pyridinium based modifiers were followed by treatments with phosphonium based ionic liquids having longer chain cations. The modified clays, characterized by spectroscopy, thermal analysis, microscopy and X-ray diffraction, were melt compounded with polypropylene. The effects of the ionic liquid structure and chain length on extent of clay dispersion, intercalation and thermal stability were investigated.
Polyethylene, PE, is characterized by molecular weight (MW), molecular weight distribution (MWD) and density. Melt index (MI2) is measured in the QC lab and is used as an indication of resin MW. Melt flow ratio (MFR or MI20/MI2) is a calculated QC lab number, which is used as an indication of MWD. Density is a measure of crystallinity. In polyethylene production, having fast reliable feedback on MW and MWD is critical for producing high quality resins. This article describes a novel/unique idea how a capillary rheometer can be used to predict MI2 and MI20.
Solid-state shear pulverization (SSSP) is an innovative processing technique that has proven to effectively disperse nanoscale structural entities to achieve compatibilized polymer blends and exfoliated polymer nanocomposites. The SSSP apparatus, which is a modified twin-screw extruder, can continuously process polymer blends and nanocomposites without the use of heat, solvent, or chemical modifiers. For an insight into this unconventional process, the effects of different processing parameters are evaluated using several polystyrene-based blends as base systems. The manner by which the materials deform, mix, and disperse depend strongly on the type of polymers as well as the configuration of the mixing and pulverization zones in the SSSP apparatus. Such key processing variables as residence time and throughput are also considered and compared with typical values in conventional melt extrusion.
Thermoplastic polyurethanes (TPU) based on aliphatic diisocyanates such as 4,4'-dicyclohexylmethane diisocyanate (H12MDI) are indispensable in a variety of industrial, optical, and medical device applications. Relative to 4,4'-diphenylmethane diisocyanate (MDI) based TPUs, H12MDI based TPUs exhibit superior aesthetics, light stability, and biocompatibility. However, the use of H12MDI as a diisocyanate has a major impact on other properties of the final TPU. In this study, the thermal, mechanical, and rheological properties of a typical H12MDI based TPU were characterized and compared to an analogous MDI based TPU.
The automotive industry is facing increasing pressure to reduce weight and cost in vehicle design and development. Blow molded seatbacks for rear seating offers an opportunity to reduce weight and cost and meet US and European government regulations, including FMVSS 207, 210 and 225 in the US and ECE 17 (luggage retention) in Europe.This new generation of rear seating design has been achieved through the combination of innovative design, blow molding processing and an unfilled thermoplastic that performs over a wide range of temperatures. The plastic seatback eliminates the need for steel reinforcements to pass the loading requirements.This technology was first introduced by Dow Automotive in 2000 for rear seatbacks. Several prototype designs were tested and optimized for different latch configurations to meet the federal requirements. This led to the successful introduction on the 2006 Audi TT in Europe. This resulted in a mass savings of 1.2Kg. High stiffness is achieved through closed sections within the double shell blow molded structure. Blow molding also offers reduced development time and tooling costs when compared to more traditional steel designs.
A high-density polyethylene with grafted maleic anhydride units has been investigated as a compatibilizer for high density polyethylene with polyamide 6. The material acts as an effective compatibilizer, causing a marked reduction in dispersed phase size as well as an increase in tensile strength and toughness. Compatibilizer also affects the glass transition temperature, crystallization kinetics and amount of crystalline material for certain blend compositions. The addition of zinc cations, which are effective in increasing ethylene-acid copolymer compatibilizer performance in low-density polyethylene/polyamide blends, has little, if any, effect on compatibilizer performance in these high-density polyethylene/polyamide blends.
Photopolymerized crosslinked polyacrylamide hydrogels are emerging as an attractive electrophoresis sieving matrix formulation owing to their ideal range of pore size, rapid polymerization times and the potential to locally tailor the gel structure through spatial variation of illumination intensity. This capability is especially important in microfluidic systems, where photopolymerization allows a gel matrix to be precisely positioned within a complex microchannel network. The achievable level of separation performance is directly related to the nanoscale gel pore structure, which is in turn strongly influenced by polymerization kinetics. Unfortunately, detailed studies of the interplay between polymerization kinetics, mechanical properties, and structural morphology are lacking in photopolymerized hydrogel systems. In this paper, we address this issue by performing a series of in-situ dynamic small-amplitude oscillatory shear measurements during photopolymerization of crosslinked polyacrylamide electrophoresis gels to investigate the relationship between rheology and parameters associated with the gelation process including UV intensity, monomer and crosslinker composition, and reaction temperature. In general, we find that the storage modulus G' increases with increasing initial monomer concentration, crosslinker concentration, and polymerization temperature. We also find an optimal UV intensity level at which the resulting hydrogels exhibit a maximum value of G'. A simple model based on classical rubber elasticity theory is used to obtain estimates of the average gel pore size that are in agreement with corresponding data obtained from analysis of DNA electrophoretic mobility in hydrogels polymerized under the same conditions.
Thermoplastic polyolefins (TPO's) based on polypropylene (PP) are desired for cut sheet thermoforming applications for their superior physical properties, weathering performance, and chemical resistance. However, their acceptance has been limited due to poor processing performance. A new generation of thermoformable TPO's was developed that extends the processing window and physical properties over currently available products. High gloss, thermoformed parts, incorporating a co-extruded gloss layer on the TPO substrate, was also demonstrated.
The objective of this work is to develop a vapor chamber based heating and cooling cycle system.. Two injection molds incorporated with the system were produced to evaluate its effect on the products, the test material is ABS.One of the products was a 2 opposite gates tensile test part. The tensile strength of the part was found increasing by 6.8% compared with the conventional one. The other product was a plate with 8 holes, the depth of the weld line is decreased from 12?m to 0.5?m. The results showed that the system can reduce the defect of the weld lines. Furthermore, adding a vertex tube cooling system will decrease the cycle time resulted from the rise of the mold temperature.
Novel olefin block copolymers synthesized via catalytic block technology were evaluated for polyolefin blend compatibilization. It was found that OBC is an effective polyolefin blend compatibilizer for polypropylene-high density polyethylene blend. Significant improvements in mechanical properties were observed. Morphology showed that OBC compatibilized blends displayed reduction in phase size. Cryo-fractured surface analysis and adhesion data from microlayered tapes with OBC as tie layers suggested improved interfacial adhesion for OBC compatibilized blends.
We present a comparative study of the biostability and structural organization of polyurethanes (PU) having chemistries of those of commercial biomedical interest. The soft segments are poly(carbonate)diol (PC), poly(tetramethylenoxide)diol (PTMO) and a mixed macrodiol composed of poly(hexamethylenoxide)diol (PHMO) and poly(dimethylsiloxane) (PDMS). In PDMS based PU, PDMS units are completely phase separated from the hard segments due to their highly non-polar character. However, ‘interphase’ mixing is achieved for the PDMS end group segments and the PHMO component. PTMO and PC-based PU present a much lower degree of phase separation and larger interdomain spacings than PDMS based PU. The mechanical properties and biostability of the samples will also be compared.
Thin-wall injection molding of hexagonal boron nitride (h-BN) / polypropylene (PP) composites with different h-BN contents were performed to improve heat conductivity. Effects of h-BN content and process parameters on processability were evaluated. Furthermore high-order and internal structures, thermal and mechanical properties of molded products were also analyzed by wide X-ray diffraction, density, SEM, thermal diffusivity and DSC measurements and tensile testing. Flow length of molded products increased with increasing injection speed and h-BN content. Molecular orientation and crystallization of matrix PP were suppressed by compounding h-BN. The thermal conductivity increased with increasing h-BN content and varied at the position of molded products. They were influenced by not only h-BN content but also polymer orientation.
In this study, a novel approach is applied to prepare polymer composites reinforced by both nanoparticles and long fibers. Carbon nanofibers were pre-bound onto glass fiber mats, and then unsaturated polyester composites were synthesized through vacuum assisted resin transfer molding. These composites were compared with those synthesized by pre-mixing carbon nanofibers into the polymer resin. Mechanical and thermal properties of composites were measured. Flexural strength and modulus of composites were improved with the incorporation of nanoparticles. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficients of unsaturated polyester resin.
The present study attempted to numerically predict residual stress and birefringence in injection molded PC specimens with different thickness, 2.0mm and 6.5mm. Numerical simulations have been done based on a viscoelastic fluid model and commercial software MOLDFLOW by three dimensional finite element methods. The former is used to compute flow-induced residual stress, while the latter for combined residual stresses, including thermal-induced and flow-induced stresses. Effects of processing conditions on the residual are considered by the numerical simulations. As for 2.0mm PC injection molded parts, the predicted residual stresses of viscoelastic model show quite precise in accordance with experimental results. But for 6.5mm PC specimen, Moldflow simulated results have less error.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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