SPE Library

A test methodology to determine the effectiveness of Ultra-Violet Light (UV) stabilization on the oxidative stability of piping materials is examined. Chlorine Resistance (CR) testing is used to determine the impact of accelerated UV exposure on the oxidative resistance of crosslinked polyethylene (PEX) pipe. Following accelerated UV exposure, samples are tested to failure under accelerated test conditions designed to simulate chlorinated potable water end use environments. CR testing in conjunction with UV exposure is shown to be a sensitive method for the evaluation of the effectiveness of UV stabilization on the oxidative stability of PEX pipe. For the particular material examined, it is demonstrated that excellent retention of oxidative stability can be achieved when suitable UV protection is employed.

Erucamide is incorporated into polymer films to reduce their coefficient of friction (COF). Such a reduction in COF is important in packaging lines where the performance of the film in contact with rollers can be governed by the frictional characteristics of the film. This research explores the COF behavior of multilayer films with either POP or LLDPE as the skin layer. Film-on-metal COF testing was performed repetitively with the same piece of film to investigate the extent of COF change with the number of runs. Film-on-film studies were also performed for comparison with the film-on-metal tests. Complementary analysis was conducted with atomic force microscopy (AFM) to investigate whether erucamide was being removed from the film surface or simply being smeared over the surface.

Rigid polyvinyl chloride (PVC) was co-injected with glass fiber reinforced PVC (GFR-PVC), polypropylene (PP), acrylonitrile-butadiene-styrene copolymer (ABS), and polycarbonate (PC) using the Mono-sandwich co-injection process. Up to three through-thickness skin-core morphologies were observed along the length of the sample. Near the gate, the core was always a single, continuous layer. In some cases, the core diverged into multiple or discontinuous layers. Further from the gate, flow of the core ceased, leaving a skin-only region. The skin and core layers were more uniformly distributed through the test plaque when injection speed was low. Adhesion between PVC and PP was poor. Skin and core layers delaminated and mechanical properties were poor. PVC adhered well to GFR-PVC, ABS and PC. No layer delamination occurred and mechanical properties were intermediate between those of the skin and core components alone. Dropped dart impact energy was controlled more by the skin layer than the core. In rigid PVC/GFR-PVC co-injected samples, impact energy was 2.5 times greater when GFR-PVC was the core than when GFR-PVC was the skin.

Gas-assist injection molding was discovered in Germany 30 years ago. Even though this technology has demonstrated significant value, a relatively small number of components are manufactured utilizing this process.Since the basic technology is straightforward, why has the acceptance of gas-assist injection molding been so limited? A number of factors have played a role, including litigation, initial licensing approaches and the unfamiliarity of designer with this process.This presentation will examine a number of the key decisions made by the suppliers of this technology as well as the OEM’s and molders that impacted the acceptance and utilization and their implication on the commercialization of gas-assist injection molding.

The Compact Slide Action Mold Technology (CSAM) has been custom designed for tamper evident closure molds for carbonated and non-carbonated beverage bottle closures, as well as mineral water bottle closures.Existing mechanisms for opening and closing slides in a slide action mold typically include angled horn pins or delta cams mounted to the cavity plate and slide retainers to retain slides in an open position.The new compact slide action mechanism for lateral movement of slides has been developed with the use of an air driven rack and pinion arrangement. This paper discusses some of the common problems associated with the conventional mechanism and how the new mechanism overcomes these problems.

Laser transmission welding of polymers is regarded as a promising alternative in a range of industrial applications by virtue of its characteristic properties. The new variant of laser transmission welding – quasi-simultaneous welding – can be seen as a pioneering technology offering advantages such as precise local and contact-free heating, small heat affected zone, negligible warpage, high flexibility, compensation of part tolerances, high achievable weld strengths, etc.Initial systematical investigations were carried out varying the parameters: laser beam intensity, scanning velocity, joining displacement, pigment content and joining pressure. Their influence on weld strength and welding time was recorded. A T-joint was used for welding PEEK, while both T-joints and butt joints were used for the material PC. Optimum process parameters were determined for each material.

In this work, corn starches with 21% and 1 % of amylose contents, processed in the presence of 30% (w/w) of glycerol (plasticizer), were characterized by X-ray diffraction, Dynamical Mechanical Thermal Analysis (DMTA), Tensile test and Scanning Electron Microscopy (SEM). The results showed differences in the crystalline structure and mechanical properties of the starches after processing. The 21 % amylose content starch showed fragile behavior and higher tensile at rupture than 1% amylose content starch, which showed higher elongation at break and ductile behavior.

Interfacial tension between molten polymers is a key factor that helps predicting the morphology of polymer blends. In this work, the theories of Tomotika and Tjahjadi et al.[1, 2, 3] to measure interfacial tension between molten polymers using the breaking thread method are evaluated and compared. In particular, both theories were tested for PP/PS polymer pair at temperatures ranging from 200 °C to 240 °C. The results obtained using both theories corroborated. It is shown that both theories should be used in a complementary manner in order to enhance the accuracy of the breaking thread method.

Vibration-assisted injection molding (VAIM), which involves applying mechanical vibration to polymer melts during the injection and packing stages of molding processes to control polymer behavior at a molecular level, was applied on polystyrene and polycarbonate. With optimized VAIM processing conditions, the strength of polystyrene was improved by as much as 28% without sacrificing cycle time while the strength variation was reduced by 67%. With polycarbonate, however, the strength was improved only 7% and a toughness reduction resulted in some cases. In the current paper, the findings and theoretical basis related to these seemingly incompatible results are presented and discussed.

Thermolators continually pump water through a mold and have been used for cooling since the beginning of mold cooling. Thermolators, in general, are relatively large and are not considered to be energy efficient. New technology has been used to develop a system that only pumps water as needed to maintain a consistent mold temperature.A study was conducted to demonstrate the differences between usage of a thermolator and a pulse cooling system. Cost is a main factor when comparing cooling systems. In this study the cost factors that were compared were energy usage and cycle time.This study demonstrated that pulse cooling is much more energy efficient and that pulse cooling could reduce cycle time using part warpage as the controlling factor.

The efficiency of low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers for low density extrusion foaming of low intrinsic viscosity (IV) polyethylene terephthalate (PET) was evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds with different functionalities were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Correlations of die pressure with extrudate swell during extrusion, and melt flow index with melt strength by off-line testing of the extrudates permitted the ranking of the modifiers according to their chain-extending efficiency. Extrusion foaming experiments indicate that production of low-density foams by a process involving one-step reactive modification/gas injection foaming is feasible, at conditions not significantly different than those employed in the simple reactive modification of the PET resin.

The selection of online analyzer technology is determined by numerous practical criteria. NIR has been established as a leading technology for online process analysis due to its versatility and proven reliability. Nevertheless, the robust, multivariate calibrations that are key to the implementation of NIR analyzers can be difficult to develop or transfer and their maintenance over time can add significantly to the cost of the analysis. Recent reports have indicated that, despite the higher initial costs, process N M R m ay offer long term cost advantages over NIR for applications where global NM R calibrations have been developed.The objective of this study was to com pare the accuracy (i.e., standard error of prediction) of multivariate calibrations (PLS)for NIR and NM R on a set of process samples taken from a terpene resin still that were referenced by G C. Particular attention was focussed on whether the uniformity of NM R intensities and the discrete nature of the spectra would offer any inherent advantages over NIR with its superior signal-to-noise.The PLS calibrations on laboratory data showed better results by NIR over NM R for the same total acquisition time. The NIR advantage w as m ore pronounced for the minor components (<5% of the neat mixture) than for the major component (>90% ). The results are consistent with the higher signal-to-noise for NIR over NM R. In both cases, the PLS regression coefficients emphasized resolved spectral features that corresponded directly to functional groups in the pure components. Due to the spectral simplicity of this mixture of small molecules, the selectivity of NM R did not yield any advantage in the calibrations. Additional work would be required to determine if NM R would offer benefits in the actual online environment.

A comparative modeling of distributive mixing has been investigated in intermeshing co-rotating, intermeshing counter-rotating and tangential counter-rotating modular twin screw extruders. This is based on the Spencer-Wiley premise of representing mixing through interfacial area increase and its relationship to shear strain of the various modular twin screw elements. It is necessary to develop flow analyses for different modular twin screw extrusion machines. We applied this analysis to understand the reactive extrusion process in various twin screw extruders. Our approach is to compute the development of interfacial area for composite modular twin screw extruders and an internal mixer, and a mixing index was determined for each processing device.

We investigated the crystallization and orientation development in syndiotactic polypropylene (sPP) during various polymer processing operations and also compared the results with isotactic polypropylene (iPP). This was carried out in fiber spinning, tubular film extrusion and injection molding. Melt-spun sPP fibers exhibit Form I helical structure at low spinline stress levels and zig-zag all trans structure (Form III) at high stress levels. In tubular film extrusion, sPP exhibits Form I structure and the a-axis is preferentially oriented in the film normal direction. Injection-molded sPP samples exhibit very low frozen-in orientation levels due to its slow crystallization rate.

The compiled data are for unfilled acetal and filled polyethylene terephthalate (PET) specimens. Various sample sets were evaluated using the ASTM D 638-95 method, “Tensile Properties of Plastics.” These tensile data are used to evaluate material candidates for making molded parts. It is important to determine if the tensile data are the same or if they are different so that selections can be made without repeating the data collection each time a decision is required. Sample sets were evaluated using two different instruments—a SATEC and an Instron. These data were obtained over a number of years by different operators following an iterative approach. One sample set was molded from Delrin® 500*, a medium viscosity, acetal homopolymer (POM). The three addition sets were polyethylene terephthalate (PET) specimens molded from Rynite® SST 35,* Rynite® 545, and Ticona Celstran® PETGF 20-02.

The elongational viscosities of a low density polyethylene in axisymmetric and planar flows are compared. The experimental data on entrance pressure loss is matched with the corresponding finite element predictions to estimate the parameters in the elongational viscosity model proposed by Sarkar and Gupta. The entrance losses in the capillary and slit rheometers are used to predict the elongational viscosities for axisymmetric and planar flows respectively. The power-law region of the axisymmetric as well as planar elongational viscosity is found to follow the time-temperature superposition principle.

In the last few years our group has demonstrated experimentally the dominant role which Plastic Energy Dissipation (PED) plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin screw extruders and counter-rotating continuous mixers/melters. We have also developed simple empirical methods of predicting the total axial distance in specific processing/compounding machines needed for melting as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores how PED behavior of single-component polymers may affect the PED (and the melting) behavior of multi-component polymer blend.

A range of films was manufactured from a medium density polyethylene (MDPE) resin of MFI 2.0 (g/10min) and density 0.94 g/cm 3 using a 75mm extruder fitted with a 290mm diameter Blown Film Die and a die gap of 0.9mm. The films were manufactured at different haul off rates and a constant blow up ratio of 1.24, using both conventional air ring and internal bubble cooling (IBC) systems. The line speed of the IBC extrusion line was approximately three times that of the conventional blown film line. Tensile analysis of the films at room temperature showed significant increase in break strength and break modulus in the machine direction for the IBC films, at all draw down ratios. Differential Scanning Calorimetric (DSC) analysis showed IBC quenched films to be more crystalline than the conventionally quenched blown films. The results also indicated the potential for significant down gauging of film thickness (by up to 25%), without reduction in film mechanical performance by using IBC systems in blown film extrusion processes.

Natural fibres at levels up to 20% have been used for years as fillers to improve the rigidity of polymers. In the past five years up to 60% wood sawdust has been used in a rapidly increasing wood polymer composite market, particularly in the US. A series of composites, using spruce sawdust and MDF sawdust at different levels, with three polypropylenes, have been produced using a single-screw extruder and an injection moulder. The impact energy, tensile and flexural strengths of these composites were measured. The results show significant differences between the impact, tensile and flexural strengths from two types of wood as well as the type of polypropylene.

Long chain branching (LCB) has long been recognized as an important molecular parameter that significantly influences both processing and property performance of polymers. In this study, we report on the effects of LCB on the blown film processing and performance behavior of both narrow and broad molecular weight distribution (MWD), linear-low density polyethylene (LLDPE) resins. The LCB was introduced by peroxide addition and by varying the finishing stabilization additives. The results showed that while improvements in some processing characteristics were observed with LCB addition, this generally came at the expense of physical properties. Thus, in contrast to the general belief in the literature, we contend that LCB addition in LLDPE type film resins involves a trade-off in improved processing at the expense of film properties.