SPE Library

In the present work the morphology and stress-relaxation of crosslinked polyethylene films were investigated. The stress-relaxation of crosslinked films was studied as a function of temperature and as a function of the irradiation dose applied. The relaxation time spectra of crosslinked films were observed to display additinal relaxation times. Irradiation dose and temperature were shown to influence the relaxation time spectrum of crosslinked and non-crosslinked films. The crystallization of crosslinked and non-crosslinked polyethylene was compared. It was shown that the lower mobility of the crosslinked molecules affects the final crystal size.

The current experimental study investigates the development of the micro-morphology across the residual wall thickness and along the gas channel of specimens moulded via a recently developed cryogenic gas-assisted injection moulding process. This novel method was developed as an alternative to conventional gas-assisted injection process (GAIM), targeting cycle time reduction by improving the internal heat transfer from the polymer melt to the gas. The cryogenic GAIM process employs the injection of nitrogen gas at cryogenic temperature into the polymer melt stream and its controlled manipulation throughout the gas holding phase. The effects on the morphology induced by the injection of gas at cryogenic temperature are investigated using polarised light microscopy and the results compared with the structure produced at conventional GAIM temperatures. Differential interference contrast (DIC) is used to characterise the morphology of the internal surface.

A new injection moulding technology is described in which a laminate structure of two or more polymers moulded in combination can be controlled. The new technology is referred to as 'Multi -Component Laminate Moulding (MLM) Technology'. The principle of the process is demonstrated with reference to a two component application. The material combinations chosen were a general-purpose polystyrene with a high-density polyethylene (GPPS/HDPE) and a general-purpose polystyrene with a high-impact polystyrene (GPPS/HIPS). The processing conditions, physical property and micromorphology relationships of conventional injection mouldings of the individual component materials were compared with multi-layer mouldings produced from them. Bright Surface Moulding (BSM) was also used to influence the layer structure of the multi-layer mouldings. The results of this study showed that the multi-layer mouldings composed of both combinations produced by MLM possessed desirable characteristics of both resins. The impact strengths of the multi-layer mouldings were, however, found to be in the range of 1.5 to 10 times greater than that of the individual components. It was also shown that the MLM process could be applied to component resins that have a large difference between their viscosities.

Multilayered monocomposite polypropylene is a new composite material. It captures the exceptional mechanical properties of oriented polypropylene tapes in a polypropylene matrix.Low density, high stiffness, high tensile strenght and outstanding impact and abrasion resistance provide the opportunity to make parts with an extraordinary performance. Due to missing reinforcement fibers like glass or carbon fibers this material is a 100% thermoplastic and totally recyclable.This paper describes the influence of manufacturing parameters (pressure, temperature, time) on semi-finished material. Afterwards an exemplary vehicle application is discussed with attention to the specific advantages of this material.

Nanocomposite polymer films are known to exhibit increased barrier properties at low additive loadings. These films, particularly at low loadings, are of interest to the food packaging industry. Current 2D models do not fully account for the characteristics of typical polymer-clay systems. The results of a new permeation simulation using Monte Carlo techniques will be presented.Efficient Monte Carlo simulations were run in three dimensions to determine the effective diffusion coefficients for typical polymer-clay systems. Systems with loadings between 0.5 and 50 vol% were simulated. The results were compared to existing models to examine the effects the added dimension had on the diffusion coefficient. The results were also viewed using Java3D to examine the diffusion path.

Nanocomposite films consisting of an ethylene co-vinyl alcohol (EVOH)/clay system were investigated to determine the effect of the nanoclay on the film properties. EVOH and montmorillonite clay at 5% loadings were compounded using a twin-screw extruder. Subsequently, these formulations were further processed into blown films using a twin-screw extruder. The morphological, mechanical, thermal and barrier properties of the films were examined. The delamination and dispersion of the clay improved in the blown films compared to the compounded material. Young's modulus and tensile strength increased significantly for the nanocomposite compared to the pure EVOH. Dramatic reduction of oxygen transmission rates occurred as a result of incorporation of the nanoclays. With improved barrier properties, these films could be used in military ration packaging systems in order to meet shelf life and survivability requirements.

Polypropylene (PP) nanocomposites were prepared by two steps: a predispersed organoclay masterbatch was first prepared by using a twin screw extruder; the masterbatch was then letdown into base PP by using a single screw extruder. The effect of single screw mixing type on organoclay dispersion and nanocomposite properties was evaluated. The results indicated that the composites obtained from the masterbatch letdown with a single screw extruder showed better dispersion and better mechanical properties than the composite obtained from the direct compounding with twin screw extruder. Furthermore, the mechanical properties of these composites from masterbatch single screw letdown process is as good as the composite obtained from masterbatch letdown with a twin screw extruder. A rheological study also shows PP nanocomposite has the same flow characteristics as neat PP, indicating the new technology can drop in the current machine set up, without adding additional cost to end users.

A new method was investigated for development of natural fiber composites of high performance thermoplastic polymers considering polyphenyleneether (PPE) and wood flour as example system. The large gap between high processing temperature of PPE, typically between 280-320°C, and low decomposition temperature of wood flour, about 200°C, was reduced by using a reactive solvent, a low molecular weight epoxy. The epoxy component reduced viscosity of the blends and accumulated around polar wood flour particles upon polymerization during the fabrication step. These composites offered lower density and better mechanical and physical properties than commercial engineering polymer blends filled with short glass fibers.

To reduce head injury of occupants in automobiles, The National Highway Traffic Safety Administration published FMVSS201U that ruled required parts performance of impact energy absorption using HIC(d) calculated from time-acceleration curve of Free Motion Head Form (FMH) . From the complexity of the calculation, it is difficult to design time-acceleration curve which minimizes HIC(d). In this paper, we propose a method of minimizing HIC(d), using CAO (Computer Aided Optimization) technique and deformation model which is constructed with energy balance between interior parts and FMH. As the results, we get time-acceleration curves which make HIC(d) smaller than rectangular wave.

The simultaneous stretching technology with linear motors provides new possibilities for the production of biaxially stretched polyolefin films, e.g. BOPP and BOPE shrink films. The development of new film types is done in the first stage on a discontinuous frame stretcher on a laboratory scale and from there, transferred in a continuous process onto a pilot line. This development environment represents the basis for the transfer to production scale and has meanwhile been realized on several large scale production lines. The given examples shall outline the outstanding properties of shrink films achieved with this technology.

Long fiber reinforced thermoplastics have excellent mechanical properties and stiffness-weight ratio, which is of particular interest to the automotive industry. The new Inline-Compounding processes for long fiber materials offer users more flexibility, as they are able to both compound and process such materials in accordance with their own formulation and also use ready-made com-pounds. The following process combinations are possible:E-LFT; In-Line-Compounding and Direct Extrusion to Profile or PlateD-LFT; In-Line-Compounding and Compression MouldingS-LFT; In-Line-Compounding and Injection Moulding

Long fiber reinforced thermoplastic composites have reached the state of processing and applications development comparable to the well known production processes GMT and SMC compression molding. The long fiber reinforced thermoplastic compounds also share a high level of market acceptance. The In-line compounding process using fiber glass, resin and additives to form a LFT part has opened possibilities for a wide range of new applications. These applications became possible due to the newest advancements in the In-line compounding process.The author will also discuss In-line compounding processing parameters, resultant material properties and the overall economics of in-line compounding as compared to other composites processes. and special blends in combination with glass, carbon and synthetic fibers.

Ethylene acrylate copolymers, particularly ethylene-methyl acrylate (EMA) with high MA content, made from a high-pressure tubular process are studied for foam applications. The crosslinked foam is soft, low density and highly resilient. With easy processing and excellent compatibility with EVA, the EMA can be used to modified EVA to attain lower density foam with balanced properties desirable for footwear foam applications. As compared with EVA foam, the EMA-modified EVA foam has a higher foam expansion that leads to lower density foam. The EMA modified EVA foam is softer and highly resilient, without sacrificing other physical properties. EMA is compared to metallocene polyethylene (MPE) as a modifier for EVA. While similar physical property results are seen, EMA provides superior compatibility, which results in improved processing and adhesion characteristics.

The need for biodegradable thermoplastics continues to grow as waste disposal remains an environmental problem. In order to meet these needs, alloying of biodegradable plastics may expand the markets in which they are used. Initial evaluation of mechanical properties of selected blends suggests that Biomax®, which is a somewhat brittle material, may be toughened by the incorporation of a low modulus copolyester, Bio® GP. Also, blends of CAPA® 6500 and Bio® GP offer a group of mid to low modulus biodegradable polymers. The suitability of blends of Biomax® and CAPA® 6500 are unknown at this time. Assessment of the mechanical properties suggests that miscibility is suspect. The addition of ECM Masterbatch Pellets® to a polyolefin is another approach for developing degrading polymers. The addition of the concentrate did not significantly change the mechanical properties of a polyolefin resin.

In this part of our investigation, several manufacturing and design variants of hot runner manifolds were tested to evaluate their effect on hot runner color change performance. It was found that melt channel layout and size optimization are more critical for engineering successful hot runner color change applications than using contoured melt channel turns or plugs, for example. It was also found that the pressure drop and processing window constraints could limit the reduction of melt channel sizes. It was demonstrated that this restriction coupled with the laminar flow of the polymer makes the optimization of some hot runner applications difficult for fast color change. In the second part of this paper a new nozzle design is presented as a solution for such cases.

This work investigates the effect of hot runner design features on the color change time. It was found that color change performance is affected mainly by the nozzle tip design. In pinpoint gated hot runners, the flow is converted from circular to annular through one or more tip portals. This flow disturbance generates melt stagnations in the nozzle-well, that hinder color change, and creates weldlines/flowlines that may affect part quality. Likewise, in valve gated hot runners, the flow disruption by the valve stem produces similar drawbacks. In view of that, the extrusion concept of spiral mandrel die was used to develop a hot runner nozzle that improves color dispersion, speeds color change and eliminates flowlines. The new nozzle's performance and the challenges of crossbreeding extrusion and injection molding technologies are reviewed.

This paper describes new injection moldable composites having resistivities within a desired static dissipative range 106 - 109 ohms/sq. The new compounds are based on very low carbon black loading (1-2 wt%) sufficient to achieve ESD protection, compared with the 15-25 wt% carbon black based conventional compounds. The phenomenon of filler encapsulation and the selective localization of carbon black particles in multi-component systems are investigated. Quaternary-component systems comprising polypropylene/ nylon/glass fiber/carbon black can be described by a triple-percolation" morphology i.e. three continuities of a continuous glass fiber network continuous nylon phase encapsulating glass fibers and continuous carbon black pathways. The minor polymer affinity to the filler and the attraction of carbon black to the minor polymer are controlling factors in determining the unique blend's morphology."

A new dynamic mechanical analyzer with special fluid bath furnace has been developed to measure the mechanical and thermal properties of materials while immersed in fluids or exposed to humidity. This technique is superior to traditional methods of first exposing the material and then performing the measurements.Such experiments are performed on several materials including oil filter paper and an epoxy coating. The former material is immersed in engine oil and shows post-curing behavior. The epoxy is measured in both air and salt water (saline). The saline experiments show that the traditional method (in air) can lead to anomalous results.

Machine Direction Orientation (MDO) can enhance many film properties such as tensile strength, elongation, stiffness, optics (haze and gloss) and water vapor transmission rate (WVTR). Few or no medium molecular weight (MMW) HDPE film have previously been offered (or available) due to MDO processing issues, namely stretch resonance, which is a phenomena where the film stretches unevenly. This paper describes a new line of MMW-HDPE MDO films that are now commercially available, made possible through the use of a proprietary processing aid (PA) that overcomes the stretching problem previously encountered with MMW-HDPE resins. Film physical property data for two MDO MMW-HDPE films are presented.

Our recent work on polymer-gas interactions under subambient conditions revealed a processing window leading to the production of ultramicrocellular foams with cell size around 0.4 ?m. We have now found that even more intriguing cellular structures with lower density can be obtained by re-saturating the ultramicrocellular foam with the blowing agent and subjecting the resulting solid solution to another expansion cycle. PMMA foams with ultrafine cell structure and with densities as low as 0.076 kg/L have been obtained in this work. Morphological characteristics of these foams along with the sorption/desorption kinetics in the system PMMA-CO2 will be reported.