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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Injection Molding of Sub-µm Grating Optical Elements
The potential applications of micro-structured optical components are numerous. The mass replication of (sub-) micron structures remains a challenge, however. For an application in a CD light path a ?/4-grating element has been designed and successfully produced that requires the replication of structures 200 nm wide and 1600 nm deep (aspect ratio of 8). A big part of the challenge is the production of mold inserts containing such structures in a suitable mold material in addition to finding the process conditions in order to successfully replicate and release such structures with a conventional thermoplastic molding equipment. It is shown that such structures can indeed be molded with Polycarbonate in a conventional molding operation. A more stable process, however, is obtained by splitting the functions over two surfaces in this way reducing the aspect ratio to 4
Deformation Mechanism of Thermoplastic Vulcanisates Investigated by Combined FTIR and Stress-Strain Measurements
Thermoplastic vulcanisates are blends of a thermoplastic matrix with a crosslinked rubber. The rubber is dynamically crosslinked during blending. Due to this procedure it is possible to get phase inversion and disperse a large amount (up to 80%) of rubber into a thermoplastic matrix. These materials, which are in our case based on polypropylene (PP) and EPDM, show a high elasticity upon tension and pressure. This, despite the fact, that the matrix consists of polypropylene, which should be deformed plastically. To understand this phenomenon we investigated these materials with time-resolved infrared spectroscopy during tensile tests. It could be shown that the amorphous and crystalline EPDM regions show orientation directly proportional to the applied strain, whereas the crystalline PP shows a very small orientation up to 300% macroscopic strain. This fact can only be explained by a model which assumes a very inhomogenous deformation of the PP matrix and a good adhesion between matrix and dispersed phase. Besides these experiments finite element calculations were done to understand the influence of the morphology of the dispersed phase and the constitutive behaviour of the matrix on the recoverability of TPVs.
Diffusion Coefficients of Single Component Linear n-Alkanes
A high coordination lattice is used in the simulations of various n-alkanes above their melt temperatures. All n-alkanes used are linear, single component, single chain systems, ranging from C12H26 to C316H634. Metropolis Monte Carlo algorithm is adopted for the moves on the high coordination lattice. All moves are possible as long as the bond length on the lattice is not altered. Short range interactions are calculated with an extended rotational isomeric state (RIS) formalism and long range interactions are calculated with a spherically isotropic Lennard-Jones (LJ) potential both of which satisfy the specifics of the coarse grained lattice.
Performance of Di-N-Hexyl Phthalate in Flexible Vinyl Formulations
Low molecular weight esters have been available to the PVC compounder for many years. They have found a significant niche in the performance vs. permanence compromise as a compound ingredient that provides manufacturing efficiency or some special property with adequate permanence for many vinyl applications. In many respects, low molecular weight esters are the processing aids of the plasticizer family. This group of plasticizer may be said to include C4 to C7 dialkyl phthalates, the benzyl phthalates and the benzoic acid esters. This paper will introduce and compare di-normal hexyl phthalate (DNHP) to other phthalates against which it will directly compete.
Dimensional Changes of PPS in Environmental Testing
The actuator arms in some hard drives were found to distort after being subjected to an 80°C environmental test. This distortion was believed to be due to a relaxation of thermal residual stresses in the glass filled polyphenylene sulfide component of the arm due to the molding process. Changes were made in the molding process and this diminished the problem but did not eliminate it. Differential scanning calorimetry test on the plastic revealed that physical aging of the PPS was occurring during the 80°C environmental test and the changes in the molding process would have little impact on the motion which resulted in this process.
Development of Filling Imbalances in Hot Runner Molds
When manufacturing plastic parts from multi-cavity tools by means of injection molding, it is common to use naturally balanced runner systems to deliver the melt to each cavity with identical flow conditions. However, a common occurrence associated with naturally balanced runner systems is that the parts molded in the inner cavities, closest to the sprue, are heavier and larger than the outside parts. Recent studies suggest the inconsistencies be due to unsymmetrical shear distributions created as the melt splits to flow through the various branches of a runner system (1-2). This paper shows the mold-filling imbalances experienced with geometrically balanced runner systems of multi-cavity hot runner molds, through computational fluid dynamics analyses.
The Effect of Phenolic Regrind on the Mechanical Properties of HDPE
The possibility for recycling cured phenolic material was evaluated by testing mechanical properties of High-Density Polyethylene (HDPE) containing phenolic regrind material. The mechanical properties evaluated were: modulus of elasticity, percent elongation, tensile strength, and impact strength. Four different levels of phenolic regrind were used for evaluation with four different levels(4.76, 9.09, 16.7%) of phenolic regrind used in the comparison. The results demonstrated that with higher levels of phenolic regrind in the base HDPE material, certain mechanical properties degraded, with increased brittleness the most apparent effect.
A Study on the Feasibility of Using Granulated Polyvinyl Chloride Coated Fiberglass Screen as a Filler and/or Reinforcement in Specimens Molded from Recycled High Density Polyethylene, Polypropylene,
This paper will analyze the feasibility of using granulated polyvinyl chloride-coated fiberglass screen as a filler and/or reinforcement in injection molded plastic products. The screen, composed of the trim cuts from large rolls and defective sections, will be granulated and blended, in different weight ratios, with recycled high-density polyethylene and polypropylene. The resulting composites will be injection molded to produce ASTM D638 testing specimens. Also, one population of specimens will be produced from a composite of the granulated screen and commingled post-consumer recyclate. The process- ability of the composites and several mechanical properties will be observed and recorded. Statistical methods will be applied to the data, in order to predict the effect of adding different levels of filler/reinforcement on the mechanical properties of the composites.
The Effect of Polyvinyl Chloride and Polystyrene on the Mechanical Properties of Plastic Parts Produced with Commingled Post-Consumer Recyclate
One way to avoid the separation of post-consumer plastic waste is to utilize commingled recyclate in the design of plastic products. However, the combination of many plastic resins can sometimes yield poor mechanical properties, due to the debonding of the different resins. It is important to understand if one or more resins in the commingled material will cause greater debonding than the other resins. This study examines the debonding in low-density polyethylene specimens filled with increasing levels of commingled post-consumer recyclate that does and does not contain polyvinyl chloride and polystyrene. The debonding in the specimens will be characterized through tensile testing.
Processability and Trends in the Mechanical Properties of Low Density Polyethylene Parts Produced Using Increasing Levels of Commingled Recyclate as a Filler
As the plastics industry is increasingly confronted with environmental demands and regulations, the need for successful and reliable recycling programs is greater than ever. One of the keys to the success of these recycling programs and to the success of recycled resins is identifying feasible end uses for commingled recycled polymers. One possibility is for plastics manufacturers to specify commingled recycled resins, as a filler, in their products. This can provide savings for the manufacturer, while helping to promote plastics recycling. When specifying the level of commingled recycled resin to be used in a product, the designer must consider the net effect it will have on the processability and the mechanical properties of the part. This study will examine and attempt to predict the net effect of increasing the level of commingled post-consumer and post-industrial recyclate, used as a filler, in the production of low-density polyethylene parts.
Interfacial Interactions in Carbon Fiber Reinforced Epoxy Composites
The effect of surface coverage and the type of coupling agent were studied in carbon fiber reinforced epoxy microcomposites. The surface of PAN based, electrochemically oxidized carbon fibers was treated with solutions of an epoxy- (EPS) and an aminosilane (AMS), 4,4'-diphenylmethane diisocyanate (MDI) and triglycidyl isocyanurate (TGIC). The amount of coupling agent bonded chemically to the surface of the fiber was determined by analytical methods. Single fiber composites were prepared from treated and non-treated fibers. The fragmentation method was used to determine the interfacial shear strength (IFSS) characterizing fiber/matrix adhesion. The amount of coupling agent bonded to the fiber surface was related to IFSS. A close correlation was found between the bonded coupling agent and adhesion in the case of the epoxysilane and TGIC, but such a correlation could not be found for the aminosilane and MDI.
Interactions of Pesticides and Stabilizers in PE Films for Agricultural Use
Polyethylene films used in agriculture are subjected to the effect of oxygen, UV radiation, rain etc. Beside these usual effects encountered in outdoor applications, also the pesticides used for the protection of the crop may influence the degradation and lifetime of the films. In an attempt to determine the interaction of pesticides and some frequently used light stabilizers in PE, films containing three different stabilizer packages were exposed to the effect of 24 commercial pesticide formulations. The effect of UV radiation was modeled by Xenotest aging. The measurement of oxidative stability after exposure indicated that pesticides interact with the stabilizers, indeed. UV and FTIR spectroscopy gave further information about these interactions. Mechanical properties of the films deteriorated considerably after exposure at some pesticide/stabilizer package combinations. According to their effect pesticides could be classified into three groups: inert compounds, formulations with moderate effect and harmful substances. Mainly formulations having sulphur as an active component belonged to this third group due to the activity of sulphur in radical reactions.
Rapid Heating and Curing of Structural Adhesives by Infrared and Radio Frequency
Structural adhesive requires a considerate curing time to achieve handling strength at room temperature. Conventional heating and curing methods are unable to cure adhesives in minutes because of the slow heat input rate to the system. Infrared heating can penetrate into the adhesive to accelerate the reaction process in a very short time. Radio frequency heating produced substantial energy input to the adhesive through the dielectric loss of the polar molecules under rapid changing electric field. The effect of operating parameters on green strength produced from these methods were studied and compared to that cured at room temperature. Both methods show significant reduction in cure time to obtain a strong bond in less than three minutes.
Optimization of Contact Hot Plate Welding of HDPE
The hot plate welding process is widely used for welding of thermoplastics. To optimize the welding processes, melt layer thickness, welding displacement and squeeze-out ratio are used as control parameters. Contact hot plate welding of high density polyethylene (HDPE) was investigated. The melt layer thickness of the high density polyethylene samples during heating was measured. The mathematical relationship between melt layer thickness and hot plate temperature and heating time was developed and used as control parameters. The effects of welding parameters (melt layer thickness, weld displacement and squeeze-out ratio) on joint quality are presented. The results show that the maximum attainable joint strength is 100% of the bulk material strength. A minimum melt layer thickness of 2.5 mm (total from both sides) is required to produce good quality joints. A minimum weld displacement of 0.7 mm (both sides) or a squeeze-out ratio of 0.3 is also required to produce good quality joints.
Hot Plate Welding of Polypropylene and Talc Reinforced Polypropylene Composites
A systematic study of polypropylene and talc reinforced polypropylene using hot plate welding was conducted. The control parameters, welding displacement, melt layer thickness, and ratio of weld displacement to melt layer thickness were studied. A constant pressuring method was evaluated. Approximate equations were obtained experimentally to calculate the melt layer thickness based on the hot plate temperature and heating time. It is found that the maximum joint strength depends on the talc concentration. The maximum joint strength for 0% and 40% talc reinforced polypropylene was 97% and 54% of the bulk strength, respectively.
Rheology of Hard-Metal Carbide Compounds
The results of an investigation of steady-state and oscillatory flow properties of hard-metal carbide powder compounds are presented. These highly concentrated compounds are intended for powder injection moulding (PIM) technology. The volume concentrations of powders, containing mainly tungsten carbide and cobalt alloy, differing in particle size distributions, varied up to 57.5 vol. %. The model relations, correlating relative viscosities with volume fraction of filler and shear rate (shear stress), were used in order to attain maximum volume fraction of powder in the compound. At the concentrations near the maximum loading an unstable flow was observed, which has been found to be influenced by the particle size distribution of the powder used as well as its concentration. In some cases, the instabilities were suppressed by repeated extrusion.
Positive and Negative Electrorheological Effect of Poly(Methyl Methacrylate) Dispersions Stabilized by the Block Copolymer Steric Stabilizer
A change of viscosity of the poly(methyl methacrylate) dispersions in decane stabilized with polystyrene-block-poly(ethylene-co-propylene) copolymer after application of an external electric field depends on the character of its original structure. When the mutual particle interactions are low, the organized structure formed in the electric field causes an increase in the viscosity of the dispersion and a positive electrorheological effect appears. If, due to strong interactions, a gel-like network particle structure exists, an application of the electric field causes a breakdown of this structure, the viscosity of the system decreases and negative electrorheological effect occurs. The type of rheological response is thus influenced by composition of dispersions.
Morphology and Compression after Impact Strength Relationship in Rubber-Toughened Composites
Morphology and compression after impact (CAI) strength relationships in rubber-toughened high performance composites are investigated using quantitative image analysis. A group of six quasi-isotropic carbon fiber-epoxy composites, with variations in CAI strength were analyzed to reveal how the particle size, particle size distribution, and location of rubber particles affect the CAI strength values and the corresponding damage mechanisms. It is found that the CAI strength of rubber-toughened composites is greatly affected by the size and size distribution of rubber particles in the interlaminar regions of the composite. In general, high CAI strength composites exhibit more uniform particle size distribution and spread evenly across the interlaminar regions. Whereas, for low CAI strength composites, the rubber particles tend to cluster together and have wide size distribution.
The Effect of Film Winding Tension and Melt Temperature on COF and Other Properties of PE Blown Film
A designed experiment has been conducted to determine the effects of sealant layer melt temperature and film winding tension on the coefficient of friction (COF) and other physical and optical properties of a coextruded blown film containing a polyolefin plastomer as the sealant layer. A statistical design program was used to model the quantitative response of the various film properties to the control variables evaluated. Evaluation of the data indicated that only the COF had a significant response to the control variables. As the winding tension of the rolls increased, the COF increased dramatically.
The Use of Polymer Processing Aids to Reduce Gel Formation in Polyolefin Plastomer Extrusion
Polymer additives have long been linked to gel formation and reduction in polyolefin film extrusion. Several hypothesis about these additive/gel links have been empirically explored in a controlled blown film experiment. A study comparing gel levels in a metallocene catalyzed polyolefin plastomer was done on a lab size blown film line with a groove feed extruder. A photo imaging process was used to count gel levels, per unit area, during a significant portion of each run. Additive packages were varied to determine the effect of potential gel reducing additives. The data support the hypothesis that Dynamar™ polymer processing aids can reduce the amount of gel particles in the film.
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