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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The Effect of Chemical Blowing Agent Dosage on the Properties of Extruded Expanded Polypropylene
This paper investigates the influence of CBA (chemical blowing agent) concentration on the properties of extruded EPP (expanded polypropylene) rod samples. A design of experiment methodology was adopted to quantify the effect of CBA (endothermic type) dosage on EPP properties. Foam characteristics measured, were density, cell structure, tensile properties, premature foaming, and extrusion parameters (melt temperature and pressure). The research revealed that an optimal blowing agent concentration of 0.5% exists in terms of obtaining the finest cell morphology and most efficient material savings/density reduction.
Reactive Extrusion of Polyolefin Blends
The incompatibility of polypropylene (PP) and high density polyethylene (HDPE) is a source of industrial problems for recycling post-consumer polyolefins. Blends of PP and HDPE with peroxide and 3 vector fluid additives have been prepared in a co-rotating reactive twin-screw extruder. Compatibilization has been examined by stress-strain tests, impact tests and scanning electron microscopy (SEM). Molecular weight of the blends has been evaluated by gel permeation chromatography (GPC). An increase in elongation at break and impact resistance of some reactive blends compared to the mechanical blend was observed, with some links between the phases, as revealed by SEM.
A New Impact Modifier for Toughening Clear APET
Polymers, as well as glasses, exhibit physical 'aging' which leads to embrittlement. Impact modifier additives counteract this embrittlement. In clear polymer systems, such as amorphous polyethylene terephthalate [APET], blends with typical commercial impact modifiers show a significant loss of optical clarity. The work presented here, based on a new impact modifier additive, shows that embrittlement of APET can be counteracted without significant loss of optical clarity.
Fractography of ABS
Fractograpy of different types of ABS has been studied in static and cyclic loading at different ambient temperature. The effects of repeated loading, notch, grades, loading level and ambient temperature on the fracture surfaces have been discussed on the basis of the phenomena of striations, tear lines, fracture origin and stress whitening patterns.
Using CMM Data to Quantify Sink Marks
For years decisions have been made about the acceptability of a molded part based upon subjective assessment of attributes such as sink marks. The mechanisms that cause sink are well documented. Yet sink marks continue to be a leading cause of rejected products. This research focused on developing a repeatable measurement technique for objectively quantifying the depth of sink marks. Following preliminary investigation, a coordinate measuring machine (CMM) was employed.
Crushed Recycled Glass as a Stiffening Agent for HDPE Compared to Traditional Plastic Lumber Fillers
bstract The objective of this study was to determine the flexural, impact, and tensile properties of a compound of crushed recycled glass, HDPE, and coupling agent using a two-level, three-factor designed experiment. This study determined that glass content, sieve size, and coupling agent all have a significant effect on the mechanical properties. The use of recycled crushed glass was found to increase the flexural modulus, but not as efficiently as calcium carbonate, wood flour, and fiberglass. Additionally, crushed glass improved the impact strength but decreased the tensile strength. It was found that smaller glass particle size performed better and the use of coupling agent decreased all mechanical properties.
An in Vitro Study of the Mechanical Property Loss of Poly(L-Lactic Acid), PLLA, Fibers during the Hydrolysis in Tissue Engineering Applications
Tissue Engineering is the use of polymer scaffolds to grow tissue cells in vitro and then implant them. The polymer is designed to degrade as the cells grow into functional tissue in vivo. These scaffolds must be porous, strong, flexible, and ultimately degrade into harmless biomasses. The polymer scaffold is usually a natural or synthetic polymer in a fiber, foam, or fabric form. Synthetic polymers are preferred due to their easily tailored properties. For specialized tissues such as arteries, the scaffold fabric is formed into a tube. While the cells are being developed prior to implantation, nutrients are pumped through the tube. The engineered artery is ready to be implanted when it has acclimated itself to blood-pumping pressures. Other engineered tissues include heart, liver, bone, cartilage, nerves, and skin.
P20 and Beyond: Mold Steel for New Challenges
The mold steel designated as P20 has a long history of successful service in the plastics molding industry. The characteristics of this steel that have established it as the grade of choice among molders and moldmakers is reviewed as well as recent variations such as P20 Hi-Hard and P20 Premium (double melted) that offer advantages for some molding applications. Alternate grades of mold steel offering distinctly different characteristics from P20 are increasingly employed in specialized applications. Grades such as Long-Run mold steel, molybdenum modified 420 Stainless Steel, and age-hardening grades RA40 and Mar-X will be reviewed for a clearer understanding of their appropriate roles in plastics molding.
Process and Tooling Factors Affecting Sink Marks for Amorphous and Crystalline Resins
A plaque tool was built to facilitate changing rib features that include rib-to-wall (R/W) ratio, proximity to the gate, orientation with respect to flow, rib-base radius, and tool steel type. Gate type was also studied along with several process conditions using crystalline and amorphous resins. A Screening study was performed to determine the most influential factors affecting sink and followed by a Response Surface study to better define the relationships. A profilometer was used to measure sink depth. Optical microscopy and DSC were used to observed crystallization and molecular orientation differences between plaques exhibiting high and low degrees of sink. Low molding temperatures, high dwell times and high hold pressures helped reduce sink depth as did positioning ribs closer to the gate and perpendicular to the flow direction. Using a Beryllium Copper mold material also reduced sink while increasing rib-base radius significantly increased sink.
Melting Phenomena and Mechanism in Polymer Processing Equipment
The research work presented here examines the heating and melting phenomena taking place, when individual polymer particulates or compacted polymer particulate systems are subjected to stresses which force them to deform and flow. The heating/ melting behavior in compression experiments of single polymer cylinders and in co-rotating twin screw extruders was examined. Different polymers and different polymer particulate solid systems were used, over a range of processing conditions. The results of this work shed light on the important roles that solid dissipative deformation and interparticle frictional phenomena play in generating the heat necessary to melt polymer particulate systems. This paper also attempts to deal with the modification of the Thermal Energy Balance Equation, so that it includes the above heat generating dissipative source terms.
A Case Study on the Application of Finite Element Modeling in Ultrasonic Resonator Design
This paper discusses the steps taken to develop an ultrasonic horn from concept through final design. Finite element modeling was used to discover the optimum geometry, which in turn resulted in superior welding results.
Initial Stages of Bubble Growth during Foaming Process
This work concerns the initial stage of bubble growth during the foaming process for filled and unfilled polymers. It was found that a certain amount of gas accumulates in the polymer/filler interface (1), and that this has a significant impact on the initial cell growth. A model was developed to describe the initial cell growth. It was found that owing to the gas accumulation at the filler-polymer interface, the gas requirement for nucleation is much lower in a filled system than in an unfilled system. This gives rise to a smaller cell size for the filled system during the initial cell growth period.
In Line Monitoring of Poly(ethylene vinyl acetate) Extrusion Process Using Fiber Optic Raman Spectroscopy
The extrusion of molten poly(ethylene vinyl acetate) (EVA) was studied using in-line fiber optic Raman spectroscopy. The properties monitored were the content of vinyl acetate (VA) in the random copolymer and the melt index of various grades. Results are presented for independent multivariate regression of VA content and melt index values. This study presents an important development of in-line monitoring techniques that have evolved from off-line bench top measurements.
Extrusion Characterization of Ethylene/Styrene Interpolymers
An investigation of the extrusion performance of ethylene/styrene Interpolymers was performed. These Interpolymers are pseudo-random copolymers of ethylene and styrene synthesized via INSITE* Technology, Dow's proprietary, single-site, constrained-geometry catalyst technology (1,2). Extrusion characteristics such as output rate, specific energy consumption, and extrudate temperature were measured as a function of screw design and processing conditions.
Rheological and Mechanical Properties of Recycled Polycarbonate
Polycarbonate (PC) is used in computer and electronic housings, and here it was sought to reuse this polymer after having been separated from electronic shredder residue. The separated stream was not pure PC; there was some cross-contamination. The separated polymer was characterized by rheological, thermal and mechanical methods; the measured properties were only slightly inferior to those of comparable virgin materials. Recovered plastic and virgin polymer were blended using a TSE to determine the minimum virgin content needed to mask the effects of addition of recycled material on the rheological and mechanical properties of the blend. Differences in processing behavior and mechanical performance of the blends as a function of composition are discussed in relation to potential material recycling strategies.
Crystalline but Fully Transparent - A New Polyamide with Outstanding Properties
Requirements for chemical resistance and transparency are usually mutually exclusive in plastics, especially for polyamides. While aromatic constituents are used to produce most amorphous polyamides, this new transparent polyamide (designated according ISO 1874: PA PACM 12, herein PA means polyamide, PACM = Bis(p-aminocyclohexyl) methane) is based on aliphatic monomers. The monomer building blocks form very small crystallites that do not scatter visible light, so consequently parts made of this polyamide are clear as glass. This so called microcrystalline structure counts for a well-balanced combination of properties, e.g. good UV-stability, high level of impact behavior, low water absorption and isotropic shrinkage. Especially its chemical resistance is superior to other transparent materials such as polycarbonate, polymethacrylate or all amorphous polyamides.
Small-Scale Testing for Brittle-Tough Transitions of Rapid Crack Propagation in PE Pipelines
The resistance to Rapid Crack Propagation (RCP) of extruded PE pressure pipe undergoes a well defined brittle-tough transition with increasing temperature. Material developers need to correlate the transition temperature with property data measured using coupon-sized samples. This paper discusses mechanisms underlying transitions in pipe specimens before presenting efforts to correlate transition temperatures of pipe with small-scale test results. A non-mechanical thermal analysis technique appears to correlate the phase transformation behaviour of raw materials with transition temperatures of extruded pipe.
The Effect of Boron Nitride on the Processability of Metallocene Based LLDPE
Melt fracture of a various shapes and related processing instabilities continue to limit processing rate in many commercially important polymer processing industries such as fiber spinning, film blowing and extrusion. Therefore, the occurrence of melt fracture needs to be limited in order to produce high quality products, which have the desired physical properties. In an effort to investigate increasing the processing rate and improving the quality of the final product, a commercial LLDPE was modified by the addition of small amount Boron Nitride (BN). BN was added to the virgin LLDPE at 180°C at concentrations of 0.05, 0.1, 0.5, 0.75 and 1.0 wt %. Also, the processability of capillary flow was investigated as functions of temperature, applied shear rate and L/D for the virgin LLDPE and LLDPE containing BN. The equipment used in this study include capillary rheometer, parallel-plate rheometer and universal test machine (UTM). The degree of processability in the capillary flow was found to depend on boron nitride concentration. The relationship between the apparent characteristic relaxation time and the critical shear rate for the onset of melt fracture and slip is also discussed.
The Comparison of Newly Proposed Cavity-Variable-Based Full Factorial Design and Artificial Neural Network in Injection Molding Process
The statistical experimental design has been used to generate useful information for injection molding process, where more precise models based on physical laws and linear relations are not available. Until now, attempts at applying traditional full factorial design have resulted in creation of many problems, due to the selection of experimental variables from the machine rather than the cavity mold. Injection molding process has plenty of variables to be carefully observed concerning parts quality. Among these, cavity pressure and temperature are the ideal candidates for process monitoring and quality control role, thanks to their capability to present the dramatic changes inside the mold.
Reclamation of Rubber Crumb from Army's Discarded Tires
Polybutadiene is obtained by acid washing the rubber tires followed by thermal treatment of the devulcanized component of the pulverized rubber powder. The process consists of tire grinding and pulverizing steps, a devulcanizing step to reduce the cross-link density, followed by thermal polymerization of the aromatic vinyl mononers and grafting of the polybutadiene followed by melt filtration of the carbon black and the steps of finishing and packaging. The devulcanizing yield can be improved by providing a cocuurent leaching step. This is compared with the yield by the in situ thermal grafting concept.
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