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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Application of Time-Temperature Superposition to Stress Relaxation in Elastomers
Williams, Landel and Ferry developed a method of shifting data horizontally along the log time scale by amounts related to a temperature difference to obtain long term properties of the material without requiring testing to those long times. This paper explores the use of the WLF Method to characterize the long-term stress relaxation of thermoplastic vulcanizates. Stress relaxation data is used to predict long-term sealability of these materials in applications such as automotive weatherseals, pipeseals, glazing seals, etc. A master curve is defined for various elastomers and a comparison is made to previous WLF models and to current data to determine its accuracy. The use of this method can allow the prediction of long-term stress relaxation obviating the requirement to submit materials for lengthy and costly testing.
New Flame Retardant TPVs for Electrical Applications
Thermoplastic vulcanizates (TPVs) have long established themselves as cost effective and durable alternatives to many traditional elastomers such as EPDM rubber and thermoplastic urethanes (TPUs). Cost effectiveness comes from lower specific gravity, while durability comes from the cross-linking of the thermoset rubber. Newly developed TPVs further expand this envelope. This paper compares physical properties, including abrasion resistance, of these newly introduced TPVs, to both ester and ether based TPUs. Data shows these TPVs are equal to or better than the TPUs in flame retardancy and abrasion resistance while at a lower final volumetric and weight cost.
Versatile New Soft Polyolefin for Compounding with Other Soft Thermoplastics Resins or as a TPV Base Resin
A high level of bipolymer “in-situ” polymerized within a polypropylene random copolymer matrix was synthesized and utilized to achieve interesting elastomeric properties and softness. This versatile new Soft Thermoplastic (STP) is crosslinkable, compatible with other non-olefin polymers and free flowing. Moreover, it is usable with all main compounding technologies, capable of improving properties with a cost-effective solution. Physical-Mechanical characterization and use of this new STP designed as a blend component for product development by compounders are reviewed. Composition properties, in which this grade plays a role as either a component with other polymers or as a base for more elastic thermoplastic vulcanizes, are also presented.
Educating Industrial Design Engineers in Failure Awareness
Industrial designers have problems imagining how their designed plastic products might fail.The paper illustrates how our students are educated about the specific structure related properties that might cause failures.A specific course about designing for reliability of plastic products is outlined. Case studies showing failed products are important.Students must be aware of failure causes like: stress concentrations, low mass and/or mould temperatures, highly stressed weld lines, faulty ribbing and incorrect joining.The course deals also with typical failure mechanisms of plastics like: creep and stress relaxation, stable crack extension, chemical attack and environmental stress - cracking.
Improved Chlorinated Paraffin Secondary Plasticizer Compositions
Chlorinated paraffins are the world's lowest cost secondary plasticizer for flame retardant flexible PVC compounds. Significant quantities are used throughout the world, primarily outside of the United States. In the U.S. the use of chlorinated paraffins has lagged behind the use of phosphate esters in flame retardant flexible PVC. This is principally due to concerns and misconceptions regarding the heat stability and compatibility of chlorinated paraffins. This paper documents the recent progress that has been made in the field of chlorinated paraffin secondary plasticizers with regard to overall economics, heat stability and compatibility in flexible PVC FR compounds.
An Innovative Plasticizer for Sensitive Applications
With the increased critical discussions about potential toxicological effects of phthalates in the midnineties, BASF took a proactive approach to search for alternatives. We are convinced that phthalate plasticizers are suitable for many PVC applications. However, in exposure sensitive applications, such as medical and toys, we felt there was a need to develop a new plasticizer.Different structural classes that could be used as plasticizers for PVC were examined. Based on our knowledge of the physico-chemical requirements and our experience in applications technology, the most promising candidates were selected for further testing. From these results, BASF commercialized Hexamoll® DINCH, the ester of cyclohexanedicarboxilic acid and C-9 alcohols.In a paper presented at Vinyltec in Chicago last year, BASF reviewed the activities of the FDA’s safety assessment of DEHP. The Vinyltec paper went on to discuss the toxicological database and profile for Hexamoll® DINCH. It recommended the use of this new class of plasticizers in exposure sensitive FPVC applications such as medical, toys, packaging and gloves.This paper evaluates the performance of the ester of cyclohexanedicarboxilic acid and C-9 alcohols in flexible PVC and plastisol formulations and compares it to a semi-linear diisononyl phthalate based compound and plastisol. An evaluation comparing DINCH to acetyl tri-n-butyl citrate is ongoing and will be reported at ANTEC.
Improved Heat Distortion Modifier for PVC and ABS
Through the use of Design of Experiments (DOE), an improved, more efficient heat modifier was evaluated and compared to products commercially available. Experimental results indicate the improved modifier is more efficient and can be used at reduced loading levels over previous modifiers. This modifier performs well in polyvinyl chloride (PVC) and acrylonitrile-butadiene-styrene (ABS) polymer systems. The incorporation of this modifier into these polymer systems can introduce cost savings to the compounder/formulator while potentially opening doors for the use of these polymers in applications where heat performance was previously a limiting factor.
Adding Value to PVC Formulations with Ester Lubricants and Fine Calcium Carbonate
The PVC formulator is constantly challenged to improve performance while lowering cost. This paper reports on a laboratory project where three lubricant systems and three calcium carbonate products were evaluated.A generic rigid PVC formulation, with 1phr TiO2, containing paraffin wax and a one-micron ground calcium carbonate, was compared with formulations containing two different ester lube packages and a finer precipitated calcium carbonate. The ester lubricated, fine precipitated carbonate filled, compounds demonstrated improved impact performance, especially at the lower test temperatures.
MBS and CPE in Rigid PVC Pipe Formulations
The impact behavior of poly(vinyl chloride) (PVC) pipe formulations containing either: chlorinated polyethylenes (CPEs) , impact-grade methyl methacrylate butadiene styrene (MBS) , MBS /CPE mixture or an acrylic core-shell impact modifier were evaluated using an instrumented impact tester. The lubricants were adjusted for each modifier to yield similar fusion times. Compounds were extruded on a laboratory-scale twin screw extruder and impact tested at low temperature [- 10°C] conditions. Fusion bowl stability testing was also performed on each blend. The results showed a 50-50% MBS/CPE blend had improved thermal stability and lower extrusion pressures than pure MBS, while retaining good output and comparable impact performance to pure MBS, CPE or acrylic formulations.
Quasi-Brittle-To-Ductile Transition in Impact Modified Poly(Vinyl Chloride)
The toughness of impact modified poly(vinyl chloride) (PVC) compounds was examined using a modified Charpy test. Increasing impact speed resulted in a quasi-brittle-to-ductile transition in all PVC compounds. In the quasi-brittle region, lower molecular weight PVC modified with 10 phr chlorinated polyethylene (CPE) exhibited a craze-like damage zone that could be described by a modified Dugdale model. Lower molecular weight PVC modified with 10 phr methylmethacrylatebutadiene-- styrene (MBS) impact modifier also exhibited a craze zone and the same intrinsic crazing energy. However, the toughness of the craze and the resistance to fracture depended on the type of impact modifier. Increasing molecular weight of the PVC resin resulted in a more complex damage zone that was not amendable to the Dugdale analysis.
Stepwise Fatigue Crack Propagation in Poly(Vinyl Chloride)
The kinetics and mechanism of fatigue crack growth in poly(vinyl chloride) (PVC) compounds of different molecular weight were studied. The fatigue crack propagation rate of all the PVC compounds followed the Paris law: da/dt=AF?KI 2.7. Fatigue crack propagation rate, as reflected by the pre-factor AF in the Paris law, was highly dependent on molecular weight of the resin, strain rate and temperature. A stepwise mechanism of fatigue crack propagation was observed in all the PVC compounds. Steps were formed by discontinuous growth of the crack through a single craze in the shape of a narrow strip. Step length and lifetime were used to characterize crack propagation.
The Effects of Process Temperature on the Weathering Performance of RPVC
Elevated process temperatures can accompany current high extrusion rates of rigid poly (vinyl chloride). Various colored weatherable siding compounds were studied in the processing range of 193 C (380 F) to 227 C (440 F). The extruded compounds showed only minor color shifts due to increased melt temperatures. Outdoor exposure through 4 years in Arizona, Florida, and Ohio demonstrated typical color change, but did not exhibit significant color shift relating to the initial processing temperatures. The extruded samples from elevated melt temperatures did demonstrate reduced impact strengths prior to outdoor exposure. Florida and Ohio exposed samples lost impact strength throughout the 5 years of exposure, with the higher temperature processed samples continuing to show lower impacts over time.
A Study of the Effect of Extrusion Temperature on the Hot-Tack and Heat Seal Performance of Extrusion Coated Polyethylene
Polyethylene is commonly extrusion coated onto a variety of substrates for use in food packaging applications. The greatest utility comes from using polyethylene as a sealant layer. It has been determined that extrusion temperature has a significant effect on the hot-tack and heat seal performance of polyethylene. In the resins evaluated, as extrusion temperature increased, hottack strength decreased while plateau heat seal strength increased. Characterization of coatings applied at various extrusion temperatures has revealed that changes in molecular weight and crystalline morphology determine heat seal and hot tack performance for polyethylene coatings.
Linear Low Density Polyethylene and Montmorillonite Layered Silicate Nanocomposites
It has been known that the properties of nanocomposites are dependent on the degree of dispersion of expandable smectites clays in the polymer matrix. The different states of dispersion are exfoliated, intercalated and immiscible systems. However we and others have demonstrated that within a single system, the dispersion is far from homogeneous. Here we investigate the effect of dispersion of clay in Linear Low Density Polyethylene (LLDPE) nanocomposite films. Cloisite 15A was used as montmorillonite layered silicate (MLS). MLS were precompounded with a carrier resin to produce a master batch. Films of 1 mil thickness were prepared by a blown film extrusion technique. The through thickness dispersion in different films was investigated using x-ray diffraction. The distribution of clays was observed by polarized optical microscopy. The effect of the dispersion on the glass transition of the polymer was studied by differential scanning calorimetry (DSC).
The Effect of Vinyl Acetate Content and Polyisobutylene Concentration on the Properties of Metallocene Polyethylene/Ethyl Vinyl Acetate Co-Extruded Film for Stretch and Cling Film Applications
A range of EVA/m-LLDPE/EVA co-extruded films, with Polyisobutylene (PIB) content from 0-20% and Vinyl Acetate (VA) co-monomer content of 6, 12 and 18%, was manufactured using a Killion cast film co-extrusion system. The films were aged at 45°C for up to 28 days, to enable tack (cling) development. The results show that film tack strength improved significantly with ageing. Increased VA concentration in the surface layer also showed significant improvement in film tack strength. The film tensile strength, elongation and tear properties in both MD and TD were not significantly affected by increase in PIB concentration. However, increased VA content showed slight improvement in MD mechanical performance of the films, TD properties were relatively unaffected.
Design of Plastic Multi-Layer Structure That Fit the Requirements of a Specific Food or Beverage
This paper presents a model that allows the determination of the permeability values of plastic multi - layer structures that may be coextruded, extrusion coated or laminated that fit the requirements of a specific food or beverage. The model includes the use of several data bases like plastic permeability data, food and beverage data related to maximum gain or loss of gases and plastic raw material costs.The computational algorithm combines automatically different polymers predicting possible multi – layer structures based on adhesion criteria, maximum number of layers and the achievement of food requirements. The different calculation routines in the model include pressure, temperature and relative humidity corrections, change of units, among others.The model predicted permeability values are compared against measured multi –layer structures for several barrier films, specifically, OTR and WVTR values.
Effect of Cold-Drawing on Oxygen-Barrier Properties of Polyesters
The improvement of oxygen-barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET-BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass-transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold-drawn polyester could be regarded as a one-phase densified glass. This allowed an analysis of oxygen solubility in accordance with free-volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess-hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero-solubility) condition.
The Use of Aqueous Based Barrier Polymer Emulsion Systems in Coated Carton Board Laminates
The water vapour transmission rate (WVTR) of carton boards can be critical in high performance packaging applications. The authors have developed moisture barrier paperboards using aqueous-based (water-based) emulsion polymers, and the results obtained with these materials are presented. These polymers include polyethylene terephthalate (PET), polyvinylidene chloride (PVdC), and styrene-based emulsions. A range of these coated and laminated carton boards were prepared using a hand coater to achieve a controlled range of barrier layer thickness (24-100 microns), and analysed for WVTR over a range of temperatures and relative humidities. In addition, some boards were pre-coated with a primer coat before the application of the barrier topcoat, to investigate the effect of carton board topography on the moisture barrier properties. Low WVTRs in the range of 5-10 g/m2/day were achieved using several of the emulsion polymers, and it is clearly shown that by precoating the surface of a board with a primer before applying a barrier coat can lower the WVTR further even with a thinner overall layer of coating. Anisotropic characteristics of boards coated on one side only are clearly shown, with lower WVTRs always being achieved when the coated side of the board is adjacent to the higher humidity.
The Effect of Frostline Height Changes on Blown Film Using Metallocene Catalysed Polyethylene
Films were prepared from a range of mPE resins of various comonomer types (hexene and octene), using a Killion blown film extrusion system. The films were manufactured at a constant blow up ratio of 1.6 by maintaining constant haul off speeds and screw speeds to give a uniform thickness of 50 microns. To effect the change in frostline height the rate of cooling was changed. Tensile analysis of the samples showed that modulus and tensile stress were related to both comonomer type and polymer density and that frostline height variation had an effect on the final film properties. DSC analysis showed that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type.
Dynamics and Criteria for Bubble Instabilities in a Single Layer Film Blowing Extrusion
In this work, the performance of a new in-line scanning camera system for the study of bubble instabilities in film blowing extrusion is presented. Three commercial film grades, metallocene catalyzed linear polyethylene (LmPE), LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating the various bubble instabilities such as draw resonance, helicoidal instability, frost line height (FLH) instability are proposed. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of take-up ratio (TUR), blow-up ratio (BUR) and frost line height. It was found that the new system can capture the main characteristics of all bubble instabilities quantitatively. It was also found that the magnitude and periodicity of radius variation during draw resonance of LmPE is decreased as TUR is increasing at a given FLH and BUR implying that the origin of draw resonance in film blowing seems not to be the same phenomenon that the one observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the center of the die decreases as TUR is increased.
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