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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Branching of LLDPE as Studied by Crystallization-Fractionation and its Effect on Mechanical Properties of Films
Linear low-density polyethylene (LLDPE) has short-chain branches that are incorporated into the polyethylene backbone by random copolymerization with varying amounts of one or more alpha-olefins (1-butene, 1-hexene, 1- octene, etc.). In LLDPE, ethylene is the predominant monomer and alpha-olefins are the comonomers that hinder the crystallization of the ethylene molecule. Thus the presence of alpha-olefin in the main molecule as a branch influences the properties of the copolymer. Diverse properties in films of LLDPE grades with similar MI, density, molecular weight and molecular weight distribution can be attributed to variation in short-chain branching distribution (SCBD), assuming that the type of alpha-olefin branches in the LLDPE grades are the same. Hence measuring the SCBD is of prime importance for predicting the performance of LLDPE. Traditional analysis of branching distribution is by using Temperature Rising Elution Fractionation (TREF) where the LLDPE solution is fractionated by taking advantage of the differing crystallizabilities of the molecules due to variations in chain branching levels. This fractionation is achieved in two full temperature cycles, crystallization and a subsequent elution. In a relatively new method called CRYSTAF (Crystallization Analysis Fractionation), only crystallization of the polymer solution is needed thereby reducing the analysis time considerably . This is the method used in this study to analyze three different solution-based, 1-octene LLDPEs prepared under varying conditions. The three LLDPEs are blown into films and tested for their physical and heat-seal properties.
Extrusion of Closed Cell Very Low Density Flexible Syntactic Foams Using Metallocene Catalyzed Polyolefins and Thermoplastic Microballoons
The purpose of this study was to develop a superior foamed jacketing compound for underwater communications cables. The cable structure and application requires a light weight foamed jacketing material to promote buoyancy while also possessing excellent hydrostatic pressure resistance, abrasion resistance, low compression set, low temperature flexibility, overall toughness, and good surface quality. The project goal was to achieve a foamed cable jacket material with a density no greater than 550kg/m3. The minimum obtainable foam density was to be determined. Cell structure, surface appearance and skin quality were also considered to be important. Small, closed cells and smooth skin were specified as necessary for an acceptable product. Analysis of variance was used to study the effects of screw speed, processing temperatures and microballoon concentration on foam density.
Using Manufacturer's Reps to Sell a Technical Product
Many small and growing firms use a network of manufacturer's reps to sell products. Experience and results using reps vary widely over the plastics industry. Commonly, smaller firms using reps complain that of low value for the money spend, and the reps for such firms counter that principals want results without investment or commitment. This paper examines issues and best practices when using reps to sell a technical product in the plastics industry. A survey was of plastics firms ranging from resin suppliers to small injection molding houses was done via telephone and mail. Results from employers and would-be employers of reps were tabulated and summarized. A similar survey was done of outstanding rep firms in the plastics industry. Answers to the both surveys are condensed with an eye to setting up a short list of do's and don'ts when setting up rep groups.
Effect of Heater Band Orientation on Cavity to Cavity Variations
This paper presents the results of a study that shows that heater band orientation on a machine nozzle can cause an imbalance of over 5% in multi-cavity molds. The amount of imbalance is material dependant. The imbalance is most directly related a material's temperature and viscosity constants.
The Effects of Stress Hardening on the Crystallization and Density of Polypropylene
When polymers undergo stress hardening, their crystallinities and densities are affected. Polypropylene was the material tested in this experiment. It was put under various levels of strain by using a tensile tester. Each sample was pulled to a predetermined strain, allowed to relax for a period of time, and measured for crystallinity using the Differential Scanning Calorimeter (DSC). Stress-hardened and original samples were used to compare the change in crystallinity. The density of each sample was also determined using the Density Gradient Column.
Comparison of Aluminum, Wood, and Epoxy as Thermoforming Mold Materials
There are many different types of materials used in the thermoforming industry for the molds used to form plastic products. The most commonly used are aluminum-alloys, soft and hard woods, and epoxy. Each of these materials has distinct characteristics that make them useful under certain design conditions and manufacturing production processes. The following addresses the qualifying factors for each of the commonly used materials based on their characteristics and manufacturing requirements.
Effects of Processing Parameter on Pinch-Off Designs
This study examines the effects of process changes on weld line strength using different pinch-off designs. Mold closing speed and melt temperature were varied with four different pinch-offs. To determine the effect of these process changes on weld line strength, 4 D.O.E.'s were used. Five specimens were taken from each D.O.E. run and tested for tensile strength at the weld.
Attachment Design Analysis of a Plastic Housing Joined with Snap-Fits
Consumer product manufacturers continually desire to make their plastic components more inexpensive by such methods as reducing part count, reducing wall thickness, eliminating tools, and reducing assembly time. Integral fasteners, or snap-fits, can be used to achieve some of these goals, but must be carefully incorporated into a product design. Many of these products, especially portable or hand-held electronic items, need to meet rigorous test requirements, including drop testing. Many common attachment designs that use snap-fits can fail under these conditions. This paper covers the investigation of a desktop telephone housing to ensure that snap-fit disengagement did not occur under drop impacts. First, a failure tree analysis of the product was performed to determine likely scenarios for disengagement. Then tests were conducted to determine impact force magnitudes. Drop testing of prototypes was conducted to determine under what conditions disengagement occurred. From these results, design changes were suggested and prototypes constructed to test the suggested changes. The results of this analysis and testing suggest some general design guidelines to make products attached with snap-fits more robust against the conditions found in typical drop tests.
Effect of Glass Fiber Sizing Molecular Weight on Interphase Durability of Glass Fiber-Vinyl Ester Composites
Model multi-component glass fiber sizings, with formulations based upon current patent disclosures, were prepared to model the full coating packages used in commercial glass fiber manufacture. The sizings consisted of silane coupling agent, film former, and emulsifying surfactant in water, and were applied to glass fibers prepared directly from molten glass. Sizing formulations were extended to vary component reactivity and molecular weight. Unidirectional multi-fiber composites were prepared with Dow Derakane 411-C-50, a vinyl ester / styrene resin system. Interphase durability was characterized by measuring interlaminar shear strength (ILSS), before and after hygrothermal exposure.
Novel Ionomer for Nylon Blow Molding Applications
A novel ionomer is being developed to modify nylon for blow-molding applications. The new ionomer that contains reactive functional groups attains excellent compatibility with nylon by a combination of physical and chemical interaction. The modifier can be dispersed in small particle size as low as 50 nm in nylon 6. This report discusses the melt rheology, blow-molding evaluation and weldline strength of the nylon modified with the novel ionomer. The particle size of the ionomer dispersed in nylon is discussed to explain the unique properties of the new modifier. For comparison, a maleated ethylene polymer (EP) and a conventional ionomer are included in the study.
Use of Polyolefin Additives in Inert Gas Extrusion Foaming of Polystyrene
Polystyrene was blended with small quantities of PP, HDPE, and LDPE and foamed using carbon dioxide as a blowing agent in a twin screw extruder to obtain low density foams. The effectiveness of these additives on the bubble nucleation, density and mechanical properties of the foams was studied. The results show that addition of PP in small quantity improves density, cell size, and surface properties of the foam drastically. The improvement is attributed to crystallization of PP before foam cell expansion; this results in bubble nucleation from the formed crystal sites that also act as gas barrier for individual cells.
Ultrasonic Monitoring of Nozzle and Cavity during Injection Moulding
Ultrasonic techniques are recognised as powerful sources of process information. Transducers are applied directly, are non-invasive, yet interrogate the entire melt cross-section, while data are available real-time. During injection moulding, two zones are considered: nozzle and cavity. In the nozzle, ultrasonic velocity measurement provides temperature and pressure information. Mean temperatures not observed by other techniques are detected. Previous extrusion based experience is used to address issues of high temperature transducer operation. In the cavity, changes in reflection coefficient and ultrasonic velocity provide information on mould filling and part cooling. Various mould geometries are monitored using a number of ultrasonic transducers.
Shearing of Plastic in Runners Causes Property Differences in Parts
This paper presents a study of the effect of shear variations, developed in a runner of a multi-cavity mold, on the impact properties of molded parts. The study has found that impact strength can vary by as much as 2:1. The effect of runner designs are also presented.
The Effects of Pulse Cooling on The Molding Cycle and Part Variation
A design of experiments study was performed that analyzed the effect of pulsed heating and cooling on warpage of an injection molded part. The study involved the following factors: inlet water temperature, melt temperature, mold temperature, and cooling time. The critical dimension was measured by an optical coordinate measuring scope with a repeatable process determined by an R&R study. The gathered data determined that, within the range of the factors study, the inlet water temperature was the only one that did not effect warpage.
Characterizing Scrap Vinyl Flooring to Determine Feasible Reuse Options
The manufacturing waste generated during the production of vinyl floor tiles is typically sent to landfills, rather than recycled, because of a lack of reuse options for this material. This waste is typically PVC loaded with approximately 80% limestone. The goals of this research are to characterize this material to determine the feasibility of reprocessing it and to measure the mechanical properties of the processed material. This study will also attempt to suggest an injection molding or extrusion application for the mixture.
A Method to Characterize the Impact Properties of Hand Tools
There does not currently exist a method for the characterization of the impact properties of hand tools, specifically screwdrivers. Without a scientific method of collecting data for various designs, it is difficult for manufacturers to determine the effect of material or design changes on the impact properties of the product. The most demanding application for these hand tools can often be a hammer blow to the handle of the product, and therefore this abuse must be strongly considered in the design criteria.
Applications of Thermal Analysis in the Design of a Bulk Continuous Acrylic Copolymerization Process
DSC analysis is conducted to obtain kinetic information of the chain addition copolymerization in bulk of a quad-monomer acrylic system. The experimental variables include reaction temperature, type of peroxide and peroxide concentration. By assuming that the copolymerization is a simple reaction, the approximate apparent order of the reaction can be identified; and along with the heat of reaction information, it is demonstrated that the DSC analysis is very useful in facilitating the parametric design process of a continuous stirred tank reactor (CSTR) operation. Selected results of conversion and cumulative copolymer composition of the CSTR samples are included. A more rigorous approach of analyzing the reaction kinetics of the copolymerization is also briefly addressed.
Non-Isothermal Modeling of Co-Rotating and Contra-Rotating Twin Screw Extruders
The quality of the mixing of different raw materials, i.e. the uniformity of the mixture, is a key issue that will determine the morphology and the specific product properties of the resulting compound [1, 2]. Numerical simulation of flow in extruder components provides a new insight, both qualitative and quantitative, into those features. 3-D transient numerical simulations of twin screw extruder (TSE) configurations are presented. A special method, the mesh superposition technique (MST), has been introduced to provide a convenient way to model intermeshing TSEs without involving any remeshing complexity . It has been validated in previous work for isothermal cases . To account for the important non-isothermal effects, the method is compared against numerical and experimental results for additional, non-isothermal validation . We present an analysis of different non-isothermal features that characterize the flow induced by a co-rotating as well as a contra-rotating configuration. Both cases are compared in terms of pressure profiles, temperature fields, resulting torque imposed on the screws and from a mixing point of view to illustrate a typical analysis of different TSEs and provide objective information to select the most appropriate configuration for specific process requirements.
Branching of Polypropylene with a Polyfunctional Monomer for Extrusion Foaming and Thermoforming Applications
Melt strength of polymers is one of the primary criteria for the success of low-density extrusion foaming and thermoforming processes. In this paper, branching of PP using polyfunctional monomer was studied in a batch mixer and a small scale co-rotating twin screw extruder as a function of modifier concentration and process conditions. Melt viscoelastic properties of the products, related to melt strength/elasticity, including die swell and recoil, were investigated to examine the degree of long chain branching, which could lead to improve foaming and thermoforming processability. The melt strength of those materials was compared with that of a commercial high melt strength PP and an unmodified general purpose PP.
Small Angle X-Ray Scattering Study of EACE Processed Semicrystalline PET
Semi-crystalline poly(ethylene terephthalate) (PET) was shear orientated by the novel Equal Channel Angular Extrusion (ECAE) process. Small angle X-ray scattering indicates that extrusion induces preferred orientation of the lamellar structure. Before passing the shear plane, the material has a weak orientation. But after passing the shear plane two preferred orientations are formed in the extruded region; one perpendicular to the shear plane; the other 45° from the shear plane. The physical and mechanical properties of the extruded PET were also investigated and found to correlate well with the ECAE-induced shear orientation.
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