SPE Library

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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Conference Proceedings

Increasing PVC Suspension Polymerization Productivity Using Temperature Programmed Reactions

George D. Longeway, Donald E. Witenhafer, May 2000

PVC polymerizations are known to be auto-accelerating. The reaction rate increases with conversion. Because of this phenomenon substantial reactor productivity at early conversion can be lost because the heat removal capacity of the reactor is not fully utilized until near the end of the polymerization. For this reason it is desirable to speed up the polymerization at the beginning and slow it down near the end. This rate adjustment can be achieved by running the polymerization hotter in the beginning and then cooling. We have written a scientifically based computer model of the polymerization designed specifically to simulate such temperature programmed reactions. The model does a complete heat balance on the polymerization, has a molecular weight predictor, and will be described and demonstrated for a polymerization at 50 degrees centigrade using Sec-Butyl Peroxydicarbonate (SBP) as initiator. Using this single initiator, and a very simple straight line temperature programmed reaction, the time to 80 % conversion can be reduced from 335 minutes to 240 minutes. This is a substantial increase in productivity.

The Strategic Research Partnership: A New Business Model for Effective Outsourcing of Business Research and Analysis

Louis N. Kattas, Thomas E. Galvanek, May 2000

Several critical issues are facing plastic industry executives today. Global cost pressures are leading to a wave of mega-consolidations and spin-offs, resulting in dramatic changes in the competitive environment. Companies/combinations such as Dow-Union Carbide, the proposed Shell-BASF polyolefins merger, Clariant, Celanese AG, BP Amoco and Exxon-Mobil to name a few, would have been unimaginable a few years ago. We are also witnessing a significant power shift toward the customer. The industry is moving from a supply driven to a demand driven dynamic. This has sometimes been whimsically referred to as the “Walmartization” of the supply chain. The cost of losing a customer has never been higher. Companies who ignore their valuable customer assets do so at their peril. At the same time, new product development cycles are being com pressed as never before. For example, new product designs developed in Europe or North America are being cloned in the Far East in a matter of months. Globalization is also proceeding at a rapid pace. Increasingly global customers are demanding suppliers who are capable of supplying products to identical specifications anywhere in the world. Management must look beyond its borders at potential competitors worldwide; competitors w ho m ay not “play by the same rules”.

Class A Thermoplastic Automotive Part Production without Painting

Stephen McCarthy, Qing Guan, Chetan Makadia, Thomas Ellison, Arthur Delusky, May 2000

Class A" automotive parts with a 1.6 square meter surface area were produced using a new process of surface finishing/compression molding SFC (The Valyi SFC™ Process (1). In the process a precut Class "A" film finish blank was placed over the mold cavity of a vertical press. Molten plastic was extruded onto the film reinforcing layers added and the mold was closed. In this SFC process the melt deposited directly onto the film backing layer heats the film finish and causes it to become pliable for forming. This process eliminates the need for painting and produces large parts at low clamp forces. This paper reports the materials and process which were used to produce full sized development parts that demonstrate the capability for production of large structural panels such as roof tops hoods or trunk lids."

Satisfying Medical Device Biocompatibility Requirements: What's a Supplier to Do?

Paul J. Upman, Robert Charton, May 2000

Since the early 1990's, the medical device industry biocompatibility programs have been driven by the international standard (ISO) 10993. This series of standards is now approaching 20 subparts. Demands on the device manufacturer in time and money have become substantial. This can be softened by suppliers of raw material resins and component parts that address some of these testing requirements in advance. Attention to testing requirements by the supplier often prevents duplication by the device manufacturer, and can eliminate surprising results that appear when various companies conduct their own biological and chemical testing. Providing results to the manufacturer can take the form of test certificates, formal brochures with data, or a material master file at the FDA. Such additions to the suppliers offerings can improve marketing position and marketing efforts.

Evaluation of a Wood Fiber-Based Compound by Torque Rheometry

Andrew Yacykewych, May 2000

The trend toward increased usage of renewable resources has led to the growing popularity of wood-filled materials. These emerging materials require extensive testing - beginning with formulation and ending with the final manufactured product. In the early stages of development, it is possible to acquire data comparing differences between recipes utilizing a Mixer/Measuring Head. The given blend can be compounded with a customized twin screw extruder and torque rheometer. Finally, a single screw extruder can quantify the rheology of the compound using a capillary die. The objective of this work is to investigate the behavior of a polyolefin based wood-filled compound using a torque rheometer.

The Occurrence of Fiber Exposure in Gas Assist Injection Molded Nylon Composites

Shih-Jung Liu, Jer-Haur Chang, May 2000

Gas assist injection molding has increasingly become an important process in industry because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that confound the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composites. The materials used were 15 % and 35% glass-fiber filled Nylon-6 composites. Experiments were carried out on an 80- ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. Two float-shape" axisymmetric cavities were used. After molding the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature mold temperature melt filling speed short-shot size gas pressure and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness mainly results from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure."

A Study of the Weldline Strength in Gas-Assist Injection Molded Thermoplastics

Shih-Jung Liu, Chung-Yuan Ho, Jer-Haur Chang, May 2000

Gas assist injection molding has increasingly become an important process in industry because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that confound the overall success of this technique. Weldlines form wherever polymer flow fronts meet is one of them. In this report, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of gas assist injection molded thermoplastics. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. A dumbbell-shape mold cavity was used. After molding, the weldline strength of the parts was measured by a tensile tester. For the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of gas assist injection molded thermoplastics. Weld strength decreases with the length of gas penetration. In addition the weldline strength of gas assist injection molded parts was found to be generally weaker than that of conventional injection molded parts. area near a gate. It has been observed that the presence of weldlines significantly reduces the strength of injection molded parts. Therefore, a number of remedies for controlling processing conditions have been investigated in order to enhance the strength of the weldline area of injection molded parts.

Rotational Molding of Polyethylene Foam by Pellets

Shih-Jung Liu, Ching-Hsiung Yang, May 2000

Rotational molding of polyethylene foams has increasingly become an important process in industry because of its thicker walls, low sound transfer, high stiffness and good thermal insulation. This report is to assess the rotomoldability of multi-layer polyethylene foamed parts. The polymeric material used is high-density polyethylene and the foaming agent used is endothermal chemical blowing agent. Two different molding methods, by powder and by pellet, were used to mold the multi-layer- foamed parts. Rotational molding experiments were carried out in a laboratory scale uniaxial machine which is capable of measuring internal mold temperature in the cycle. Characterization of molded part properties has been performed after molding. The final goal of this study is to investigate how the blowing agent and processing conditions can influence the process of rotational molding and the final product quality. It was found that the rotational molding of two-layer polyethylene foams has the advantage of better impact properties as well as fine outside surfaces. In addition, rotational molding of foamed parts by pellets needs shorter cycle time, but is counteracted by uneven inner surfaces.

Weldability Diagram for the Ultrasonic Welding of Thermoplastics in Far-Field

Shih-Jung Liu, Yew-Khoy Chuah, Bo-Chien Chang, Liang-Han Chien, Gwo-mei Wu, May 2000

Ultrasonic welding has proven itself to be an efficient way of joining thermoplastic parts. It is accomplished by applying high frequency, small amplitude vibrations to the pieces to be joined together. To make satisfactory products, the material, the horn, and the process parameters determine the weldability of a specific system. The concept of welding areas on the critical plane can be extended from injection molding to the ultrasonic welding system of thermoplastics. This research is devoted to the development of a proper weldability diagram for ultrasonic welding in far-field. The first part of this study is to identify the relative importance of process parameters. The results show that weld time and amplitude of vibration are the two factors which most significantly affect the ultrasonic welding process. The second part of this study defines the weldability based on critical parameters. The application of the weldability concept is demonstrated in selecting the optimum part and energy director geometry. In addition, the temperature variations at the joint interface were recorded to better understand the welding process. These weldability studies are intended to give first guidelines for system optimization.

Optimizing the Joint Strength of Ultrasonically Welded Thermoplastics in Near-Field

Shih-Jung Liu, Wen-Fei Lin, Bo-Chien Chang, Gwo-Mei Wu, May 2000

Ultrasonic welding of thermoplastics has become an important process in industry because of its relatively low cost and high quality joints. However, the optimization of this technique has been essentially based on a trial-and-error process. In this report, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the joint strength of ultrasonically welded thermoplastics. For the factors selected in the main experiments, weld time and amplitude of vibration were found to be the principal factors affecting the joint property of ultrasonically welded thermoplastics. A weldability diagram was proposed based on the statistical results to give first guidelines for system optimization. In addition, amorphous polymers required less energy to be successfully welded than semi-crystalline polymers. Semi-circular energy directors were found to bond parts of highest strengths.

Influence of Applied Pressure on Erucamide Diffusion in LLDPE Films

Linwood B. Muire, Douglas E. Hirt, May 2000

There are many factors that influence the diffusion of an additive to the surface of a polymer film. One of the factors that is not often studied is applied pressure, which is an important factor because the pressure exerted on film near the inside of a roll may be significantly different than the pressure exerted on the film near the outside of a roll. We have demonstrated previously that a higher applied pressure tends to hinder additive diffusion. This paper studies additive accumulation at film/film interfaces as a function of applied pressure. The results indicate that a decrease in additive at the surface coincides with an increase in applied pressure.

Developing a Surface Texture with Film Insert Molding (FIM)

Paul E. Koch, Michael P. McCarren, May 2000

The surface texture of an Injection molded part in the film insert molding process is affected by the Molding injection machine parameters. Other variables include the molded material, the film texture and thickness, the quality of the applique, and the mold finish. In this study three different films, using two thicknesses were processed. The injection speed and mold temperatures were varied. Three different resins were evaluated. A 102 mm x 152 mm (4 in x 6 in) part with six different textures was used to determine the gloss and roughness of the finished part with each set up. The goal was to determine the affects on the finish of the final part in the FIM process.

PEN-Poly(ether imide) Blends: Melt Rheology and Stress Relaxation in Semi-Crystalline Films

J.R. Gillmor, J. Greener, May 2000

Past studies on the stress relaxation of biaxially oriented polyester films are extended to a blend of poly(ethylene-2,6-naphthalate) (PEN) and poly(ether imide) (PEI) at a composition of 85/15 by wt. At this composition the polymers are fully miscible and the melt viscosity and flow activation energy of the blend are dominated by the PEN component. PEI plays a more important role in controlling the sub-Tg stress relaxation response of films produced from the corresponding blend. We show that the relaxation time of a biaxially oriented, semi-crystalline film is increased upon addition of PEI to the PEN matrix, consistent with the rise in glass transition temperature. Also, using stress relaxation data in combination with the concept of aging acceleration factors, we probe the kinetics of the physical aging process for the neat PEN and blend films over a temperature range spanning from ca. Tg - 5O°C to Tg + 10°C. Over this temperature interval both films eshibit thermorheological simplicity with respect to time-aging time and time-aging temperature superposition and the rate of physical aging peaks at ca. Tg - 20°C. However, the relative increase in the rate of aging is much lower for the blend, thus suggesting that the PEI component is well dispersed in the PEN matrix and is effectively retarding the segmental mobility of PEN.

On-Line Analysis of Stress and Birefringence Development in Simultaneous Biaxial Elongation of Poly(ethylene terephthalate)

Hiroshi Ito, Takahiro Suzuki, Takeshi Kikutani, Kazuo Nakayama, May 2000

On-line measurements of elongational stress and birefringence of poly(ethylene terephthalate) film were performed under simultaneous equal-biaxial elongation at various strain rates and temperatures. The strain hardening started to occur at a true strain of about unity, which was practically independent of drawing condition. Even though the drawing was done under the equal-biaxial condition, the PET films started to show optical anisotropy in the film plane before the strain hardening. The optical anisotropy was more significant under the drawing conditions of high strain rate and low temperature, however it only appeared in the limited range of strain and disappeared again in all the samples when strain was high enough. The starting point of the optical anisotropy corresponds to the off-plane birefringence, which is defined as the refractive index difference in the directions parallel and normal to the film plane, of about 0.03. This birefringence also corresponds to the critical point above which the stress-optical law is not applicable because of the starting of spontaneous molecular orientation. A similar spontaneous orientation behavior was also observed in the uniaxial elongation process.

Low Extractable, Low Blush, Low Color PVC with Improved Processibility for Medical Application

Lillian Buan-delos Santos, Dean Laurin, Daniel Lynch, May 2000

The present paper provides an additive system for a PVC formulation to improve processing and functional characteristics. This additive system improves melt fabrication and heat stability of the PVC (e.g., increased thermal stability for faster melt flow during extrusion without discoloration or formation of black specks; eliminates further plate-out or build-up on the processing equipment; decreased scrap and equipment down-time; permits higher use of regrind) and the desired product charateristics (e.g., low color, high clarity, low-blush, extractables and particle generation).

Temperature-Moisture-Mechanical Response of Vinyl Ester Resin and Pultruded Vinyl Ester/E-Glass Laminated Composites

S.P. Phifer, K.N.E. Verghese, J. Haramis, J.J. Lesko, May 2000

Pultruded E-glass composites are gaining acceptance in the civil infrastructure market due to their low maintenance and high durability; yet polymer composites are more sensitive than metals to temperature and moisture effects. The present requirements for polymer composites are stringent, with lifetime expectancies for some applications being around 50-75 years. The goal of the present work is therefore to lay the groundwork for future accelerated aging research and analysis. In order to achieve this, the present paper outlines the quasi-static tensile response of vinyl ester polymer and pultruded vinyl ester/E-glass (cross-ply and angle-ply) composite specimens subjected to both different test temperatures as well as hygrothermal aging for different periods of time. Performance at test temperatures ranging from -50 to 95°C and moisture contents varied by saturation in water baths at 45°C and 80°C are presented. Damage induced by exposure of specimens to varied temperatures and elevated water temperature immersion during quasi-static testing are also analyzed for future durability studies.

Study of Blending Coextruded Film Reprocessed with LDPE and HDPE

A. Méndez–Prieto, A. Herrera-Guerrero, S. Sánchez-Lopez, M. Palacios-Mesta, May 2000

Blends of five layer coextruded films: linear low density polyethylene LLDPE/tie/polyamide-6 (PA6)/tie/LLDPE and low density polyethylene (LDPE) and high density polyethylene (HDPE) were reprocessed by melt mixing. The object of this work is to study mechanical properties and processability of multicomponente blends of coextruded film reprocessed with LDPE and HDPE resins. These blends were run on an injection molding machine and the effect of the reprocessed blend content on their mechanicals properties were determined. An increase in mechanical properties as well as a reduction in flow properties was observed when increased the reprocessed blend content.

Structure-Properties of PP-EPDM Thermoplastic Elastomer: Origin of Strain Recovery

Takashi Inoue, Petr Svoboda, May 2000

The question is why PP-EPDM TPE can shrink back from the highly stretched states at ambient temperature, even though the two-phase material consists of a ductile polymer (PP) matrix. To answer the question, we carried out the structure characterization by WAXD and TEM and the FEM analysis on deformation mechanism. The elastomeric nature was shown to originate partly from a characteristic morphology of PP crystallites; i.e. the rather fragmented crystal lamellae formed in the presence of polymer impurity (EPDM) occluded in PP matrix under high shear fields during dynamic vulcanization. That is, the PP matrix itself is expected to be less ductile and more elastomeric than neat PP. The FEM analysis revealed that the plastic deformation of PP matrix can be healed by the volumetric strain of the rubber particles with high Poisson's ratio (~0.5; very small volume change with deformation).

Computer-Aided Thermoformed Product and Process Design

James L. Throne, May 2000

Thermoforming is the process of shaping heated sheet against a cooled mold. Products range from very thin packaging disposable packaging to very thick transportation components. Thermoformed parts are recognized as having very large surface area-to-thickness ratios. They are also know for nonuniform wall thicknesses across their surfaces. As with other single-surface processes such as blow molding and to some extent, rotational molding, commercial thermoformed part wall thickness variation is typically +/- 20-30%. Three areas of computer aids have grown in popularity recently. Computer-aided multi-axis CNC trimming machines are being extensively used in heavy-gauge thermoforming to ensure accurate peripheral and mating surface dimensions. Computer programs are now available for predicting heating and cooling cycles for diverse polymers, thus allowing for more rapid material and mold changeover. And finite element analysis is used to predict local part wall thickness and plug design, among other facets. The impact of these newer developments on part-to- part dimensional reliability is discussed in this paper.

Heat Affected Zone Structure in Vibration Welded Polyvinylidene Fluoride and its Copolymer

D. Valladares, M. Cakmak, May 2000

In this study, the structure development of the heat affected zone (HAZ) of PVDF based materials was investigated. For this purpose, an instrumented vibration welding machine was employed. With the precise control of built in the design of the instrumented vibration welding machine, a series of samples were welded at different welding times. This allowed for the detailed analysis of the evolution of surface features and thus fundamental mechanisms that take place during the early stages of welding. The results reveal that the mechanism of structural formations starts at highly localized regions, which coalesce in subsequent stages. Further in the process, the formation of wave-like patterns, which found to extrude fibrillar structures from the sides of the sample. This behavior was attributed to the high melt elasticity exhibited by these polymers.