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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Applied Rheology for Understanding Flow Instabilities in Polymer Processing
Due to the fact that polymer melts behaves as non- Newtonian viscoelastic fluids, their flow behavior is rather complex and leads to number of flow phenomena which have negative impact on their processing and final product properties [1-19]. The polymer melt elasticity, high shear viscosity, extensional viscosity and its tendency to slip at the solid surfaces causes the flow destabilization. Typical flow instabilities occurring during polymer melt flows are die drool [1-2, 11-12, 15-18], neck-in [3, 5, 7, 15, 17], film blowing instabilities [3, 5, 14, 15-17] and interfacial instabilities in coextrusion [4, 5, 6, 10, 15, 17]. In this work, it is demonstrated how the polymer melt rheology and modeling of polymer processing can be used to understand and minimize the above mentioned flow instabilities occuring in extrusion and coextrusion technologies.
Slow Crack Growth Fracture Resistance Parameter Evaluation for Parent and Joint HDPE Materials
Slow crack growth (SCG) under sustained loads (pressure and axial loads) is one of the limiting failure modes that affect the long term performance of High Density Polyethylene (HDPE) pressure piping identified for use in replacement of existing steel piping for Class II applications in nuclear power plants. Several different tests have shown  the much lower time to failure of joint HDPE material when compared to the parent HDPE material, indicative of the much lower SCG resistance of the joint HDPE material. Hence, the integrity of the HDPE pipe joints and the critical flaw size evaluation is an area of increased focus for the nuclear industry and regulators, and the plastic pipes industry. Towards this end, task and working groups have been formed within the ASME Boiler and Pressure Vessel Code Committee Sections XI, IX, and III to address the needs for the HDPE piping evaluations in nuclear safety related applications. This current study is a comparison of the resistance to the SCG exhibited by the parent and fusion HDPE materials in the SENT specimen testing. Analysis of the crack growth resistance parameter through crack-mouth-opening-displacement (CMOD), and crack-opening-angle (COA) revealed a marked difference between the parent and fusion HDPE material. The experimental analysis also revealed a similar crack growth in normalized time indicative of the same constraint in the experimental specimen, but differing fracture energy in the parent HDPE material versus the butt-fusion joint material. The findings are in line with the large difference observed in the time to failure between the parent and fusion HDPE materials from creep tests at constant load.
Microinjection Molding: Influence of Molding Parameters on the Electrical Conductivity of Polypropylene Filled with Multi-Walled Carbon Nanotubes
Polypropylene (PP) composite with 10 wt% multi-walled carbon nanotubes (CNT) was prepared by melt dilution and then subjected to microinjection molding (?IM) process. A mold with a three-step configuration along the flow direction was adopted. The influence of actual injection molding parameters on the electrical conductivity of the microparts was evaluated by design of experiments (DOE) method. The distribution of maximum shear rates within the microparts was simulated via Autodesk Moldflow Insight, and the distribution of CNT along the flow direction was examined by scanning electron microscopy (SEM). Results indicated that the distribution of overall maximum shear rates follows an order of thin section>middle section>thick section, in harmony with the state of dispersion of CNT within the micro-components.
Improving the Mechanical Properties and Flame Retardancy of Multilayered PP Foam/Films via the Introduction of Flame Retardants
In this work we improve the mechanical properbities and flame retardancy of polypropylene (PP) foam/films produced by continuous multi-layered co-extrusion.Two different types of PP were used and named as PP1 and PP2. The nitrogen/phosphorous based flame retardant (FR) particles play the dual role of nucleating agent and flame retardant. FR particles were used to fabricate PP-FR composites. To investigate the effect of FR on PP crystallization and rheology, DSC thermograms, small amplitude oscillatory shear (SAOS), transient extensional viscosity were measured on both PP1 and PP2 system. FR particles played role of a nucleating agent for both PP1 and PP2 system. PP2 system has a 4x higher zero shear viscosity than PP1, while PP1 system showed much stronger strain-hardening than PP2. PP1 foam/ PP2 film structures were fabricated with different FR content. Both neat PP1 foam/PP2 film and PP1 foam/PP2 film-20%FR have good 16 layered film/foam structures and well-defined ellipsoidal shape bubble cells. The compressive modulus of PP1 foam/ PP2 film samples is 5-6 times higher than that of PP1 foam samples. Compressive strain of PP1 foam/ PP2 film samples is 2-3 times higher than one of PP1 foam samples. PP1 foam/ PP2 films showed excellent flame retardancy.
Properties of Melt Blended Chitin Nanowhisker-Polypropylene Composites
Chitin is a well-known biopolymer that can be extracted from crustacean shells and inherently has good mechanical properties. This paper focuses on using chitin nanowhiskers as a filler to improve the properties of neat polypropylene. Melt blended chitin nanowhisker polypropylene composites with chitin nanowhisker loadings ranging from 2 to 10 wt% was used for analysis. A combination of thermal, barrier, and mechanical properties were examined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), water vapor transmission test, and tensile test respectively. It was observed that the chitin nanowhisker helped improve thermal stability and crystallization. Additionally, an improvement of about 20% and 17% in elastic modulus and ultimate tensile strength respectively was observed at 5 wt% chitin nanowhisker loading. Lastly, a 258% improvement in water vapor resistance was displayed for the 2 wt% chitin nanowhisker loading. Results from the study showed that chitin nanowhisker is a suitable biodegradable filler material for polypropylene to strengthen its thermal, barrier, and mechanical properties.
Extensional Mixing Elements for Twin-Screw Extrusion: Effectiveness at Dispersive Mixing Operations in Composites
The extensional mixing element for twin-screw extrusion was applied to the melt mixing of two different polypropylene/carbon nanofiller systems and compared to a standard shear kneading block in an effort to improve the state of dispersive mixing of the operation. It was concluded that there was a qualitative and quantitative difference in microscale dispersion for both carbon nanotubes and graphene nanosheets when implementing the extensional mixing element, as evidenced by the optical microscopy images and subsequent image analysis. However, the composites exhibited minimal differences in rheological or electrical percolation, indicating that the reducing the initial agglomerate size is only a small part of effective composite production.
Improving the Barrier and Mechanical Properties of PET/Clay Nanocomposites
In this study, an investigation of oleic acid-modified clay versus plain clay with regard to the physical and barrier properties of PET/clay nanocomposites was performed. The contribution of the active and passive oxygen barrier approaches by modifying nanoclays with an unsaturated fatty acid (oleic acid) as an oxygen scavenger was studied. Montmorillonite (MMT) and Cloisite 30B nanoclays were modified by long-chain oleic acid and identified as ol-MMT and ol-30B, respectively. PET/clay nanocomposites were prepared with modified ol-MMT and modified ol-30B by using a twin screw extruder. XRD indicated that there was a significant improvement on the dispersion of nanoclays modified with long-chain oleic acid into the PET matrix, and an exfoliated structure was achieved. DSC data also revealed that crystallization behaviors of nanocomposites prepared with oleic acid modified clays are similar to that of extruded PET. Significant improvements in the mechanical and barrier properties of stretched PET/clay nanocomposites were achieved.
Use of Conductive AFM for Composites of PP Modified with Carbon Nanofillers
In this paper, composites of polypropylene (PP) with four different carbon based fillers are compared. These are single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), nanodiamonds (ND) and nanohorns (CNH). The geometry and properties of these filler and the effects on composites’ properties such as conductivity and morphology are correlated. Initial conductivity was measured by electrometer, then secondarily by atomic force microscope (AFM) in the conductivity mode. Morphology studies were performed using the AFM as well using the topography mode.
The results show that MWCNTs had the lowest electrical percolation threshold of about 1 wt%, followed by SWCNTs, whereas ND and CNH were not conductive up to 10 or 15 wt% loading. In conductive AFM conductive areas could be only found in composites with MWCNTs, here studied at 5 wt% loading. There was a singular instance of conductivity found composites with 5 wt% SWCNTs as well, but the MWCNT composite was the only sample with significant conductivity. The conductivity was correlated to the presence of the MWCNTs present on the surface through the analysis of morphological AFM scans.
A Process for Generating Composites of Acrylonitrile-Butadiene-Styrene Reinforced with a Thermotropic Liquid Crystalline Polymer for Use in Fused Filament Fabrication
In this paper, processing conditions were determined to blend Thermotropic Liquid Crystalline Polymers (TLCP’s) with acrylonitrile butadiene styrene (ABS) for use in Fused Filament Fabrication. Differences between the available TLCP’s based on rheology were also determined for generation of longer fibrils in the ABS matrix. Rheological tests on the matrix polymer (ABS) and TLCP’s of various melting points were carried out to find the temperature ranges where viscosity of the TLCP is lower than that of ABS, which leads to successful generation of longer fibrils when processed using a novel blending technology referred to as the dual extrusion system. All the TLCP’s tested viz. HX3000, HX6000 and HX8000, supplied by DuPont, are composed of various ratios of terephthalic acid, 4-hydroxybenzoic acid (HBA), hydroquinone, and hydroquinone derivatives. Only HX8000 had its complex viscosity below that of ABS in the stable temperature range of ABS. Moreover, only HX8000 had a long overlap of temperature with ABS for favorable conditions leading to longer fibril generation.
Impact of Elevated Temperatures on Surface Properties of Erucamide-Containing Polyethylene Films
Erucamide is a migratory slip agent added to polyethylene (PE) films to reduce their coefficient of friction (COF). While a low initial COF can be achieved with the addition of small amounts of erucamide to PE, COF increases as the films are exposed to elevated temperatures during transportation and storage. In order to understand the cause(s) of COF increase, a broad suite of complimentary analytical techniques were employed to study changes in (i) surface erucamide content, (ii) erucamide surface coverage, and (iii) film surface morphology caused by exposure to elevated temperatures. Significant reduction in surface erucamide content and lack of crystal stacking were observed in films heated at 60 and 75 °C, all of which correlate well with increase in COF. However, films heated at 45 °C did not show any measurable change in these properties, even though COF did increase.
Effect of different fiber tex feeding on mechanical properties of glass fiber reinforced RPET composite by DFFIM process
Two different linear densities of Glass fiber (GF) consisting 1200 and 2400 tex, which were reinforced recycled PET (RPET) composites fabricated by DFFIM process. The results indicated that processing ability of GF/RPET composites with 180-rpm injection screw speed on fiber loading content were in range of 16 wt.% to 55.7 wt.% It was found that the incorporation of glass fiber into RPET composites improved tensile properties, bending properties and impact properties. However the improving tendency on mechanical properties of GF/RPET composites was constant, when fiber loading content was over 40 wt.% for impact strength and 50 wt.% for tensile and bending strength, respectively. At high fiber loading content, 2400 tex of glass fiber exhibited in higher agglomeration of glass fiber especially in core layer when compared with 1200 tex of glass fiber. In addition the fiber length was decreased with the increasing of fiber loading content. The decreasing of fiber length, fiber distribution, effectiveness coefficient and poor fiber orientation resulted in the declination of mechanical properties.
Inversed Cooling Channel Design for Injection Moulds Based on Local Cooling Demand and Material Properties
Due to the high influence of the cooling phase in injection molding, the thermal mold design is a crucial element for high precision injection molded parts. Thus, a method for an automated cooling channel design phase o the local cooling demand of the part is introduced. A hybrid simulation chain is used to calculate this demand and derive cooling channels afterwards. Also an outlook how to influence and control the local cooling supply of the derived cooling channel system is given and implemented as an extension to the methodology. First results show a promising perspective to combine local cooling demand and supply for an improved and suitable thermal mould design.
Modeling of Dispersive Mixing in a Twin-Screw Extruder with Three Parameter Residence Stress Distribution
In twin-screw extrusion compounding processes, dispersive mixing has a significant effect on final properties. Due to the complex flows that develop in a twin-screw extruder, prediction of dispersive mixing is difficult. The Residence Stress Distribution (RSD) is an in-line, experimental method to quantify the stress in a melt that induces dispersion. The RSD method uses the percent break-up (%BU) of stress-sensitive micro-beads to quantify the stress history in a twin-screw melt at any set of operating conditions. Using the %BU information across an operating condition domain, a predictive equation is generated to estimate the stress level in a melt as a function of operating conditions. In the following paper, predictive equations are generated with the variables of screw speed, specific throughput, and barrel temperature. Results show that increases in screw speed and specific throughput increase the %BU, while increases in barrel temperature decrease the percent break-up. In addition, the effect of screw speed and specific throughput is lessened as the barrel temperature increases. These equations allow for prediction and control of a twin-screw compounding process with three separate operating conditions.
Trouble Shooting Hot Tip Induced Polycarbonate Splay
Splay is a primary source of fallout when injection molding parts using polycarbonate. Elimination of splay is a difficult proposition, but maintaining acceptable baseline fallout across production is crucial to keeping waste under control and shipment of defects to customer to a minimum. Overall splay was reduced from 1.8 to 0.9 percent on parts running in excess of 1.4 million annually. The analysis provided in this paper shows how the extent of splay waste was identified, root cause analysis conducted, corrective action implemented, and results verified for one source of polycarbonate splay in a production environment.
Getting to Compliance: A Guide to Setting up a Medical Plastics Processing Operation
Navigating the highly regulated world of medical manufacturing and clean room operations can be a daunting, time-consuming task. Regulations and standards, developed by such organizations as the U.S. Food & Drug Administration, the International Organization for Standardization (ISO) and others, are many and complex. For those who want to begin manufacturing medical plastic products and components, understanding the regulatory requirements is only the first hurdle to be overcome. Then specialized facilities, including cleanrooms (Figure 1), white rooms and hybrid rooms, need to be designed and built, and processing equipment needs to be sourced with special attention not only to performance, efficiency and quality, but also to cleanliness, calibration, maintenance and record-keeping. Mistakes can result in delayed start-up, lost production, quarantined parts, rework and lack of process validation. This paper will review the standards and regulations that apply to medical plastics processing, and discuss the complications involved in setting up a compliant operation and resources available to simplify the process.
The Effect of Hot Melt Extrusion Operating Conditions on Degradation and Water Content of a Pharmaceutical Solid Dispersion
The processing of pharmaceuticals using twin-screw extrusion has many benefits over alternative manufacturing processes. However, several failure modes may develop as a result of the extrusion processing. In this paper, the effect of extrusion on degradation of an active pharmaceutical ingredient is considered, as well as the effect on water content of the extrudate. These properties were measured across an operating condition range of screw speed, specific throughput, and barrel temperature. From the property response, predictive equations for degradation and water content were generated as a function of the significant operating conditions. Results showed that as barrel temperature increased, the degradation increased while water content decreased. Increasing specific throughput decreased degradation and increased water content. Changes in screw speed did not significantly affect the water content and had competing effects on degradation. When designing a pharmaceutical extrusion process, this analysis can generate predictive equations that allow for evaluation of the tradeoffs between degradation and water content across the operating domain.
Accurate Three Dimensional Cooling Simulation of the Gas-Assisted Plastic Injection Molding Process
The simulation of the cooling phase of the gas assisted plastic injection molding process has not been extensively implemented for true 3D models. Gas assisted injection molding has become a mature process where an inert gas is injected into the core of a hot polymer part driving the polymer into the mold until it is completely filled. After the filling phase, the gas driven packing and cooling phase occurs before part ejection. This process requires lower injection pressures, lower clamp forces, smaller injection molding machines and shorter cycle times while requiring less material to manufacture parts. This results in cost savings. Early tests on midplane models and process observations indicate that the position of the gas core and the temperature of the surface of the mold were strongly dependent upon each other. In order to simulate cooling for the gas assisted injection molding process on 3D meshes the mold and the part domains were combined into a single temperature matrix with the flow and cooling phase simulated together in order to get the most accurate temperature solution. This paper outlines the implementation of a simulation method for the cooling phase of gas assisted injection molding. Finally results are demonstrated on real world models.
Application of Air Gap to Enhance Acoustic Performance of Biobased PLA Foams
There is an increasing need for lightweight, biodegradable and efficient sound absorbers in various industries. Polylactic acid (PLA) open cell foams have been previously identified as an effective sound absorber. This study investigates the integration of air gap to enhance acoustic performance of PLA foams. PLA foams of two different cell sizes were characterized and tested for the frequency range of 800-6300 Hz. It was identified that increasing the gap caused an increase in maximum absorption and a shift in peak frequency to lower values. The data recorded will allow for determination of parameters such as pore size and air gap for acoustic solutions in the industry.
Foaming Effects on the Percolation Threshold in Conductive Polymer Composites: A Systematic Analysis
In this research, a systematic analysis was conducted to clarify the foaming effects on the electrical percolation threshold of rod-like conductive fillers in polymer composites. In order to decouple the volume exclusion and the cell growth effects, instead of using the “final” volume content of filler in foamed samples the “initial” volume concentration of filler was considered in the analysis. This provided a means to investigate the sole effect of cell growth action. By independently analyzing the effects of void fraction and cell size on the filler orientation and inter-connections, and the subsequent electrical conductivity, a clear understanding of the filler motion in conductive polymer composite foams was obtained. The results of this study provide a useful theoretical guideline for future research.
Effects of Injection Molding Processing Parameters on Experimental Fiber Length Distribution of Glass Fiber-Reinforced Composites
Effects of injection speed on the experimental fiber length distribution of long, semi-flexible glass fiber-reinforced polypropylene composites using an end-gated plaque geometry exhibiting a complex 3-dimentional flow field were quantified. Three injection speeds were considered with constant mold and screw temperatures. Samples were subsequently used to obtain experimental fiber length distribution data. Fiber length distribution data was obtained using the epoxy method, which is a technique for fiber population selection. Injection speeds of 1, 2, and 4 seconds were used with a mold temperature of 79oC. Fiber length data at the middle of the plaque were obtained and compared. Preliminary results suggests that the fiber length data does not change considerably for each injection time being considered. More data is needed to conclude whether fiber lengths are changing significantly as a function of varying injection times.
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