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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Strain-Induced Crystallization, Structure, Orientation and Thermal Property of Polypropylene Film during BOPP Process with Sequential Stretching
Biaxially Oriented Polypropylene (BOPP) films prepared with a laboratory film stretcher KARO IV were studied by Small-Angle X-ray Scattering (SAXS) and Differential Scanning Calorimetry (DSC) in order to understand the crystal orientation, structure and crystallinity at processing temperatures, and to differentiate crystals induced by stretching and cooling processes, respectively. The present study shows that stretching in partially melt state can promote Shish-Kebab structure due to significantly less chain relaxation. Annealing at a higher temperature before stretching in Transverse Direction (TD) can lead to appreciably higher crystal orientation, presumably due to the melting of smaller crystals which were less oriented initially. Orientation of BOPP films at room temperature can be very different from its orientation in partially melt state which is more related to shrinkage property. The crystallinity of the partially melt polypropylene (PP) can be evaluated by DSC together with SAXS. Stretching induced crystals are larger in size and have significantly higher melting point than crystals formed during a cooling process.
Importance of Processing and Converting Conditions on the Use of Carbon Nanotubes in Thermoplastic Applications
In recent years, multiwall carbon nanotubes (CNTs) have progressively captured wider industrial acceptance as an alternative to deliver electrically conductive materials. Currently, CNT-containing polycarbonate (PC) is widely used in the manufacture of integrated circuitand hard disk-trays. In this work, the influence of the extrusion parameters in an industrial environment on the dispersion of CNTs in PC was investigated in details. In addition, the effect of injection molding parameters on electrical conductivity, surface quality and mechanical properties is investigated. Under optimized extrusion conditions, the PC-CNT compounds displayed remarkable electrical conductivities (0.5 x 10-3 Siemens.cm-1) at only 1 wt% loading.
Effect of Different Coupling Agents and Chemical Treatments on the Mechanical Properties of Polypropylene-Rice Husk Composite
In this study, rice husks and polypropylene were applied as the fibers and matrix polymer to make natural fiber composites (NFCs). Polypropylene grafted maleic anhydride (PP-g-MA) and styrene ethylene butadiene styrene graft maleic anhydride (SEBS-g-MA) were used as coupling agents. In addition to coupling agents, rice husks were treated with NaOH, silane and NaOH+HCl+silane.alkaline or silane to enhance the effect of coupling agents. The results showed that adding both PP-g-MA and SEBS-g-MA improved the mechanical properties of composite significantly. In addition, an optimized ratio of coupling agents was found. On using a combination of 2 wt % PP-g-MA and 1 wt % SEBS-g-MA, the impact strength of the composite increased significantly, but the tensile strength and modulus were not reduced to any appreciable extent relative to the use of PP-g-MA alone. Finally, all of the three treatments improved impact strength of the composites.
Internal and Free-Surface Viscoelastic Flow Simulations Using the Corotational Maxwell Constitutive Model
Understanding and modeling of viscoelastic fluid flows is essential for several industrial applications. Simulations of internal viscoelastic flows as well as of viscoelastic free-surface flows are quite complex and it is necessary to utilize advanced material models. This work focuses on the study of the Corotational Maxwell constitutive model which is implemented in the viscoelasticInterFoam solver developed with the OpenFOAM computational fluid dynamics package. Simulations of viscoelastic secondary flows in a square channel are presented and validated with experimental results. This is followed by a viscoelastic free-surface flow application to simulate a process developed within the Polymer Engineering Center that uses a microcapillary die for the production of micropellets.
Improvement of Thermal Stability of PVC Plastisol Dip Molding Products
Electrical insulator products used in the automotive and electronic industries are made from polyvinyl chloride (PVC) plastic using dip molding process. The thermal stability of the insulators is less than 90 °C which limits the application. The addition of additives to increases the thermal stability of polymers but the softness of the products decreased. This research aimed to study the additives which will increase the thermal stability of the PVC products but maintains the softness of polymers. The PVC plastisol type PG-740 with organic plasticizer, TOTM and AC-256 as stabilizer showed standard physical properties and good thermal stability at 180 °C for 45 min.
Friction Riveting of Pultruded Thermoset Glass Fiber Reinforced Polyester Composite and Ti6Al4V Hybrid Joints
The challenge of the present work is to apply the innovative joining technology Friction Riveting for pultruded glass fiber reinforced thermoset composites for emergency bridges. Pultruded glass fiber reinforced polyester plates and Ti6Al4V rivets were used in this work. Adequate levels of deformation at the tip of the rivet inserted into the composite plate led to good anchoring of the rivet. The correlation between joining parameters, energy input, process temperature and rivet deformation was studied. Two affected zones could be observed in the composite: the polymer heat affected zone and the polymer thermal mechanically affected zone which consists of two distinct parts, the partially and highly degraded. The maximum average ultimate lap shear force achieved for the selected conditions was 6.7 ± 1.6 kN,indicating the potential of Friction Riveting as an effective joining technique for thermosetting composites.
Friction Staking: A Novel Staking-Based Joining Method for Hybrid Structures
One of the most used methods for assembling simple structures of plastics and metals is staking. FricStaking is an alternative joining technology based on principles of staking, intended to overcome the limitations of current technologies. Sound joints can be produced in cycles of 10-20 seconds, with efficient use of material, creating a strong and aesthetically pleasing joint. This paper presents a preliminary study of FricStaking, investigating the joint microstructure, local and global mechanical properties, as a function of different levels of tool rotational speed. Local effects on the polymer can be seen through microscopic analysis and microhardness testing. The investigated joints achieved up to 1590 ± 95 N in lap shear tensile testing, and 463 ± 38 N for stake head strength in cross tensile loading.
Applications of Electrospinning to Develop New Biocomposites
Electrospinning has emerged as a versatile method to produce submicron fiber mats from natural or synthetic polymers. Electrospinning is a physical process used for the formation of ultrathin fibers by subjecting a polymer solution to high electric fields. At a critical high voltage (5-35 kV), the polymer solution droplets distort and forms the so-called cone of Taylor that erupts from the solution to form a charged polymer jet. This stretches and is accelerated by the electrical field towards a grounded and oppositely-charged collector. As the electrospun jet travels through the electrical field, the solvent completely evaporates while the entanglements of the polymer chains prevent it from breaking up. This results in the generation of highly functional and flexible ultrathin polymer fibers in the form of non-woven mats. Core-shell structures, produced by coaxial electrospinning, are of great interest for use in food packaging applications. In this area, our group has recently developed high throughput equipment based in a multinozzle coaxial technology that allows high productivity of fibers.
Experimental Investigation of Combined Electrical and Mechanical Joints for Thermoplastic Composites
Textile-reinforced thermoplastics including embedded sensor networks allow for the production of competitive lightweight structures with integrated functionalities. With regard to assembly processes, material- and function-adapted techniques are needed to join such components efficiently. A combined joining technique based on blind riveting is investigated in the present paper, which enables both the transmission of mechanical loads and electrical signals. Therefor, specimen plates made of glass-fiber-reinforced polypropylene (GF/PP) with embedded conductors were joined by blind riveting. Different joint configurations were analyzed regarding their electrical performance. Also, the characteristics of the rivet joint under mechanical loading were investigated revealing a stable electric connection until the ultimate failure of the joint.
A Parametric Study of the Crack Growth Behavior of High Density Polyethylene Based on Crack Layer Theory
Due to unique characteristics of the crack growth behavior of polymers, conventional fracture mechanics approaches on the crack growth have not been very successful. Crack Layer theory (CL) can be a good theoretical approach to model the sophisticated crack growth behavior of polymers. According to CL theory, polymers have different size and shape of process zone (PZ), and, especially, in the case of high density polyethylene (HDPE), a crack commonly propagates in a discontinuous manner under fatigue and creep loading conditions. In this paper, a parametric study was performed by a computer program based on CL theory for HDPE with two general types of test specimens, i.e. single edge notched tension (SENT) specimen and compact tension (CT) specimen. The effects of key parameters, i.e. the stress ratio (R-ratio) which is defined as the ratio of minimum and maximum stress of loading, specific fracture energy, and draw stress, on the crack growth behavior of HDPE were studied.
Electrospun Protein and Polysaccharide Nanostructures to Improve Barrier Properties of Multilayer Systems Based on Polyhydroxyalcanoates and Biopolyesters
This work studies de effect of incorporating high barrier se lf-adhesive nanostructured interlayers of zein, pullulan and whey protein isolate between of polyhydroxyalkanoate (PHA) materials. Oxygen and water vapour barrier properties were greatly influenced by the morphology, thickness and inherent barrier of the electrospun interlayer materials. Thus, zein (in agreement with previous works) and pullulan formed fibrillar structures which significantly contributed to improve barrier properties of the multilayer systems. On the other hand, electrospun WPI formed bead microstructures and did not improve oxygen and water barrier properties of these multilayer systems. While the oxygen barrier properties was significantly improved by the presence of a zein nanostructured interlayer, the water vapour permeability of this multilayer system was seem to vary among materials since the zein interlayer was only efficient as a barrier element in the PHA materials as compared to polylactic acid (PLA).
The Influence of Process Parameters on the Mechanical Properties of Textile-Reinforced Thermoplastic Composite Structures and the Functional Capability of Integrated Sensor Elements
Within the Collaborative Research Centre 639 “Textile-reinforced composite components for function-integrating multi-material design in complex lightweight applications” novel processes for the manufacturing of structures are developed. In this context the process chain from the filament to the part is considered [1, 2]. One focus is on the production of biaxial reinforced multi-layer fabrics (MKF) out of hybrid yarn textile thermoplastics (HYTT) and their processing to complex structures using novel mold- and manufacturing technologies. Based on preliminary tests it is known that process parameters like temperature, applied pressure and holding time have an influence on the mechanical properties of the analyzed material combination glass fiber and polypropylene (PP). Hence, the correlation of these parameters was analyzed using a statistical design of experiments method to set and achieve high mechanical properties of the samples. Furthermore, to exploit possible application and function integration, the capability of this applied material combination can be utilized by embedding sensor elements. In this context, the integration of sensors was investigated in some random tests. Here, different exemplary chosen production processes were compared concerning the functional capability of the sensors.
Influence of Interfaces/ Weld Lines on Fracture Behavior of Polypropylene Specimens Related to Material Properties
In this study the correlations between inner properties and fracture behavior were investigated on the “cold” interface that occurs during a multi-shot injection molding process and “hot” interface or well known as weld line, which represents two melt streams meeting. By using Nanoindentation, inner properties, like Young’s modulus, were measured through the cross section and had shown similarities to break surfaces. With reference to in-situ SEM tensile test the fracture behavior becomes clearer. Imbalances of mold design, caused by core mechanisms, which are required for multi-shot injections, are reasons for deviation of properties. As basis for complex components, these results provide fundamental approaches.
On the Microstructure and Mechanical Performance of Friction Spot Joining with Additional Film Interlayer
Friction Spot Joining (FSpJ) is a new technology for joining polymer-metal hybrid structures. The technique is environment-friendly and involves very short joining cycles. The feasibility of FSpJ to produce composite to metal structures has already been demonstrated. The intention of the current work is to investigate the FSpJ of aluminum AA2024-T3 / CF-PPS with additional polymer film interlayer. The joints showed similar bonding mechanisms to other composite-metal FSp joints, i.e. mechanical interlocking and adhesion forces. Sound joints with promising mechanical strength (up to about 2000 N) were produced. The temperatures involved during the joining process were also studied (peak temperatures between 350 to about 400°C). The strength of the FSp joints with interlayer proved to be affected largely by the tool plunge depth in the selected range.
Abrasive Wear Behavior of Different Fillers in PP Measured by Means of a Novel Injection Molding Wear Apparatus
The aim of this work was to investigate the abrasive wear of test platelets inserted in a novel injection molding wear apparatus with a capillary slit die in regard to the filler amount, type and geometry in the polymer melt processed through the slit. Furthermore the arrangement of the filler material along the slit was considered. We found, that the geometry of the filler has a high influence on the abrasive wear. From all tested filler materials, the long glass fibers induce the highest damage to the surface.
Optimization of Pack and Hold times for Hot Runner and Valve Gated Systems in Injection Molding
For cold runner molds, the pack and hold times are optimized by conducting a gate freeze study (or gate seal study) where the part weight is recorded as a function of the pack and hold times. When the gate freezes the part weight remains constant with increasing pack and hold times. A second or so is added to the lowest value of time where the part weight stays constant and this number is taken as the total time for the setting of the pack and hold times. However, in hot runner systems or in valve gated systems the gate area always has molten plastic and therefore the above method does not produce acceptable results. A method for optimizing this value in hot runner systems or valve gated systems is proposed based on the Cosmetic and Dimensional Process Window concept that was introduced by the author in an earlier paper. This was followed up with experimental results.
Test Method Development for Outdoor Exposure and Accelerated Weathering of Vinyl Siding Specimens
This paper provides an overview of extensive research conducted by the Vinyl Siding Institute (VSI) on the development of new test methods for exterior plastic building products. The purpose of the VSI study was to develop an accelerated testing protocol for use in certifying materials. This paper describes the development of an outdoor certification test program and subsequent efforts to create an accelerated weathering test method that could be used to predict the results of the outdoor protocol with a high degree of accuracy. Outdoor weathering tests were conducted in Florida, Arizona and Northern temperate locations to obtain baseline data for comparison. This part of the research led to the development and subsequent publication of ASTM D6864. Accelerated laboratory tests were performed in Fluorescent UV/Condensation test apparatus and Xenon Arc test chambers. The process involved the examination of multiple types of equipment, multiple cycles, and multiple conditions, and comparing the various results to the outdoor exposures. Testing suggested that for this particular material, one method was more suitable than the other. The proposed method was verified with repeat testing and rugged statistical analysis. Round robin testing was conducted to determine repeatability and reproducibility. Although the proposed accelerated method was not adopted into the VSI’s certification program, its results demonstrated high rank order correlation with outdoor test results, giving the user much greater confidence that materials passing the accelerated test will pass the outdoor test. The accelerated method, therefore, is useful during research and development because it provides a fast and reliable method for evaluating small formula changes. It is useful for selecting formulations to include in a 2 year certification test.
Formation of Morphology as a Function of Process Control by Foam Injection Molding of a Functionally Graded Component
A special mold technology enables the production of foam injection molded components with locally differing foaming ratios. Thus, components with functionally graded foam structures can be produced in one processing step. The method (pull and foam method) is based on the idea of creating components with thin-walled areas with a high surface quality and partially foamed, thick-walled areas (e.g. with the function of integrated structural elements) in a controlled foaming process. This paper describes the characteristics of the structure and density in the differentially foamed areas in correlation with the essential processing parameters.
Investigation of Melt Modulation Control and its Effect on Cold-Runner Injection Molding Packing Parameters and Final Product Quality
This paper describes current efforts to investigate and expand melt modulation capabilities in controlling the packing parameters of cold-runner based injection molding processes. Packing parameters, including packing pressure and packing time, have significant impact on the internal molecular orientations, mechanical properties and optical performance of injection molded polymeric products. This investigation focuses on manipulating and controlling packing parameters using melt modulation in order to produce molded parts with different optical and physical properties in each injection molding cycle. Numerical simulations of common thermoplastic optical polymers, such as PMMA, PC, and PS are also demonstrated herein.
Improved Processability and Productivity of Thermoset Compounds Using Sp Scorch Protected Peroxides
Peroxides are used to vulcanize a wide variety of elastomers and plastics including saturated polymers that are not curable by other means. The cure rate obtained varies depending on the stability of the peroxide. Some peroxides provide relatively fast cures but could suffer from premature crosslinking which is also known as scorch. This may result in higher scrap rates and clogged processing equipment. Other peroxides cure more slowly and are less prone to scorch but require longer cycle times. To address this predicament, Arkema has developed a series of scorch protected peroxides1 which are capable of providing protection against premature crosslinking while not affecting the overall cure time. This allows the use of faster curing peroxides to reduce cycle times without concern about scorch. It also allows for more rigorous mixing and processing conditions to increase output without sacrificing efficiency.
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