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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G. Kokturk, T.F. Serhatkulu, A. Kozluca, E. Piskin, M. Cakmak, May 1999
Polylactic acid, PLA, is a relatively new biodegradable polymer primarily used for biomedical as well as mass-market packaging applications. PLLA is a polyester comprising repeating units of the lactide residue with an asymmetric carbon atom. Because of its biodegradability to nontoxic products and good plastic properties of that polymer makes it suitable for use in film studies. De Santis and Kovacs showed that the unit cell of PLLA is pseudo-orthorhombic with dimensions of a=10.7 Å, b=6.45 Å, c= 27.8 Å and ?=?=?=90°, where the molecules assume a 10/3 helical conformation. (1).Eling et al reported the existence of another modification, which they called ?-crystal modification (2) Hoogsteen et al. studied the influence of the preparation conditions on the presence of the crystal modification (3). Fischer et al investigated solution grown crystals of lactide polymers (4). Also Kalb and Pennings estimated the crystallization of PLLA from bulk state and solution (5). Tadakazu and Masuko investigated the relationship between the fine structure of PLLA and its physical properties (6). The need for polymeric biodegradable films is well established. The use of films occurs in the packaging and disposable article industries. In light of depleting landfill space and adequate disposal sites, there is a need for biodegradable films. Currently films from nylon, polypropylene, polyethylene, polystyrene, PVC, are noncompostable, which is undesirable from an enviromental point of view (7). In this paper, we present our results on the development of structure in uniaxial and biaxial stretching of PLA and subsequent heat setting process as followed by the new spectral birefringence technique we adapted for rapid acquisition of birefringence during the course of heat setting.
This paper deals with a methodology for designing an effective layout of cooling channels to make a desired temperature distribution on cavity surface in injection molding. A cooling channel is modeled as several Cooling Elements that remove heat from a cavity surface. These elements move in the mold according to the information that is ordained by Source Elements located on a cavity surface to estimate temperature distribution on cavity surface. A layout of cooling channels is autonomously decided through an interplay between Cooling Elements and Source Elements. Several numerical experiments assuming heat-transfer to be steady-heat conduction have been a good indication that this method can design an effective layout of cooling channels and can estimate the necessary number of cooling channels.
Edward Kosior, Anna Forrest, Syed Masood, Pio Iovenitti, May 1999
Polypropylene (PP) from bottle caps is present in High Density Polyethylene (HDPE) in post consumer recycled resin, and it acts to reduce the overall toughness. This study is concerned with quantifying the influence of PP on the physical properties of recycled HDPE resins and evaluating toughening recycled HDPE/PP blends by the addition of metallocene catalysed linear low density polyethylene (m-LLDPE). The toughness of HDPE was found to decrease significantly with as little as 5 wt% PP, and at 20 wt% the toughness was reduced to levels comparable to that of PP alone. The addition of m-LLDPE was effective in increasing the toughness of the blends to values comparable or greater than those of recycled HDPE alone. The principal mechanism seems to arise from the suppression of crystallinity of HDPE matrix for levels of up to 20% m-LLDPE, and the introduction of amorphous phase content within the samples.
The structural hierarchies in injection molded isotactic polypropylene are mapped at two different mold temperatures and injection speeds in order to quantitatively understand their spatial variation. The mechanisms of formation of structure in various locations of three-dimensional objects and their quantitative representations are addressed at different levels of size hierarchy (superstructure, lamellar, and unit cell) using Optical Microscopy, Hot Stage Video Microscopy, SALS, SAXS, and Microbeam WAXD. A structural model describing the overall behavior is presented.
The solvating strength of a plasticizer for poly (vinyl chloride) resin is a measure of the interactive forces between these two materials. Hansen’s three dimensional solubility parameters provide a quantitative measure of these interactive forces. Using COACTSM service, a computer program designed for solvent systems with various resins, plasticizers were found to lie near the edge of the solvency “sphere” of PVC. The relative positions of various plasticizer structures are in the expected order, while known solvents show strong association and lubricating additives fall outside the solvency sphere of PVC.
The ease with which plasticizer is combined with poly (vinyl chloride) resin is a measure of processing characteristics critical in the dryblending of suspension PVC, and the gelation of plastisols. Using commercial grade plasticizers, this study developed predictive equations for the following processing parameters of dialkyl phthalates in PVC: • Relative dryblend rates in suspension PVC as a function of plasticizer viscosity. • Relative initial gelation temperatures in plastisols as a function of plasticizer molecular weight and solvating strength. • Relative final gelation temperatures in plastisols as a function of plasticizer solvating strength. This information allows one to predict the relative processing characteristics of any dialkyl phthalate plasticizer for PVC on the basis of its chemical and physical properties.
Helmut Potente, Barbara Krell, Frank Reckert, May 1999
The manufacturing process of complex blow molded parts does not only consist of the extrusion blow molding process but is finished of by hot plate welding. Especially with plastic fuel tanks more and more parts such as nipples, holders for hoses or clips, etc. are being welded on. The strength of the weld seam does not only depend on the welding parameters but also on the quality of blow molding such as wall thickness, wall thickness distribution or warpage. These characteristics result in different deformation during the heating and the joining phase. The correlation between the blow molding process, the quality of the blow molded part and the weld strength is shown.
Harm Veenstra, Jaap van Dam, Abe Posthuma de Boer, May 1999
Blending poly(ether-ester) and SEBS thermoplastic elastomers (TPEs) with ordinary pseudoplastics, at temperatures where the TPEs are microphase separated, results in stable co-continuous morphologies over a wide composition range. Processing the same blends at temperatures where the TPEs have a single phase melt, showing normal pseudoplastic behaviour, results in a much smaller range of co-continuity. Therefore, dispersed as well as co-continuous morphologies can be obtained at given compositions. The mechanical properties of dispersed blends are compared to those of co-continuous blends and it is shown that the elastic moduli of co-continuous blends are significantly higher than the moduli of the dispersed blends. No significant difference in tensile strength or impact strength was found.
Ravi K. Sura, Prashant Desai, A.S. Abhiraman, May 1999
Stereoregular polypropylenes can be prepared using metallocene-based catalyst systems. The objective of this work is to investigate structure development during melt spinning of syndiotactic polypropylene. The fibers are well crystallized at low spinning speeds, but are only poorly crystallized at higher speeds. The helical nature of the preferred crystal form is responsible for the substantial differences in crystallization behavior of the syndiotactic PP compared to isotactic PP. Implications regarding crystallization kinetics in oriented systems with conformation-dependent crystallization are also addressed.
In this work the use of high quality natural fibres as reinforcements was studied using the resin transfer moulding (RTM) processing technique. The fibres were unidirectional high quality ArcticFlax and the matrix was an epoxy resin. The mechanical properties of the composites were compared to conventional RTM manufactured glass fibre composites, traditionally retted UD-flax fibre composites and to the pure epoxy. The results from mechanical testing showed that the (50/50) high quality ArcticFlax/epoxy composite has a stiffness of about 40 GPa compared to the stiffness in pure epoxy of 3.2 GPa. The same composite has a tensile strength of 280 MPa compared to 80 MPa of the epoxy. RTM showed to be a suitable processing technique for natural fibre composites when high quality laminates are preferred.
Because of their high barrier properties, high temperature capability, and resistance to chemicals, liquid crystal polymers (LCPs) are ideally suited for use in multilayer containers. This paper will describe a coextrusion die and process for orienting the LCP layer in a PET-tie-layer/LCP three-layer container with approximately 13 percent LCP, showing oxygen barrier properties over 10 times better than a PET container of equal volume and wall thickness. Low shrinkage after hot fill, and excellent resistance to flavor loss will also be demonstrated. The process is applicable to other thermoplastics with LCP, and applications for packaging of beverages, fragrances, solvents, and other chemicals will be discussed, along with comparison against alternative multilayer containers.
Liquid crystalline (LC) epoxies have been of great interest to academic and industrial communities because they combine the performance of epoxies with the anisotropic properties of LC polymers. In this study, we investigated the effect of structural changes on the frequency dependent dielectric relaxation in a series of aromatic thermotropic main chain LC epoxies by broadband dielectric relaxation spectroscopy and differential scanning calorimetry. Various polarization mechanisms were identified over a wide range of frequency and temperature. The molecular origin of these relaxations was assigned and dipole dynamics was described in terms of the location and intensity of relaxation spectrum.
Many activities during the manufacturing of mouldings and the appropriate mould are carried out simultaneously. This proves the need to apply the basic principles of systemic technology theory to the development and production system of polymeric mouldings. The development of an appropriate mould for injection moulding can be regarded as a real sub-system of the development and production system of the mouldings. The planning of a systemic model in this case means defining of the exact sequence of activities during the mould development. Thus the guidelines for mould development are created, which can serve especially to inexperienced mould designers.
Previously we reported to SPE'96 the optimized mechanical performance of linear vibration welded nylon 6 and 66 butt joints. Under the optimized vibration welding conditions (amplitude, pressure, meltdown, thickness of interface), the tensile strength at the nylon butt joints was equal to or 14% higher than the tensile strength of the base polymer (matrix). H. Potente and A. Brubel presented to SPE'94 and SPE'98 an analysis of the welding performance in a family of amorphous and semi-crystalline thermoplastics including nylon 6 using hot-plate welding technologies. For hot-plate welded nylon 6 with a range of glass-fiber reinforcement from 0 to 40% (by weight), the tensile strength at the weld was 40-60% less compared to the tensile strength of the base polymer. We performed a comparative study of mechanical performance of welded nylon's butt joints. In this study we analyzed the efficiency of both widely used joining technologies: vibration welding and hot plate welding. Under the optimized hot plate welding conditions, tensile strength of both nylon 6 and 66 joints is close to or slightly higher than the tensile strength of the base polymers. Presented results will help plastic parts designers, material developers and manufacturers, by giving them alternatives when choosing types of nylon (6, 66, 66/6, 46, etc.) and welding technologies for a wide range of applications.
K.B. Migler, C.L. Gettinger, V.P. Thalacker, R. Conway, May 1999
Flow profiles of a linear low density polyethylene (LLDPE) were measured in an optical slit die situated at the exit of a twin screw extruder. The velocities of tracer particles were measured as a function of position across the slit die at various flow rates. The results show that the presence of a PPA (Dyanmar) in the polymer melt induces slippage on the surfaces of the die. The occurrence of slippage indicates that the process improvements obtained with this high energy additive occur via migration to the polymer-metal surface and subsequent reduction in the effective friction" between the polymer and the wall."
Isothermal chemical reactions of network forming monomers or functional polymers produces a continuous increase in the systems Tg and the accompanying cooperative segmental relaxation time (? process). Both broad-band dipolar relaxation spectroscopy (DRS)-probing the ? process via dipolar reorientational mobility, and dynamic light scattering (DLS)-probing the ? process via correlation times of density fluctuations, were used to monitor the system in-situ (to our knowledge, the first study of its kind). An excellent agreement was found between DRS and DLS for the ? process characteristic parameters: relaxation time and KWW stretched exponential parameter (characterizing the relaxation breadth). It was concluded that the broadening of the ? process is due to a general phenomenon: the microscale heterogeneous nature of glass formers.
Dipole dynamics in network-forming polymers were investigated by broadband dielectric relaxation spectroscopy (DRS). The changes in reorientational dynamics during the advancement of reactions were used to (1) describe the molecular origin of various relaxation processes (?,?), (2) propose a methodology for evaluation of the kinetics of network formation, (3) describe the dynamics in terms of the location and intensity of relaxation spectrum, and (4) advance an interpretation of network dynamics in terms of intermolecular cooperativity. The chemical state of network at various stages of cure was identified by simultaneous DRS and remote fiber-optic FTIR.
Dipak Rana, Hak Lim Kim, Changwon Rhee, Taewoo Woo, Sang Hoon Park, S. Choe, May 1999
The rheological and morphological behaviors of three binary blends of polyethylenes regarding the melt index and density, one component made by Ziegler-Natta and the other by metallocene catalysts, have been investigated to elucidate miscibility and phase behavior. If the comonomer contents are similar, then the melt viscosity is weight average value, otherwise it shows different behavior: the FA+FM blend is miscible, but the RF+EN and RF+PL blends inform immiscible. The microtomed cutting surface indicates that all the blends are not homogenous regardless the density, melt index and cooling processes, and show banded spherulites.
The mechanical responses of two phenolic thermoset resins during curing were monitored as a function of time and temperature using dynamic rotational rheometry. The tangent of the phase angle tan ?, the ratio of elastic to viscous modulus, was used to characterize the reactions because of foaming and emission of by-products. For resole phenolic resins, gelation was interpreted as the cross-over of the storage and loss moduli, i.e. tan ?=1. This assumption proved to be reasonable, as activation energies derived thereby agreed with those found using in-line ultrasonic measurements. The gelation time of the novolac resin was successively assumed to be the first occurrence of tan ?=1 or the minimum of tan ?. The activation energies found using these assumptions were both significantly higher than those found using ultrasonic measurements. Resolution of this discrepancy may require a knowledge of the influence of the foam structure on tan ?.
This paper studies thin elongated packaging for large size silicon chips and its warpage caused by temperature changes during the packaging process. An integrated circuit device is composed of several materials with various different properties, of which, differences in the thermal expansion coefficients of the materials poses the largest influence on the resulting product. In the course of IC encapsulation, as the product goes through numerous processes, temperature will rise and fall and causes the composing materials to experience repeated thermal expansion and shrinkage. Since the material layers are under perfect adhesion, if two neighboring materials have different thermal expansion coefficients, the stress from the temperature change will cause the product to deform. Current IC warpage analytical models researches base mainly on Dr. Suhir's theory of the compatibility conditions for the interfacial strains. The analytical model in Dr. Suhir's theory is constructed upon four layers of two-dimensional materials. There are two sections in the model: one is the section comprising the silicon chip and one is the section without the silicon chip. The latter section is only roughly simulated with a single homogenous material and is unable to correctly simulate the geometric shape of an actual encapsulation component. This paper, extends Dr. Suhir's analytical model to possessing unlimited layers and consisting of many sections, thus not only increases the completeness and correctness of the analysis results but also resolves the problem of accommodating models with different geometric shapes.
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Society of Plastics Engineers
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