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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Polymer/Clay Nanocomposite Foams Prepared by CO2
Polymeric foams are widely used in many applications. In this study, we prepared polymer/clay nanocomposite foams using carbon dioxide as the foaming agent. The effect of clay dispersion (intercalation vs. exfoliation), clay concentration and types of polymers on foam morphology were investigated. It was found that clay nanoparticles serve as an efficient nucleation agent. The nucleation efficiency is affected by both clay dispersion and polymer-clay-CO2 interaction. By controlling nanocomposite composition and foaming conditions, PMMA nanocomposite foams with cell size as small as ~0.4 ?m and cell density as high as ~1012 cells/cc can be produced. These foams exhibit good combination of stiffness, toughness, weight saving and dimension stability. In addition, PLGA nanocomposites foams were also prepared and they can be used for tissue engineering scaffolds.
Copolycarbonate of Bis-Phenol A and 4,4'-Dihydroxydiphenyl
In comparison to a bisphenol A polycarbonate, a copolycarbonate of bisphenol A and 4, 4’- dihydroxydiphenyl has a higher birefringence, higher heat-distortion temperature (HDT), better resistance to boiling water and ASTM Reference Fuel C, higher notched Izod impact strength at thick section and low temperatures, and better resistance to embrittlement after heat aging.The high birefringence and HDT as well as the better resistance to boiling water and Reference Fuel C of the copolycarbonate are attributed to the linearity and rigidity of the diphenylene unit in the copolycarbonate chains. In contrast, its outstanding impact strength under a variety of test conditions is attributed to its propensity to shear yield due to the low rotational-energy barriers of the phenylene rings around the axis of “inter-ring” C-C bonds in the diphenylene units.
Mechanochemical Devulcanisation of Unfilled SBR Vulcanisates
The feasibility of the mechanochemical process for devulcanisation of model sulphur-cured unfilled SBR vulcanisates was investigated. The effect of mechanochemical devulcanisation on crosslink density and gel content of vulcanised SBR was measured using swelling methods. The devulcanised SBR samples were revulcanised utilising the same recipe and curing conditions as used for the virgin compound. The cure characteristics and mechanical properties of the devulcanised SBR were compared with those obtained for vulcanised SBR. It was found that the devulcanisation resulted in a significant decrease in the crosslink density and the gel content. The cure characteristics of devulcanised samples differed from those of the vulcanised samples. The stress-strain results for the revulcanised vulcanisates were comparable to that of vulcanised SBR.
Anionic Copolymerization of Lauryl Lactam and Polycaprolactone to Produce Polyesteramide Tri-Block Copolymer
This paper examines the anionic polymerization of lauryl lactam to polyamide12 and copolymerization of lauryl lactam with a diisocyanate end capped polycaprolactone to produce a polyester amide block copolymer. The molecular weights of polyester polyols used in the preparation of diisocyanate end capped polycaprolactone are varied in this study.The products were characterized by Fourier Transform Infrared Spectrum (FTIR), Differential Scanning Calorimeter (DSC), mechanical properties were measured in a Instron mechanical tester. The influence of the molecular weight of polyol was considered.
Relationship between Structure and Properties of PBT Injection Moldings in the Thickness Direction
Poly(butylene terephthalate) injection moldings have definite skin-core morphology because of the rapid rate of crystallization. In this study, in order to investigate the relationship between structure and properties of PBT injection moldings in the thickness direction, specimens were sliced. Then, tensile properties and microstructure were studied. It was obvious that necking starts at high strain region with increasing depth from surface, and the decrease of tensile modulus and yield stress near the surface mainly depends not on the orientation but on the crystallinity.
Morphological and Mechanical Evaluation of Hybrid Organic/Inorganic Thermoset Copolymers of Dicyclopentadiene and Polyhedral Oligomeric Silsesquioxane
A new class of organic/inorganic hybrid thermoset copolymers have been by prepared by ring opening metathesis polymerization (ROMP) catalyzed with bis(tricyclohexylphosphine)ruthenium dichloride. Dicyclopentadiene (DCPD) and norborylene-substituted polyhedral oligomeric silsesquioxane (POSS) with isobutyl pendent groups have been copolymerized at 60 °C over a range of POSS concentrations. The X-ray structure of the copolymers shows small aggregates of POSS at higher concentrations with uniform dispersion below 10 wt % POSS. These copolymers exhibit a decrease in Tg from128 °C for PDCPD to 114 °C with the addition of 20 % wt POSS. The stiffness, in tension and compression, is decreases with increasing POSS concentration. Additionally, the incorporation of POSS changes the fracture mechanism from shear banding or ductile to brittle failure and is accompanied by a decrease in the fracture toughness of the copolymers.
Characterization of Polymer Resins Produced by Melt Disentanglement
Disentangled polymers (PC, PET) were produced by a patented technology of viscosity reduction by melt disentanglement described elsewhere. The new process generates pellets from original ones supplied by the resin manufacturers, after the melt has passed through a succession of treatment stations designed to reduce their viscosity by a combined effect of shear and extensional force under vibration. In order to understand the characteristic differences between the disentangled resins and the original ones, we submitted the resins to a variety of tests.We show that disentangled resins, produced by melt disentanglement, exhibit novel properties consistent with the fact that they are, indeed, disentangled, ant that the changes depend on their level of disentanglement. In particular, disentangled polymer resins show a higher fluidity, and therefore better processability, when remelted, a lower density at room temperature, a greater gas permeability, and have less Internal Energy, as determined by DSC. For semi-crystalline polymers, both the crystallinity percent and the rate of crystallization are interactively affected by the state of disentanglement of the melt. Benefits will be discussed in the paper and at the conference.
The Effect of Surface Tension and Contact Angle on the Filling Behavior of Flip-Chip Underfill Dispensing Process
In this work, the capillary flow, which is influenced by the surface tension of encapsulant and the contact angle among encapsulant, bumps and substrate of dispensing process for flip chip underfill would be discussed by the theoretical and numerical analysis. The velocity field, melt-front shape and melt-front position are solved using a method base on 3D Collocated Cell-Centered Finite Volume Method. Most of the past studies neglected the dynamic contact angle of encapsulant and the influence of bumps. By applying different dynamic contact angle model parameters, we found that the contact angle changes during flow will influence the flow time greatly. By applying different boundary conditions at bump walls, we found that bump will influence both the flow time and the melt-front. Consequently, the influence of dynamic contact angle and bumps shall not be neglected. By applying suitable model parameters and wall boundary conditions, the flow behavior of Flip-Chip encapsulation is simulated correctly in this work.
Effects of Spinning and Process Conditions on Appearance and Diameter of Electrospun Polyamide-6 Nanofibers
In this work, polyamide-6 in formic acid was used to study the effects of various spinning and process conditions on the appearance and diameter of the ultrafine, electrospun fibers obtained. These influencing conditions include concentration of the solutions, molecular weight of polyamide-6, polarity and level of the applied electrostatic field, and nozzle-to-collector distance. The resulting polyamide-6 fibers were characterized for their appearance and diameter, using scanning electron microscopy (SEM) technique. It was found that the fiber diameter was in the range of 60 to 300 nm. Interestingly, flat fibers were observed when negative electrostatic field was applied on polyamide-6 solutions of high viscosity.
Structure Development during Uniaxial Deformation of PEN Using Real Time Spectral Birefringence Technique
During uniaxial deformation of amorphous PEN poly (ethylene 2,6 naphthalate) films, necking is developed even at rubbery temperatures above the glass transition temperature. To elucidate the structural changes occurring during neck formation and further strain hardening, a real time spectral birefringence technique together with a true stress / true strain measurement technique is applied. These techniques are able to track the changes in birefringence and stress levels as the film is being deformed. The results obtained by these two techniques permit determination of the stress optical constant and the limits at which it starts deviating from the linear behavior as well as large deformation behavior. Further investigation by X-ray and DSC measurements helps to understand and clarify the structure developed during the deformation process of the material.
Effect of Rolling Process on the Uniformity of Extended PTFE
Polytetrafluoroethylene (PTFE) is a remarkable material having a high melting temperature, high chemical resistance, low frictional and dielectric coefficients, etc. Due to its high melting point, PTFE cannot be manufactured by using the conventional polymer process, such as the injection molding, extrusion and blow molding, etc. In this research, PTFE powder–lubricant mixture were carefully prepared and followed by a series of techniques including paste extrusion, rolling and calendering. Effect of rolling behavior on laminated PTFE film was investigated. PTFE were laminated with combination layers of different initial rolling orientations varying from 0 degree, 45 degree to 90 degree in consequent layers. It was found that the rolling direction in each laminate layer affects the pore size of the final extended PTFE film significantly. It was also found that laminate with different combination in rolling direction would influence the characteristics of paste flow and the associated rolling pressure. The deformation on PTFE film with 0 degree laminate was serious. The final pores extend in both vertical and parallel to the rolling direction for the laminated film with 90 degree rolling direction difference in each layer. The laminated PTFE film with laminate 45 degree achieves most uniform distribution of pores.
Effects of Morphology on the Tribological Behavior of Thermoplastics in Sliding Contact
An industry demand for plastic parts that have to withstand tibological stress is to optimize the part performance with respect to friction and wear behavior. By varying the processing conditions during molding formation, the morphology of the part’s surface can be affected significantly. This is essential for the lifetime, e.g. of a plastic gear of bearing. Therefore, an optimum can only be achieved, when the processing is carried out at appropriate conditions. Polyamide-66 as well as two polyoxymethylenes were employed as model materials. The effect of the morphology settings on the tribological behavior of plastic specimens in sliding contact was investigated, and the relationships between tribological and mechanical parameters and the morphology as well as the crystallinity were described.
Plastics Part Design: Low Cycle Fatigue Strength of Glass-Fiber Reinforced Polyethylene Terephthalate (PET)
This paper summarizes our extensive investigation on the low cycle (up to Nf = 5x104, where Nf is the number of cycles to failure) fatigue behavior of short glass-fiber reinforced poly(ethylene, terephthalate), or PET, thermoplastic. The modes of fatigue test include tensiontension, compression-compression, four-point bending (flexural) -- all at frequency f = 1-3 Hz, and flexural fatigue at f = 30 Hz (ASTM D-671). All tests were stresscontrolled with stress ratio R = Smin/Smax = 0.1, except for flexural fatigue at f = 30 Hz where stress ratio R = -1. The fracture surfaces of tested specimens were analyzed using scanning electronic microscopy (SEM).The results from this investigation provide comprehensive, up-to-date information and recommendations concerning methods for fatigue testing of injection molded specimens and models, prediction and optimization of low cycle fatigue properties that play a key role in determining a highly stressed plastic parts life and enduse performance, pre-selection of PET based plastic for various industrial applications.
Production of Thick Microcellular Thermoplastic Sheets
Microcellular foams have largely been explored for thin – sheet applications, with thickness on the order of 1 mm. In this study, the basic batch microcellular process is scaled up to produce thick flat sheets, in the 3 – 15 mm range, from a number of thermoplastics such as PMMA, PS and ABS. It is shown that an unfoamed integral skin of desired thickness can be produced, making it possible to create sandwich structures with a microcellular core and a solid skin. It is hoped that these materials will open up the use of microcellular foams in load bearing applications, and as novel materials for construction.
Fundamental Study of Thermoplastic Foam Structure and Properties
This paper presents “cube” cell modeling development to investigate PE foam compression modulus as a function of material distribution between strut and cell wall, and open cell contents. The model shows that compression has a stronger dependency on cell wall stretch than strut strength. As a result, open cell becomes a critical factor for compression strength. PE foam samples with various degrees of open cell were made. Compressive strength is measured. Modeling results show greatly improved agreement to experimental data by considering the stretch of cell walls and bending of struts parallel to compressive force.
Effect of Physical Foaming Agents on the Viscosity of Various Polyolefin Resins
The effect of temperature and type of physical foaming agent (HCFC-142b, n-pentane and carbon dioxide) on shear viscosity has been investigated for various types of polyolefin resins (PP, LLDPE, and HDPE). The viscosity changes have been monitored using a commercial on-line process control rheometer mounted on a twin-screw extruder.A plasticization index, based on the respective molecular weights of the foaming agent and the repeat unit of the polymer, is proposed. Comparison with an amorphous polymer, namely polystyrene, is also made, for mixtures using the same physical foaming agents.
A Study of Strain-Induced Nucleation in Thermoplastic Foam Extrusion
The conditions that induce the phase separation and the bubble nucleation for the thermoplastic foam extrusion process in which physical foaming agents (PFA) are involved are obviously linked to the solubility parameters: temperature, PFA content, and pressure. However, it has been reported that flow or shear can significantly modify these degassing conditions. An inline detection method based on ultrasonic sensors was used to investigate the influence of the shear on the foaming conditions of polystyrene/ HFC134a mixtures, for PS resins of various melt flow rates. An increase of the degassing pressure at low melt temperature was observed for high viscosity resins. Deviation from solubility data has been attributed to the combined effects of elongational and shears stresses.
Cell Morphology and Impact Strength of Microcellular Foamed HDPE/PP Blends
Polymer blends such as result from recycling of postconsumer plastics often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell-population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Neat HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins due to the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well-developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. Improvement in impact strength was associated with well-developed microcellular morphology.
Material Classification and Applications of New Propylene-Ethylene Copolymers
A new family of random propylene-ethylene copolymers ranging from 0 to 19 mole % ethylene were produced by The Dow Chemical Company using INSITE™ technology including a new catalyst. These copolymers exhibit relatively narrow molecular weight distributions and unique micro-molecular structures. Based on the combined observations from melting behavior, dynamic mechanical response, morphology, and tensile deformation, a classification scheme with four distinct categories is proposed. Type IV consists of copolymers with less than 3 mole % ethylene and crystallinity greater than 48 wt. %. The morphology is characterized by large space-filling spherulites. Type IV materials exhibit thermoplastic behavior. With increasing ethylene content, the neck becomes more diffuse. These copolymers are of Type III and Type II. With 3 to 7 mole % ethylene, Type III has a crystallinity between 48 and 33 wt. %. The spherulites are sheaf-like with some non-space-filling regions. Type II materials have a comonomer content between 7 and 15 mole % ethylene. They span a range of crystallinity from 18 to 33 wt. %. The structure is characterized by non-impinging axialites. Type I materials have more than 15 mole % ethylene and less than 18 wt % crystallinity. They exhibit elastomeric behavior with high recovery. The crystalline morphology consists of embryonic axialites. The utilities and potential applications of these new copolymers will also be discussed in this paper.
Solid State Properties of New Propylene-Ethylene (P/E) Copolymers
A series of ethylene-containing propylene copolymers (P/E) have been synthesized with up to 19 mol % ethylene. Tapping mode atomic force microscopy (AFM), wide angle X-ray diffraction (WAXD), optical microscopy (OM), differential thermal analysis (DSC) and stress-strain behavior were employed to characterize the solid state structure. Based on the combined experimental observations, a classification scheme with four distinct categories is proposed. Type IV copolymers (0-3 mol % ethylene and crystallinity greater than 48 wt. %) are comprised of space-filling ?-mixed spherulites that are primarily ?-phase crystals. Spherulites of Type III copolymers (3-7 mol % ethylene and 48-33 wt % crystallinity) are sheaf-like and non-space-filling. Unimpinged regions are comprised of an epitaxially crystallized cross-hatched network. Type III copolymers have both ? and ?-phase crystals. An increase in ?-to-? ratio suggests that spherulites are primarily ?-phase whereas the cross-hatched network is a mixture of ? and ?-phase. Type II copolymers (7-15 mol % ethylene and 33-18 wt % crystallinity) are characterized by axialites surrounded by a loosely woven cross-hatched network. Type I copolymers (more than 15 mole % ethylene and less than 18 wt % crystallinity) contain occasional assemblies of radial lamellae epitaxially grown off of a single lamella. Type IV materials exhibit thermoplastic behavior. With increasing ethylene content, the neck becomes more diffuse. Type I copolymers exhibit elastomeric behavior with uniform deformation and high recovery.
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