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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The Effect of Gamma Sterilisation on Colour and Mechanical Performance of Medical Rigid PVC Compounds
A range of commercially available gamma sterilisable medical rigid PVC (clear) compounds were characterized for hardness, specific gravity, Vicat softening, heat stability and rheological properties. In addition, the effect of exposure to gamma irradiation at 25 and 40 kGy on the colour, mechanical performance and dynamic mechanical response of the various PVC compounds was investigated. The results show no significant difference in hardness of the materials tested. However, significant differences in heat stability, Vicat softening temperature and rheological properties were evident. The results showed that exposure to gamma irradiation had only a slight effect on the mechanical performance of the PVC compounds tested. However, the results show exposure to gamma irradiation had a significant effect on the colour of PVC compounds B, C and D. All three compounds showed significant increases in b-value (yellowness/blueness index) following exposure to gamma radiation. PVC compound A showed superior gamma resistance, with only slight changes in b-value recorded after exposure to gamma irradiation.
Study on the Thermoforming of PC Films Used for in Mold Decoration
Preparation of thermoformed film is one of the critical steps for successful application of mold decoration to parts of complex shape. In the present study, PC films of 0.125mm thick were thermoformed into a cup shape by Drawing Die under various process conditions. Square mark was printed on the surface of film before forming. From the dimension variation of squared mark and thickness distribution of the formed film, one can understand the characteristics of thermoforming. We found the depth of thermoforming increasing will cause wrinkle phenomenon occurrence especially in thinner film. The result indicates that film temperature exhibits the most significant effect on the stretching ratio of the film. Multiple stage of thermoforming was also applied to reduce the residual stress build during forming process and was found to be useful in the reduction of the warpage and wrinkle of the formed film due to the partial relaxation of deformation caused in each stage of forming.
Visual Computer-Based Simulation of the Penetration Length of the Core Melt in Sandwich Injection
The sandwich injection molding technique can be used in wide ranges of engineering applications. On the chance of understanding the melt flow behavior and the mechanism of sandwich injection molding, we made dynamic simulation researches on sandwich injection molding process by employing the software of Moldflow Plastics Insight. In this study, the penetration length of the core melt in sandwich injection molding was investigated by changing the viscosities of melts and process parameters. We find that decreasing the viscosity ratio R of core/skin melts will give rise to enhance the penetration length of the core melt, owing to the relative fluidity of the skin and core melts. Furthermore, the injection velocity of the melts will greatly influence the penetration length of the core melt among the process parameters, while the influences from mold temperature and melt temperature are comparatively inapparent.
Oxypolypropylene as a Radical Initiator for the Production of Polypropylene Grafted Copolymer
Oxypolypropylenes are high MFR propylene polymers that contain bound peroxide functionalities which can be used as polymerization initiators to produce polypropylene grafted copolymers. Upon heat treatment, the peroxides functionalities in the Oxypolypropylene act as a source of free radicals, reacting with unsaturated double bond of the monomers. The grafting reaction is carried out in the solid state in a reactor. The advantage of grafting via Oxypolypropylene is that it eliminates expensive and environmentally unfriendly organic peroxide. A number of monomers have been grafted on Oxypolypropylene, including vinyl acetate, vinyl pyrrolidinone, methacrylic anhydride, maleic anhydride… Applications of these grafted copolymers in nylon blends or in a glass reinforced formulation are also discussed.
Fatigue Behaviour of Two-Layer Materials (PA 6-GF and PP-PET-Fiber, PP or PSU) under Cycle-Dynamic Load
The fatigue behaviour of two-layer materials of glass fiber reinforced polyamide (PA 6-GF) as first layer and polypropylene with polyethylenterephtalat fibers (PPPET- FIBER), polypropylene (PP) or polysulfone (PSU) as second layer is examined by means of the hysteresis measuring method. To determine practice-relevant stress limits for constructional applications fatigue tests with constant and increasing cycle-dynamic load are performed under temperature influence (-40 °C to 82 °C). The experiments have been carried out with a special bending test equipment by means of which a multiaxial stress can be simulated. Microscopic investigations and REM photographs give information on structural failure mechanisms.
PET/PC, PC/PC Flow Properties from Disentanglement Processing (TekFlow)
An extrusion grade PC is mixed with an injection molding grade PET. The mix is alloyed in a Dual TekFlow Processor. A similar procedure is employed on two grades of PC. In each case (PET/PC and PC/PC), the melt is processed at low temperature, low pressure, and under high throughput conditions, made possible by the action of shear-thinning and disentanglement produced by cross-lamination under extensional flow and shear vibration in the TekFlow processors. The melt exiting the TekFlow machine is transparent and homogenous. Analytical testing indicates that the PC/PET alloys present all the characteristics of a molecularly fused new material, exhibiting one Tg, no cold crystallization, no crystallization at all, and a high fluidity. It is shown that the TekFlow PC/PET blends have better flow characteristics than PET. For the PC/PC alloy, it has the same mechanical characteristics as its reference counterparts, at identical Mw.
Characterization of Ternary Blends with Metallocene Copolymers and PA-6
The effectiveness as impact modifier of two maleated metallocene copolymers was studied in ternary blends with polyamide-6 as matrix and two metallocene copolymers as dispersed phase. Also, the effects of the grafting degree on the morphological and tensile properties were investigated. A reduction in tensile modulus and yield stress was observed in all reactive blends and an improvement in adhesion was clearly observed by SEM micrographs. The tensile strength values of blends were lower than that of neat PAs. The results indicated that the effectiveness of the grafted copolymers as impact modifier depend on the morphology of the blends and a combination of tensile properties of the blend components; such as, Young and Poisson’s modulus and break stress of these grafted materials.
Effect of Shear Rate and Mixer Residence times on Morphology Development and Correlation to Young’s Modulus in PS/PP Blends Approaching Co-Continuity
Mixer residence times and shear rates are crucial for development of desired morphologies in polymer blends. Immiscible blends of PS and PP are being studied for development of morphology in a single screw extruder in the co-continuous region. The effect of mixer resident times and shear rates on the morphology development is analyzed. Flexural modulus measurements show strong correlations to selective morphologies obtained at intermediate shear rates and resident times. The influence of morphology on crystallinity of the semi-crystalline phase is considered, and theoretical investigations into the relationships between morphology and mechanics presented.
Dynamic Mechanical Analysis of Polypropylene-Clay Nanocomposites
Polypropylene-clay nanocomposites have become of great interest over the last several years due to their enhanced properties with uncommonly low filler loadings. Dynamic mechanical thermal analysis (DMTA) is a valuable characterization tool because it will give us information about the polymer chain relaxations in the presence of nanoparticles, thermodynamic transitions, and the extent of polymer confinement/clay gallery intercalation. DMTA results are combined with x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy to give a more complete picture of the effect of montmorillonite nanoparticles and a compatibilizer on polypropylene properties.
Effect of Nanoclay on Efficiency of Low Profile Additives (LPAs) on Shrinkage Control of Unsaturated Polyester (UP) Resin
The addition of a small quantity of nanoclay (3 wt%) can greatly enhance the efficiency of low profile additives (LPAs) on volume shrinkage control of low profiled unsaturated polyester (UP)/styrene (St) /LPA systems. In this study, the effect of nanoclay on volume shrinkage of low profiled UP resins containing polystyrene, poly(methyl methacrylate) and poly(vinyl acetate) respectively has been investigated by an integrated approach of static phase characteristics of uncured resin mixture, morphology of the cured samples, reaction kinetics, and shrinkage measurement. The results revealed that nanoclay greatly increased the fraction of LPA-rich phase, leading to a more micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases, and therefore an prominent improvement of volume shrinkage control. The effect of structure/properties of low profile additives and surface property of nanoclay on shrinkage of UP resin were also investigated.
Rapid Crack Propagation (RCP) Failures in HDPE Pipes: Structure-Property Investigations
The RCP resistance of a wide variety of HDPE pipes was measured using the S4 test, and the relationships between molecular architecture and low-temperature toughness of HDPE pipes are presented. Specifically, we conclude that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important. Further, for a given HDPE, our investigations clearly demonstrate that the room-temperature impact energy (razor-notched Charpy Impact test per ASTM F2231) is an inadequate or a poor indicator of the RCP resistance (S4 critical temperature) of the ensuing pipe. However, the ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the S4 critical temperature of the resultant pipes.
Influence of Branching Distribution on the Physical Properties of High Density Polyethylene
Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. In this study, the influence exerted by such selective placement of branching on the physical properties of the resulting blends is discussed. We find that while the instantaneous tensile properties depend exclusively on crystallinity, the ultimate tensile properties depend strongly on branching distribution. Resistance to slow crack growth, impact toughness and the ductile-brittle transition temperature were all noted to depend strongly on branching distribution, with preferential placement of branches along the longer molecules being beneficial. Lastly, the tear resistance and impact toughness of oriented cast films produced using the above blends were also observed to depend on branching distribution.
Analysis of Ductile and Brittle Failures from Creep Rupture Testing of HDPE Pipes
A comprehensive analysis of ductile and brittle failures from creep rupture testing of a wide spectrum of HDPE pipes was conducted. The analysis indicates that the ductile failure of such pipes is primarily driven by the yield stress of the polymer. Examination of ductile failure data at multiple temperatures indicates a systematic improvement in performance with increasing temperature. It is proposed that testing at higher (above-ambient) temperatures leads to progressive relaxation of the residual stresses in the pipe; this causes the pipe to perform better as residual stresses are known to help accelerate the fracture process. Finally, our investigation indicates no correlation, whatsoever, between brittle failures in pressurized pipes and the PENT failure times. Therefore, one has to be extremely cautious in interpreting the true value of the PENT test when developing polymers and pipes for high-performance pressure pipe applications.
Application of Co-Rotating Twin-Screw Extruders Based on Torque, Volume and RPM
Twin-screw extrusion processes, while in general very robust and flexible, can have limitations in throughput and/or product quality that will reduce their economic efficiency. The source of these limitations can be one of the many unit operations performed in the twin-screw extruder, such as feeding, plastification, mixing, degassing and discharge. For example feeding is often volume limited when one of the feed ingredients has a very low bulk density or is prone to fluidize.In order to minimize the potential for process limitations, twin-screw extruders have different design criteria. There are both high torque and high volume machines, and both use screw rpm as an independent variable to provide broader operating flexibility.The utilization of both machine variations is shown for several typical applications. On one hand, there is the latest design for high torque compounding technology resulting in a machines with a specific torque (M/a3, M = torque, a = centerline distance between screws) of 13.6 Nm/cm3. On the other, there is the high free volume design with an outer to inner diameter ratio (Do/Di) up to 1.8. The third variable, screw rpm, has values up to 1800 rpm. Therefore, there is not one solution of all processes, but rather the best one for each task.
Use of Surface-Confined Photografting to Tailor the Wettability of Poly(Lactic Acid) Film
The major objective of this research is to modify the surface characteristics of poly(L-lactic acid) (PLA), by grafting a single or a combination of hydrophilic polymers to produce a continuum of hydrophilicity with an ultimate aim of making a bioactive surface. The PLA film was solvent cast and the film surfaces were activated by UV irradiation. A single monomer or combination of two monomers selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm) were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR-FTIR spectroscopy and contact angle goniometry. Results showed that Aam dominated the hydrophilic characteristics of the film when copolymerized with VAc and AA, while PLA films grafted with copolymers of poly(vinyl acetate)-poly(acrylic acid) (PAA-PVA) showed linear variation of water contact angles.
Controlled Growth of Linear Carbon Nanofibers
This approach investigates how the changes on surface area of the tip effect growth of linear nanofibers using a standard electrospinning procedure with modification to the collection surface and implementation of a step-down voltage collection uptake. The apparatus consists of a tip, a syringe pump, a rotating deposition disk, a rotating uptake disk, and two voltage supplies. The system works in the following manner, a high voltage is applied to the tip, a low voltage is applied to the deposition disk, and the uptake disk is grounded. Polymer solution from the tip is elongated by an applied electric field which is collected on the rotating deposition disk and transferred to the uptake disk by the change in voltage. Coupling this apparatus with the developments made in electrospinning temperature-controlled air blowing, which facilitates additional shearing-stretching forces of the nanofibers and allows for controlled solvent evaporation rates, will result in linear carbon nanofibers.
Structural Development in Thin-Wall Injection Molding Process
Thin-wall injection molding of polypropylene (PP) and cycloolefin copolymer (COC) were performed to clarify the structure and mechanical properties of microscale molded products. Effects of mold thickness and process conditions on processability in micro-scale injection molding were evaluated. Furthermore, the structure and mechanical properties of molded products were analyzed using wide angle X-ray diffraction, birefringence, DSC measurements, and tensile testing. In the case of PP, the molecular orientation in the vicinity of the gate was higher than that at any other positions. Birefringence increased with decreasing mold temperature, whereas crystallinity decreased with decreasing mold temperature. The molecular orientation of COC showed a similar tendency as in the case of PP, where birefringence showed the highest value at low mold temperature and in the vicinity of the gate.
Evaluation of Material Properties and Processability Using the Intelligent Micro-scale Polymer Processing System
A new system has been developed for measurement of material properties such as melt shear viscosity and PVT behavior. The new rheometer and high-pressure dilatometer comprises of four pistons, a pressure gauge, and heaters. The melt viscosity and PVT behavior were analyzed using a small amount (<10 g) of resin. The combined rheometer and dilatometer were combined and installed to a micro-scale injection molding machine. The measurements of material properties and micro-scale injection molding (micromolding) process were carried out simultaneously. We call this system as the Intelligent Micro-scale Polymer Processing System. The measurements of material properties of polypropylene and cyclo-olefin copolymer were conducted. The melt shear viscosity and PVT behaviors were found to be similar to those measured using a conventional measurement apparatuses. The processabilities of PP and COC also were analyzed using this system.
Injection Moulding of ?- and ?-Polypropylenes: Morphology Consequences
The specific effects of mould temperature (MT) and holding pressure (HP) on the structure of neat and ?- nucleated isotactic polypropylenes have been studied. Commercially available isotactic polypropylene was modified by 0.03 wt.% of ?-specific nucleator. From both original (?-iPP) and ?-nucleated (?-iPP) materials test specimens were injection-moulded using two sets of processing parameters. In the T-set the MT was varied within a range of 40-120 °C by 10 °C steps, while in the Pset the HP was changed from 5 to 13 MPa in 1 MPa steps. Polarized-light microscopy showed a strong effect of MT but minute influence of HP on the morphology of ?- and ?-iPP specimens. The increase of MT positively influenced the crystallinity and the ?-form content, particularly in the skin of specimens as wide-angle X-ray scattering displayed. On the contrary, the rising HP depressed the crystallinity within the bulk of specimens proportionally.
On-Line Check-Ring Failure Detection and Compensation in Injection Molding
The performance of check-ring affects strongly the product dimensional and weight stability in injection molding. Check-ring valve may fail to close properly during injection thus causes a drop of the product weight. In this paper, an on-line method has been developed to detect check-ring failure based on the available real-time process measurements. A model has been established to predict online the weight loss due to check-ring failure. A compensation mechanism has also developed to maintain product weight consistency despite of the failure. Experiments show that the proposed detection and compensation methods are very effective in controlling weight consistency.
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