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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Modification of Physical and Chemical Properties of Polyethylene Resins through Electron Beam or Gamma Irradiation
Polyethylene resins have been modified with electron beam or gamma radiation to adjust some of their physical and chemical characteristics before their conversion into formed parts, with positive impact on the properties of end products produced from these resins. This paper provides results from characterization studies which give evidence of structural changes, including long-chain branching and oxidation, from the modification of certain polyethylene resins, as well as data on important property enhancements in extruded, injection molded and blown film end products produced from these resins. The property enhancements allow the material to be more competitive with other resins and offer good prospects for overall cost savings.
Hygrothermal Aging of Recycled-PET Sandwich Injection Moldings
Thermal instability and hydrolysis have been the major factors and driving force behind the continued efforts by researchers to improve the properties of recycled poly(ethylene terephthalate) (RPET) in order for them to be considered useful. This study aims at enhancing the resistance of RPET moldings to hygrothermal aging without making any chemical modifications to the resin. The only means of modification that is done here is through alterations in terms of processing conditions and techniques. The sandwich injection molding technique is capable of producing specimens with a distinctive skin and core structure. Water absorption rate of the sandwich moldings was found to be much lower compared to conventionally molded specimens. Tensile and bending properties have also shown significant improvement favoring the sandwich specimens. The change in morphology due to ‘double-resin-flow’ in sandwich injection moldings could have created a layer between the skin and core that has excellent barrier properties that prevents water absorption into the inner parts of the specimens.
Single-Step Foaming of Polypropylene in Rotational Molding
It is well known within the plastics industry that foaming of polypropylene is a very challenging process. A new generation of polypropylene, offering improved processability, has been produced recently by using a metallocene catalyst technology. A fundamental study of single-step foaming of the newly developed polypropylene in rotational molding was conducted, using polymer microspheres as a blowing agent. The influence of polymer rheology on tensile properties, flexural modulus, and cell morphology of the foamed polypropylene parts was investigated. Comparisons are made between conventional and metallocene polypropylene materials.
Quantification of Melting Progression during Twin Screw Extrusion Using the Pulse Perturbation Technique Part I: Method, Experiment and New Insights
Steady state and pulse perturbation monitoring of the melting process in a twin-screw extruder has been carried out. While steady state measurements quantify the total mechanical energy input, they provide no information about the melting progression in the working section. Previously , Polypropylene and Polystyrene data were presented for several operating conditions. In this paper, the behaviors of four different resins are examined in more detail. Quantification of melting time and intensity using pulse perturbation power and RTD responses has been attempted. The effects of operating conditions and simple changes in screw design are examined. Multivariate statistical analysis using Principal Components Analysis of independent operating variables, monitored and derived parameters is described.
Using Synchrotron Radiation to Follow Structure Development in Commercial and Novel Polymeric Materials
The crystallinity in a polymer material influences its aesthetic and mechanical properties and so to develop useful materials it is essential to have a deep understanding of the kinetics involved with this process. Exploring the macro and micro-structure development associated with crystallization in polymer materials such as polyethylene and polypropylene can be achieved using Small-and Wide- Angle Scattering techniques (SAXS/WAXS). Here, SAXS probes the long range ordering or macrostructure and WAXS gives information on the atomic level of ordering (microstructure). Following the structure development and hence the crystallization process in polymers, is particularly important as it leads to the stabilisation of the final product.
Melt Fracture of Polyethylene and the Role of Extensional Flow Behavior
The melt fracture and extensional flow behaviors of a series of linear polyethylenes were characterized from capillary extrusion and uniaxial extension melt rheology experiments with the SER Universal Testing Platform. Based on the experimental results it was determined that the critical shear rates for the onset of both sharkskin and gross melt fractures were found to correlate with the highrate extensional flow behavior of the polymer melts. These findings were found to mechanistically support the generally accepted observations of melt fracture phenomena occurring at the exit (sharkskin) and entrance (gross) regions of the capillary die. In addition, it was found that the presence of a small amount of boron nitride (BN) filler behaves as an energy dissipater that acts to suppress the rapid increase of extensional stress associated with gross melt fracture, and enables the BN to act as an effective processing aid in postponing the onset of gross melt fracture.
Quantification of Melting Progression during Twin Screw Extrusion Using the Pulse Perturbation Technique Part II: Physics of Melting
Further analysis of steady state and pulse perturbation monitoring of the melting process in a twin-screw extruder discussed in Part I has been carried out with respect to the physics of melting. This paper examines why the total specific energy changes with operating conditions. New parameters are defined, the differential specific energy, ?P/?Q and ?P/?N, that can be determined from either monitoring method. It is proposed that the differential specific energy may be used to characterize an extrusion system and applied to the prediction the total specific energy at any rate and screw speed. From pulse and RTD responses, a modified description of the progression of melting based on plug and fluid flow regimes is made using concepts advanced previously. Energy input related to back mixing or mass spreading during melting is discussed.
Structure-Property Correlations for PE Blown Films
In order to develop correlations between the properties and microstructural characteristics of polyethylene (PE) blown films, three polymers were evaluated in this study: LDPE, LLDPE and HDPE. Series of blown films were produced at different process conditions. Morphological characteristics of the films were analyzed using SEM and AFM. Herman’s orientation factors of the films were determined via both wide angle X-ray diffraction pole figures and FTIR. DSC, WAXD and SAXS were used to determine the degree of crystallinity, lamellar thickness and crystal dimensions. Finally, key mechanical properties including Elmendorf tear, dart impact, tensile properties in both MD and TD and optical properties such as haze and clarity have been measured. By using the statistical design of experiments and multivariate modeling, the properties of PE films are correlated to the microstructural parameters including; lamellar thickness, crystal size and Herman’s factors.
Study on the Properties of Gear Disk in Co-Rotating Twin Screw Extruder
Gear disk is one of the most important mixing screw elements. It can meet the demand in distribution mixing of filler in polymer, and can be used in co-rotating twin-screw extruder with other screw elements in different configurations. In order to study which screw configurations can get the best mixing capability, flow fields of different configurations of gear disk and common screw elements were studied. Pressure profile and shear stress profile were calculated. The mixing ability of different flow fields was compared. The result can be concluded that alternate short mixing zones have better mixing ability than a whole long mixing zone. The simulation results of the flow field in different screw configurations of gear disk and common screw elements were verified by experiments.
Development of Thermoplastic Polyurethane Electrolytes and Their Ionic Conductivity
The ionic conductivity of linear segmented thermoplastic polyurethane (TPU) in-situ reacted with alkali metal salts is investigated. The kinetics of thermoplastic polyurethane (TPU) electrolytes complexed with varying molar concentrations of lithium perchlorite (LiClO4) salt has been studied at various temperature (100, 120, 140, and 160°C) by differential scanning calorimeter (DSC). The relationship between ion conductivity and cationic size in TPU electrolytes is discussed with different salts including LiClO4 and KI. Fourier transform infra-red (FTIR) spectroscopy was used to determine the interaction of LiClO4 and KI salts with TPU. The temperature dependency of TPU electrolytes is also studied by using the modified LCR meter.
Erosion and Continuity Development in High Viscosity Ratio EPDM/PP Blends
Blends of EPDM and PP provide an interesting model system to examine continuity development in very low interfacial tension systems. In this work an emphasis is placed on the study of high viscosity ratio blends. The SEM micrographs of the dispersed phase, after matrix dissolution, demonstrate a variety of unusual morphological features including: isolated nanometer-scale fibers, very large particles, and numerous particles interconnected by fibers. It is found that the high viscosity EPDM phase slowly erodes during melt blending by a number of different mechanisms: i) simple erosion, at low compositions, ii) via droplet alignment, elongation in the direction of first normal stress and the subsequent strangulation in the flow direction, and iii) collisioncoalescence- separation type erosion, at higher compositions of the dispersed phase. It is found that the unique morphologies generated enable the dispersed phase to percolate and become cocontinuous at unexpectedly-low compositions of the dispersed phase.
Dimensional Stability of Pre-Shaped Nylon-6 Tubes
During the fuel tank assembly process, preshaped Nylon-6 vapor lines were subjected to 148.9°C. At this elevated temperature the bent tubes tended to return to their original straight shapes, which created undesirable contact with the tank shell. A series of experiments were performed in lab to quantify the effect of several design and processing variables – bend radius, angle, and orientation; forming temperature; and storage temperature – on the tube dimensional stability. Experimental results indicated that the bend radius, forming temperature, and storage temperature affected the tube dimensional stability significantly while the other factors did not. Curved beam theory was employed to calculate the equivalent bending moments associated with the radius change measured in the experiments. Those bending moments were then applied to FEA models to predict the dimensional change of vapor lines at assembly positions. The CAE predictions correlated well with the assembly test results and successfully resolved the contact issue.
Rapid Thermal Response Mold Design
Rapid thermal response (RTR) technology has been successfully applied to the injection molding and hot embossing processes. This technology was found to be durable and reliable for manufacturing disposable plastic parts with micro/nano scale features. This paper focuses on the mold design challenges. Thermally induced surface deflection and stress of the mold were simulated and used for optimal mold design with respect to thermal fatigue failure. A mold was constructed and tested to verify simulation results by experimental study. In a thermal fatigue test, the optimal designed mold showed no signs of fatigue after 10,000 thermal cycles.
Development of a Technology for Large Scale Production of Continuous Fiber Reinforced Thermoplastic Composites
New highly economical process technologies for long-fiber reinforced thermoplastics such as the LFT-D process are the current trend of the market in the automotive industry in Europe. The next step on the way to enhanced LFTs is the use of engineering thermoplastics (e.g., PA66, SAN and PBT) as well as co-molding with local reinforce ments and tailored fiber placement [1, 2, 3, 4]. The process described in this paper shows how continuous fiber reinforcements such as fabrics, profiles, and preforms are co-molded with an LFT material in one step (Tailored LFT). Process parameters for a sufficient bonding of the thermoplastic preform with LFT-material as well as an example of an automotive application are given in the paper. A pilot-scale production plant has been built to demonstrate the ability of serial production.
Research of Screw Configurations on Dispersing Nano-Particles in Polymer
Melt compounding is one of the methods in dispersing nano-particles in polymer. In this paper, 12 different screw configurations in co-rotating intermeshing twin-screw extruder for preparing nano-particles/polymer composite (by Melt compound processing) were studied. The physical property test and TEM of extrudates were carried out. The results show that VCR which characterized as having highly tensile effects, are much more preferred in the melting zone of the intermeshing twin-screw rather than in the melt conveying zone, as well as the forward kneading block which have remarkable shearing performance. While the reversed kneading block and NIMPE elements being set in melt conveying zone of the twin-screw will have much more advantage over those in the melting zone.
The Effect of Sorbitol Based Nucleating Agents on Tear Strength in Polyethylene Film
Ziegler-Natta (Z-N) based polyethylenes have been generally known to display higher tear strengths in blown film applications, especially in the machine direction, than their metallocene-based counterparts. Z-N films display an oriented lamellar morphology, while the metallocene film morphology is more spherulitic and hence less oriented. The objective of this work, in part, was to try to duplicate the Z-N film morphology in metallocene films by adding nucleating agents that orient during film blowing. It was shown that addition of sorbitol based nucleating agent to metallocene based films gives rise to increased lamellar orientation and hence improved tear strength since the nucleant forms an oriented gel in the melt.
Optimization Model Based on a Heuristical Method for Barrier Films Design
This paper presents an optimization model based on a heuristical method to support the design of plastic barrier packaging for food and beverage. The goal is to minimize the cost of a multilayer film structures satisfying the end product requirements. The technical conditions for every layer and its polymer material (support, tie and barrier materials) are considered.The algorithm of this optimization model was evaluated by means of numerical experiments considering accuracy and precision for obtaining the target results. The oxygen and water vapor barriers for several multilayer films up to seven layers were measured and compared with the results of the model.
Polypropylene - Polyethylene Multilayer Films
In this study, we investigated the properties and some structural parameters of multilayer and blends films of polypropylene (PP) and polyethylene (PE) obtained from the extrusion blowing process. Three PP’s (a homopolymer, copolymer and a high melt strength PP compound) and one LLDPE were used. In general, tensile strength and modulus were larger in MD than TD and tear resistance higher in TD than MD, with some differences between the different sets of polymers. The modulus and strength were lower for the films made from the blend. Haze depended strongly on the PP used and whether it was pure, multilayer or blend, with the lowest haze obtained for the multilayer films made of copolymer PP and the highest with the multilayer films with homopolymer PP. Other properties such as oxygen permeability will also be discussed. The oriented crystalline structure of the PP’s was such that b-axis oriented in ND-TD plane and c-axis oriented in MD. PE crystalline morphologies at the interface were different for the different PP’s multilayer films and blends. PP had similar crystalline orientation for blends and co-extruded films but not PE.
Optimise Organoclay Exfoliation in Polymer Nanocomposites by Customising the Extrusion Temperature Gradient
This is a communication article describing a novel and simple approach to optimise the exfoliation and dispersion of organoclay layered-silicate in the extrusion processing of polymer nanocomposites. A range of HDPE nanocomposites were processed by configuring the extrusion temperature gradient in a single-screw compounder. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of organoclay exfoliation, which is directly associated with the various property improvement in nanocomposites, was influenced by the extrusion temperature gradient. These nanocomposites exhibited significant difference in their rheological flow characteristic and mechanical properties, owing to the difference in the resultant organoclay structures. Regardless of the level of organoclay exfoliation, all the nanocomposites exhibited better processability and improved mechanical properties compared to the virgin HDPE. The elongation at break of all the nanocomposites was considerably greater than the virgin HDPE despite recording an increase in crystallinity.
Comparative Study between Metallocene Polyolefin Blends Modified by Beta-Irradiation and a Silane Crosslinking Process
Three binary groups of metallocene blends of ethylene- 1-Octene copolymer (80 and 50 weight %) with two metallocene ethylene-1-Octene copolymers of different crystalline density and a metallocene EPDM were made in a co-rotating twin-screw extruder. The first group corresponds to blends without chemical modification. In the second group the dispersed phase was grafted with vinyl-triethoxy silane by means of a reactive extrusion process (SIOPLAS). The blends of the third group were crosslinked with Beta-Radiation at 200 KGy as final dose. The gel content of the crosslinked blends showed higher values for those blends crosslinked by Beta- Irradiation than SIOPLAS process. DSC using a heat treatment known as Successive Self- Nucleation/Annealing (SSA) and DMA techniques were used to analyze the effect of the comonomer content on the crystalline morphology of the crosslinked materials. Important changes in crystalline morphology of the blends due to the crosslinking process were observed.
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