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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Interfacial Modification in Polyolefin Blends
Blending of thermoplastic polymers is of great commercial interest since the resultant material combines the properties of the different polymeric phases. The mechanical properties of these multiphasic blends are to a large extent determined by the morphology, i.e., the size, shape and distribution, of the components. One of the key factors for controlling morphology is modifying the adhesion between the phases since the interface represents a weakness across which stress may be poorly transmitted. Graft or block copolymers which locate preferentially at the interface, referred to as compatibilizers, are used to modify the blend morphology. In this work, we have evaluated a new type of interphasic polymer, formed in a two-stage process which results in a segmented compatibilizer with a linear molecular structure for each segment and narrow molecular weight and composition distributions. Improvements in the mechanical properties of blends, as well as changes in the morphology, are presented.
Flame Retardant Polypropylene
To improve the fire retardant properties of polypropylene (PP), it was compounded with aluminum hydroxide (ATH) using two different compounding lines, a twin screw extruder and a co-kneader. Flame retardant, rheological and mechanical tests were performed. The effects of processing machines and process parameters on the properties of the compounds were investigated. The influence of the properties of filler and matrix material was also examined.To minimize the content of additives without loss of the flame retardant properties, modified layered silicates (Nanofil, Suedchemie) were dispersed within PP/ATH compounds and their influence on the processing and compound properties was studied.The present investigation demonstrates the possibility to use a polypropylene as matrix material for halogen free cable compounds.
Thermoplastic Elastomer Nanocomposites Based on Dynamically Vulcanized PP/EPDM: Microstructure, Mechanical and Viscoelastic Properties
Thermoplastic elastomer nanocomposites based on dynamically vulcanized PP/EPDM with three different viscosity ratio and nanoclay content have been prepared by a melt compounding process. Based on the results of X-ray diffraction measurements, dynamic mechanical testing and thermal characterization, the microstructure of the prepared nanocomposite was found to be sensitive to the viscosity ratio of PP/EPDM and the nanoclay content. Xray diffraction and dynamic mechanical studies also suggested that nanoclays were exfoliated into the polypropylene and EPDM. Tensile modulus of the nanocomposite samples increased from 20 to 90% depending on nanoclay content and the viscosity ratio of PP/EPDM. Tension set of the nanocomposite samples also decreased in comparison with unfilled samples. Moreover, the presence of the nanoclay significantly increased the onset temperature of thermal degradation in the nanocomposite samples.
Optimization of the Properties of Polymethylmethacrylate Nanocomposites for Optical Applications
Transparent plastics like polymethylmethacrylate are widely used for optical components. Some disadvantages of plastic components like low hardness and abrasion resistance may be optimized through the modification with nanomaterials. The application of nanoparticles in polymers can also increase its refractive index and thereby broaden the fields of application of optical components.Polymethylmethacrylate nanocomposites with different nanomaterials were prepared by melt extrusion. The distribution of nanoparticles in the polymer matrix and optical properties of nanocomposites were optimized by means of modifying the surface of the nanoparticles and by varying the process parameters. The influence of the particle type and content on the mechanical and rheological properties was studied.
Next Generation of Soft TPUs
The demands made on elastomeric plastics – particularly those destined for applications where tactile properties are key – are growing ever more rigorous. Many such applications make use of thermoplastic polyurethanes (TPUs), drawing on their excellent properties of abrasion resistance, flexibility, chemical resistance and freedom from plasticizers. To gain the softness desired by the marketplace, TPUs are softened by the addition of plasticizers or compounded with other softer materials. Unfortunately these practices usually come at a cost of reduced mechanical or physical properties or raise potential environmental issues. Bayer MaterialScience has recently developed a new series of softer, processing friendly TPUs that are free of plasticizers and are not compounded with any other materials. The basis of these materials is explained below, illustrated using practical examples.
Mono- and Multi-Layer Tubing Incorporating a Silver Based Antimicrobial
The occurrence of device related infection is a common and problematic issue in the medical healthcare industry. This paper examines the effect of antimicrobial content on the rheological, mechanical and bactericidal properties of a range of mono- and multi – layer medical tubing products. The incorporation of antimicrobial masterbatch was shown to have negligible effect on rheological and processing properties of the materials tested. Mechanical properties were altered to some extent, but more importantly the antimicrobial efficacy of all the tubing samples was shown to be acceptable.
Hydrolytically Resistant Polyester
Polyesters are widely used in the automotive industry due to good molding and mechanical properties. However, unmodified polyester including PBT and PET, sometimes show failure in extreme long-term heat aging and humidity aging per USCAR III and USCAR IV tests. A new polyester technology was developed to improve both heat resistance as well as humidity resistance of impact modified polyesters. In addition, design of experiment (DOE) approach has been used to identify key factors to control mechanical properties and viscosity. This new technology has been successfully validated in automotive applications.
A New and Flexible Process for Thermoplastic Foams
Foam injection molding is a special injection molding process and offers many advantages to the processor. Enhanced part properties as well as decisive improvements in the production process are possible. When it comes to processing of physical blowing agents, different concepts are commercially available. These concepts differ mainly in the necessary effort by means of machine technology. The recently introduced Optifoam system is characterized by flexibility and the capability of retrofitting existing machines. It is based on an earlier development by the IKV Aachen. In this paper, the requirements on a foaming process with physical blowing agents are discussed. The process as well as latest research in this area is presented.
Thermogravimetric Analysis of Water Associated with Cellulose Fibers
A new classification of water in a fiber-water system, termed “hard-to-remove (HR) water”, was defined from an isothermal TGA experiment. This HR water was found to include some free water (trapped water) as well as bound water (freezing and non-freezing water). Specific experimental conditions have been defined for an appropriate measurement of the HR water content. The HR water content was correlated with important characteristics of cellulose-based fibers including water retention value and freeness. This test can be performed on extremely small samples as a convenient, insightful characterization technique for cellulose-based fibers.
Experiments in Impulse Welding a Thin Film Lid for Sealing Micro-Channels in Microfluidic Applications
The rapid increase in demand for polymer based MEMS has led to the development of various techniques for joining micro-devices. This paper describes experiments in impulse welding of thin polycarbonate films on a carbon filled polycarbonate substrate similar to the sealing of micro-channels on a microfluidic device. Pressure burst testing was carried out in order to measure the weld strength. The effects of power and heating time on weld width and weld strength were studied. The weld width was found to increase with power and welding time. Weld strength was found to increase with power and time until a point beyond which the strength dropped due to possible degradation. The temperature history on the film and the substrate surfaces was measured using thermocouples. The heating during impulse sealing was then modeled using a two dimensional transient finite element model. Fracture surface analysis revealed that weaker welds had a visually similar fractography irrespective of the welding conditions or thickness of nichrome wire used. Similar observations were made for the strong welds. To evaluate the effects of stress concentrations within the weld during the burst test, experimental and mathematical analysis were conducted. A closed form solution was used to calculate the stress based on the displacement values for the film that were obtained from experimental measurement.
Manipulation of Fiber Orientation by Shear Rotation in Injection Molding
The development of fiber orientation in injection molding was manipulated by a special molding tool, the RCEM mould, which imposes a rotation action of one of the cavities wall during mould filling. Central gated disc moldings were produced in a glass fiber reinforced polypropylene, GFRP, with different cavity rotation velocities, inducing distinct distributions and levels of fiber orientation. The microstructures of the moldings were characterized by optical and electronic microscopy. The through-the-thickness profiles of fiber orientation (orientation tensor) were measured. The relationship between the processing thermomechanical environment and the fiber orientation are established.
Study of the Loading Capacity of Biodegradable Core-Shell Nanospheres
Core-shell nanospheres have recently emerged as novel drug delivery systems. The performance of the particles depends upon several characteristics including loading capacity, size, composition, etc. The amount of drug that can be loaded into the core is a function of several factors, such as the size and hydrophobicity of the core, the hydrophobicity of the encapsulant, and specific interactions. These parameters are used to optimize the performance of the formulations. In this work, we studied the loading capacity of biodegradable nanospheres as a function of the size of the nanospheres and hydrophobicity of the encapsulant using encapsulants of varying hydrophobicity and different molecular weight linear amphiphilic block copolymers of pullulan and polycaprolactone (PCL). The established relationship is a useful tool in predicting the loading capacity for other substances based on their hydrophobic character and hence in designing an optimum drug delivery system.
Measurement of Surface Polarity of Organically Treated Nanoclay Using Contact Angle Method
In this paper, we measured surface free energy and surface polarity of organically modified montmorillonite clay (OMMT) using contact angle and Wu’s harmonic-mean equation. The effect of heat treatment, as in polymer processing operations, on polarity was studied. It was observed that the surface polarity reduced significantly with heat treatment owing to degradation of the organic modifier of clay. It was observed that a nonpolar polymer, polypropylene (PP), spread more on heat treated surface than a polar polymer polyamide 6 (PA6). This has significant consequences on morphology development in the blending of PP and PA6.
Vibration Welding Short- and Long-Glass-Fiber-Reinforced Polyppropylene Compounds
Two short-glass-fiber-reinforced polypropylene and two long-glass-fiber-reinforced polypropylenes were vibration welded using a laboratory scale welder. The tensile properties of butt-welded plates were measured as a function of vibration welding pressure and meltdown. The weld strength was observed to decrease with increasing fiber content and length. Increases in weld pressure caused small decreases in weld strength for short-glass-fiber-reinforced polypropylene and a small increase in weld strength for long-reinforced-reinforced polypropylene. The initial fiber orientation in the welded plate and meltdown also had small effects on weld strength.
Comparative Studies between Charpy Impact Test and Dynatup Impact Test
Fracture dynamics of various bimodal HDPEs were investigated based on the loadtime history and impact energy recorded in a Dynatup impact tester. The crack propagation energy (A2) obtained from the Dynatup impact test showed a good correlation to the impact energy from the Charpy test. It is believed that A2, revealing the resistance to crack propagation after the crack has been initiated, reflects a closer relation to the genuine crack energy. Whether or not A2 is a better parameter than ‘Charpy energy’ for predicting rapid crack propagation (RCP) performance requires data support from S4 or full-scale test. Also, a crossover temperature (Tx), which is defined as the temperature where the crack initiation energy (A1) and the propagation energy (A2) intersects in a plot against temperature, is found to exhibit a good correlation with A2.
Development of Flaw Criteria for Short-Term Performance of Electro-Fusion Pipe Welds
The effects of lack of fusion defects on short term performance of electro-fusion polyethylene gas pipe welds were evaluated when it is subjected to loadings that are experienced by the joint in service. Recently improved ultrasonic non-destructive evaluation techniques were developed for detecting some of these defects. However, it was necessary to develop criteria for determining the size and location of defects that would result in unacceptable short term performance of the weld. We performed a variety of short term tests on joints with pre-designed defects including tensile, crush, and pressure leak tests. In addition, finite element modeling was used to find the stress distribution for joints with and without defects. The experimental results were then used together with modeling work to propose criteria for the size and location of the defects. It was found that for short term performance, defects that are near the outside edge of the socket were most critical.
The Control of Creep Memory in Extruded Polypropelene Tubes
The bend memory of extruded polymer tubes creates major problems during the high-speed automatic assembly of extruded and injection moulded components. This work investigates the effect of water bath quenching conditions, during tube extrusion processing, on the crystalline development, mechanical and creep performance, bend memory and recovery of small bore tubes manufactured from polypropylene (PP). Characterisation of the various tube samples was performed using mechanical (tensile, flexural) and thermal (DSC) analysis techniques. The results indicate that the water bath temperature was a critical processing parameter affecting the bend memory characteristics of these tubing products.
Deformation of PET Nanocomposites
The toughening mechanism in polyethylene terephthalate (PET) nanocomposites is investigated as a function of MLS concentration of 1 and 3% using effective area under the stress-strain curve coupled with infra red (IR) thermal wave imaging techniques. 1% MLS concentration, which had an exfoliated structure exhibited slight enhancement in toughness as compared to neat PET whereas 3% MLS composition showed drop in toughness by 87%. From IR thermography, it was concluded that the toughening mechanism in neat PET is due to the chain mobility induced by thermal heating. On the other hand in 1% MLS concentration, the increase in temperature (plastic deformation) is negligible. Differential scanning calorimetry results indicate the absence of cold crystallization peak. This implies that that the interlamellar disorder is completely removed. In the case of 3% MLS nanocomposite, strain embrittlement is seen. This effect of embrittlement is pronounced at higher rate of testing where ductile-brittle transition is evident in 3% nanocomposite.
Nonlinear Creep of Polyethylene Nanocomposites
A compatibilized linear low density polyethylene (LLDPE) modified by montmorillonite layered silicates (MLS) was analyzed for nonlinear creep. To separate the influence of the compatibilizer and the MLS, separate systems of LLDPE with the compatibilizer, LLDPE with MLS were also investigated. Tensile tests were done on all samples. The samples were then loaded to 50% of their yield stress and creep was conducted for an hour followed by an hour of recovery.The viscoelastic nature of polymers was used to explain creep behavior in PE nanocomposites. Nonlinearity in the creep response was modeled using mechanical analogs such as Burgers model.
Enhanced Wood-Plastic Composite utilizing Controlled Architecture Materials (CAM)
Controlled architecture materials (CAMs) (ie. Block copolymers) are being explored as specialty additives in wood polymer composite processing with the goal of improve processing, surface aesthetics, reducing edge tear, improving flexural and tensile strength. Performance testing of these materials versus known additive systems in profile extrusion and injection molding environments are reported. Migratory additives based on fluorinated block copolymer s and their ability to modify polyolefin surface properties at low loading levels and low fluoromonomer content are introduced.
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