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.
Forced air convection is the most common method for heating and cooling the mould in the rotational moulding process. However, it is generally accepted that this is a very inefficient method of heat transfer and so interest has grown in the use of more direct methods of heating and cooling the mould. This paper reports on an experimental study where oil was used to heat and cool the mould. This method is used commercially in a small sector of the market, but there has never been a detailed study of its effectiveness. The results to be presented in this paper show that oil heating and cooling of the mould offers much higher thermal efficiency and reduced cycle times. The performance of the oil heated machine is compared directly with a conventional hot air oven. It is shown that ovenless rotomoulding machines are more amenable to process control because monitoring equipment on the mould is easily positioned outside the heated environment.
Direct electrically heated oven-less rotational moulding machines have been introduced to the rotational moulding market over the past few years. Whereas some of these systems used composite mould technologies, the MECH™ system developed by PPA Teo of Ireland, employs conventional steel tools heated directly by electrical elements surrounding the mould. The elements are supplied with current though slip rings. This paper will present the results of an initial study into the moulding and cycle time characteristics of the MECH™ system and compares it with two types of conventional hot air rotomoulding machines. Machine efficiencies, as well as heating and cooling times have been compared for the three machines. The effects of processing parameters on the mechanical properties of the mouldings have also been assessed.
The quality of a rotationally molded part is highly dependent on its cooling rate, perhaps more so than its heating rate. A trade off between part quality and cycle times is often necessary to ensure economical feasibility. This paper presents an overview of the effect of cooling rate on final part quality. The temperature profile through the part wall during cooling is related to the part’s mechanical properties, morphology, shape and general appearance. Six different mold cooling rates are investigated; they range from quiescent cooling (average 2C°/min) to water spray cooling (average 15C°/min).
The objective of this paper is to provide a better understanding of how test temperature and test frequency affect the crack initiation and propagation energies of rotomoulded materials. Trials were carried out on a range of rotomolded linear low density polyethylenes. Instrumented impact tests and dynamic mechanical thermal analysis (DMTA) were carried out on each material at a wide range of temperatures and frequencies. It was found that there is a linear relationship between the crack initiation energy of the samples and the tan ? values at all test conditions. By using this relationship it is possible to predict the crack initiation energy of a polymer part over a wide range of conditions by carrying out a small number of tests.
Process control for the rotational molding industry has been continually evolving in recent years. Initially, impact strength, and bubble content in the wall of the molded parts, were used to gauge the level of cure and also to control the process. More recently, the development of the Rotolog process control device has provided a more scientific means to ensuring good process control.This paper highlights some recent work that expands upon the methods previously mentioned, applying new methodology to measure and control the process. The effects of various processing conditions are considered, in particular, with respect to the cooling cycle, and how they relate to process variation. The results outlined provide new processing knowledge that can be used to further develop the control of the rotational molding process.
Thermotropic liquid crystalline polymers (TLCPs) have a number of potentially useful physical properties for rotational molding: excellent chemical resistance, good barrier properties, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance. However, it is possible that the nature of the molding process is such that full advantage of these properties cannot be obtained. To determine how well TLCPs perform when rotationally molded a commercially available TLCP, Vectra B 950, was studied under static conditions as well as with a single axis rotational molding unit capable of measuring the internal air temperature. The processing temperature was determined by measuring shear viscosity at several temperatures. The tensile strength and modulus of both statically molded and rotationally molded samples were measured. Samples were evaluated for complete densification by inspecting the fractured surface.
Polyolefins based on metallocene catalyst technology appeared in the early 90’. These polyolefins were first used in application like blown film for metallocene polyethylenes, cast film and fibers for metallocene polypropylenes.This paper will highlight the interest of metallocene based polyolefins, polyethylene and polypropylene resins, for rotational molding applications. Polymer characteristics, processing behavior and rotomolded item properties will be compared to conventional Ziegler-Natta based resins. These new polyolefins show a real potential in terms of cylce time, dimensional properties, impact and optical properties improvements.
Polymer sintering plays a major role in processes such as rotational molding, governing the heating cycle and the properties of the final parts. This work aims at determining the impact of changes in the material formulation and processing history on the sintering behavior. These changes are known to introduce variations in the material morphology and thus affect the material processability and properties of the end-product. Variations in the thermal treatment were found to have an effect on the particle morphology but a limited impact on the sintering process. It was also found that the addition of a nucleating agent can be detrimental to the sintering process. The impact of these changes, however, seems to be related to the viscosity of the material as well as the molecular structure.
Reliable sources estimate that about 75% of molded polyolefin technical parts need surface refinement. Those surfaces have to be lacquered, dyed, glued, coated, or printed. Also, polyolefin resins offering better adhesion to PU foams are requested.The ARPLAS process offers improvements in quality, economics, and flexibility. This plasma process modifies the chemical structure of the polyolefin powder surface, that non-polar, hydrophobic materials become polar, hydrophilic materials, which can be lacquered, coated, and foamed without any other additives.The modification of the powder is achieved by implantation of functional groups into the polyolefin molecules. Characteristics of the material, i.e. impact strength, ESCR, and other major specifications remain unchanged as well as processing compared to non-modified PE.The new ARPLAS technology offers molders new application possibilities, opens up new market sectors, and reduces adhesion problems.If serious sticking/adhesive problems are to be solved, the use of ARPLAS-treated powders make sense. This is also true if an acceptable paint coating is to be applied or a strong bond is to be made with PU foam.
The DC electrical conductivity of composite microfibers consisting of carbon nanofiber and carbon nanotube reinforced polypropylene is examined. Carbon nanofibers with an average diameter of 100 nm can serve as ideal precursor system to carbon nanotubes for the development of polymeric fibers with superior electrical, mechanical and thermal properties. Electrical conductivity of the microfibers was measured over a range in the nanofiber weight fraction of 0.5-10 percent and carbon nanotube fraction of 0.1 to 0.5 percent. The results provide a comparison between the property enhancement levels achieved in the microfiber by the addition of similar weight fractions of carbon nanofiber and carbon nanotube reinforcements in the dilute range.
The aim of Molded Interconnect Devices is to integrate in an injection moulded part with structured plated surfaces electrical and mechanical functions. One of the promising manufacturing methods of 3D-MIDs is the In- Mould Decoration-Process, which uses a plastic-film with a circuit-pattern plated on its surface. Problems which occur sometimes in the conventional In-Mould-Decoration- Process are the damage of the circuit structure or the plastic- film due to high shear stress and pressure during injection. Another problem could be the warpage of the device. Different process-variants which are capable to overcome this difficulty like thermoplastic foam moulding and injection compression moulding were evaluated. Of major concern in the investigation was beside the warpage the adhesion between the plastic-film and the substrate depending on different process-variants of In-Mould Decoration.
Whereas prior related work involved batch devices, an industrially relevant continuous flow chaotic mixing process has been used in this study to form structured distributions of carbon black in extruded films. Methods were also applicable to other extrusion profiles. Carbon black masterbatch was formed into numerous filamentary striations that yielded conducting states at low overall compositions. A range of electrical properties were selectable via process parameter specification. Differences in directional conductivities along the width and length of the film were controllably obtained. The progressive formation of structure was related to electrical properties and process conditions.
Polyaniline (PANI) films 20 to 50 microns thick cast from N, N’-dimethylpropylene urea (DMPU) solution and stretched to different draw ratios were examined. The thickness of these visibly opaque PANI films posed severe limitations on available structural characterization tools. NIR wave guide coupling, X-ray diffraction and FTIR infrared dichroism methods were used. Two new infrared transition moment angles for weakly absorbing bands were determined for the PANI molecule. This allowed the Hermans’ orientation function for the thick PANI films to be determined nondestructively.
Loose buffer tube designs in fiber optic cables (FOC) generally include hydrocarbon oil based gels to fill the tubes for mechanical and moisture protection. Conventional olefinic polymers typically show reduced performance in compatibility testing due to a high level of hydrocarbon oil permeability. In particular, impact-modified polypropylene (IMPP) requires specially formulated and, therefore, more expensive gels to retain modulus and tensile properties after oil exposure. Described herein is the gel compatibility performance of a developmental product made with INSPIRE* Performance Polymers that provide a substantially improved balance of impact toughness, high modulus and gel compatibility for the optic buffer tube application versus the conventional polyolefin materials currently used. Also outlined are preliminary results of ongoing material studies targeting further improvement in gel compatibility performance.
Fillers are used in the molding compounds to minimize the stress of electronic packaging by reducing the coefficient of thermal expansion (CTE) mismatch between the silicon die and the molding compounds.This study concentrates on the effect of filler particle spatial distribution. Quantitative measures of the particle distribution were experimental determined, including area fraction, size and interparticle distance (IPD). A 2×3×3 ANOVA test was also conducted to assess the statistical significance of these variations of measures. The difference of filler volume fraction at different positions within one chip can be as big as 10%, and cause a CTE difference of about 4 ppm/°C.
This work aims at developing lightweight low-cost bipolar plates for use in proton exchange membranes (PEM) fuel cells. New material formulations using polypropylene (PP) and polyphenylene sulfide (PPS) as matrices and carbon black, graphite, and carbon fibers as conductive additives were developed. These formulations have properties suitable for bipolar plate manufacturing, such as good chemical resistance, sufficient fluidity, and high electrical and thermal conductivity. Two prototype plates of different design were successfully fabricated by over-molding aluminum plates or simply by injecting the high conductive materials into the final shape.
Today, most flip chips are encapsulated by dispensing the encapsulant along the periphery of the sides of chip. As the dispensing process fills the space between chip and substrate by capillary force, the flow is very slow and could result in filling incomplete or voids. Therefore, as chip size increases, the filling problems become more serious. For this reason, it is critical for flip-chip technology to speed up the encapsulation process and avoid defects.This paper studies the theories of the material properties, contact angle and surface tension,etc. Moreover, some transparent molds with different number/size of bumps and different layout patterns are used to study molding phenomena. The experimental results are further used to verify the use of CAE tools.
Chemical modification of isotactic polypropylene in solid-state using various monomers –initiator systems has been investigated. In particular porous iPP is modified in solid-state by grafting silanes or acrylates using free radical initiators. Silica like nano-particles were formed in-situ via sol-gel reaction in pre-modified solid porous iPP. These silica-clusters were of nano-scale varying from 30-200 nm in size, and retained the size even after processing (extrusion). Grafting and silica formation via sol-gel is characterized using FT-IR and 29Si Solid-state NMR. Morphological characterization (using TEM and SEM) showed uniform distribution and dispersion of silica particles in matrix before and after processing. DSC and WAXD results revealed that silanes, when grafted on iPP, nucleate and induce ?-phase. Improvement in toughness and effect on thermal properties of polymer were also investigated and mechanism of toughness enhancement is proposed.
Polypropylene (PP) nanocomposites were obtained by melt compounding of PP and organoclays in the presence of maleic anhydride grafted polyolefin compatibilizer. The effects of compatibilizer type and content and the mixing sequence on the morphology and properties of the PP/clay nanocomposites were investigated. PP nanocomposites exhibit enhanced mechanical properties compared with neat PP and they also are thermally more stable. Rheological properties are sensitive to the composite structure and thus are a valuable indication of the degree of exfoliation.
Molecular-level blending of reactive polymers can provide an alternative and economical route to producing new polymers with special structures and improved properties. In this paper, we report results of our experimental efforts to generate compatibilized polypropylene (PP)/polyamide 6 (PA6) blend via in situ polymerization and in situ compatibilization of polypropylene, ? -caprolactam and maleic anhydride grafted PP that is impossible to achieve using conventional polymer blending methods reported in the literature. The intrinsic molecular-level blending and compatibilization of the preparation method allowed formation of nanostructured PP/PA6 blends with interesting stable interpenetrating or co-continuous morphologies that can be controlled during processing. Thermal and morphological measurements revealed that the compatibilization effect of the blend is significantly better than that obtained from conventional reactive blending of premade polymers. With proper control of the thermodynamics, interfacial tension (through use of chemically modified functional polymer) and deformation rates, particle coalescence could be suppressed, making it possible to generate the polymer blends with very small (< 100 nm) polydispersities. These blends could find applications in a number of high-end uses such as optics, drug delivery, tissue engineering, and permeable membranes for separation phenomena.
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