Showing papers in "Cellular Polymers in 2009"
TL;DR: The properties of rigid polyurethane foams can be modified over a wide range depending on the raw materials used for its synthesis as mentioned in this paper, such as polyols, chain extender and blowing agent.
Abstract: The properties of rigid polyurethane foams can be modified over a wide range depending on the raw materials used for its synthesis. The polyols, chain extender and blowing agent have major impact o...
17 citations
TL;DR: In this article, an amorphous material and a semi-crystalline material have been evaluated and the properties of maximal impact force and energy absorbed have been correlated with the morphological parameters of skin thickness, cell size and foam density.
Abstract: Injection moulded thermoplastic foams, which are always structural foams, combine the versatility of thermoplastic materials with substantial material and energy savings. Through different studies, it has been demonstrated that their mechanical properties can be improved through the control of the foam morphology. In a study conducted at the IKV, several foam morphologies have been prepared and their impact properties have been studied through instrumented puncture tests. Both an amorphous material and a semi-crystalline material have seen tests. Both an amorphous material and a semi-crystalline material have been evaluated. The force vs. displacement curves have been obtained for each material and the properties of maximal impact force and energy absorbed have been correlated with the morphological parameters of skin thickness, cell size and foam density. The results show that the absorption capabilities of the foam can be substantially improved if the foam morphology is controlled. Furthermore, the foam structure affects the fracture behaviour during impact.
16 citations
TL;DR: In this article, the effects of shot size, injection pressure and mold temperature on the relative density, unfoamed skin thickness, cell population density, surface hardness and fiexural strength of various regions of the injected parts were investigated.
Abstract: This paper presents an experimental study on microstructural and mechanical properties of injection molded microcellular foamed parts. The effects of shot size, injection pressure and mold temperature on the relative density, unfoamed skin thickness, cell population density, surface hardness and fiexural strength of various regions of the injected parts were investigated. A conventional injection molding machine was modified to produce microcellular acrylonitrile butadiene styrene (ABS) foamed plates. Nitrogen gas was used as the blowing agent. The results showed that surface hardness of microcellular foamed parts are higher and their flexural strength is lower than those of the unfoamed parts. Examining the properties throughout the parts confirmed distinct variations.
13 citations
TL;DR: In this article, the quality of life in Western populations is becoming an evergrowing concern and higher demands are made in regard to for example comfort and safety, for example low emissions of volatile organic compounds and odourless odours.
Abstract: Quality of life in Western populations is becoming an ever-growing concern. Higher demands are made in regard to for example comfort and safety. Low emissions of volatile organic compounds and odou...
12 citations
TL;DR: In this article, the effects of chemical composition on cellular structure as well as the effect of structure on their thermal, mechanical and combustion properties were explored. But the results were limited to cell sizes below 100 microns.
Abstract: Composites of LDPE/ATH (up to 70 wt. %) were foamed to create new materials with good fire retardancy properties and low weight, proving the feasibility of developing cellular structures when high levels of inorganic fillers are included. An experimental study was carried out to explore the effects of chemical composition on cellular structure as well as the effect of structure on their thermal, mechanical and combustion properties. Samples fabrication was carried out using an improved compression moulding route consisting of polymer compounding, precursor preparation and foaming under pressure. The polymer matrix consisted of low density polyethylene as well as certain amount of LLDPE-g-MAHas compatibilizer agent. The inorganic filler used was aluminium trihydroxide (ATH) ranging from 0 wt.% to 70 wt.%. Furthermore, azodicarbonamide (ADC) was used as chemical blowing agent. Foamed samples with cell sizes below 100 microns were produced. These samples showedsimilarfire retardancy than their solid precursors. The compatibilization was proved indispensable to achieve a good adhesion between mineral filler and polymer and to improve the cellular structure. The increase of the amount of filler has an interesting effect on the cellular structure, going from a closed-cell (at low contents) to an open-cell (at higher contents) cellular structure. As a result of this investigation, halogen-free flame retardant cellular materials were processed, leading to a notable reduction of material compared to the solid one and to new properties which can result in new applications.
11 citations
TL;DR: In this article, a batch foaming process has been employed to obtain microcellular materials from polystyrene plus a SBM copolymer (polystyrene-co-1,4-polybutadiene-copoly(methyl methacrylate).
Abstract: A batch foaming process has been employed to obtain microcellular materials from polystyrene plus a SBM copolymer (polystyrene-co-1,4-polybutadiene-co-poly(methyl methacrylate). In the first part of the process, raw materials were mixed and extruded in a proportion 90:10 to obtain the precursor materials, leading to a nanostructured assembly in which SBM self-organizes in the polystyrene matrix. In a second stage, foaming was carried out by means of supercritical CO(2) in a single step-process. Foamed samples were produced using a technique based on the saturation of the polymer under scCO(2), and final properties were controlled by varying the temperature. The swelling in scCO(2) was performed at 300 bar during 16 h, and subsequently releasing the gas with a fixed depressurization rate of 60 bar/min. Temperature was varied from 30 degrees C to 80 degrees C, leading to densities from 1.0 g/cm(3) to 0.5 g/cm(3) and cell sizes from 2 micron to 100 micron. In this part of the work, a comparison between foaming behaviour of neat PS and a nanostructured PS+SBM blend is reported, investigating the role of the nanostructured phase as nucleating agents for microcellular foaming. Finally, low rate compression tests were carried out, analyzing the dependence of mechanical parameters such as elastic modulus, yield stress and densification strain with density.
9 citations
TL;DR: In this article, density graded polyethylene foams were produced by imposing a temperature gradient while foaming the sample, and the resulting morphologies were presented with their respective flexural moduli.
Abstract: For any type of polymer foam, it is well known that careful control of the processing temperature has an important effect on final morphology. In this work, density graded polyethylene foams were produced by imposing a temperature gradient while foaming the sample. This was done by controlling independently the top and bottom plates of a compression mold at different temperatures. By doing so, different density profiles across the part's thickness are produced. In this work, the resulting morphologies are presented with their respective flexural moduli.
8 citations
TL;DR: In this article, a unique bimodal structure was observed, consisting of closed microcells with an interconnected nanoporous interior, which was successfully foamed with a microcellular structure at foaming temperatures above the melting point.
Abstract: In this paper processing conditions are presented to fabricate HDPE foams with a microcellular structure. The conventional microcellular foams are normally produced by heating a gas-saturated thermoplastic to a foaming temperature near the glass transition of the gas-polymer system. Efforts to foam HDPE in the conventional process have largely been unsuccessful, due to the low glass transition temperatures and low gas solubility in these polymers. We have found that HDPE can be successfully foamed with a microcellular structure at foaming temperatures above the melting point. Density reductions of up to 65% were obtained using sub-critical carbon dioxide as blowing agent. A unique bimodal structure was observed, consisting of closed microcells with an interconnected nanoporous interior.
8 citations
TL;DR: In this paper, the structural and mechanical properties of structural and conventional foams based on a low density polyethylene have been characterized and the results have showed that the sandwich structure of structural foams improves a 50% the mechanical behaviour in bending, however no improvements in compression or tension have been found.
Abstract: Structural foams are composed of two solid layers enclosing a foamed core. The application of sandwich structural foams has rapidly increased in the lastdecade. Injection moulding is currently used to produce these foams, being not common to produce conventional foams ofsimilardensities and chemical compositions in a similar process. In this paper an alternative route to produce structural foams has been used. This method allowsfabricating conventionalfoams with the same chemical composition and density than the structural foams, so comparisons between properties of both kinds of materials can be made in a proper way, i.e. avoiding effects of different chemical compositions and/or different densities. The structural and mechanical properties in tension, compression and bending have been characterized both for structural and conventional foams based on a low density polyethylene. The results have showed that the sandwich structure of structuralfoams improves a 50% the mechanical behaviour in bending, however no improvements in compression or tension have been found.
6 citations
TL;DR: In this paper, the impact of selected processing parameters (temperature, time of pre-heating, speed of deformation, magnitude of stretching) on the microcellular foam morphology and density was reported.
Abstract: Cyclo-olefin copolymers (COC) based on ethylene-norbornene (E-NB) structures have been investigated with respect to their foamability. COC present interesting characteristics, such as extremely low water absorption, excellent water vapor barrier properties, high strength and very good electrical insulating properties. Varying the ratio of E versus NB monomers enables to tune the glass transition temperature (T g ) over a wide range. Due to the rigid ring structure of NB, the resin remains amorphous. This study presents basic information related to the foam processing of different grades of COC resins with T g varying between 80 and 130 °C, adding a special emphasis on process-relevant material characteristics: rheology, solubility and plasticization. CO 2 -laden COC sheets, where the gas sorption was obtained using high pressure autoclave, were foamed using a biaxial stretcher. The impact of selected processing parameters (temperature, time of pre-heating, speed of deformation, magnitude of stretching) on the microcellular foam morphology and density will be reported throughout this paper.
5 citations
TL;DR: In this paper, the synthesis and characterization of polyurethane (PU)-chitosan(CH) porous prepared by thermal induced phase separation (TIPS) is described, the obtained products were characterized b...
Abstract: In this work the synthesis and characterization of polyurethane (PU)-chitosan(CH) porous prepared by thermal induced phase separation (TIPS) is described, the obtained products were characterized b...
TL;DR: In this paper, Azodicarbonamide (ADCOC) was used as the foaming agent for cellular foams based on the cyanate ester, viz., (2,2-bis (4-cyanatophenyl) propane) have been processed.
Abstract: Cellular foams based on the cyanate ester, viz., (2,2-bis (4-cyanatophenyl) propane) have been processed. Azodicarbonamide (ADC) was used as the foaming agent. Cyanate ester foams with different de...
TL;DR: In this paper, an extrusion setup was prepared to produce foam insulated coaxial cable using butane as the physical foaming agent, and the effect of die geometry (die gap and die outlet diameter) on foam morphology and loss-attenuation were investigated using a blend of LDPE (90%) and HPE (10%).
Abstract: This paper presents an experimental study on manufacture and characterization of an insulating foam coating in the coaxial cables where a physical blowing agent (butane) is used. Coaxial cables with foam insulator are widely used in communication industries. The insulatingfoamplays a key role in the attenuation properties of the coaxial cables. In this research work, an extrusion setup was prepared to produce foam insulated coaxial cable using butane as the physical foaming agent. The effect of die geometry (die gap and die outlet diameter) on foam morphology and loss-attenuation were investigated using a blend of LDPE (90%)-HDPE (10%) as the main material. The results show that an acceptable low loss-attenuation is achievable via using a polyethylene compound and adjusting processing parameters.
TL;DR: A review of data and references is provided to demonstrate the efficacy oftitanates and zirconates in foamed unfilled and filled polymers with an emphasis on their recent application in nanocomposites as mentioned in this paper.
Abstract: A review of data and references are provided to demonstrate the efficacy oftitanates and zirconates in foamed unfilled and filled polymers with an emphasis on their recent application in nanocomposites. Titanates (and zirconates) are shown to catalyze a polymer - called Repolymerization by the author - to increase its stress-strain strength thereby creating finer cells and reducing open cell structure because the polymer bubble does not break while being foamed. Additives such as foaming agents, fillers and reinforcements are shown to be dispersed better reducing interfacial failure. The chemistry of the Six Functions of the titanate molecule are discussed along with selection, dosage, the physics of mixing, catalysis and rheology, mixing temperatures, compounding considerations such as initial boiling point, and the chemistry at the interface of nano particulates.
TL;DR: In this article, three UK manufacturers offlexible polyurethane foam collaborated in a study in which cushion sized samples made from different formulations were stored for a period of ten years.
Abstract: Three UK manufacturers offlexible polyurethane foam collaborated in a study in which cushion sized samples made from different formulations were stored for a period of ten years. Samples were monitored at approximately 6 monthly intervals for retained flame retardant. Two chlorinated phosphate ester flame retardants were investigated - TCPP and TDCP. Neither of these was prone to migration losses during the study period and foam ignition resistance was maintained.
TL;DR: In this article, the effect of weld lines and density reduction on the morphology and mechanical properties of injection moulded fibreglass reinforced polypropylene structural foams is reported, and the results are related to a change in fibre orientation along the sample length which is the main factor controlling the mechanical response of composite foams.
Abstract: In this work, the effect of weld lines and density reduction on the morphology and mechanical properties of injection moulded fibreglass reinforced polypropylene structuralfoams is reported. In this first part, cell size, cell density, skin thickness as well as tensile and shear mechanical properties are reported. As expected, all mechanical properties decreased with density reduction. On the other hand, the presence of a weld line produced a more complex behaviour: lower tensile properties with higher torsion modulus. These results are shown to be related to a change in fibre orientation along the sample length which is the main factor controlling the mechanical response of these composite foams.