bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a New Large Flaming Ignition Source for Upholstered Seating and Mattress Tests. Part 1: Characterisation of Ignition Sources
Authors: Laperre J. , Paul K. T.
Published: September 2018

Flaming ignition sources are used in standard tests to assess the ignitability of upholstery seating and mattress composites. These sources should preferably be equivalent to the ignition source occurring in real life situations. BS 5852 defines a total of seven ignition sources of which the No. 5 Crib is used for testing upholstered seating and mattresses designated for use in public premises. In this paper this ignition source is compared to two newspaper ignition sources of 20 grams and several other ignition sources. Extensive rate of heat release measurements in the cone calorimeter tests and heat flux distribution measurements towards the back and the base of an inert L-shaped test rig simulating the seating test rig are presented and discussed.

Flaming ignition sources are used in standard tests to assess the ignitability of upholstery seating and mattress composites. These sources should preferably be equivalent to ignition sources occurring in real life situations. BS5852 defines a total of seven ignition sources of which the No. 5 Crib is used for testing upholstered seating and mattresses designated for use in public premises. This paper discusses different candidate ignition sources and compares them with the 20 gram newspaper ignition source required by the EC as part of the earlier draft Furniture Directive. Modified crib structures as well as multi-jet gas burners have been studied and the final selection of the ignition source was based on extensive tests on upholstery seating and mattress composites.
Development of a New Large Flaming Ignition Source for Upholstered Seating and Mattress Tests. Part 2: Ignition Behaviour of Different Large Flaming Sources on Mattresses and Upholstered Composites
Authors: Laperre J. , Paul K. T.
Published: September 2018

Flaming ignition sources are used in standard tests to assess the ignitability of upholstery seating and mattress composites. These sources should preferably be equivalent to ignition sources occurring in real life situations. BS5852 defines a total of seven ignition sources of which the No. 5 Crib is used for testing upholstered seating and mattresses designated for use in public premises. This paper discusses different candidate ignition sources and compares them with the 20 gram newspaper ignition source required by the EC as part of the earlier draft Furniture Directive. Modified crib structures as well as multi-jet gas burners have been studied and the final selection of the ignition source was based on extensive tests on upholstery seating and mattress composites.
Effect of Recycling on the Rheological Properties and Foaming Behaviors of Branched Polypropylene
Authors: Naguib Hani E. , Wang Jin , Park Chul B. , Mukhopadhyay Anjan , Reichelt Norbert
Published: September 2018

The effects of recycling of branched polypropylenes on their rheological properties and foamability are studied in this paper. The rheological properties and foamability of branched polypropylene are compared with those of the virgin sample. The main purpose of the study was to explore the possibility of using recycled materials to make the acceptable foam products. The recycled polypropylenes showed the lower melt strength due to the lowered molecular weight and disentanglement of molecules. However, the high-shear viscosities of the virgin and recycled resins exhibited almost the same values whereas the zero-shear rate viscosity was lower for recycled ones. The rheological behavior of the resins was correlated to the foaming behavior. It was observed that the contribution of the storage modulus (G’) was more pronounced than the loss modulus (G”). The foam morphology of recycled branched polypropylene and the virgin material was studied at various processing temperatures using a single-screw tandem foam extrusion system. The volume expansion ratio and cell population density results were correlated with the rheological data. Despite the noticeable drop in the melt strength, it was found that the foamability did not significantly deteriorate by recycling.
Viscoelastic Properties of Foamed Thermoplastic Vulcanizates and their Dependence on Void Fraction
Authors: Park Junhong , Siegmund Thomas , Mongeau Luc
Published: September 2018

Experimental techniques to measure the viscoelastic mechanical properties of foamed elastomers at high frequencies were developed and applied to study foamed thermoplastic vulcanizates. The measurements were performed for foams with a wide range of void fractions such that a transition from a true porous solid to a foam was present. The frequency and time dependence of the dynamic and relaxation moduli, respectively, were measured and were shown to depend on the loss factor of the elastomer. The measured variation of the dynamic and the relaxation moduli with the void fraction did not depend on frequency and time in the frequency and time range of interest. This suggested that the time and frequency dependence of elastic moduli was determined mostly by the void fraction and the corresponding material microstructure. Property measurement results were compared to predictions for porous solids using the Mori-Tanaka method as well as methods for cellular solids.
Novel Reduced Density Materials by Solid-State Extrusion: Proof-of-Concept Experiments*
Authors: Schirmer Henry G. , Kumar Vipin
Published: September 2018

The feasibility of extruding polymer in a solid phase encapsulated in a lower melting point polymer in a low-temperature extrusion process is demonstrated. Such solid-state extrusion has been accomplished in two different resin systems, using different mechanisms. The first system is based on rigid PVC pellets coated with a plasticizer and dusted with highly plasticized PVC powder. Here, PVC pellets, pre-foamed in a batch solid-state microcellular process, were extruded in a way that preserved the microcellular structure of the individual pellet. In the second system hollow pellets were co-extruded using polystyrene as the core material and encapsulating it with polyethylene and polyethylene methacrylate co-polymer (EMA). During extrusion, the softer, lower melting polyolefins carried the polystyrene through the extruder in the solid-state. The unique feature in both examples is that the polymer to preserved in the solid phase is not melted inside the extruder barrel.
Polyethylene-Kevlar Composite Foams I: Morphology
Authors: Zhang Yaolin , Rodrigue Denis , Aït-Kadi Abdellatif
Published: September 2018

Polyethylene-Kevlar composite foams were investigated in order to understand the effect of fibers. In this first part, cell sizes, cell density and cell size distribution of the foams were measured as well as the shear viscosity of the unfoamed composites and matrix. It is shown that reinforcing fibers can act as nucleation sites for foaming depending on the processing conditions of the composites. The results are discussed in terms of fiber content and polymer-fiber interface in relation with the rheological properties of the unfoamed materials.
PP-Blends with Tailored Foamability and Mechanical Properties
Authors: Reichelt Norbert , Stadlbauer Manfred , Folland Rick , Park Chul B. , Wang Jin
Published: September 2018

The optimisation of physical foaming of branched Daploy™ WB130HMS polypropylene foam resin and corresponding blends with a Polypropylene Blockcopolymer are described in this paper. The resulting foam morphologies of blends consisting of linear and branched polypropylene materials produced at various processing temperatures were studied using a single-screw tandem foam extrusion system and their volume expansion behaviours were compared. Three different die geometry's were tested for physical foaming of PP-blends using 5 and 10 wt% of butane. A correlation between extensional rheology and lower limit of foam density for blends was found. Depending on die geometry the use of different concentrations of branched polypropylene resin in the blends was required to achieve foam densities < 50 kg/m3. The influence of foam density and blend ratio on mechanical properties of foams will be discussed on a model and representative samples.
Characterisation of Microcellular Foams using X-Ray Microtomography and Raman Spectroscopy
Authors: Nygaard Jens V. , Pyrz Ryszard
Published: September 2018

Closed cell polycarbonate foam is investigated using X-ray microtomography (XRMT). A specimen is prepared using the solid state processing route and a graded microstructure is obtained containing cell sizes from 10 to 90μm. The cell size distribution was estimated by modelling the foam dynamics and compared to a reconstructed geometry obtained from a XRMT experiment. The graded specimen contains regions with a microcellular structure. These regions are not suitable for XRMT investigations since the smallest details of the structure are below the resolution limit. An alternative approach for the characterisation of microcellular foams is suggested by using carbon nanotubes and Raman spectroscopy. A polycarbonate/carbon nanotube composite is molded and microcellularly foamed. Raman investigations verify that nanotubes are present within the structure and indicate straining of the nanotubes at intermediate steps during sample preparation and sample compression.
Synthesis of Rigid Polyurethane Foams from Recycled Poly(ethylene Terephthalate) Waste
Authors: Azim Abdel Azim A. Abdel , Atta Ayman M. , El-Ghazawy R.A.
Published: September 2018

Glycolysis of poly(ethylene terephthalate), PET, waste using trimethylol propane (TMP) or pentaerytheritol (PEr) was used to produce suitable hydroxyoligomers for polyurethane foams. The glycolysis was carried out in the presence of manganese acetate as a catalyst, under high and normal pressure atmosphere in xylene and m-cresol at 220 °C. The prepared oligomers were reacted with 2,4- 2,6- toluene diisocyanate to produce different types of polyurethane foams. The compressive and flexural strengths, open and closed cell%, oxygen index% and curing times were determined and the results were correlated to the chemical structure of the produced oligomers.
Experiments on Solid-state Cell Nucleation in Polystyrene and Polycarbonate as a Function of Foaming Temperature and Foaming Time
Authors: Nakano Susumu , Shimbo Minoru
Published: September 2018

In this paper, the equivalency between the foaming time and foaming temperature of the cell density, the number of cells per unit volume remaining in the foamed plastics, will be discussed. The foaming was carried out by the following method. The blowing agent was soaked into the solid resin at high pressure under temperature lower than the glass transition temperature of the resin. After the blowing agent reached its saturation state, cell nucleation and cell growth were induced by heating various foaming temperatures higher than glass transition temperature and various foaming times after decompression. Finally, cell growth was halted by cooling. Concretely, using a device that can accurately control temperature and the decompression rate, polystyrene (PS) and polycarbonate (PC) resins which are amorphous resins were foamed under various the foaming temperatures and the foaming times by the above-mentioned method. The following results were obtained. (1) Cell density of foamed PS and PC plastics shows time and temperature dependence as the cell density becomes large when foaming temperature is low and foaming time is short. (2) Equivalency is maintained between the foaming time and foaming temperature dependence of the cell density of PS and PC foamed plastics, and they can be expressed with one master curve respectively. That is, the time-temperature equivalent law is held about cell density. (3) These results seem to become one technique to select the foaming condition of foamed plastics having required cell densities.
Influence of Different Endothermic Foaming Agents on Microcellular Injection Moulded Wood Fibre Reinforced PP Composites
Authors: Bledzki Andrzej K. , Faruk Omar
Published: September 2018

Microcellular wood fibre reinforced polypropylene composites, a new development using bio-fibre strengthened plastic, were prepared in an injection moulding process. The influence of three different endothermic chemical foaming agents was examined. The effects of various concentrations (1 to 4 wt.% of the composites) of the chemical foaming agent on the properties of the composites was studied with a view to establishing the concentration-structure-property relationships for these materials.

The influence of wood fibre type (hard wood and soft wood) on the microcellular structure and physico-mechanical properties of the composites was also investigated. Microcell morphology (cell size, shape and distribution) was observed using scanning electron microscope.

The chemical substance of different endothermic foaming agent affected the microcellular structure of hard and soft wood fibre-PP composites. Endothermic foaming agent with chemical substance polymeric microsphere (ESC 5313) showed finer microcellular structures compared to other foaming agents and 4 wt.% content of chemical foaming agent exhibits finer microcellular structures than the other contents. The reinforcing of soft wood fibre showed significantly finer microcellular structures than the hard wood fibre reinforcements. Density reduced maximum 30% and decreased up to 0.721 g/cm3 at soft wood fibre 30 wt.% content with coupling agent maleic anhydride grafted polypropylene (MAH-PP). With the addition of MAH-PP, specific tensile strength and specific flexural strength increased maximum 60% and 55% respectively with foaming agent ESC 5313 at soft wood fibre 30 wt.% content.
Cellular Structure of Halogen-Free Flame Retardant Foams Based on LDPE
Authors: Román-Lorza S. , Rodriguez-Perez M.A. , De Saja Sáez J.A.
Published: September 2018

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-MAH as 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 showed similar fire 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.
Assessment of Fire Performance of Typical Furniture Foams with and without Fire Retardants Using a Cone Calorimeter
Authors: Chow W.K. , Han S.S. , Zeng W.R.
Published: September 2018

Both thermal and smoke aspects on typical samples of furniture foams with and without fire retardants available in the market were tested with a cone calorimeter. To study their behaviour under big fires, high incident radiative heat fluxes up to 70 kWm-2 were adjusted. Transient curves on heat release rate, mass loss rate, carbon monoxide concentration, carbon dioxide concentration, smoke release rate and other key parameters were measured. Further, chemical constituents of the fire retardants were analyzed by X-ray fluorescence, Fourier Transform Infrared, Gas Chromatography/Mass Spectrometry and Pyrolysis Gas Chromatography Mass Spectrometry.

It is observed that foam treated with fire retardant would not be ignited under an incident heat flux of 10 kWm-2. However, when burning under heat fluxes higher than 20 kWm-2, there is not much improvement in the thermal aspect for foam treated with fire retardants. Even more smoke and toxic gases such as carbon monoxide was emitted. Therefore, testing ignitibility of furniture foam materials under a small match flame is not adequate. Tests with high radiative heat flux encountered in big fires are suggested. Cone calorimeter tests proposed in this paper would give a better assessment on fire safety. Finally, three risk parameters are proposed to work out a combustibility database.
Polyethylene Foams Produced under a Temperature Gradient with Expancel and Blends Thereof
Authors: Yao Jiaolian , Barzegari Mohamad Reza , Rodrigue Denis
Published: September 2018

Thermoplastic polymer foams can be produced using expandable beads like Expancel microbeads. In this work, density graded polyethylene foams were produced by imposing a temperature gradient using compression moulding. This was done by controlling independently the top and bottom plates of the mould at different temperatures. Foaming was done by using different grades of Expancel and blends of them to produce a complex cellular morphology. In this work, a complete morphology in terms of cell size and cell density will be presented in relation with density profile across the foam thickness. The foam behaviour under different types of mechanical loadings will also be discussed.
Comparisons of Microcellular PHBV/PBAT Parts Injection Molded with Supercritical Nitrogen and Expandable Thermoplastic Microspheres: Surface Roughness, Tensile Properties, and Morphology
Authors: Peng Jun , Li Ke , Cui Zhixiang , Turng Lih-Sheng , Peng Xiang-Fang
Published: September 2018

Solid and foamed tensile bars made of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/ poly (butylenes adipate-co-terephthalate) (PBAT) blends with a weight ratio of 45/55 were prepared via conventional and microcellular injection molding processes, respectively. To fabricate the degradable PHBV/PBAT foamed parts, two kinds of blowing agents, namely, supercritical nitrogen (SCF N2) as the physical blowing agent and expandable thermoplastic microspheres (ETM) as the chemical blowing agent, were employed. Various properties were investigated and compared in terms of surface roughness, mechanical tensile properties, and cell morphologies. Through surface roughness comparisons using a 2D surface roughness analyzer and a 3D white-light interferometer surface profiler, microcellular injection molded parts with ETM exhibit a better surface quality. The tensile property results show that PHBV/PBAT–N foamed with SCF N2 have a longer strain-at-break. The microcellular morphologies and sandwich-like multilayer structure on the fractured cross-sectional surfaces were characterized by using a scanning electron microscope (SEM). As shown by the test results, the cell microstructures - such as cell size, cell density, and multi-layered structures with a foamed core sandwiched by skin layers - played an important role in the surface quality and mechanical properties. The rather interesting and unusual cell morphology of PHBV/PBAT–N explains why the Young's modulus and ultimate strength are lower.
An Improved Analytical Model for the Elastic Constants of Auxetic and Conventional Hexagonal Honeycombs
Authors: Grima Joseph N. , Attard Daphne , Ellul Brian , Gatt Ruben
Published: September 2018

Cellular solids, in particular hexagonal honeycombs have been the subject of numerous studies in the last decades in view of their extensive use in many applications. In particular, there have been various studies aimed at expressing the mechanical properties of honeycombs in terms of the geometrical parameters used to describe the structure of such honeycombs. Despite improvements over the first established model, finite element simulations performed in this work on honeycombs having ribs with a realistic thickness-to-length ratio suggest that the mechanical properties for such systems differ from those predicted by current models, sometimes to a very significant extent. In view of this, we analyse in detail the deformed structures in an attempt to gain insight into how and the extent to which the shape of the ligaments, in particular its thickness and mode of connection affects deformation in conventional and re-entrant hexagonal honeycombs. Based on these observations, we propose a modified version of the previous analytical models that take into consideration the finite thickness of the ligaments.
Thermal Conductivity of Closed-cell Microcellular Ethylene-Octene Copolymer Foams
Authors: Nayak Nimai C.
Published: September 2018

The thermal conductivity of the unfilled as well as aluminium silicate, CaCO3 and silica filled systems have been studied by guarded hot plate method. It is observed that thermal conductivity of both unfilled and filled vulcanizates decreases with decrease in volume fraction of the solid, which is due to presence of air bubbles. The thermal conductivity values of both solid and microcellular vulcanizates varies in order of aluminium silicate filled > CaCO3filled >silica filled >unfilled. This can be attributed to the variation in thermal conductivity values of the fillers, which are in the order aluminium silicate > CaCO3> silica. The results reveal that the thermal conductivity (k) of microcellular ethylene-octene copolymers does not follow the theoretical model equation. The experimental values are found to be higher than that of the theoretical values for both unfilled and filled systems. This can be attributed to the stretching of polymer matrix during expansion. With increase in temperature, the thermal conductivity of both unfilled and filled vulcanizates decreases. This may be due to the increase in free volume with rise in temperature, which decreases the inter-chain coupling and hence, increases the resistance to energy transfer between the molecules resulting in the decrease of thermal conductivity.
Fabrication of Microcellular PP-MMT Nanocomposite Foams in a Sub-Critical CO2Process
Authors: Dolomanova Viktoriya , Kumar Vipin , Pyrz Ryszard , Madaleno Liliana A.O. , Jensen Lars R. , Rauhe Jens Ch. M.
Published: September 2018

The present paper is dedicated to fabrication of microcellular PP-MMT nanocomposite foams blown by CO2at 3-7 MPa pressure range. XRD and TEM studies showed that MMT particles were well exfoliated upon PP-MMT nanocomposite processing, however presence of the nanoclay particles did not facilitate the foaming process, resulting in non-uniform cell structure and low expansion ratios. SEM images demonstrate that clay nanoparticles have not improved the foam morphology; and no nucleation effect of the clay was observed in the produced foams. These data were supported by DSC studies.
The Effect of Different Peroxide on LDPE Foam Properties in the Presence of Polyfunctional Monomers
Authors: Sipaut C.S. , Mansa R.F. , Yugis A.R. , Ibrahim M.N. Mohamad , Ariff Z.M. , Abdullah A.A.
Published: September 2018

The crosslinking promotion effect of different peroxide decomposition temperatures in the formation of crosslinked low density polyethylene/polyfunctional monomers (LDPE)/(PFM) foam was investigated. Two peroxides, namely Dicumyl Peroxide (DCP) and 2,5-Dimethyl-2,5-di(tert-butylperoxy) hexyne-3 (T145), were compared. This was conducted to establish a base performance for the T145 and would essentially open new grounds for work for higher temperatures crosslinking materials. From this work the results indicate that at similar peroxide concentrations, T145 gave a higher crosslinking level than DCP. Comparisons between DCP and T145 indicated that similar gel content was achieved by taking into account molar masses and radicals generated per peroxide molecule. It was determined that the curing cycle time of DCP alone could be reduced by approximately 67% by increasing the curing temperature from 165°C to 185°C. Polyfunctional monomers containing allylic groups, which can generate allylic and alkyl radicals, appeared to be significantly more effective than methacrylates, which generate only alkyl radicals. Foaming behaviour can be predicted from the swell ratio obtained from testing solid crosslinked polymers while the more traditional predictive parameters, gel content and melt modulus, are not universally applicable. Irrespective of peroxide, curing temperature and polyfunctional monomer type and concentration, foam density is shown to be a function of swell ratio. Independent of the type of peroxide, crosslinking promotion was shown to be in the order of TAC > DALP > TMPTMA where the latter actually suppressed crosslinking at higher peroxide concentrations.
Fracture Behavior of Closed-cell Polyvinylchloride Foam Subjected to Low-velocity Impact
Authors: Rizov V.
Published: September 2018

Mode I impact fracture experiments were carried-out on three grades of Divinycell foam using single edge notched bend (SENB) specimens. A drop-weight rig was used to perform the low-velocity impact fracture tests. SENB specimens were tested at various impact potential energies by varying the drop-height in order to determine the critical impact potential energy at which the crack growth initiates from the notch tip. Three-dimensional linear-elastic finite element simulations of impact behavior of the SENB specimen were carried-out. The virtual crack closure technique was applied to analyze the strain energy release rate under impact loading. The mode I impact fracture toughness was characterized in terms of the critical dynamic strain energy release rate at the onset of crack growth from the notch tip. It was found that the impact fracture toughness increases rapidly with increasing the foam density. SENB specimens were tested also under static loading. The mode I static fracture toughness was extracted from the test data by the virtual crack closure technique in conjunction with finite element simulations. It was found that the impact fracture toughness is between 20.5% and 28.2% lower than the static one for the different grades. This finding indicates that the static fracture toughness should not be used in the fracture mechanics based design of rigid foam structures which are subjected to impact loading during their lifetime.
Foams and Wood Composite Foams Produced by Rotomolding
Authors: Raymond Alexandre , Rodrigue Denis
Published: September 2018

In this work, a simple method is presented to produce foams and wood composite foams by rotational molding. As a special case, wood flour (maple) / linear low density polyethylene (LLDPE) was used to study the effect of chemical blowing agent (CBA) concentration (0-0.6%wt.) and wood content (0-20%wt.). From the samples produced, a complete characterization was performed including density, morphology, and mechanical properties in tension and flexion. The results show that tensile and flexural moduli increased with wood content, while tensile strength and elongation at break decreased. The optimum wood content was found to be around 20%wt. for the composites and around 0.4% wt. CBA for the range of conditions studied.
New Class of Brominated Polymeric Flame Retardants for use in Polystyrene Foams
Authors: Beach Mark W. , Beaudoin Daniel A. , Beulich Inken , Bloom J. Chris , Davis John W. , Hollnagel Heli M. , Hull John W. , King Bruce , Kram Shari , Lukas Christine , Matteucci Michal , Morgan Ted , Stobby Bill
Published: September 2018

Flame retardant producers and end users are continually looking for more sustainable solutions through innovation in their customer offerings. Successful solutions need to satisfy a range of characteristics, from processing to technical and environmental performance, which sometimes conflict. This paper covers a new class of brominated polymeric flame retardants designed and developed by The Dow Chemical Company for use in polystyrene foam to meet existing fire and use requirements and have an improved environmental profile to meet regulatory guidelines. An overview of the environmental, health and safety performance of these new polymeric flame retardants will be presented along with preliminary performance data of their use in polystyrene foam.
A Novel Approach in Mold Design in Regards to Weight Reduction of Foam Injection Molded Parts
Authors: Ahmadzai Ahmad Zia , Behravesh Amir Hossein , Shahi Peyman
Published: September 2018

This paper presents an experimental study on the mold design and the effect of processing parameters on the expansion of foam injection molded parts. Plastic foaming technology has been developed for producing light weight articles along with reducing shrinkage, warpage and sink marks. Limitation in foam expansion is a primary challenge in foam injection molding process. The processing parameters have limited effects on the expansion ratio (or relative density) and cell population density of foam. In this study a novel approach in mold design is introduced to take advantages of concepts such as counter-pressure and mold opening to further extend the expansion range. A modular sheet mold with a rectangular cavity and a fan gate was designed and manufactured. The mold includes a main cavity, the thickness of which could be varied, connected to an overflow channel via a secondary gate, the size of which was also varied in this research. The investigated parameters were part thickness, secondary gate width, blowing agent amount, injection pressure, mold temperature and part thickness. Two-level test experiments were carried out in this research work. The results indicated the high effectiveness of the proposed approach in further reducing the foamed part weight. For the parts with a larger thickness, a noticeable decrease in bulk density and an increase in cell population density along with an improvement in cellular structure uniformity were observed. The expansion was increased as the chemical blowing agent content increased. Other investigated processing parameters, such as injection pressure and mold temperature, had insignificant effects on the relative bulk density within the selected range.
A Novel Method to Deliver Natural Fibre for Mechanical Reinforcement of Polyurethane Foam
Authors: Hussain Sadakat , Kortschot Mark
Published: September 2018

Introducing glass fibre to polyurethane foams increases the foam stiffness without raising the isocyanate content. This allows glass fibre reinforced polyurethane foams to be used in structural applications. Glass fibre reinforced polyurethane foams can be manufactured on a large scale using a chopper gun spray system. The glass fibre is commonly supplied as a roving (long strands of fibre wound into a spool) and the chopper gun breaks the roving into equal length pieces, which delivers a stream of glass fibre at a constant mass flow rate. Residual natural fibre is cost-effective, abundant and renewable making it an ideal candidate to replace non-renewable glass fibre in reinforcing polyurethane foam. However, residual natural fibre are often supplied as loose tufts and require multiple steps to be made into roving. In this study, a novel concept was developed that can meter natural fibre at a constant mass flow rate. The concept has the potential for developing natural fibre reinforced polyurethane foams on a large scale, with uniform fibre dispersion and high fibre volume fractions. The concept is verified through mathematical simulations and a prototype.
Mixed-Mode II/III Fracture in Foam Core Sandwich Beams
Authors: Rizov V.
Published: September 2018

This paper is motivated by the fact that no mixed-mode II/III fracture studies of foam core composite sandwich beams were found in the literature available. In order to generate mixed-mode II/III crack loading conditions, it is proposed here to load an End-Loaded Split (ELS) foam core composite sandwich beam in torsion and bending by applying a transversal load at one of the beam corners. The fracture behavior was studied theoretically using the methods of linear-elastic fracture mechanics. The strain energy release rate mode components distribution along the crack front was analyzed by the virtual crack closure technique. For this purpose, three-dimensional linear-elastic finite element simulations of the ELS foam core sandwich beam configuration were performed. The analysis yielded non-uniform distribution of the strain energy release rate mode components along the crack front. The influence of the sandwich beam core material on the mixed-mode II/III fracture was studied assuming that the core is made by three different rigid cellular foams. The mixed-mode I/II/III fracture was analyzed too. The results obtained indicate that the mixed-mode II/III and the mixed-mode I/ II/III fracture performance of the sandwich beam can be improved using a foam core with higher density.
Effect of Trolamine and Dibutyltindilaurate on the Structure and Properties of Polyurethane-imide Foams
Authors: Wang Yaru , Tian Huafeng , Bian Qibo , Xiang Aimin , Ge Xiang , Liu Qian
Published: September 2018

Polyurethane-imide foams are prepared from polyphenyl polymethylene polyisocyanates, pyromellitic dianhydride and castor oil in presence of trolamine and dibutyltindilaurate catalysts. FTIR spectra proves the successful preparation of polyurethane-imide foams in prepolymer method. The investigation on catalytic mechanism shows that trolamine and dibutyltindilaurate are effective in promoting blowing and gelling reaction, respectively, so trolamine and dibutyltindilaurate are identified to be blowing catalyst and gelling catalyst, respectively. With the fixed amount of trolamine, the density and compressive strength of the resulting foams are enhanced with the increase of dibutyltindilaurate, but average cellular diameter and open cell contents are reduced. Similarly, with the fixed amount of dibutyltindilaurate, open cell contents of the resulting foams are enhanced with the increase of trolamine, while the density, compressive strength and average cellular diameter decreased. Thus PUIFs with variable properties can be prepared through changing the kind and ratio of mixed catalysts.
Compressive Properties of Syntactic Foam Reinforced by Warp-knitted Spacer Fabric
Authors: Zhi Chao , Long Hairu
Published: September 2018

Syntactic foam composites are widely used as aviation, construction and marine materials because of their high specific strength, specific modulus, damage tolerance and low moisture absorption. The present work aimed to investigate the compression behaviours of syntactic foam reinforced by warp knitted spacer fabric (SF-WKSF). Eight kinds of SF-WKSF samples were produced with warp knitted spacer fabrics of various surface layer structures and parameters including inclination-angle, fineness of spacer yarns, different microballoons types as well as contents. The compression tests were carried out on aMTS material testing system and the compression properties of SF-WKSF were analyzed based on the experimental compressive stress-strain curves and modulus values. It was indicated that the SF-WKSF made with preferable spacer fabric showed higher compressive modulus and yield strength values compared to neat syntactic foam (NSF). The results also demonstrated that all the parameters had significant effects on the compression performances of SF-WKSF. The composites could gain better anti-compression capacities by selecting larger inclination-angle, coarser spacer yarn, denser surface layer structure, higher microballoon density and higher S60HS microballoon contents.
A Green and Structure-Controlled Approach to the Generation of Silicone Rubber Foams by Means of Carbon Dioxide
Authors: Xu Hao , He Yunchuan , Liao Xia , Luo Tinggang , Li Guangxian , Yang Qi , Zhou Chuanjian
Published: September 2018

Silicone rubber foams were successfully generated by environmentally friendly blowing agent, supercritical carbon dioxide (scCO2), in this research. Firstly, the effect of the saturation time on the cellular structure was investigated. The diffusion of scCO2 into the rubber matrix would be enhanced thus decreasing the viscosity as increasing the saturation time. It would further promote the cell growth, which has a close connection with the cellular structure. After that, the effect of pre-curing time on cellular morphology of silicone rubber foams was further researched in detail. When increasing pre-curing time in the short time range, cell nucleation would be affected more than cell growth in the foaming process. If continuously increasing pre-curing time, both cell nucleation and growth would be restricted thus resulting in the formation of silicone rubber foams with small cell density and small cell size. This investigation not only provided a green way to produce silicone rubber foams, but also guided us to control cellular morphology via the saturation time and pre-curing time.
Fractional Derivative and Hereditary Combined Model of Flexible Polyurethane foam Viscoelastic Response under Quasi-Static Compressive Tests
Authors: Elfarhani Makram , Jarraya Abdessalem , Abid Said , Haddar Mohamed
Published: September 2018

The flexible polyurethane foam exhibits a highly nonlinear and viscoelastic behavior under quasi-static and uni-axial compressive tests. The dependence of the displacement rate during the loading phase is significantly higher than that of the unloading phase. A new identification of the Force-Displacement curve based on experimental observations is proposed. The total foam response is modeled as a sum of a nonlinear elastic component and a viscoelastic component. The elastic force is modeled as a sum of orthogonal polynomials in displacement, while the viscoelastic force is modeled according to the hereditary approach in the loading half-cycle and the fractional derivative approach in the unloading half-cycle. The objective of this paper is to develop a model able to make predictions of the total foam force as well as simulations of its components. A parameter calibration procedure is established according to the difference force method between two unloading responses corresponding to two different displacement rates of the same foam sample. The validity of the model results is discussed by addressing three efficiency requirements: the accuracy of simulations to experimental measurements, the repeatability of results for both tests, and the accordance of predicted components of the total response with the phenomenological identification of the Force-Displacement curve. The proposed optimization methodology is found to simulate reasonably well the responses of three different types of soft foam. Some morphologic characteristics of these foams have clear influence on viscoelastic damping and residual effects.
Influence of Processing Conditions on the Morphological Structure and Ductility of Water-Foamed Injection Molded PP/LDPE Blended Parts
Authors: Zhou Ying-Guo , Su Bei , Turng Lih-Sheng
Published: September 2018

Water-foamed injection molding (WFIM) uses conventional injection molding (CIM) with water as a physical foaming agent. Compared to CIM, WFIM is a much more complicated process. As such, it is critical to determine the processing conditions for fabricating quality parts using WFIM. We used the design of experiment (DOE) method based on the Taguchi method to determine the influence of the processing conditions on the morphological structure and ductility of PP/LDPE WFIM parts, which were investigated by tensile testing and scanning electron microscopy (SEM). Our research suggests that fabricating PP/LDPE super-ductile parts using WFIM is indeed feasible. Our research also indicates that there is a close relationship between the ductility and the foamed structures, both of which are deeply influenced by the processing conditions. The analysis of variance results shows further that the water content had the greatest influence on the ductility, followed by the melt temperature, packing time, packing pressure, and PP/LDPE ratio. However, the ductility was only slightly influenced by the mold temperature, injection pressure, and injection time in WFIM. As to the number of cells, the order of influence was melt temperature, water content, packing time, packing pressure, mold temperature, injection pressure, PP/LDPE ratio, and injection time, in that order. In addition, applying DOE is a quite effective method for deducing the optimal set of effective factors in WFIM to produce super-ductile parts with a maximum number of cells. To our knowledge, this is the first time that the relationship among the processing conditions, ductility, and foamed structure of PP/LDPE WFIM super-ductile parts has been investigated and reported.
Compression Properties of Syntactic Foam Reinforced by Warp-knitted Spacer Fabric: Theoretical Compression Strength Model and Experimental Verification
Authors: Zhi Chao , Zhu Guoqing , Meng Jiaguang , Jiang Jinhua , Long Hairu , Yu Lingjie
Published: September 2018

In this study, a theoretical model based on the fiber buckling theory was established to predict the compression strength of a new type of syntactic foam, namely the syntactic foam reinforced by the warp-knitted spacer fabric (SF-WKSF). In order to verify the availability of this model, compression strength values of theoretical simulations were compared with the experiment results. The comparison results showed that the model can accurately simulate the compression strength values of different SF-WKSF samples with slight deviation. Finally, the causes of deviation was analyzed in detail.
Multi-Stage Recycling Induced Morphological Transformations in Solid-State Microcellular Foaming of Polystyrene
Authors: Singh Indrajeet , Gandhi Abhishek , Biswal Manoranjan , Mohanty Smita , Nayak S. K.
Published: September 2018

In this article, the general-purpose polystyrene was reprocessed four times. The effect of repeated reprocessing of polystyrene on its polymeric properties and on its microcellular, foaming behaviour were investigated. It was observed that reprocessing leads to break of long polymeric chains into short chains, which resulted increment in PDI and MFI. Molecular weight and Glass transition temperature were found to decrease with increasing recycling stages. Reprocessing resulted abruptly decrement in viscosity of neat polystyrene. Effect of reprocessing on foaming behaviour was analysed properly in this report and it was found that reprocessing resulted in improvement in cell sizes and their distribution. A positive effect on expansion ratio was also observed during foaming of reprocessed specimens. Cell density was found to decrease with increasing recycling stages. The effect of saturation pressure and foaming temperature on microcellular foam morphology along with recycling were investigated. Effect of foaming time on cell size, cell size distribution, cell density, expansion ratio and cell wall thickness was investigated.
How is sexuality after stroke experienced by stroke survivors and partners of stroke survivors? A systematic review of qualitative studies
Authors: McGrath Margaret , Lever Sandra , McCluskey Annie , Power Emma
Published: September 2018

Objective:

To synthesise how post-stroke sexuality is experienced by stroke survivors and partners of stroke survivors.

Methods:

MEDLINE, PubMed, SCOPUS, CINAHL and PsycINFO were searched from inception to May 2018 using a combination of relevant Medical Subject Headings and Free Text Terms. Only papers published in English reporting original qualitative research were included. Methodological quality was assessed using the Critical Appraisal Skills Programme Qualitative Research Checklist. All text presented as ‘results’ or ‘findings’ in the included studies was extracted and subjected to a thematic analysis and synthesis which was discussed and agreed by the research team.

Results:

The initial search yielded 136 unique papers with a further 8 papers identified through reference checking. Following full-text review, 43 papers were included in the final synthesis. Two analytical themes were identified: sexuality is silenced and sexuality is muted and sometimes changed, but not forgotten. These themes were made up of six descriptive themes: struggle to communicate within relationships, health professionals don’t talk about sexuality, sexuality and disability is a taboo topic, changes to pre-stroke relationships, changed relationship with the stroke survivor’s own body and resuming sexual intimacy – adaptation and loss.

Conclusion:

Stroke has a profound impact on how sexuality is experienced by both stroke survivors and partners of stroke survivors. Despite this, post-stroke sexuality is rarely discussed openly. Stroke survivors and partners value sexuality and may benefit from strategies to support adjustment to post-stroke sexuality.
Rapid effectiveness of intravenous ketamine for ultraresistant depression in a clinical setting and evidence for baseline anhedonia and bipolarity as clinical predictors of effectiveness
Authors: Thomas Rejish K , Baker Glen , Lind John , Dursun Serdar
Published: September 2018

Background:

Intravenous ketamine has been established as an efficacious and safe treatment, with transient effect, for treatment-resistant depression. However, the effectiveness of intravenous ketamine in non-research settings and with ultraresistant depression patients remains understudied.

Aims:

This study aims to measure the response and remission rates in ultraresistant depression patients in a clinical setting by means of a retrospective, open label, database study. Secondarily, the study will attempt to support previous findings of clinical predictors of effectiveness with intravenous ketamine treatment.

Methods:

Fifty patients with ultraresistant depression were treated between May 2015–December 2016, inclusive, in two community hospitals in Edmonton using six ketamine infusions of 0.5 mg/kg over 40 min over 2–3 weeks. Data were collected retrospectively from inpatient and outpatient charts. Statistical analysis to investigate clinical predictors of effectiveness included logistic regression analysis using a dependent variable of a 50% reduction in rating scale score at any point during treatment.

Results:

At baseline, the average treatment resistance was severe, with a Maudsley Staging Method score of 12.1 out of 15, 90.0% were resistant to electroconvulsive therapy, and the average Beck Depression Inventory score was 34.2. The response rate was 44% and remission rate was 16%. As a single predictor, moderate or severe anhedonia at baseline predicted a 55% increased likelihood of response. As a combined predictor, this level of anhedonia at baseline with a diagnosis of bipolar depression predicted a 73% increase in likelihood of response.

Conclusion:

In a clinical setting, intravenous ketamine showed effectiveness in a complex, severely treatment-resistant, depressed population on multiple medication profiles concurrently. This study gave support to anhedonia and bipolar depression as clinical predictors of effectiveness.