Cross-linked PVC Foam Research Articles

Preparation and Properties of a Lightweight, High-Strength, and Heat-Resistant Rigid Cross-Linked PVC Foam.

A rigid poly(vinyl chloride) foam with a cross-linked network structure was prepared by adding 3-glycidoxypropyltriethoxysilane (KH-561) into the universal formulation. The resulting foam had excellent heat resistance because of the increasing degree of cross-linking and number of Si-O bonds with a high heat resistance. The as-prepared foam was verified using Fourier-transform infrared spectroscopy (FTIR), energy-dispersive spectrometry (EDS) and foam residue (gel) analysis, which demonstrated that KH-561 was successfully grafted and cross-linked on the PVC chains. Finally, the effects of different KH-561 and NaHSO3 additions on the mechanical properties and heat resistance of the foams were studied. The results showed that the mechanical properties of the rigid cross-linked PVC foam were raised after adding a certain amount of KH-561 and NaHSO3. The residue (gel), decomposition temperature, and chemical stability of the foam significantly improved compared to the universal rigid cross-linked PVC foam (Tg = 72.2 °C). The Tg of the foam could reach 78.1 °C without any mechanical degradation. The results have important engineering application value regarding the preparation of lightweight, high-strength, heat-resistant, and rigid cross-linked PVC foam materials.

Introduction and Influence of Water in the Preparation of Crosslinked PVC Foam by Isocyanate

Introduction and Influence of Water in the Preparation of Crosslinked PVC Foam by Isocyanate

Preparation of rigid cross-linked PVC foam with excellent thermal insulation through adding high-reflectivity IR opacifier

For polymer foams with low-density, the thermal radiation propagating through the foam still contributes significant to the total thermal transfer. It is very promising to enhance the absorption or reflection of IR radiation by the foam matrix. However, it is still a question which of the reflected infrared or absorbed infrared is more effective in reducing radiative thermal conductivity. In this work, we studied theoretically and experimentally the effectiveness to reduce the radiative thermal conductivity of polymer foams by reflection mode and absorption mode. The relationship between the optical parameters of foam and the heat radiation transmission in the foams was quantitatively investigated. It was found that, taking into account the re-emission, the radiative thermal conductivity was further reduced merely by increasing the absorption coefficient, but in theory it could continue to drop to zero by increasing the reflection fraction. Both the flake aluminum powder (FAP) that mainly reflects infrared and the flake graphite powder (FGP) that mainly absorbs infrared were added to the rigid cross-linked PVC (c-PVC) foam. The results demonstrated that the reduction of radiative thermal conductivity of the c-PVC foam with FAP was more significant than of the c-PVC foam with FGP. The experimental results were in good agreement with the theoretical prediction.

The energy-absorbing behaviour of composite tube-reinforced foams

Abstract This paper investigates the energy-absorbing characteristics of composite tube reinforced PVC foam cores for use in lightweight impact-resistant sandwich structures. Compression tests have been conducted on crosslinked PVC foam cores with densities ranging from 40 to 130 kg/m3, reinforced with both glass fibre and carbon/glass fibre composite tubes. The energy-absorbing capability of these reinforced foams was evaluated by determining the specific energy absorption of each configuration. The mechanical response of the tube-reinforced foams was also modelled using the finite element method. The validated models shown good agreement with the experimental data, with the model accurately predicting the compressive responses and failure characteristics in the samples. Drop-weight impact tests have also been undertaken in order to investigate their dynamic performance and ability to absorb energy under crash conditions. It has been shown that embedding the tubes in a foam panel serves to modify the failure process occurring within the composite tubes, greatly enhancing their ability to absorb energy. However, when normalized by the mass of the test sample, the SEA values of the hybrid tube reinforced foams were found to be largely insensitive to variations in foam density, suggesting that reinforced low density foams, where the associated crushing forces are low, are best suited to energy-absorbing applications. In contrast, the SEA data for the unidirectional glass tube reinforced systems steadily increase with increasing foam density. The dynamic values of SEA for the tube-reinforced systems were lower than those measured at quasi-static rates, suggesting a rate-sensitivity in the fracture processes within the composite. Finally, it is shown that the energy-absorbing capability of tube-based foams is higher than many comparable core systems, where their potential for use under conditions of extreme crushing are highlighted.

A numerical study of the energy-absorption characteristics of metal tube-reinforced polymer foams

This article investigates the energy-absorbing behaviour of lightweight foam structures reinforced with aluminium and steel cylindrical tubes. Initial testing focuses on establishing the influence of the inner diameter to thickness ratio ( D/ t) of the metal tubes on their specific energy-absorption characteristics under quasistatic compression and low velocity impact loading. Following this, individual metal tubes are embedded in a range of crosslinked PVC foams, and the specific energy-absorption characteristics of these reinforced systems are determined. The effect of increasing the number of tubes on the energy-absorbing response of the tube-reinforced structures is also studied. The crushing responses of both aluminium and steel structures are then predicted using the finite element analysis package Abaqus/Explicit, and the predictions of the load–displacement responses and the associated failure modes are compared to experimental results. Agreement between the numerical predictions and the experimental data is good across the range of structures investigated, with the model accurately predicting the compression response and failure characteristics observed in the structures. It has been shown that the stiffness of the foam does not significantly alter the energy-absorbing behaviour of the stiffer metal tubes, suggesting that the density of the foam should be as low as possible, whilst maintaining the structural integrity of the part.

Full-field shear analyses of sandwich core materials using Digital Image Correlation (DIC)

Mechanical properties and global stability of foam core sandwich structures are highly controlled by the shear response of the core material. In this work, we have studied the shear deformations of three common structural core materials with the aid of full-field optical analysis. The chosen core materials are namely extruded PET foam (ρ=105kg/m3, Gxz=21MPa,) and cross-linked PVC foam (ρ=60kg/m3, Gxz=22MPa) which have comparable shear properties, as well as Balsa wood with the lowest density commercially available (ρ=94kg/m3, Gxz=106MPa) as a reference core material. Both global and local shear strains in the core materials are calculated and graphically visualized. In the elastic region, foam cores showed more uniform deformations than Balsa. Yielding and shear failure of the two foam core materials were quite different. The PVC foam experienced a high local deformation under the load introduction bars, from which sub-interface shear failure initiated. The PET foam, in contrast, showed no sign of stress concentrations, resulting in a homogenous evolution of shear deformations in the mid-core regions. A comparison between the direct foam shear test and sandwich specimen bending suggested that the former method might not be capable of capturing a full picture of the in-service core shear response.

The energy-absorption characteristics of metal tube-reinforced polymer foams

This paper presents a study on the potential offered by lightweight energy-absorbing foam structures reinforced with aluminium and steel cylindrical tubes subjected to compressive crushing. Initially, attention was focused on establishing the influence of the length as well as the diameter to thickness ratio of the metal tubes on the specific energy absorption (SEA) characteristics. The metal tubes were then embedded in a range of cross-linked PVC foams to investigate how the stiffness of the foam influences the SEA of the tubes and the failure modes. The results show that aluminium tubes offer a superior energy-absorbing capability relative to their steel counterparts and the SEA of the metal tubes remains roughly constant with an increase in the tube length. The energy-absorbing capability of the two types of metal tubes increased with decreasing value of inner diameter/thickness ratio. Small D/t tubes were also embedded into a range of polymer foams and tested at both quasi-static and dynamic rates of strain. It has been shown that that the stiffness of the foam does not modify the energy-absorbing behaviour of the metal tubes. This evidence suggests that it should be possible to predict the response of an energy-absorbing system containing an array of tubes using a simple rule of mixtures approach. The output of this study provides useful data on core materials for sandwich construction.

The energy-absorbing behaviour of foam cores reinforced with composite rods

This paper investigates the energy-absorbing characteristics of composite reinforced PVC foam cores for use in lightweight impact-resistant sandwich structures. Compressive tests have been undertaken on crosslinked PVC foam cores with densities ranging from 40 to 200kg/m3, reinforced with carbon fibre and glass fibre rods with nominal diameters of 2,3 and 4mm. It has been shown that the compression strength of the reinforced foams can be optimised through the correct selection of rod arrangement and foam density.A limited number of drop-weight impact tests were also conducted on selected samples to investigate their dynamic performance. Here, it was shown that increasing the volume fraction of rods above 2.5% has little effect on the measured SEA of the two types of reinforced foam. Finally, a theoretical analysis has been undertaken to predict the peak load and the corresponding compressive displacement of the reinforced PVC foam cores.

Rigid cross-linked PVC foams with high shear properties: The relationship between mechanical properties and chemical structure of the matrix

Semi-IPN PVC foams with cross-linked polyurea network modified by epoxy resin (E51) were prepared in this work. Chemical structure and H-bonding of the foam matrix were characterized by FTIR. The effects of E51 content in the starting mixtures on tensile, compressive and shear properties of the resultant foams were studied. The changing trend of energy absorption capacities of the foams showed an inflection point at the content of 2 wt% E51. In this case, the foam with the density of 65 kg/m3 presented a 35% shear failure strain with shear modulus of 25 MPa and shear strength of 1.05 MPa. Its energy absorption capacity was 1.8 times as that of the foam without E51. The relationship between mechanical properties and chemical structure of the matrix was discussed.

The energy-absorbing characteristics of polymer foams reinforced with bamboo tubes

This paper investigates for the first time, the energy-absorbing characteristics of a range of lightweight bamboo-reinforced foam structures. Initial attention focuses on characterizing the energy-absorbing characteristics of the individual bamboo tubes and assessing the influence of tube geometry on energy absorption. Here, it has been shown that the specific energy absorption of the bamboo tubes decreases with increasing tube length as a result of axial splitting associated with barreling of the samples under compressive loading. The influence of the tube inner diameter/thickness (D/t) ratio was also investigated using a number of tube sizes, where it was shown that there is a small increase in specific energy absorption with decreasing D/t. The tubes were then embedded in crosslinked PVC foams in order to investigate the influence of varying degree of external support applied to the reinforcement on the failure modes in the tubes as well as the measured specific energy absorption values. Finally, alternative techniques for enhancing the energy-absorbing capacity of the tubes were investigated. Here, tubes of different length were wrapped circumferentially in epoxy-impregnated kenaf fibers to enhance their resistance to axial spitting. It was shown that reinforcing the tubes in this manner can significantly enhance the ability of the tubes to absorb energy under conditions of axial quasi-static crushing.

Study of Rigid Cross-Linked PVC Foams with Heat Resistance

Three heat resistant cross-linked PVC foam plastics were prepared and their performances were compared with universal cross-linked PVC structural foam. The results show that these three heat resistant foams have higher glass transition temperatures (close to 100 °C) than universal structural foam (83.2 °C). Compared with the universal structural foam, the three heat resistant foams show much higher decomposition temperature and better chemical stability due to the crosslinking of PVC macromolecular chains. The heat distortion temperature (HDT) values of the three heat resistant foam plastics are just a little higher than that of universal structural foam. The three heat resistant foam plastics have good dimensional stability at 140 °C, and when used as core material can closely adhere to the face plates in medium temperature curing processes. Compared with universal structural foam, the three heat resistant foam plastics have slightly better mechanical properties.

The perforation resistance of sandwich structures subjected to low velocity projectile impact loading

AbstractThis article presents the findings of a study to investigate the impact perforation resistance of sandwich structures. The dynamic response of sandwich panels based on PVC foam cores has been evaluated by determining the energy to perforate the panels. The impact response of the sandwich structures was predicted using the finite element analysis package Abaqus/Explicit. The validated FE models were also used to investigate the effect of oblique loading and to study the impact response of sandwich panels subjected to a pressure differential equivalent to flying at an altitude of 10,000m.Low velocity impact testing has shown that the energy to perforate the sandwich panels is dependent on the properties of the core. It has been shown that increasing the density of the crosslinked PVC foams by a factor of two yielded a 600% increase in the perforation resistance of the sandwich structures. At higher densities, the crosslinked foam sandwich structures offered a superior perforation resistance to the linear PVC structures. The numerical analysis accurately predicted the perforation energies of the sandwich panels, as well as the prevailing failure mechanisms following impact. Finally, it has been shown that sandwich panels impacted at high altitude offer a similar perforation resistance to those tested at sea level.

The low velocity impact response of foam-based sandwich panels

Abstract This paper describes the results of a combined experimental/numerical study to investigate the perforation resistance of sandwich structures. The impact response of plain foam samples and their associated sandwich panels was characterised by determining the energy required to perforate the panels. The dynamic response of the panels was predicted using the finite element analysis package ABAQUS/Explicit. The experimental arrangement, as well as the FE model were also used to investigate, for the first time, the effect of oblique loading on sandwich structures and also to study the impact response of sandwich panels on an aqueous support. Testing has shown that the perforation resistance of the plain foams and their sandwich panels is strongly dependent on the properties of the foam core. For example, increasing the density of the crosslinked PVC foams from 60 to 200 kg/m 3 yielded an eight fold increase in the perforation resistance of the sandwich panels. At intermediate and higher densities, the crosslinked PVC foams and their associated sandwich structures offered a superior perforation resistance to their linear PVC counterparts. The FE analysis reasonably predicted the impact load–displacement responses and the perforation energies of both the plain foams and the sandwich panels. Finally, it has been shown that sandwich panels impacted in an aqueous environment offer a lower perforation resistance than those tested in air.

Preparation and Properties of Rigid Cross-Linked PVC Foam

High performance rigid cross-linked PVC foam has been prepared by molding process and boiling foam process with the main materials including polyvinyl chloride paste resin (PVC), liquefied methylene bis-phenyl diisocyanate (MDI-L) and methylhexahydrophthalic anhydride (MHHPA). The chemical structure, cellular structure and thermal properties were respectively characterized by fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), thermomechanical analyzer (TMA) and thermogravimetric analyzer (TGA). Results showed that the foam had a uniform cellular structure, and cell size was about 760μm. The glass transition temperature (Tg) was 81°C and 5% weight loss temperature (T5d) was 252°C.

Finite element analysis of Carbon composite sandwich material with agglomerated Cork core

Composite sandwich structures were developed for the hydrofoil sail boat hull using biaxial carbon fabric/epoxy composite facing and agglomerated cork core. These ultra-light weight structures were tested through four point bending tests to characterize their flexural behavior. The material exhibited an initial linear elastic behavior followed by non-linear elastic-plastic behavior. Finite element analysis of the sandwich beams was performed to analyze the flexural behavior of the structure. It was found that the transition from linear elastic to non-linear elastic-plastic behavior is the result of compressive yielding of core material which leads to indentation in the beam. This also causes initiation of failure in the core. A shift in the centroid axis of the beam towards the tensile face was also observed. The sandwich structures made of cross-linked PVC and PMI foam cores were also analyzed for comparison. Further, a parametric study on the effect of areal density and ply angle of the facing fabric and core thickness were performed using finite element method. The parametric study revealed that the transition from linear to non-linear trend is caused by different mechanisms with the change in the mentioned parameters.

Polymer and composite foam for hydrogen storage application

Abstract Polymeric foams are a potential practical method of on-board vehicular hydrogen storage. The underlying concept by which these foams are being pursued is hydrostatic pressure retainment (HPR). An HPR pressure vessel uses a microscopic foam structure as a structural membrane to store the gas in enclosed cells. The accomplishments of this study were three-fold. First, ideal structural arrangements have proven to be a feasibly sound method for hydrogen storage. Second, an efficient methodology for examination of cellular polymers under internal pressure was developed. Third, this method was applied to two actual polymeric foams for examination as a hydrogen storage media. Cross-linked PVC foam and elastomeric polyurethane foam were chosen, neither of which will meet the hydrogen tank performance characteristic specified by the FreedomCAR project. The work of this study used scanning electron microscopy (SEM), X-ray computed micro-tomography (micro-CT), compression testing, rapid prototyping and finite element methods (FEM).

High Strain Rate Response of Cross-Linked and Linear PVC Cores

The compressive response of cross-linked and linear PVC foam core materials, namely, H130 and HD130 having identical densities were evaluated. Both cores were subjected to compressive loading at various strain rates ranging from quasi-static to 1560 s1. At quasi-static loading, the compressive strength of the H grade was approximately 30% higher than the HD grade. On the other hand, at HSR loading the HD grade was 20% higher. HSR tests were also conducted at various temperatures ranging from 25 to 12°C. It was observed that degradation of strength was more severe for the HD grade as temperatures increased. A recovery of the cores original volume was also noticed during high strain rate and elevated temperature tests. Accordingly, residual properties were determined. Results show that only the residual properties of the HD grade were affected by temperature.

Fatigue of Crosslinked and Linear PVC Foams under Shear Loading

When a sandwich structure is subjected to transverse loads, the face sheets carry bending moments as tensile and compressive stresses and the core carries transverse forces as shear stresses. The core is typically the weakest component of the structure and is the first to fail in shear. In this study the shear fatigue behavior of two closed-cell cellular PVC foams, Divinycell HD130 (linear) and H130 (cross linked), with the same nominal density of 130 kg/m3, were investigated. Static shear tests reveal that HD130 foams are more ductile, have almost twice the energy absorption capability, and an extraordinary crack propagation resistance when compared to the H130 foams. Shear fatigue tests were conducted at room temperature, at a frequency of 3 Hz and at a stress ratio, R = 0.1 on the HD130 and H130 foams. S–N curves were generated and shear fatigue characteristics were determined. The number of cycles to failure for the linear foams was substantially higher than that of the cross-linked PVC foams. HD foams have smaller cells with thicker faces and edges. This microstructure supports absorption of larger amounts of liquid resin forming a resin rich sub interface zone just below the actual core skin interface. The high intrinsic toughness of the sub interface delays the initiation of fatigue cracks and thereby increases the fatigue life of the HD foams. For both foams, shear deformation occurs without volume change and the materials fail by shearing in the vicinity of the centerline of the specimen along the longitudinal axis. In both cases numerous 45° shear cracks form across the width of the specimen and are equidistantly spaced along the length of the specimen. The occurrence of these through the thickness shear cracks signals the final failure event during fatigue. Details of the experimental investigation and the evaluation of the fatigue performance are presented.

Static and Dynamic Characterization of Polymer Foams Under Shear Loads

When a sandwich structure is subjected to transverse loads, the face sheets carry bending moments as tensile and compressive stresses and the core carries transverse forces as shear stresses. The core is typically the weakest component of the structure and is the first one to fail in shear. In this study the shear fatigue behavior of two closed-cell cellular PVC foams, Divinycell HD130 (linear) and H130 (cross-linked), with the same nominal density of 130 kg/m3, were investigated. Static shear tests reveal that HD130 foams are more ductile, have almost twice the energy absorption capability, and an extraordinary crack propagation resistance when compared to the H130 foams. Shear fatigue tests were conducted at room temperature, at a frequency of 3 Hz and at a stress ratio, R=0.1 on the HD130 and H130 foams. S–N curves were generated and shear fatigue characteristics were determined. The number of cycles to failure for the linear foams was substantially higher than that of the cross-linked PVC foams. HD foams have smaller cells with thicker faces and edges. This microstructure supports absorption of larger amounts of liquid resin forming a resin rich subinterface zone in the core. The high-intrinsic toughness of the subinterface delays the initiation of fatigue cracks and thereby increases the fatigue life. For both foams, shear deformation occurs without volume change and the materials fail by shearing in the vicinity of the centerline along the longitudinal axis. In both cases numerous 45° shear cracks form along the length and across the width of the specimen immediately prior to the final failure event. Details of the experimental investigation and the evaluation of the fatigue performance are presented.

Influences of Foam Density and Core Thickness on Debond Toughness of Sandwich Specimens with PVC Foam Core

Face/core debond toughness, expressed as the critical strain energy release rate (Gc), was determined for sandwich specimens with composite and aluminum face sheets over various cross-linked PVC foam cores. Crack propagation occurred in the core, near the face/core interface for specimens with adequate face/core adhesion. Only for the highest density foam it was possible to propagate the crack in the immediate vicinity of the actual core/resin interface. The face/core debond toughness increased with increased foam density and reduced core thickness. For thick cores, the face/core toughness was independent of the core thickness.