Cross-linked PVC Research Articles

Synthesis and characterization of modified PVC waste with different diamines for Hg(II) removal

PVC waste, after removing contamination (P1), was cross-linked with 1,3-diaminopropane, hexamethylenediamine and 1,4-diaminonaphthalene (P2, P3 and P4). The cross-linked PVC was characterized by FTIR, SEM and CHN elemental analysis. The influence of the type of crosslinking agent on the thermal properties and swelling of PVC was also investigated. P3 was characterized by the highest water absorption, and P4 had the best thermal stability. All cross-linked polymers showed good effectiveness in removing Hg(II) ions, especially PVC modified with hexamethylenediamine.

Feedstock recycling of cable plastic residue via steam cracking on an industrial-scale fluidized bed

The use of plastic materials in a circular way requires a technology that can treat any plastic waste and produce the same quality of product as the original. Cable plastic residue from metal recycling of electric wires is composed of cross-linked polyethene (XLPE) and PVC, which is a mixture that cannot be mechanically recycled today. Through thermochemical processes, polymer chains are broken into syngas and monomers, which can be further used in the chemical industry. However, feedstock recycling of such a mixture (XLPE, PVC) has been scarcely studied on an industrial scale. Here, the steam cracking of cable plastic was studied in an industrial fluidised bed, aiming to convert cable plastics into valuable products. Two process temperatures were tested: 730 °C and 800 °C. The results show that the products consist of 27–31 wt% ethylene and propylene, 5–16% wt.% other linear hydrocarbons, and more than 10 wt% benzene. Therefore, 40%–60% of the products are high-value chemicals that could be recovered via steam cracking of cable plastic.

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.

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.

Preparation of cross-linked PVC-g-(St-MA) copolymer/organoclay nanocomposites and investigation of chemical characteristics, morphology, thermal, and mechanical properties

The goal of this work is to investigate the effect of incorporating organoclays on the cross-link structure, morphology, and thermomechanical properties of cross-linked organoclay/polyvinyl chloride grafted with styrene and maleic anhydride (PVC- g-(St-MA)) copolymer nanocomposites (CPN). Cloisite30B (C30B) and Cloisite15A (C15A) organoclays were used for the preparation of cross-linked PVC- g-(St-MA) nanocomposites by the solution mixing route. The nanoclay content in nanocomposites varied from 0.2 wt% to 1 wt%. The chemical structure and interaction between PVC- g-(St-MA) cross-linked segments and nanoclays were studied by Fourier transform infrared (FTIR) peaks deconvolution method. FTIR spectroscopy suggested the lowest extent of hydrogen bonding interaction for C30B containing sample, which decreased with clay content increment. The morphology of nanocomposites was studied by X-ray diffraction and transmission electron microscopy methods. Morphological observation revealed a near to the exfoliation state for organoclays in PVC- g-(St-MA) nanocomposite containing 1 wt% C30B. However, C15A/PVC- g-(St-MA) nanocomposite (C15A-CPN) exhibited partially intercalated and agglomerated morphology. Differential scanning calorimetry examination was conducted to measure the glass transition temperature ( Tg) of the segments. At the same clay content, the Tg of the C30B containing nanocomposites were higher than that of C15A samples. The mechanical properties of these nanocomposites were also investigated. As a consequence, C30B-CPN showed improved mechanical properties compared to C15A-CPN and cross-linked PVC- g-(St-MA) samples.

A Methodology for Characterizing the Interfacial Fracture Toughness of Sandwich Structures using High Speed Infrared Thermography

An experimental method is proposed for obtaining the fracture toughness of an interfacial crack in sandwich structures. The method relates the interfacial fracture toughness with temperature change developed at the crack front. The focus of the paper is the development of an experimental approach that uses high speed infrared (IR) thermography to capture the temperature evolution during the crack growth. The feasibility of using IR thermography is demonstrated on sandwich structure specimens with E-glass/epoxy face sheets and cross-linked PVC H100 foam core loaded in mixed-mode bending. Different crack propagation paths, in the foam core and at the face sheet/core interface are considered. It is shown that IR thermography with 15 kHz frame rate is able to make a quantitative measurement of the crack front temperature associated with the crack growth. A constant of proportionality ψ is derived between the temperature change per unit area at the crack front and the fracture toughness provided by a validated FE model. It is shown that ψ obtained from specimens with the same crack propagation path is identical, even though the specimen dimensions and loading mode-mixities are different. Thus, it is demonstrated that for a particular interface, once ψ is obtained from a known loading condition, the interfacial fracture toughness from any loading configuration can be determined from a direct temperature measurement.

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.

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.

Characterization of Thermal Reversible Cross-Linking Agents for Flexible Poly(vinyl chloride)

In order to improve thermal stability of Poly (Vinyl Chloride), a kind of thermal reversible cross-linking agents, the end cyclopentadienyl ethanethiol salts, sodium cyclopentadienyl ethyl mercaptan (CPD-C2H4SNa) was synthesized in this paper. The DSC results proved that the prepared CPD-C2H4SNa has obvious thermal reversible characteristics and the thermal reversible temperature was at 177 °C. The effects of cross-linking agent amount, cross-linking reactive time and temperature on flexible PVC compounds were evaluated through gel content testing. It was showed that the cross-linking agent with 3 Phr is optimum for PVC compounds. Moreover, both the cross-linking reactive time and temperature has effects on gel content of PVC compounds. The gel content of CPD-C2H4SNa cross-linked PVC compounds reaches maximum at 76% for 20 min at 160 °C.The static thermal stability of flexible PVC was measured according to congo red method. The results showed that the thermal stability of PVC compounds was enhanced with increasing cross-linking agent amount.

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.

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.

Understanding the Compressive Behavior of Linear and Cross-linked Poly(vinyl chloride) Foams

The work reported in this article was initiated by the IUPAC Subcommittee ‘Structure and Properties of Commercial Polymers’ to study the ‘Structure and properties of linear and cross-linked structural poly(vinyl chloride) (PVC) foams’, and intends in particular to give a good understanding of the compressive response of these PVC foams with various foam densities. From a careful review of chemical reactions of polymeric methylene diphenyl diisocyanate [a mixture of 4,4'-methylene-bis(phenyl-isocyanate) and oligomeric isocyanates] with water or phthalic acid, it is known from the material supplier that a semi-interpenetrating polymer network of polyureas and/or polyamides is formed by cross-linking. The amide groups in these polymers are hydrophilic and can affect the overall mechanical response of PVC foams, especially under water. Scanning electron microscopy is used to study the morphology of linear and cross-linked foams and their heterogeneous foam deformation. Compression testing of these PVC foams is conducted in air and water, and illustrates the influence of foam density and cross-linking. Correlation of compressive testing of foams with the corresponding cross-linked PVC bulk materials suggests that elastic collapse of cells during compression may be linked to strain-softening of the corresponding bulk material. Finally, new predictive models are adopted for the PVC foams to give reasonable estimates of their compressive modulus and yield strength.

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.

Dynamic mechanical analyses and flexural fatigue of PVC foams

Flexural fatigue tests were performed on cross-linked PVC foams of densities in the range from 75 to 300 kg/m 3 at a frequency of 3 Hz and at a stress ratio, R=0.1. S– N diagrams were generated, and the failure mechanisms were examined. The fatigue behavior was found to be similar to structural materials with a fatigue strength that increased with increased foam density. The final failure event was catastrophic due to crack propagation initiating at the tension side of the specimen. SEM analyses performed on the R300 foam specimen revealed cell wall cracking and densification of the foam during the earlier part of the fatigue life. This densification contributed to stiffening of foam specimens. Viscoelastic parameters of the foams were determined using a dynamic mechanical analyzer over a frequency range of 1–10 Hz. For the virgin specimens it was found that the viscoelastic moduli and damping ratio were quite independent of frequency over this range of frequencies. Viscoelastic parameters were also extracted at intermediate stages of fatigue life and the residual properties were studied with respect to the number of fatigue cycles. It was observed that the variation of dynamic mechanical analysis (DMA) parameters with the number of fatigue cycles was consistent with the variation of residual global stiffness of the material. Experimental details and the analyses of fatigue behavior are presented in this paper.