Surface Treatment and Adhesive Bonding of Commercial PVC
The bonding of rigid PVC to a plasticised PVC film using a reactive hot melt\ud polyurethane adhesive has been investigated in order to improve the stability and durability of the bonding between the PVC and the adhesive. (The primers used to modify the surface of rigid PVC are mainly solvent-based products, either methylene chloride based or methyl ethyl ketone based). With Adhesion Promoters, such concerns are environmental (High VOC emissions and clean-up costs), introductions of dirt, high maintenance costs, and safety. Chlorinated solvents, most commonly used in Adhesion Promoters, are highly flammable and toxic which in turn is dangerous to plant and personnel alike. These solvent-based products were band by European Union environment agency in2011. Alternative surface modification technique should replace the solvent prima to modify the surface of the commercial PVC.\ud Consequently the flame treatment technique was employed to modify the surface of the commercial PVC before bonding to a plasticised PVC film by using a reactive hot melt polyurethane adhesive.\ud \ud Before surface modification of the PVCs, the PVC samples were investigated by employing surface analysis’s techniques such as X-ray photoelectron spectroscopy (XPS), contact angle measurements (CAM), atomic force microscopy (AFM) and energy dispersive X-ray (EDX) and DMA. In order to avoid the damage of the PVC samples while they expose to X-ray irradiation. Initially, XPS and EDX were employed in a X-ray degradation study of PVC to determine the maximum time a PVC sample can be exposed to an X-ray source where X-ray has minimum effect on the surface of PVC.\ud The samples used in the degradation study were pure PVC (drop cast in THF on to aluminium foil to produce a PVC film as reference) and three industrial PVC blends.\ud \ud EDX analysis of a pure PVC specimen exposed to an X-ray source showed 5% degradation after ten minutes X-ray exposure. Additionally, a further degradation study was undertaken in which a 1mm diameter gold disc was sputter coated on to PVC sample surfaces. This study revealed that the PVC concentration decreased due to Xray degradation, however, the Au/C ratio remained constant suggesting there was no redisposition of C on to the PVC samples.\ud \ud A liquid propane gas (LPG) based flame treatment was used to modify the surface of rigid PVC (Veka) to improve its wettability and its adhesive properties. The surface properties and chemistry of the modified surface were characterised by CAM, XPS and AFM. Results show that the LPG flame treatment of the PVC (Veka and Rehau) produces both morphological and compositional changes of the surface. LPG flame treatment of the PVC V and R resulted in an increase in the surface free energy of the\ud PVC surface. CAM result for the LPG flame treated PVC showed increased wettability of the PVC sample. The ultra-low-angle microtomy (ULAM) technique was developed to impart a ultra-low –angle taper through polymeric multilayers at ambient temperatures. Here the ULAM technique has been enhanced by in situ cooling of the samples using a cryo-stage (C-ULAM). XPS line scan analysis across a UV primer/PVC interface exposed using C-ULAM indicates penetration of UV primer in to the PVC formulation. XPS line scan analysis of C-ULAM exposed PU/PVC and PVC/PU/PVC interfaces shows penetration of PU in to PVC formulation. The UV\ud primer shows greater penetration in to the PVC (ΔZ = 8nm) than reactive hot melt PU adhesive (ΔZ = 5nm) due to its application in the liquid phase at ambient temperature.\ud \ud The penetration of PU in to the PVC increased after LPG flame treatment of the PVC due to changing surface roughness of PVC by flame treatment.\ud Dynamic Mechanical Analysis (DMA) was employed to investigate effect of LPG flame treatment on the mechanical property of the PVC samples, nineteen months after surface modification of PVCs samples by LPG flame treatment. The DMA results indicate that when the PVC sample treated by flame while the release agent is on the surface of the PVC, the release agent and PVC promote a strong bond and therefore become one solid\ud sample together. The result was indicated that, an increase of 10% in storage modulus, from 8083 MPa for samples without RA to 8822 MPa for samples with RA. These results are in agreement with the results from AFM analysis.\ud By comparing the result of the tan delta of PVC-V with release agent before and after flame treatment, it can be seen that the effect of flame treatment on tan delta profile is not significant. Also the temperature value at tan delta peak indicates the value of glass transition temperature. The fact that this has not significantly changed indicates that the nature of the material has not changed after the flame treatment.\ud \ud In order to study the mechanical property of sandwich layer samples, made of (Rigid PVC/PU adhesive/ Plasticised PVC), with different curing system the Dynamic mechanical analysis (Three point bending/ DMA) of all sandwich layer samples were carried out nineteen months after they have bonded together. The result obtained from DMA results shows 10% increase on loss modules test of sandwich layers, which bonded while prima was applied on the surface of the PVC.