Preparation and characterisation of UV irradiation cross-linked LDPE/EVA blends

Abstract

Ultraviolet induced cross-linking of low density polyethylene/ethylene vinyl acetate melt mixed blends were explored in presence of trimethylolpropane trimethacrylate (TMPTMA) and benzophenone (BP) as cross-linking agent and photoinitiator respectively. On the basis of gel content, it was found that 1 wt-%TMPTMA, 1 wt-%BP and irradiation time of 100 s represent the optimum parameters for photocross-linking of this system. Infrared spectroscopy was also used to follow the cross-linking reactions. Differential scanning calorimetry analysis showed that the heat of fusion reduces upon cross-linking development in the system, implying that crystallisability of the samples is suppressed with increasing cross-link bonds. Thermal stability of samples as a function of irradiation time goes through a maximum and then diminishes. Mechanical examinations in tensile mode proved that elongation at break of neat and blended specimens drops significantly with increasing degree of cross-linking, while variations of Young's modulus of the blends show a composition dependent behaviour in which crystallisability of the samples is a major determinant.

Preparation and characterisation of PCL shape-memory films via photo-crosslinking

“…When crystalline polymers are irradiated by high-energy electrons or γ -ray, radicals generated in the crystalline regions have much lower mobility and longer lifetimes than those in the amorphous region because macromolecular diffusion movement is strongly hindered, and therefore they migrate to slowly amorphous phase [27]. A similar circumstance occurs in the photo-crosslinking process, and there have already been some reports which have confirmed it [20, 28]. Based on these facts, if more crystalline phase can be transferred to the amorphous phase, the efficiency of photo-crosslinking should be improved largely, so some films were photo-crosslinked at 55°C (around its T m ) to be compared with those at 25°C.…”

“…It is inferred that when the film is irradiated by UV light, BPs in PCL films can generate free radicals as analysed previously, which would then react and combine to form crosslinking networks in the films, and these networks could further provide the reinforcement effect to the films in resisting the applied straining stress. Longer irradiation time makes more BPs involved in generating free radicals, which form more crosslinking networks [20,30], so tensile strength gets higher. However, since the difference in gel fraction between PCL films with different BP contents is slight, changes between their tensile strength are very small.…”

“…Wu [19] photo-crosslinked LDPE using a 2 kW high-pressure mercury lamp. Shamekhi [20] photo-crosslinked LDPE/EVA blends using a 2 kW UV lamp; Nagata [21] prepared PCL pendent coumarin group by solution polycondensation and then photo-crosslinked it using a 400 W high-pressure mercury lamp ( λ = 280 nm); Wang [22] synthesised PCLF and then photo-crosslinked PCLF dissolved in BAPO/CH 2 Cl 2 mixture under UV light ( λ = 315–380 nm). Defize [23] synthesised coumarin end-capped 4-arm star-shaped PCL through three steps, and photocured it under UV irradiation (200 W, λ = 365 nm).…”

Electron beam cross-linking of EVA/TPU blends

“…The blends of EVA with polymers such as low density PE and ethylene a-olefins have been studied extensively. [6][7][8][9][10][11][12][13] Maity and Das studies showed that polyurethane is able to cross-link with EVA at high temperatures without any curatives. The studies showed the blend properties largely depend on blend ratio and also blending techniques; also infrared studies showed that heating results in interchain cross-linking between PU and EVA.…”