Measured Gel Content Research Articles

Improved performance of dual-cured organosolv lignin-based epoxy acrylate coatings

Abstract Organosolv lignin (OL) was used to synthesize organosolv-lignin-based epoxy acrylate (OLBEA) coatings. The reaction process was determined by epoxy and acid values. OLBEA coatings were prepared by dual (Ultraviolet (UV) and thermal) curing to achieve a deep and complete process. The structures of lignin-based epoxy (OLBE) and OLBEA were characterized by Fourier transform infrared spectroscopy (FTIR). The properties of the dual- and UV-cured coatings were then compared by measuring gel content and mechanical properties. Results revealed that the dual-cured films had higher cross-linking degree and better mechanical properties than the UV-cured films. The chemical resistance of the dual-cured coatings was also examined. The properties of OLBEA coatings obtained by dual curing were shown to be excellent and promising for wide-ranging applications.

The impact of electron beam irradiation on Low density polyethylene and Ethylene vinyl acetate

Improvement of measured gel content, hardness, tensile strength and elongation at break of Ethylene vinyl acetate (EVA) have confirmed positive effect of electron beam irradiation on EVA. Results obtained from both gel content tests show that degree of cross-linking in amorphous regions is dependent on dose. A significant improvement in tensile strength of neat EVA samples is obtained upon electron-beam radiation up to 210 kGy. Similarly, hardness properties of Low-density polyethylene (LDPE) improvewith increasing electron beam irradiation. This article deals with the impacts of electron beam (EB) irradiation on the properties of LDPE and Ethylene-Vinyl Acetate (EVA) as the two common based formulations for wire and cable applications.

Electron-Beam Irradiation of Halogen Free Flame Retardant Polymers for Wire and Cable Applications

Effect of addition different polymers and fillers with electron beam irradiation on changes of physical, electrical and flammability properties of low density polyethylene (LDPE) / trimethylol propane trimethylacrylate (TMPTMA) / Irganox/ zinc borate (ZB) have been investigated. Results of measured gel content (GC), tensile strength (TS), elongation at break (EL), hot set (HS) tests, melt index (MFI), dielectric strength (DS), volume resistivity (VR), flammability and limiting oxygen index (LOI) have confirmed positive effects of adding maleic anhydride grafted LDPE (LDPEgMAH), ethylene vinyl acetate (EVA) and CS whereas effect of ATH to blends drastically had negative effects on improvement of physical properties of blends. Meanwhile, presence of TMPTMA and enhancing irradiation could improve properties seriously. Keywords Halogen free; polymers; irradiation; wires and cables

Electron-beam irradiation of low density polyethylene/ethylene vinyl acetate blends

Abstract In this work, the properties of electron-beam irradiated low density polyethylene (LDPE), ethylene vinyl acetate (EVA) and blends were investigated. EVA addition had an enhancement effect on crosslinking of irradiated LDPE/EVA blends. The measured gel content increase of the blends and the improvement of thermal elongation, tensile strength, elongation at break, thermal aging and heat deformation, have confirmed the positive effects of electron-beam irradiation on the blend properties. The crystallinity of the blends decreased with irradiation. The gel content and hot set tests showed that the degree of crosslinking in the amorphous regions was dependent on the dose and blend composition. Increasing the EVA content resulted in tighter network structures. A significant improvement in the tensile strength of the neat EVA samples was obtained upon electron-beam irradiation up to 210 kGy. The irradiated LDPE/EVA blends showed improved tensile strength and elongation at break, when compared to LDPE. The enhanced irradiation crosslinking of the LDPE/EVA blends was proportional to the good compatibility and the increasing degree of the amorphous region’s content of the LDPE/EVA blends. The possible degradation mechanism of LDPE/EVA blends was discussed quantitatively with a novel method step analysis process of irradiated LDPE/EVA blends in the thermal gravimetric analysis (TGA) technique. It was found, with measuring thermal conductivity (k) and specific heat capacity (Cp) of the blends, that the k values of the LDPE samples at a prescribed temperature range decreased with increasing irradiation. An increase in the crystallinity led to an increase in the k values and a decrease in the Cp values of the LDPE samples. Irradiation below 150 kGy decreased the Cp (at 40°C) and k in average values, whereas increasing the EVA made enhanced the Cp and k values of LDPE/EVA blends at each irradiation. The surface resistance and volume resistivity (VR) of the blends reached a maximum at a 170 kGy irradiation and 30 wt% of EVA. Increasing the amount of EVA contents resulted in enhancement of the dielectric loss factor for the irradiated blends.

Synergetic effects of silane-grafting and EVA on water tree resistance of LDPE

The synergetic influence of silane-grafting and polar additives (EVA) on the water tree resistance of the low density polyethylene has been investigated. A series of samples obtained before and after hydration have been characterized by measuring gel content, infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric measurements. The results obtained clearly show that the silane condensation occurred and that the silane-grafting and polar additives have synergetic effects on the water tree resistance of LDPE with little influence on its dielectric properties, e.g. the dielectric breakdown strength, dielectric permittivity and loss tangent.

Production of high melt strength polypropylene by gamma irradiation

High melt strength polypropylene (HMS-PP) has been recently developed and introduced in the market by the major international producers of polypropylene. Therefore, BRASKEM, the leading Brazilian PP producer, together with EMBRARAD, the leading Brazilian gamma irradiator, and the IPEN (Institute of Nuclear Energy and Research) worked to develop a national technology for the production of HMS-PP. One of the effective approaches to improve melt strength and extensibility is to add chain branches onto polypropylene backbone using gamma radiation. Branching and grafting result from the radical combinations during irradiation process. Crosslinking and main chain scission in the polymer structure are also obtained during this process. In this work, gamma irradiation technique was used to induce chemical changes in commercial polypropylene with two different monomers, Tri-allyl-isocyanurate (TAIC) and Tri-methylolpropane-trimethacrylate (TMPTMA), with concentration ranging from 1.5 to 5.0 mmol/100 g of polypropylene. These samples were irradiated with a 60Co source at dose of 20 kGy. It used two different methods of HMS-PP processing. The crosslinking of modified polymers was studied by measuring gel content melt flow rate and rheological properties like melt strength and drawability. It was observed that the reaction method and the monomer type have influenced the properties. However, the concentration variation of monomer has no effect.

Radiation Induced Crosslinking of Ethylene Vinyl Acetate Copolymers Hosting Sulfonic Acid Groups and Their Potential Applications

The effect of ionizing radiation on the properties of untreated ethylene vinyl acetate copolymer (EVA), sulfonated EVA and polyethylene‐ethylene vinyl acetate blend (PE/EVA) was investigated. The crosslinking of the samples was studied on the basis of gel‐content measurements, as well as some thermal and mechanical properties of the specimens. The results indicated that EVA and sulfonated EVA were more sensitive to the electron beam irradiation. The improvement in the measured gel content, tensile strength, and elongation at break and heat resistance of the EVA and sulfonated EVA has confirmed the positive effect of low doses electron beam irradiation on such copolymers. The crosslinked sulfonated EVA membranes were used for sucrose hydrolysis. The catalytic activity of the membranes was found to be dependent on the reaction temperature and the amount of the sulfonic acid groups hosted in the EVA membranes. The results of this work suggest that crosslinked sulfonated EVA membranes have a strong potential to replace liquid sulfuric acid and ion exchange resins in sugar hydrolysis processes.

Radiation effects on LDPE/EVA blends

The effect of radiation on the properties of low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) blends were investigated. The improvement of the measured gel content, thermal elongation, tensile strength, elongation at break and heat deformation of the blends have confirmed the positive effect of electron beam irradiation on the blends.

Electron beam curing of coatings. The influence of the voltage on the curing process.

The specific influence of the electron energy on the Electron Beam Curing process of coatings on metal surfaces is shown. For that purpose coatings of different thickness ( 20 to 80 microns) were cured at constant beam intensities and substrate velocity but varying the voltage of the beam in a range of 60 to 140 kV. The effectivity of the cure was tested by measuring gel content and hardness as well as double bond content of the coating films. Additionaly adhesion and elasticity of the samples were measured. The results show that for a maximum cure of a certain coating thickness there exists an optimum voltage. Additionally, the adjustment of the voltage to the thickness of the coating allows one to achieve a “profile cure” within the coating layer. Thereby it is possible to influence the mechanical properties, for instance elasticity and adhesion of the cured film to the substrate in a specific way.

γ‐Irradiation of polystyrene emulsions

AbstractAqueous polystyrene emulsions were subjected to γ‐irradiation at 30°C and 0.6 Mrad/hr dose rate. Analogy with water‐soluble systems suggests that such conditions might suppress chain scission and favor crosslinking. The (extrapolated) infinite‐dose gel content and gel‐permeation analysis of the polymer in the pre‐gel region indicate that the extent of chain scission was negligible. The G (crosslink) value obtained from the dose for incipient gelation and molecular weight variations in the pre‐gel region is 0.051. Charlesby‐Pinner plots were linear, but linearity cannot be construed as indicating that chain scission has produced an effective random molecular weight distribution. Our results are consistent with the conclusions that crosslinking events are random and directly proportional to dose. The probability that a given crosslink is effective in increasing the gel content decreases with dose past the incipient gel point, however, because of cyclization on preformed gel. The crosslink density/dose ratio is a decreasing function of dose in this range. Attempts to predict dose–gel relations with assumptions of various initial molecular weight distributions were unsuccessful, possibly because of the neglected influence of cyclization on the measured gel content.

On the mechanism of ionizing radiation damage in SBR elastomers

Studies were made to provide information for use in the development of SBR elastomers with improved resistance to attack by high energy radiation. Changes of molecular structure were investigated by viscometric techniques and by measuring gel content. Chemical changes were followed by use of infrared spectrophotometry. Results indicate that the polymer in toluene, when subjected to radiation doses in the range 0–100 Mrep, is randomly scissioned. When similarly treated in chloroform, the polymer is initially randomly crosslinked and then the newly formed elastomer network undergoes random scission. The nature of the end chemical changes is shown to depend on environmental factors. In the presence of a limited supply of oxygen, the polymer is partially oxidized. The oxidation reaction appears to have no influence, however, on the random nature of the degradation process. The external butadiene structures are shown to be attacked more rapidly than the internal groups. The phenyl rings of the styrene groups in the polymer molecules, on the other hand, are only moderately affected in this respect. The results obtained in these solution studies are used to predict the effects of radiation damage to SBR vulcanizates.