Modification Of Polyethylene Research Articles

Surface modification of polyethylene by radiation‐induced grafting for adhesive bonding. V. Comparison with other surface treatments

AbstractHelium gas plasma treatment of low‐density polyethylene (LDPE) yields much lower peel strength than oxidative treatment using chromic acid and oxygen gas plasma. The practical adhesion, the bondability retention, and the bond durability of oxidatively treated LDPE sheets, bonded with epoxy adhesives, have been compared with those of partially hydrolyzed LDPE–methyl acrylate surface grafts. The oxidized surfaces easily lose the bondability by light rubbing with tissue paper, solvent extraction, heat aging, and artifical weathering, whereas the grafted surfaces retain the bondability. The bondability loss is due to removal of the oxidized layer, and the bondability retention is due to retention of the surface homopolymer layer. Conventional antioxidants stabilize the grafted but not the oxidized surfaces against thermal oxidative degradation. The grafted LDPE joints have much higher bond durability in humid environments than those of the oxidized LDPE joints. The dry and wet peel strengths of oxidized LDPE joints are greatly improved by application of primers consisting of a base epoxy resin and organic solvents. An adhesion mechanism involving penetration of epoxy adhesives into the oxidized layers and subsequent reinforcement of the layers by curing of the penetrated epoxy is proposed.

Surface modification of polyethylene by electrical discharge treatment and the mechanism of autoadhesion

A reexamination of previous studies concerning the electrical (‘corona’) discharge treatment of polyethylene and the resulting enhancement of autoadhesion has been carried out. X-ray photoelectron spectroscopic data provide new insight into the phenomenon by showing surface oxidation to result from treatment in ‘inert’ gases. Treatment in hydrogen is an exception and results in no autoadhesion enhancement even though energy input into the film is more efficient than in air. Autoadhesion theories based on electret formation are rejected; those based on hydrogen bonding are largely up-held and shown to be more generally applicable than at first imagined.

Surface modification of polyethylene by radiation-induced grafting for adhesive bonding. I. Relationship between adhesive bond strength and surface composition

A number of vinyl monomers have been surface grafted onto a polyethylene sheet by the mutual irradiation in monomer vapor and by a trapped-radical technique. The surface composition of the grafted sheets has been determined by means of ATR infrared spectrophotometry and compared with the peel strength of the joints bonded with conventional structural adhesives. In the methyl acrylate grafts followed by a saponification treatment, only the surfaces having graft compositions of more than 80 mole-% methyl acrylate give a high peel strength. A similar relationship between peel strength and surface composition is found in the surface grafts of vinyl acetate, acrylic acid, acrylamide, and methylolacrylamide. It is concluded that the formation of a surface with such a high monomer content is a necessary condition for the strong adhesive bonding of grafted polyethylenes at bonding temperatures below the softening point. Moreover, the adhesive bondability of the highly modified surfaces with epoxy adhesives is significantly enhanced by the introduction of carboxy and carbamyl radicals.

Surface Modification of Polyethylene by Radiation-Induced Grafting for Adhesive Bonding. 2. Relationship between Adhesive Bond Strength and Surface Structure

Surface Modification of Polyethylene by Radiation-Induced Grafting for Adhesive Bonding. 2. Relationship between Adhesive Bond Strength and Surface Structure

Modification of polyethylene by anisodiametric grafted structures

High pressure polyethylene films (PE) have been modified by graft polymerization of acrylonitrile and vinylidenechloride and have then been subjected to orientational drawing at temperatures exceeding the melting point of PE and the glass transition temperatures of the grafted polymers. Under these conditions, oriented structures are found in PE and the grafted polymers: these form a “framework” which prevents the relaxation of the oriented PE structures and the reversion of the drawn specimens when heated in the free condition above the melting point of PE. The additive contributions of PE and the grafted structures of polyacrylonitrile and polyvinylidenechloride towards the strength and pliability of the films cause special features in the mechanical properties.

Graft copolymer modification of polyethylene–polystyrene blends. II. Properties of modified blends

The use of graft copolymers of styrene onto polyethylene as additives to improve the mechanical properties of polyethylene–polystyrene blends is described. Blends containing equal proportions of low-density polyethylene and polystyrene were selected for this study since this composition represents the poorest balance of properties in this system. Graft addition generally increased both the yield strength and the elongation at break of the blend. Of the grafts employed, those prepared at an irradiation dose near 0.5 megarad appear optimal for this purpose. These conditions apparently balance the beneficial effects of grafting extent and the detrimental effects of crosslinking, both of which increase with irradiation dose.

Graft copolymer modification of polyethylene–polystyrene blends. I. Graft preparation and characterization

The preparation and characterization of styrene–low-density polyethylene graft copolymers for addition to blends of polyethylene and polystyrene to improve blend mechanical properties is described. The direct method of grafting with 60Co radiation was employed using the polyethylene in pellet form. This approach gave good grafting efficiency with maximum yields limited to about 1 g of styrene reacted per gram of polyethylene. Excessive crosslinking at radiation doses beyond about 1 mrad was detrimental to the melt processibility of the graft. Crystallinity, dynamic mechanical properties, morphology, and stress–strain behavior of the grafts were examined and compared with melt blends of similar composition in order to better characterize the material produced.

Stereospecific ring cleavage homopolymerization of cycloolefins and structural examination of the resulting homologous series of linear crystalline trans polyalkenamers

AbstractUnsubstituted cycloolefins can be polymerized via ring cleavage to high molecular weight, linear, unsaturated polyalkenamers having the structure (CHCH(CH2)n)p using catalyst systems prepared from tungsten or molybdenum salts and organoaluminum compounds. The polymerization of cyclobutene to polybutenamer (1,4 polybutadiene) and of cyclopentene to polypentenamer is known. In the present paper the polymerizations of cyclohexene, cycloheptene, cis‐cyclooctene, and cis/trans‐cyclododecene are investigated in the presence of the same catalyst systems. While cyclohexene, due to the high stability of its ring, does not yield high molecular weight products, the other higher cycloolefins could be polymerized with good conversions to pure linear polyalkenamers.The resulting linear polyalkenamers are built up of head‐to‐tail linked monomeric units containing mainly trans‐double bonds. The chemical and the pronounced steric regularity cause the crystallizability of these polymers.The investigation of the crystal structure shows that the polymers, in which the methylene sequence n is an odd number, crystallize in orthorhombic unit cells, similar to those of the normal modification of polyethylene and of the n‐alkanes. The trans polyalkenamers, in which the methylene sequence n is an even number, on the contrary, crystallize in monoclinic and in triclinic unit cells. Trans polyalkenamers having an odd methylene sequence are well distinguished from those with an even methylene sequence also in the completely different conformation of the polymer chains in the crystal.Interesting correlations could be observed on the trans polyalkenamers. The melting temperatures depend on the length of the structural unit.