Polyolefin surface modification

Let us discuss now the problem of the stability of polyolefins surface modifications induced by treatments in the oxygen, nitrogen or air plasmas. 

Some applications of polyolefins surface modifications induced by gas phase treatment were already mentioned in previous sections of this chapter. 

In addition, there are many surface modification processes that use triplet sensitizers to permit oxidation reactions. In a typical process, polyisocyanate is applied on a polyolefin together with a sensitizer such as benzo-phenone and then irradiated with UV light. As shown in Eq. (15) the sensitizer has an oxidizing effect to produce hydroxyl groups over the polymer surface. These hydroxyl groups finally react with isocyanate to provide a functional polymer [56,57]. 

Abstract Polyolefins such as polyethylene, polypropylene and their copolymers have excellent bulk physical/chemical properties, are inexpensive and easy to process. Yet they have not gained considerable importance as speciality materials due to their inert surface. Polyethylene in particular holds a unique status due to its excellent manufacturer- and user-friendly properties. Thus, special surface properties, which polyethylene does not possess, such as printability, hydrophilicity, roughness, lubricity, selective permeability and adhesion of micro-organisms, underscore the need for tailoring the surface of this valuable commodity polymer. The present article reviews some of the existing and emerging techniques of surface modification and characterisation of polyethylene. 

Polyolefins are amongst the most widely used polymers. Polyethylene in particular holds a unique status due to its excellent user-friendly properties. Tailoring of its surface properties would open an avenue to the most lucrative markets. The present article reviews some of the existing as well as emerging techniques of surface modification and characterisation of polyethylene. 

As mentioned, polymer hybrids based on POs are effective as a compati-bilizer between the olefinic materials and polar ones. Furthermore, some polymer hybrids, such as PP-g-PMMA, etc., show good mechanical strength as polymer materials. On the other hand, surface modification of the molded polymer is one of the most attractive methods to let polyolefin materials functionalize. In this sense, surface polymerization of functional monomers on polyolefins is an important subject for polyolefin hybrids. As previously referred to, the growth of PS on PP via the RAFT process has been reported [92]. 

There are many different methods for modifying polymer surfaces to improve their adhesion and wetting properties. They include chemical etching and oxidation, ion bombardment, plasma treatments, flame treatment, mechanical abrasion and corona-discharge treatments (1.2). Especially flame and corona treatments are widely used for the modification of polyolefin surfaces to enhance, for instance, their printabilify. Despite the widespread use of such processes in industry, the understanding of the fundamental processes which occur at the polymer surface is very limited. This is undoubtedly due to the shallow depth to which the polymer is modified, typically 5 nm or less. 

The photosensitizing action of Ti02 pigments in isopropanol depends on their crystal structure and the presence of any surface modifications. The Ti02-ZnO-photocatalysed oxidation of hexane is a good model for polyolefins. Using e.s.r. and luminescence spectroscopy, Ti centres have been... 

The attachment of trialkoxysilane functionality to polyolefins (HDPE, LDPE, PP) though grafting of vinylsilanes e.g. 40, 41) or silane functional acrylates e.g. 42) has been widely studied. The principal application of these materials is the preparation of moisture curable crosslinked polyolefins that arc widely used in the cable industry. Silane treatment has also been used for surface modification of polyolefins " and silane grafted polyolefins might also serve as precursors to graft copolymers. 

Modern electron processors offer high speed (high dose-rate) curing of low viscosity liquid coatings so that surface modification of films becomes practicable. A process has been developed for grafting vinyl monomers to polyolefin film surfaces with the aid of functional silane primers using electron initiated polymerization. 

Surface modifications of polyolefins are very important for many industrial applications such as adhesion to (1) another polymer, (2) composite, and (3) metal bonding. 

For many industrial applications of polyolefin materials that depend on adhesive bonding, surface treatment by cold plasma became preferred in industrial process. The plasma treatment is a surface modification process by which the bulk properties of the material are retained [51]. Plasma surface treatment is a very effective way to... 

L.G. Beholz, C.L. Aronson, A. Zand, Adhesion modification of polyolefin surfaces with sodium h)qK)chlorite in acidic media. Polymer 46, 4604-4613 (2005)... 

J. Friedrich, S. Wettmarshausen, M. Hennecke, Halofoim plasma modification of polyolefin surfaces. Surf. Coat Technol. 203, 3647-3655 (2009)... 

Surface-modified polyolefin materials are widely used in biomedical field. Low-temperature plasma-treated PE was well suited for biomedical application. UHMWPE after surface modification with low-temperature plasma is the principal material used to replace damaged cartilage in total joint arthroplasty or the surgical reconstmction of a diseased joint [73]. The UHMWPE having desirable mechanical properties and biocompatibility is used in orthopaedic implants and joint socket in bone replacement. 

The inferior adhesive properties of polyolefins result in many serious problems especially if gluing or printing on these materials is considered. The effective surface modification of polyolefin should lead to a formation of a very thin surface layer with the thickness of several micrometers without affecting the bulk properties of the material. The fine layer of modified polymer on the surface of polyolefin should contain sufficient concentration of the polar moieties leading to an increase of the surface energy of polymer. 

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