Chemical modification flame treatment

It can be seen that to achieve a given level of chemical modification, flame, corona and plasma require much shorter treatment times than ozone or UV or a combination of UV plus ozone. 

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. 

Pores accessible to water molecules are not necessarily accessible to chemical agents. Chemical modification is required to impart many desired properties to cotton fabric. These include color, permanent press, flame resistance, soil release, and antimicrobial properties to name a few. Thus, a knowledge of cotton s accessibility under water-swollen conditions to dyes and other chemical agents of various sizes is required for better control of the various chemical treatments applied to cotton textiles. 

Polymer surface modifications are omnipresent in applications where the surface properties of materials with favorable bulk properties are insufficient. By altering the surface characteristics using physical or chemical modification the desired surface properties may be achieved. Such treatments are required e.g. to enhance printability of films, the adhesion of paints, metal or other coatings, biocompatibility, protein resistances/reduced biofouling, etc. The diverse approaches met in practice include, among others, wet chemical and gas phase chemistry, plasma or corona, UV/ozone and flame treatments. In most cases surface chemical modification reactions take place that alter the surface energy in a desired way. For example,... 

The treatment with a fuel gas-oxygen flame (propane/butane or acetylene with excess oxygen, recognizable by the blue coloration of the flame) results in a chemical and physical surface modification, also with oxidative effects. This method is particularly suitable for handycraft applications, because of its low effort and expenditures. The flame treatment time is in the range of seconds, the distance of the flame to surface should be approximately 5-10 cm. In the case of thermoplastics like polyethylene and polypropylene, care should be taken that surface melting is avoided. 

As nofed in Section 22.3, flame treatment of polymer films is fypically implemenfed using natural gas (which is largely methane) and air as the reactants. Propane is also commonly utilized as a fuel. If is well known, however, fhaf fhe characferisfics of premixed flames depend greatly on the reactant species. Thus, the addition of secondary species to the primary reactants to alter the thermal and/or chemical behavior of the flame may be envisioned. The addition of an oxidizing additive, nitrous oxide (N2O), is reviewed here as an example of fhe effecfs of this type of flame-chemisfry modification. 

A more dense coating can be obtained by a laser treatment. In the course of this treatment, the polymer coating is remelted. Several laser types have been tested, the most suitable laser is the carbon dioxide laser to get more compact coatings. The laser-treated coating shows an amorphous structure. However, no obvious chemical modification is observed after the flame spraying process and the laser treatment. ... 

The modification of polymer surfaces both in terms of structure and functionality is a subject that has been evidenced to be of theoretical and practical interest [ 1,2]. In this sense, a large amount of literature has been published describing a wide variety of surface chemical modification approaches such as flame or corona treatments, chemical reactions (in solution), plasma or UV treatments or the application of polymer coatings among others [3-11],... 

The surface chemical analysis made possible by XPS has proved useful in a number of areas. Simple detection of surface contamination has already been mentioned another technically important area is the detection of changes in surface functionality introduced by treatments such as plasma and flame modification and chemical etching. These treatments are extensively used in practice to modify surface properties such as adhesion and wettability and the use of XPS and other surface analysis techniques permits one to associate these changes with the introduction of specific chemical functionality at the surface. Excellent entries into the extensive literature in this area may be found in the monograph by Garbassi et al. (1994) and the review by Briggs (1990). 

Surface Treatment. Most film surfaces require surface treatment for use in subsequent steps of coating, printing, lamination, or metallization. This treatment results in the chemical modification of the polymer at the surface. The most widely employed surface modification is oxidation of the polymer to create a polar smface (43). Processes that are widely employed are corona and flame treatment. Wet chemical oxidative treatments are seldom used and are restricted to low speed operations. A new surface oxidation technique has been recently developed which uses an atmospheric plasma generated in a hollow cathode with helium or helium gas blends (44). 

Surface modification refers to the modification that occurs only on the surface of a polymer material without further internal modification. Surface modifications of polymeric materials include surface chemical oxidation, corona surface treatment, surface flame treatment, surface heat treatment, surface plasma treatment, surface metallization processing, ion implantation, and surface grafting polymerization. Because surface modification occurs only on the surface of materials, the performance does not change uniformly. 

Surface modification techniques these can include such approaches as the laser ablation of the surface using, for example, excimer lasers. Other possibilities are to use plasma, corona and flame treatments to modify the laminate surface, chemically, to make it more amenable to adhesive bonding. As for thermoplastic matrices, it should be possible to introduce highly polar groups onto the surface to improve bonding across the interface. 

Important applications of XPS pertain to the characterization of polymer surfaces. These applications include the detection of oxidation products and impurities, and observations of molecular rearrangements and chemical modifications of polymer chains. Moreover, XPS is an appropriate tool to follow up flame and plasma treatments of polymers. In polymer processing, XPS can help to optimize surface properties while retaining desirable bulk properties. 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

The technical synthesis of graphite, diamond and a variety of other forms of sp2 carbons (Fig. 3) is described in a review [39] and is not covered here. As the unintended formation of carbon in deactivation processes and the modification of primary carbon surfaces during chemical treatment (in catalytic service and during oxidative reactivation) and their chemical properties arc frequent problems encountered in catalytic carbon chemistry, it seems appropriate to discuss some general mechanistic ideas which mostly stem from the analysis of homogeneous combustion processes (flame chemistry) and from controlled-atmosphcre electron microscopy. 

A wide array of surface modification techniques, ranging from simple to sophisticated, wet to dry, and vacuum to nonvacuum, are available for a host of polymeric materials. They include plasma surface treatment laser surface treatment corona, flame, UV, ozone, UV/ozone, photochemical, photografting, chemical grafting, and chemical methods of stuface modification and modification of polyamide surfaces by microorganisms [7]. 

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