Flame treatment oxidation

Flame Treatment - In adhesive bonding, a surfaee preparation technique in which the plastic is briefly exposed to a flame. Flame treatment oxidizes the surface through a free radical mechanism, introducing hydroxyl, carbonyl, carboxyl, and amide functional groups to a depth of 4-6 nm, and produces chain scissions and some cross-linking. Commonly used for polyolefins, polyacetals, and polyethylene terephthalate, flame treatment increases wettability and interfacial diflfusivity. 

Antimony Oxide as a Primary Flame Retardant. Antimony oxide behaves as a condensed-phase flame retardant in cellulosic materials (2). It can be appHed by impregnating a fabric with a soluble antimony salt followed by a second treatment that precipitates antimony oxide in the fibers. When the treated fabric is exposed to a flame, the oxide reacts with the hydroxyl groups of the cellulose (qv) causing them to decompose endothermically. The decomposition products, water and char, cool the flame reactions while slowing the production and volatilization of flammable decomposition products (see Flaa retardants for textiles). 

If corona, plasma, or flame treatment is chosen as the surface treatment, it is important to bond quickly after the treatment. Waiting several hours will reduce the effectiveness of the treatment. In some cases, attempts to bond 24 h after the treatment can give the same poor bonding results as if the plastic had never been surface treated. If surface oxidation is not possible, priming the surface with a chlorinated polyethylene primer is a second choice [95]. 

Oxidation by flame treatment for polyolefins exposure to a flame of methane, propane or butane and oxygen in excess for a very short time (less than 0.2 seconds) to create oxidation and reactive sites such as hydroxyl, carbonyl, carboxyl... Particularly used for polyethylene and polypropylene. 

Oxidation by ultra-hot-air treatment for polyolefins exposition to a blast of hot air (roughly 500°C) for a short time to oxidize the surface and create reactive sites such as hydroxyl, carbonyl, carboxyl, amides... Rather similar to flame treatment, it is particularly used for polyethylene and polypropylene. 

Flame is probably the oldest plasma known to humanity and flame treatment is one of the oldest methods used by industries for the modification of polymeric surfaces. Flame treatment is very often used to treat bulky objects. It is mainly employed to enhance the ink permeability on the polymer surface. Though a very simple set-up (comprising of a burner and a fuel tank) is required for this technique, a very high degree of craftsmanship is needed to produce consistent results. Oxidation at the polymer surface brought about by the flame treatment can be attributed to the high flame temperature range (1000-1500 °C) and its interaction with many exited species in the flame. For an efficient flame treatment, the variables like air-to-... 

In flame treatment, an oxidizing flame is deployed so as to impinge on the surface for a very short time (thus avoiding melting the plastic). As time is... 

Oxidation of alcohols is normally carried out with Cr(VI) reagents (Chapter 24) but these, like the Jones reagent (Na2Cr2C>7 in sulfuric acid), are usually acidic. Some pyridine complexes of Cr(Vl) compounds solve this problem by having the pyridinium ion (p Ta 5) as the only acid. The two most famous are PDC (Pyridinium DiChromate) and PCC (Pyridinium Chloro-Chromate). Pyridine forms a complex with CrO but this is liable to burst into flames. Treatment with HC1 gives PCC, which is much less dangerous. PCC is particularly useful in the oxidation of primary alcohols to aldehydes as overoxidation is avoided in the only slightly acidic conditions (Chapter 24). 

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. 

A second relevant example is the surface oxidation of polyolefins, such as LDPE, which is carried out frequently for thick specimens using an oxidizing flame treatment. For instance, while untreated LDPE surfaces are non-polar and thus fairly hydrophobic, flame-treated LDPE possesses a much higher surface energy and therefore improve the binding of these surfaces with other substances, such as adhesives, printing inks, paints, and various metal surfaces. 

In this hands-on example we follow closely a recently published procedure [171]. Additive free LDPE films (with a thickness of 0.2 mm, e.g. obtained from DSM, Geleen, the, Netherlands) is cut into pieces of ca. 1 x 1 cm2 prior to treatment. To remove contaminants, the samples are refluxed in dichloromethane for 30 min, followed by a rinse with ethanol and drying in a stream of nitrogen immediately prior to use. For the flame treatment a mixture of natural gas and air are combusted by a nozzle type burner (using a typical flow rate of the mixture of natural gas and air of ca. 12.3 cm3/s and an equivalence ratio, which is defined as the stoichiometric oxidizer fuel ratio divided by the actual oxidizer fuel ratio of ca. 0.93). The LDPE... 

Surface ozone oxidation is applied in polymers because it has the following advantages it introduces peroxides uniformly on the polymer surfaces it is applicable to complex geometries it can be handled easily and it is relatively economical as compared with other techniques such as corona discharge, plasma treatment, flame treatment, irradiation with gamma rays.I 1... 

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. 

A major application of surface treatments is for print key or adhesion related to printing, labelling, etc., by oxidative-type surface treatments. These include corona (films), flame treatments (containers), each of which can give a marginally different effect. 

Flame treatment is a commercial process to render polyolefins and polyethylene terephthalate adherable. The polymer article (e.g., film) is passed over an oxidizing flame formed by of an oxygen-rich (relative to stoichiometry) mixture of hydrocarbon gas. Variables affecting the extent of oxidation include the flame characteristics (e.g., excess oxygen) and the speed of the article movement. Gas flame... 

Elements of the mechanism for the surface oxidation of polypropylene by flame treatment have been proposed in previous papers [16,17,19,20,27] and the flame chemistry... 

The formation of LMWOM is associated with reaction of O atoms and O3 molecules [17,31,32], with the alkoxy functional group being the main precursor to LMWOM formation. This, coupled with the chemistry effects of flame impingement discussed in the previous section, suggests that it is unlikely that the alkoxy functional group is a dominant surface oxidized species in the flame treatment process [17,20,31,32]. 

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. 

In flame treatment, plastic objects such as bottles and film are passed through an oxidizing gas flame. Momentary contact with the film causes oxidation of the surface, which makes it receptive to material used in decorating the product. 

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