Pretreatment methods plasma treatment

Pretreatment methods such as flaming, corona treatment, or ND plasma treatment are not useful, or even disadvantageous, with cyanacrylate adhesives due to the formation of acidic cleavage products or components on the surface. 

Many pretreatment techniques are used in practice (Table 8.2). The normal physical method used to improve the adhesive strength of the coating to the substrate is to slightly roughen the surface by solvent treatment, abrasion, or blasting. Some plastics (e.g., polyolefins) require special pretreatment methods processes that modify the surface molecular layers of the plastic to increase their polarity have proved suitable (e.g., flaming, immersion in an oxidizing acid, immersion in a benzophenone solution with UV irradiation, corona treatment, plasma treatment). 

Polyolefins, such as PE and PP, are commonly used in many applications in the biomedical sector. PE and PP can achieve biocompatible and antimicrobial properties using the suitable surface treatment [131, 132]. Many modification methods of the polymer surfaces have been employed, for example, techniques based on the plasma treatment [133]. A deposition of chitosan on the plasma-pretreated PP surface provides antifungal and antibacterial properties because chitosan exhibits an efficient antimicrobial activity [134]. If PE films were modified by a multistep process using plasma discharge, carboxylic groups and antibacterial agent can be developed over the surface. Immersion of these films into the solution of chitosan leads most likely to the adherence of a chitosan monolayer on the treated film. Small concentration of chitosan was enough for the induction of antimicrobial properties to the modified material [135]. 

Industrial application of plasma treatment for cotton gray fabric pretreatment results in poorer hand feel and sofmess, but these adverse effects can be compensated by the subsequent finishing process. Plasma treatment can reduce effluents and cost of energy compared with conventional pretreatment processes. In terms of energy use, plasma treatment consumes about 9.8 ml of gasoline per meter of fabric while conventional pretreatment method consumes 62.5 ml of gasoline. In addition, the residues that remain after plasma treatment can be removed easily by the subsequent washing process. The plasma treatment shortens the treatment time when compared with conventional pretreatment with chemicals, but similar results can be achieved (Chen, 2005). 

As shown in Table 3.2, there was an increasing trend after BTCA treatment in the presence of SHP (catalyst) and TiO (cocatalyst). WRAs of plasma-pretreated fabrics further improved compared with those of the untreated fabrics. This confirms that plasma treatment with a lOmm/s speed, a O.lL/min oxygen flow rate, and a 4 mm jet-to-substrate distance is the most effective method for improving wrinkle-resistance properties of BTCA-treated fabric in the presence of SHP (Lam et al., 2011). 

Plasma treatment of microchannels can be useful for improving the functionality of microdevices. For example, previous studies have shown that PDMS microchannels can be made hydrophilic by the addition of silane molecules with polar head groups [6]. In this process (3-mercaptopropyl)trimethoxysilane (3-MPS) was absorbed to PDMS to increase the hydrophilic properties of microchannels. Additionally, plasma polymerization has been used to induce in the long-term hydrophilic surface modification by covalently bonding a polymer layer to the surface. Barbier et al. [7] describe a method based on plasma polymerization modification with acrylic acid coatings. First, argon plasma pretreatment was used to activate trace oxygen molecules in the chamber, which partially oxidize the top layer of the substrate. This step cross-linked the surface to reduce ablation of silicon... 

Pretreatment of carbon materials can significantly improve their catalytic activity toward ORR and change their electrochemical behavior. A variety of treatment methods have been used, including polishing the electrode, radio frequency plasma treatment, heating at low pressmes, in-situ laser irradiation. 

An acrylate-based photocurable ink is used. The surface of the substrate to be printed must be pretreated in several steps, including oxygen plasma treatment, surface hydroxylation, and an anti-adhesion treatment. Onto this surface, the ink can be printed by the drop-on-demand method. The angle of the lenses depends on the method of pretreatment (20). 

Some of the most important factors to consider when selecting a pretreatment method are its ease of use and ageing behaviour. One method often chosen is the PlasmaTreat system for enhancing adhesion used in particular for polypropylene. The basics of the plasma-treatment are described in Fig. 50. In Section 6.5.4. the method Open Air Plasma Treatment is further explained. 

In recent years, efforts have been directed to develop surface pretreatment methods on PHAs for the introduction of polar groups without affecting their bulk properties. Among them, ozone, plasma, and alkali treatments are often used to modify the PHA surfaces. 

Among the different types of pretreatment methods proposed, plasma treatment represents probably the most versatile and efficient method for surface modification. The properties of plasma-modified surfaces mainly depend on parameters controlled by the reaction conditions (i.e., type of gas, pressure, radiofrequency, effective power, and time of treatment) and by the physicochemical properties of the polymer used. By using short plasma treatments, the surface modification can be confined to the first atomic layers of the polymer surface. Moreover, plasma treatment offers the ability to choose the nature of the chemical modification as a function of the gas used. As an example, the introduction of amine functionalities on PHB surfaces has been achieved using ammonia plasma [47, 51]. However, the number of functional groups formed at the surface is difficult to control. 

For this reason, the polymer substrate treatment represents a very important step in the technology of metallic or ceramic coating on the polymer substrate. Therefore, noble metals and other low reactivity metals do not wet the untreated polymer surfaces, forming three-dimensional spherical clusters growing in a Volmer-Weber mode. Surface modification of the hydrophobic polymer surface onto a hydrophilic one can be achieved by wet (acid, alkali), dry (plasma), and radiation treatments (ultraviolet radiation and laser), without affecting the bulk properties. Consequently, application of different pretreatment methods represents an efficient way to improve wettability and thin metal adhesion. 

Polyolefins, such as polyethylene, polypropylene, and polymethylpentene, as well as polyformaldehyde and polyether, may be more effectively treated with a sodium dichro-mate- sulfuric acid solution. This treatment oxidizes the surface, allowing better wetting. Activated gas plasma treatment, described in the general section on surface treatments is also an effective treatment for these plastics. Table 7.17 shows the tensile-shear strength of bonded polyethylene pretreated by these various methods. 

The data obtained in the study indicated that the overall effects of the treatment are similar to those observed for certain plasma treatment and flame treatment, even though the actual mechanisms of the surface chemical changes may be different. Unlike glow discharge treatments, the process can be applied under ambient conditions as a continuous treatment method. The data presented indicate that the method may be commercially exploitable for film treatment and further, that the method might be particularly useful for the applications where a controlled level of surface oxidation is required, for example, for surface pretreatment or preparation of delicate films. 

The use of various pretreatments of the plastic wastes such as chemical soaking, heat treatments, microwave, and plasma treatments, etc. in conjunction with the pressurized method might be attractive areas for future research. Co-pyrolysis with other wastes such as food wastes is also plausible. Much work has been carried out on other pressurized carbonization methods such as biomass hydrothermal carbonization [111, 112]. If an industrial process is to emerge from the research, the combined use of various carbon sources would be attractive for economy-of-scale purposes. Producing porous carbons for further applications from plastic wastes would not only yield useful products from cheap precursors, but it would also help reduce the problems associated with the ever-growing plastic waste stream. 

The first method, although effective, was soon abandoned for safety reasons, while the use of chromic acid has been largely discontinued. The other two have remained the most widely used pre-treatments, not only for LDPE but also for high-density polyethylene (HDPE) and polypropylene (PP). Other methods have been found to be effective, but for reasons of cost, safety or convenience, they have not been widely used. The pre-treatments include fuming nitric acid, potassium permanganate, ammonium peroxydisulphate, ozone, fluorine, peroxides, UV radiation, grafting of polar monomers, plasmas (see Plasma pretreatment), electrochemical oxidation (see Electrochemical pre-treatment of polymers) and the use of solvent vapours. The corona, flame and plasma methods and the use of trichloroethylene are now discussed briefly the latter is included because it involves a different mechanism. 

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