Pretreatment methods alkali treatment

Several studies have been made to optimize the properties of natural fiber-reinforced PLA composites from the point of view of fiber-matrix adhesion. Pretreatment of fibers, such as chemical modification, seems to be the most promising approach, in which covalent bonds are formed between the fiber and matrix. One of the most common and efficient methods is alkali treatment (for example, with 2% sodium hydroxide aqueous solution) of fibers, which has been used to... 

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. 

Peroxide treatment The functional group of peroxide can be represented as -ROOR-. Most commonly used peroxides for this treatment are benzoyl peroxide and dicumyl peroxide. The main advantage of peroxide treatment is the quick decomposition of a peroxide yielding free radical that can react with the hydrogen group of the matrix and fiber. Like some of the other treatment methods, fibers are pretreated with alkali before treating with peroxides [2], The reactions that take place during peroxide treatment are represented in the Equations 9.7a, 9.7b, 9.7c, and 9.7d. The matrix used in these equations is polyethylene (PE). 

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. 

The pretreatment of any lignocellulosic biomass is cmcial before enzymatic hydrolysis. The objective of pretreatment is to decrease the crystallinity of cellulose which enhances the hydrolysis of cellulose by cellulases (17). Various pretreatment options are available to fractionate, solubilize, hydrolyze and separate cellulose, hemicellulose and lignin components (1,18-20). These include concentrated acid (27), dilute acid (22), SOj (25), alkali (24, 25), hydrogen peroxide (26), wet-oxidation (27), steam explosion (autohydrolysis) (28), ammonia fiber explosion (AFEX) (29), CO2 explosion (30), liquid hot water (31) and organic solvent treatments (52). In each option, the biomass is reduced in size and its physical structure is opened. Some methods of pretreatment of Lignocellulose is given in Table I. 

As the support of catalyst, the pretreatment of activated carbon is necessary. The main purpose of pretreatment is to improve the physical structure and chemical properties of the surface in order to meet the requirements of the catalytic supports. The method of pretreatment includes high temperature (graphitization), acid-alkali, gases and microwave treatment and so on. 

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