Surface modification silane treatment

Natural fibers are hydrophilic and do not tend to be easily wetted or bond well with many matrix materials, particularly the commodity thermoplastics. Coupling agents, such as maleated polyolefins, silanes, and isocyanates, are often necessary for adequate performance. A wide variety of coupling agents, fiber surface modifications, and treatments has been investigated for use in natural fiber plastic composites and are reviewed elsewhere [22]. 

Avseenko et al. (2001) immobilized antigens onto aluminum-coated Mylar films by electrospray (ES) deposition. Various surface modifications of the metallized films were studied to determine their abilities to enhance sensitivity. The plastic surfaces were firsf cleaned by plasma discharge treatment, followed by coating with proteins (BSA and casein) or polymers such as poly (methyl methacrylate) or oxidized dextran, or they were exposed to dichlorodimethyl silane to create hydrophobic surfaces. Protein antigen was prepared in 10-fold excess sucrose and sprayed onto the surfaces to form arrays with spot diameters between 7 and 15 pm containing 1 to 4 pg protein. 

The production of mica for polymer applications has been reviewed by Hawley [89]. The aim of the processing is to purify the deposit and to produce particles of relatively small diameter with an aspect ratio of 50-200. The natural minerals are generally of much larger size than required and so the milling has both to delaminate and fracture the particles. The milling is the key process and a variety of methods, both wet and dry, are used, accompanied by various classification methods. Surface modification is important in many mica applications and a variety of treatments are used, especially organo-silanes. The methods of treatment are generally not disclosed. 

Many surface modifications are used with aluminium hydroxide, which responds to both silane and fatty acid treatments. Special proprietary silane coatings seem to be preferred for polypropylene applications [99]. Despite the production being water based, the preference seems to be for dry coating procedures. 

Special surface modifications are available to further improve reinforcement. The objective of the surface treatment is to increase filler loading and/or improve physical properties without loss of rheological characteristics. A variety of surface-modified kaolins have been introduced including clays treated with silane, titanate, polyester, and metal hydroxide. Silane-treated kaolin is used in applications requiring maximum aging characteristics in the service environment. 

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. 

Zeolite membranes are amenable by surface modification with a variety of chemical functional groups using simple silane chemistry that may provide alternative surface chemistry pathways for enzyme immobilization. In this context, Shukla et al. [338] have recently used a chemically modified zeolite-clay composite membrane for the immobilization of porcine lipase using glutaraldehyde to provide a chemical linkage between the enzyme and the membrane. The effects of pH, temperature, and solvent on the performance of such biphasic zeolite-membrane reactors have been evaluated in the hydrolysis of olive oil to fatty acids. Similarly, Algieri et al. [339] have immobilized tyrosinase on FAU membranes for the enzymatic conversion of the 1-tyrosine to 1-DOPA as an effective drug for Parkinson s disease treatment. This approach combines the active role of zeolite membrane as enzyme support and inhibitor suppressor. Moreover,... 

Oxide surfaces can be functionalized using a silane-based self-assembled monolayer. Amine functional groups are commonly utilized for functionalizing surfaces with biomaterials, by forming amide bonds. A common method is to expose the surface to 0.1 M aminopropyltri-methoxysilane (APTS) in toluene at 100 °C for 10 min to 1 h. This treatment renders the surface linkable with many biomaterials with a carboxylic group (-COOH). Various silanes can be utilized to decorate the surface with desired functional groups. Readers are referred to the article methods for surface modification for further understanding. 

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... 

Several silane treatments were compared to evaluate the role of surface modifications in the formation of the silica structure in a rubber compound. 

The work carried out by Kalaprasad and Thomas [34] shows different chemical surface modifications such as alkali, acetic anhydride, stearic acid, permanganate, maleic anhydride, silane, and peroxides improving the interfacial adhesion and compatibility between the fiber and matrix. A polyethylene thermoplastic matrix with sisal and glass hybrid composites was developed. The results showed that in all treatments, tensile strength increased about 10-30% and peroxide treatment showed maximum tensile strength and Young s modulus [34]. 

Figure 2.1 5000x images of pine surfaces following silane modification (without pre-treatment) with EDAX spectrums with elemental compositions (a) Pine-1 wt% APTES (b) Pine-1 wt% VTMES and (c) lwt%TESPM [4],... 

In order to improve the interfacial adhesion, the addition of functionalized polymers, i.e., MAPP or MAPE to the composite is employed. The presence of these polymers slightly modifies stiffness, but significantly increases tensile yield stress, tensile strength, and in some cases deformabillty [69,70], The numerous other surface modification techniques like silane treatment [71,72], isocyanates [73,74], surfactants [75], and various monomers as well as chemical modification [76,77] are also utilized. 

Silane treatment in surface modification of glass fiber composites have been applied by various researchers [42-45]. They have found that Silane coupling agents are effective in modifying natural fiber-polymer matrix interface and increasing the interfacial strength. 

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