Silane treatments

By forming stable covalent bonds, the silane treatment would improve the contact angle against water by increasing the hydrophobicity. The mechanism of this treatment can be explained as a silane chemical reacts with water and forms a silanol and an alcohol. With the moisture present, the silanol reacts with the hydroxyl groups of the cellulose and bonds itself to the cell wall [8]. 

Decrease in water absorption behavior is reported to occur with silanizing of banana stem and bunch fibers [26]. Ganan et al. [26] reported an increase in contact angle and decrease in surface free energy and polar component. They foxmd silane deposition on fibers surface according to Fourier transform infrared spectrometry (FTIR) analysis. 

Bleaching causes the fiber parameters to become more uniform [5]. Due to removal of some extra-cellular materials, the degree of chrystallinity increases [28], fibers acquire a whiter color and the inherent yellowness is decreased. Fibers lose some weight and become finer [12]. Increase in water absorption was reported to occur with bleaching of okra bast fibers. This might be due to the removal of hydrophobic substances which exposes hydrophilic cites [5]. Contrarily, the water absorption of banana fibers was reported to decrease from 61% to 45% for 70 hour water immersion upon sodium hypochlorite bleaching [28]. 

After NaOH treatment, natural fibers of interest are normally washed or rinsed sufficiently with tap or distilled water in order to remove the excess of NaOH or unreacted NaOH for neutraUzation and then dried before use [8, 16, 19]. A large number of studies [12, 40-50] on the effect of alkaU treatment on the properties of biocomposites consisting of various natural fibers and polymer matrices have been extensively performed by many research groups. Some papers [51-53] explored the combination effect of alkali treatment and silane treatment to improve the mechanical properties through the interfacial modification between natural fibers and polymer matrix. 

Since both glass fibers and natural fibers have reactive hydroxyl groups, extensive research efforts on silane coupHng agents for processing composites have been performed [18, 57-66]. Additional silane treatment done to the fiber after aUcaH 

By silane treatment under proper experimental conditions, natural fibers, which are normally hydrophilic or hygroscopic, can be converted into hydrophobic fibers for nonpolar polymer matrices [28], reducing the water absorption rate. Silane treatment of natural fibers may more or less increase the thermal stability of natural fibers depending on the treatment conditions. Silane treatment normally does not damage the natural fibers because no fiber-damaging elements such as an acidic catalyst are present in the silane solution and high temperature treatment 

The chemical and/or physical interaction between the silane-treated natural fibers and the polymer matrix is an important factor for improving the mechanical properties of biocomposites. Physical mixing of silane-treated natural fibers with thermoplastic resins can enhance the fiber-matrix interaction through in-termolecular entanglement or acid-base interaction [56]. In this case, limited improvement in the mechanical properties may be expected. The mechanical properties may be marginally increased by the increased wettability and the uniform dispersion of silane-treated natural fibers into the thermoplastic matrices [71]. The molecular chains may be interdiffused into the natural fiber surfaces, forming a (semi)interpenetrating polymer network [65, 72]. 

Acetylation treatment of natural fibers is originally applied to wood cellulose to stabilize cell walls against moisture, improving dimensional stability and envirormiental degradation [73]. Therefore, acetylation may contribute toward decreasing the moisture absorption of natural fibers [37]. Plasticization of cellulose-based natural fiber can be introduced by this treatment, which is related to an esterification method. During the treatment of natural fibers with acetic anhydride, the hydroxyl groups 

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Optimized grit blast/silane treatments can provide wedge test durability as good as PAA with failure entirely cohesive within the adhesive (Fig. 21) [89]. Maintaining the process parameters within acceptable tolerances is critical with the heat drying of the silane on the treated surface being the most sensitive process parameter. 

Organofunctional group Chemical structure OSi-Specialties Germany GmbH product Critical surface tension of glass with silane treatment [dyne/cm] Applied polymers (abbreviations according ASTM 1600)... 

Table 9. Effect of silane treatment on the mechanical properties of kaolin-filled polyethylene compositions [276]...

Figure 1(a) compares the XRD spectra of both Beta sample the conventional one and that prepared from organofunctionalized seeds, showing their high crystallinity. However, for the sample prepared using the seed silanization treatment, the peaks are less intense and broader compared to those corresponding to the conventional zeolite, suggesting that the Beta (PHAPTMS) presents smaller crystalline domains. 

If such fillers are to be used, they should have a neutral or slightly alkaline pH, otherwise additives such as ethylene glycol and triethanolamine, which are preferentially adsorbed on the surface of the filler, should be used, preventing any undesirable interference reactions between the filler and the crosslinking peroxide. These additives must, however, always be added to the mix before the peroxide. With some mineral fillers, such as some types of clay, the polymer may be bound to the filler by means of silane treatment, and the surface of the filler becomes completely non-polar. Consequently, the interaction with the polymer matrix increases, while the adsorption of the crosslinking peroxide by the filler is severely suppressed. 

Silane Treatment. Glass bars, fibers or fabric were soaked 5 min In stirred solutions (0.5, 1.0, 1.5, or 2.0%) of 3-amlnopropyl-trlethoxysllane In 95% ethanol, then for 10 min. In 95% ethanol, and finally for 1 min. In absolute ethanol. The glass was heated overnight In a vacuum oven at 110 C to form a polyslloxane layer bonded to the glass (2 ). 

Improvement in flexural strength due to silane treatments in glass liber thermoplastic matrix composites"... 

While organo-silane treatments are extensively used in both thermoset and elastomer applications, their use in thermoplastics has so far been somewhat restricted. This is because they do not react with the surface of calcium carbonate, one of the principal fillers used in this type of polymer and because of the lack of a suitable reactive functionality for most of the thermoplastic polymers. Today they are principally used in conjunction with glass fibres, calcined clays, aluminium and magnesium hydroxides, micas and wollastonite. The main thermo-... 

Figure 10 Dark and photocurrents with FeCp 70 redox couple before and after interfacial passivation, (a) Effect of blocking recombination at the Sn02 surface, reaction (5) (Fig. 9a), by electropolymerization of PPO. (b) Effect of blocking recombination at both the Sn02 and Ti02 surfaces, reactions (4) and (5) (Fig. 9b), by vapor-phase silane treatment without PPO. (Data from Ref. 49.)...

Added % Silane/treatment Wet adhesion b MPa/ % detached Recovered adhesion MPa/ % detached... 

The best of the silane treatments, AAMS, equilibrated at 26 MPa after TO weeks and all three silane treatments reached equilibrium at an acceptable level well above that of the non-silane control. 

Figure 3. Water-vapor adsorption isotherms for glass fibers after the silane treatment the isotherms for the untreated fibers with 0% and 6% B,0, are included. APS - 1% solution of y-aminopropyl-silane at pH 10 0%—O,4% Oand6% B.

The primary effect of B,0, in the silane-treated glass fibers was found to be an enhancement of the water adsorptivity. This dependence on B203 was also observed in the water adsorption behavior of untreated fibers, water-vapor hydrated fibers, and water-leached fibers [8], but was significantly greater after the silane treatment. It was also found that the presence of B,03 influenced the amount of silane adsorption per se. Altogether it can be concluded that there is a direct effect of B,0, on water adsorption. There is also an influence of B,03 on the adsorption and condensation of aminosilane which determines the water adsorptivity of the silane-treated fiber. 

All of the silane treatments in this study diminish the physisorptive capacity of glass fiber substrates, as shown by the isotherms (Fig. 2) and the desorption volumes of physically adsorbed water (Table 4, peak 1). This is one reason for their efficacy at promoting wet strength retention and enhancing other composite properties that degrade when moisture adsorbs at the fiber-matrix interface. Chemisorptive properties for probe adsorbates that are imparted to the substrate by silane deposition may also influence fiber-matrix interaction. 

Substrate nonwetting at resist coat has been observed most frequently with reworked and mistakenly overpromoted wafers. It occurs after repeated treatments, when the wrong liquid silane treatment has been applied, or when vapor times exceed the optimum time for that respective substrate. It can also occur in selected circuit pattern areas and not for the whole layer. Nonwetting is also... 

In Fig. 7, the difference in C Is ESCA spectra for vapor phase HMDS vs. liquid phase silane treatments is provided. The C Is XPS spectral changes are... 

The method adopted for the comparison of silane treatment effects on fiber-matrix bond strength was the determination of interfacial shear strength (IFSS) in single-filament composite (SFC) specimens [13, 14], which we have used extensively in investigating fiber-matrix interactions. The conditions of silane treatment of single fibers as well as the corresponding effects on IFSS could thus be carefully controlled, measured, and compared. 

IFSS are much more striking, emphasizing the fact that the effectiveness of silane treatment is more important in retaining fiber-matrix adhesion under conditions of exposure to moisture. 

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