Composites latex-cast

The crystal structure was type I. MCC was dispersed in concentrated NR latex, cast into sheets, air dried and then heat cured. Tensile properties overall decreased for MCC composites compared with pure NR sheets. However at 20 pphr a maximum tensile strength and break strain was obtained. Water absorption and biodegradability were enhanced by presence of MCC. ... 

The resulting latex suspensions were cast into film materials by evaporating the water. Analysis of an ultrathin cross-section of the film by cryo-TEM indicated successful composite latex particle coalescence and film formation, the clay plates forming a three-dimensional honey-like structure as a consequence of their original localization at the external surface of the polymer particles (Fig. 4.20). 

The percolation threshold for MWCNT/PMA composites, prepared using the conventional latex-based technique (S2-FD/CM), was compared to latex-cast composites [S2-LC). The results of the conductivity measurements are given in Figure 4.13 (/) along with the linear fittings of the equation given in Table 4.1. The determined percolation thresholds, ultimate conductivities, and critical exponent values are summarized in Table 4.5. 

Many synthesis methods for nanopartides of these materials and thdr surface functionalization have been devdoped. Nanocomposites based on polyolefins were prepared by mdt compounding with nanoscaled ZnO and 1102. Amphiphilic copolymers and surfadants were used to stabilize pattides for film casting in polystyrene, " polycarbonate, and PMMA. By in situ partide preparation in MeOH and subsequent mixing with acetone and PMMA for solvent evaporation transparent ZnO/PMMA films could be realized even without further surface modification. Poly(acrylic add-co-sodium aaylate)/ZnO composite latex partides were obtained via inverse miniemulsion polymerization. ... 

PAn composites have been formed by polymerizing aniline in the presence of a latex.50 The latexes were chlorinated copolymers (Haloflex EP 252), which were film-forming latexes. Interestingly, the thermal stability of the resultant composite was better than either of the individual components. Polyaniline-polyacrylamide51 composites have been prepared by carrying out a chemical oxidation of aniline in the presence of polyacrylamide. Films that could be cast were stable up to 250°C. However, conductivities were low (approximately 5 x 10-2 S cm-1). 

The fourth group of methods is connected with casting of polymer solutions and latexes or monomer compositions polymerizable at film formation and containing Cl for the inhibited films [4,41,53]. 

PIC is a precast and cured portland cement concrete that has been impregnated with a monomer that is subsequently polymerized in situ. This type of cement composite is the most developed of polymer-concrete products. PCC, on the other hand, is a modified concrete in which a part (10%-15% by weight) of the cement binder is replaced by a synthetic organic polymer. It is produced by incorporating a monomer, prepolymer-monomer mixture, or a dispersed polymer (latex) into a cement-concrete mix. To effect the polymerization of the monomer or prepolymer-monomer, a catalyst (initiator) is added to the mixture. The process technology used is very similar to that of conventional concrete. So, unlike PIC which has to be used as a precast structure, PCC can be cast-in-place in field applications. PC can be described as a composite that contains polymer as a binder instead of the conventional portland cement. 

Unlike PIC, which requires a precast structure, PCC has the advantage that it can be cast in place for field applications. Most of the PCC composites are based on different kinds of lattices obtained especially by emulsion polymerization. A latex is a stable dispersion of fine polymer particles in water, also containing some nonpolymeric constituents used in emulsion polymerization recipe. The lattices obtained through emulsion polymerization contain small polymer particles of 0.05-5 tm. 

Solution mixing is probably the most common method for preparing CNT-reinforced polymer composites because it needs mild conditions, xmsophisti-cated equipment, and it is easy to control. The large majority of the NR/CNT composites described in the literature were prepared by solution mixing, in which the CNTs were previously dispersed in either a solvent or polymer solution, and then further mixed with NR latex to produce a homogeneous NR/ CNT mixture the mixture was then cast in a mould, and the solvent was finally evaporated to produce a composite film. " ... 

Pasquini et al. reported that cellulose whiskers with high aspect ratio extracted directly from cassava bagasse were used to prepare NR nanocomposite films by mixing with the NR latex emulsion. The mixtures were cast on Teflon plates and dried overnight to obtain composite films. These NR nanocomposite films were not vulcanized by standard process. They found that a significant increase of the storage tensile modulus was observed upon filler addition by dynamic mechanical analysis. 

Abraham et al. reported that films of pre-vulcanized NR nanocomposite were fabricated by casting and evaporating a mixture of NR latex and aqueous suspension of cellulose nanofibrils (CNF). By this method, the CNF were evenly distributed in the NR composites. The increase of CNF content in the NR matrix caused the increasing the Young s modulus and tensile strength of materials, but the decreasing characteristic rubber elongation. The enhancements in mechanical and dynamic mechanical properties were attributed to the formation of a Zn ellulose complex and the three dimensional network of the CNF in the NR matrix as a result of the deprotonation of the cellulose. 

The dispersion of fibers in polymer latex to prepare composite has been reported for poly(6-hydroxyoctanoate) (PHO) [101, 102], polyvinylchloride (PVC) [103], waterborne epoxy [104] and polyvinyl acetate (PVAc) [94]. Most of the works focus on the use of non-polar, non-water-sensitive polymers, while keeping an aqueous media for the processing of the films to preserve the dispersion of the nanoparticles. In their pioneering work, Favier et al [94] adopted the technique of solvent casting using a synthetic latex obtained by the copolymerization between styrene (35 wt%) and butyl-acrylate (65 wt%) (poly(S-co-BuA)). Nanowhiskers were dispersed in the latex and evaporated. The nanocomposite films were obtained by water evaporation and particle coalescence at room temperature, that is at a temperature higher than Tg of poly(S-co-BuA), around 0 C. 

SWCNT/PS composites prepared using three processing techniques are addressed. For one series, the latex-based route, described in Chapter 2, was strictly followed. For two other series of composites, alternative processing techniques were used [see Table 4.2), namely, film casting/compression moulding and spin coating. 

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