In-situ composite formation

Strong elongational deformation and use of matrix polymers whose viscosity is higher than that of TLCP phase are better to ensure uniform and fine fibril formation. But application of compatibilizing techniques to in situ composite preparation can be useful to get the most desirable products. These can reduce the high costs of the liquid crystalline polymers and expensive special engineering plastics used for the in situ composite preparation and reduce the processing cost, whereas they can increase the performance of produced in situ composites, hence, their applications, too. 

Siebert and Riew (4) described the chemistry of the in situ particle formation. They proposed that the composition of the particle is a mixture of linear CTBN-epoxy copolymers and crosslinked epoxy resin. The polymer morphology of the CTBN toughened epoxy systems was investigated by Rowe (5) using transmission electron microscopy by carbon replication of fracture surfaces. Riew and Smith (6) supported the... 

Palandri J. L. and Reed M. H. (2001) Reconstruction of in situ composition of sedimentary formation waters. Geochim. Cosmochim. Acta 65, 1741-1767. 

We observed some differences in morphology between the samples prepared by these two ways. For the systems obtained in situ the formation of NiO phase proceeded both on the surface of the spheres of the silicate and inside its pores. The composite material obtained by the second (two-step) way differed from the in situ obtained material by preferable incorporation of the NiO inside mesoporous and nanotubes of the Ti-silicate (Fig. la). It is likely that microemulsion provides a uniform distribution of the chelated nickel ions Inside the micelles over the total surface of the silicate, whereas suspension guarantees higher completeness of a transfer and concentration of the NiO crystallites inside the pores of the silicate. 

The water sequestered in the hydrate lattice is preferentially enriched in 0 and deuterium (D), thus the isotopic composition of the water in the pore spaces collected from gas hydrate bearing sediment can provide additional information on the abundance and the characteristics of these deposits. Pore fluid samples that had been modified by hydrate decomposition upon core recovery during ODP Legs 146 (Kastner et al. 1998), and 164 (Matsumoto and Borowski 2000) provided the first field data to derive the oxygen isotope fractionation factor for in situ hydrate formation. A more comprehensive sampling... 

Figure 8. In situ gel formation and degradation behavior of composite hydrogels. From A to E showed the photograph took at Id, 3d, 7d, lOd and 14d after injection respectively (From left to right S4, S3, S2 and SI). F and G presented the photograph took at 2h and 6h after Pluronic FI27 hydrogel injection.

From the viewpoint of composite mechanics, the better performances of composites come from the effective reinforcing effect of the reinforcements and effective stress transferring from the mafiix to the reinforcements. The reinforcing LCP fibrils in in situ composites are generated during the melt processing of LCP blends, which is different fi om conventional glass or carbon fiber-reinforced composites. So the formation of LCP fibrils becomes one of the most important aspects in the preparation of in situ composites, except the common interfacial interaction in fiber-reinforced plastics. 

At the early stage of research on in situ composites, most work has been conducted on the LCP microfibril formation connected with the melt viscosity or viscosity ratio, composition, and flow mode, etc. These results have been summarized and reviewed by several researchers [11-17]. In the aspect of flb-rillation, the current work is only a supplement to those reviews, with additional new insights and results. We will summarize and review the recent work on the compatibility of LCP blends in this chapter. 

The effect of LCP content is closely related to the viscosity ratio of the LCP to the matrix. Blizard and Baird [29] concluded that at 10 wt% LCP (PHB/PET) with Nylon 66 and PC, the volume fraction of the minor LCP phase was too low to allow coalescence of the droplets necessary for fibril formation. The author has hypothesized when the LCP content is very low, such as 10%, the coalescence of the LCP phase is limited, the deformation of the dispersed phase is difficult, and the rather low viscosity ratio is not sufficient to make the LCP phase form fibrils only at a much lower viscosity ratio can the deformation and coalescence of the LCP phase occur [33]. At a lower LCP content, significant LCP fibrillation takes place when the viscosity ratio is far below unity. The author found that even in extrudates of LCP [a copolyester polycon-densed from p-hydroxybenzoic acid, naphthalene diphenol, terephthalic acid, and poly(ethylene terephthalate)]/polysulfone (PSF) 2/98 (by weight), LCP fibrils were generated when the viscosity ratio of LCP to PSF was smaller than 0.01 [34]. The purpose of developing in situ composites is to make strong materials at a reasonable cost. Practical formulations with lower LCP contents are readily accepted by the manufacturers, which will be accomplished only by viscosity ratios far below unity. 

It should be noted that there is not simply an addition of thermotropic LCPs into fiber-reinforced plastics to get in situ hybrid composites. Bafna et al. used glass fibers to decrease the anisotropy of LCP fibril-reinforced polyetherimide [136]. He et al. improved the processability and mechanical performances of glass fiber-reinforced polypropylene by the addition of LCPs [159]. However, these two works did not actively and purposely generate a reinforced composite with the reinforcements having their diameters at two orders of magnitude. The key point for in situ hybrid composites is the formation of LCP fibrils in the material system. As a combination of in situ composite and hybrid fiber reinforcing, the fabrication of in situ hybrid composites utilizes fabrication... 

Li Z M, Yang M B, Huang R, Yang W and Feng J M (2002) Poly(ethylene terephthalate)/poly-ethylene composite based on in situ microfibril formation, Polym Plast Technol Eng 41 10-32. 

Thomas et al. [16] used CSLM to observe in situ the formation of polyamide membranes and the measurements were used to study polymer precipitation kinetics. Turner and Cheng [17] applied CSLM and hydrophilic fluorescent probes of varying molecular weights to image the size distribution of poly(methacrylic acid) (PMAA) hydrogel domains in polydimethylsiloxane (PDMS)-PMAA interpenetrating polymer networks. The combination of CSLM with AFM, SEM and X-ray spectroscopy allowed characterization of the structure of stimuli-responsive polymeric composite membranes [18]. 

PET/PE composites in an in situ fibre formation are used for compatibilisation of PET-e-caprolactone copolymers. 

The effect of miscibility of the host and reinforcing phase formations in in-situ composites have been studied by Zhang and co-workers (Narh et al. 2000a). Seppala et al. (1992) blended Vectra with various thermoplastics and the blends were injection molded. LCP was found to act as a reinforcing agent in the matrix polymers and improves their dimensional stability. They also found that there is a poor interfacial adhesion between the LCP and the matrix polymers. 

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