In-situ composites

In situ composites are composites composed of a thermoplastic polymer and a LCP. The concept is applicable to various classes of polymers. Recent studies and polymers are that form in situ composites are summarized in Table 16.4. 

During fabrication, the LCP forms fine fibrils that reinforce the thermoplastic polymer matrix. The mechanism of reinforcement resemble those of glass fibers. However, when light weight is a key issue, in situ composites are superior in comparison to glass fibers.  

Styrene-(ethylene butylene)-styrene triblock copolymer  

In addition, LCPs display viscosities that are considerably lower than other polymers. For this reason, the processability of LCP reinforced composites is better. Of course the price of LCP is much higher than the price of glass fibers. 

The particular orientation of the LCP in the course of flow effects a shear thinning at low shear rates. High shear forces favor the formation of fibrils. In aromatic poly(ester)/LCP blends, the viscosity ratio is more responsive in controlling the morphology.  

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M. Rabiaovitch and J. M. Hauser, iuJ. L. Walter and co-workers, eds.. Proceedings of the Conference on In-Situ Composites III, Ginn Custom PubHshers, Lexington, Mass., 1979, pp. 246—247. 

An important example of an MMC in situ composite is one made by directional solidification of a eutectic alloy. The strength, (, of such an in situ metal-matrix composite is given by a relationship similar to the HaH-Petch relationship used for grain boundary strengthening of metals ... 

Conference on In-Situ Composites II, edited by M. R. Jackson, J. L. Walter, F. D. Lemkey and R. W. Hertzberg, Xerox Publishing. 191 Spring Street, Lexington, Mass. 02173, USA, 1976. 

III. THE ROLE OF BLENDS MISCIBILITY IN THE GENERATION OF IN SITU COMPOSITES... 

Therefore, we can conclude that there exists an optimum amount of compatibilizer for the best dispersion of TLCP phase and for the most improvement of the in situ composites with high fibrillation. Excess amounts of PEsI coalesce the TLCP droplets. The adhesion at the... 

Figure 9 (a) Tensile strength versus PEsI content for PEl-TLCP in situ composite at a draw ratio of 4. (b) Tensile modulus versus PEsI content for PEI-TLCP in situ composite at a draw ratio of 4, Source Ref. 11. 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

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. 

According to the composite theory, tensile modulus of fiber reinforced composites can be calculated by knowing the mechanical constants of the components, their volume fraction, the fiber aspect ratio, and orientation. But in the case of in situ composites injection molded, the TLCP fibrils are developed during the processing and are still embedded in the matrix. Their modulus cannot be directly measured. To overcome this problem, a calculation procedure was developed to estimate the tensile modulus of the dispersed fibers and droplets as following. 

In situ air stripping, in soil and ground water treatment, 25 844 In situ bioremediation, in soil and ground water treatment, 25 836-842 In situ combustion enhanced oil recovery method, 18 630-631 In situ composites, 13 503 In situ diagnostics, for MOCVD, 22 155-156... 

Singh, M. and Lewis, D., In Situ Composites Science and Technology, Pittsburgh, PA, Proceedings of a Symposium, 1993. 

Lattice imaging studies by TEM on a "young" fraction showed extensive regions of crystallinity with minimal evidence of crystallite fracturing. By contrast, similar investigations of an "old" fraction, combined with in situ compositional analysis, revealed small "islands" of crystallinity within a "sea" of disordered material that was once crystalline. Fracture lines at crystallite boundaries are absent. Instead, the small USY crystallites within the "old" fraction are in intimate mixture with the collapsed zeolite. 

The RHEED technique has recently been used successfully in the in-situ compositional control of the MBE growth of InxGai.xN, 0 < x < 0.4 [12], This was achieved by monitoring the oscillations of the specular beam intensity during deposition of the alloy. 

The steady state in situ composition of the catalyst melt is affected by the composition of the gas that is passing around the melt. It varies down the catalyst beds. 

Gotman, I., Koczak, M. J., and Shtessel, E., Fabrication of A1 matrix in situ composites via self-propagating synthesis. Mater. Sci. Eng., A187, 189 (1994). 

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

Chen CM, Zhang LT, Zhou WC, Hao ZZ, Jiang YJ, Yang SL (2001) Microstructure, mechanical performance and oxidation mechanism of boride in situ composites. Comp Sci Technol 61 971-975... 

Goto T, Hirai T (1987) Preparation of SiC-TiC in-situ composites by chemical vapour deposition. In Cullen GW (ed) Proceedings of the 10th international conference on chemical vapour deposition. Electrochemical Society, Pennington, NJ, ppl070-1079... 

Figure D.20 is reprinted from the Electrochemical Society, T Goto and T Hirai, Preparation of SiC-TiC in-situ composites by chemical vapour deposition, in G W Cullen ed, Proceedings of the 10 international conference on chemical vapour deposition, 1987, pp. 1070-1079, with permission from the Electrochemical Society. Figure D.21 is reprinted from Surface and Coatings Technology, Vol. 76-77, M Fitzsimmons and V K Sarin, Comparison of WC16-CH4-H2 and WF6-CH4-H2 systems for growth of WC coatings, pp. 250-255, 1995, with permission from Elsevier.

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