1,721,075 research outputs found
Can liquid crystalline polymers find application in the field of protective coatings?
No full textGlycidyl terminated rigid-rod monomers can be cured in a liquid crystalline state. The resulting thermoset offers high potential as protective coating thanks to its outstanding properties. In particular a superior fracture toughness and a reduced internal stress are two typical parameters offered by this new class of compounds. Transport properties are not strongly affected by the state of order of the cross-linked resin, in the sense that gas permeabilities are of the same order of magnitude of conventional epoxy resins. Glycidyl terminated rigid-rod monomers can be cured in a liquid crystalline state. The resulting thermoset offers high potential as protective coating thanks to its outstanding properties. In particular a superior fracture toughness and a reduced internal stress are two typical parameters offered by this new class of compound. Transport properties are not strongly affected by the state of order of the cross-linked resin, in the sense that gas permeabilities are of the same order of magnitude of conventional epoxy resins
Epoxy-based liquid crystalline coatings
No full textLiquid crystalline epoxy resins display properties which make them suitable for coating application. In fact, they exhibit superior fracture resistance, low coefficient of thermal expansion, good bonier properties and good heat and solvent stability. Moreover, the onset during the curing reaction of the liquid crystalline phase, creates on increase in the reaction rate which could lower the reaction times or temperature, whilst increasing the conversion obtained on curing. In this paper, an account is presented of the properties exhibited by these materials
Incompatible blends of liquid crystalline polymers and engineering thermoplastic
No full textThe increasing demand for the high technology market for new applications in the aerospace industry has led to the research on high performance thermoplastics as composite matrices. The inclusion of solid fibres in this class of materials during manufacturing may result in processing conditions that are too demanding. High temperature and pressure in stamping or injecting tools may result in thermal degradation of the organic matrix. Moreover, the load transfer through the fibre-matrix interface produces fibres breaking into fragments shorter than the critical length, affecting their aspect ratio, and consequently reducing the final performance of the product. The possibility of producing the reinforcing filler during the cooling cycle of the composite processing has suggested the definition of 'in situ' composite. In this paper the addition of thermotropic liquid crystalline polymer to engineering thermoplastics has been investigated. X-ray diffraction techniques have been used to evaluate the molecular orientation of the dispersed phase. The rheology and the mechanical properties of the in situ composites is related to the morphology of the material and to the processing operations
Phragmen-Lindelof Principles for Nonlinear Elliptic Equations
No full textThis paper is devoted to show Phragmen-Lindelof principles in the framework of fully nonlinear second order elliptic equationswith superlinear gradient terms in the viscosity sense
Novel approach to the tailoring of polymers for advanced composites and optical applications, involving the synthesis of liquid crystalline epoxy resins
No full textThe authors describe the features of liquid crystalline epoxy resins having both high and low crosslinking densities. These materials seem to be very promising as matrices in advanced composites and in optical and electro-optical applications because of their peculiar properties. The importance of factors like molecular rigidity, nature of the curing agent, and curing temperature for the development of such properties are analyzed. The authors showed that amines produce thermosets having high T gs and high fracture toughness. In particular, the enhancement of this last parameter is very promising if a new generation of matrices is to be sought for manufacturing composites. In the case of acids as curing agents, thermosets having lower T gs and more ordered mesophases can be obtained. In this case, LC elastomers can be prepared that can find applications in the optical industry as waveguides or electro-optical devices
Liquid crystalline epoxy thermosets
No full textRigid rod epoxy compounds can be cured in liquid crystalline structure. The so obtained networks exhibit better mechanical properties with respect to the isotropic ones. The mesogenic character of the epoxy compounds appears more crucial than the molecular geometry of the curing agent in developing liquid crystallinity. The curing temperature plays an important role in affecting the state of order of the thermosets
Liquid-crystalline epoxy resins: curing of blends of mesogenic and non-mesogenic epoxy monomers
No full textLiquid crystalline epoxy based thermosetting polymers
No full textIn recent years many examples of liquid crystalline thermosetting polymers have been reported in the literature. The main reason for the development of this new class of materials comes from both technological and theoretical implications. Among the different anisotropic thermosets, epoxy resins represent a family of polymers whose properties make them primary candidates in different fields ranging from high performance matrices in advanced composites to polymers for optical applications. The chemistry of curing process of amine hardened conventional epoxy resins is well known from the literature; however some substancial differences arise during liquid crystalline epoxy monomers crosslinking. The level of order of the cured resin can be strongly affected by the nature of the hardener, as well as the physical properties of the cured material. This review will present the results of synthesis and physico-chemical characterization of liquid crystalline epoxy resins in relation to their applications in some specific fields
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