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Study On Liquid Crystalline Epoxy Toughening Composite Resin Matrixes

Posted on:2002-04-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:L X ChenFull Text:PDF
GTID:1101360032453968Subject:Materials science
Abstract/Summary:PDF Full Text Request
Epoxy resin (EP) and Bismaleimide (BMI) for their outstanding advantages on strength, modulus and technique as advanced resin matrix have been widely used in high science and technique fields, such as aviation, spaceflight, etc. However, EP and BMI used as high performance flying instrument structural composite matrixes are confined because of the cured resins having not enough toughness. The modifying work about these thermoset resins has been very active. The methods of toughening EP and BMI are reviewed, and the toughening mechanism is summarized. On the basis of the previous work, it is point out liquid crystalline epoxy in-situ composite toughens EP and BMI to enhance their toughness. The route of toughening EP and BMI domestic and overseas at present is mainly rubber, thermoplastic, chain-extending and thermotropic crystalline polymer toughening. These methods have themselves'disadvantages in varying degrees. For its structural distinguishing feature, liquid crystalline epoxy can in-situ self-reinforce to improve cured resin toughness during the cross-reaction of forming network with cure agent. At the same time, liquid crystalline epoxy is compatible with EP and BMI. Liquid crystalline epoxy links EP and BMI with strong chemical bond by ammoniac cure agent chain-extending. Moreover, the addition of liquid crystalline epoxy with low molecule weight can't lead to poor processability problem. Therefore, it is a new and worthy of studying route that liquid crystalline epoxy toughens and modifies EP and BMI. 4-hydroxyphenyl-4-hydroxybenzoate is synthesized by the reaction of 4- hydroxyphenyl methyl acid with 4-hydroxyphenol and catalyzed by concentrated sulphuric acid and boric acid, and then a novel liquid crystalline epoxy resin with the aromatic ester mesogen ?the diglycidylether of 4-hydroxyphenyl ?4-hydroxybenzoate (PHBHQ) is synthesized by the reaction of 4-hydroxyphenyl?-hydroxybenzoate with epichlorohydrin. The effect of synthesis technique and extraction way on yield has been discussed. The structure and phase behavious of the synthesized PHBHQ have been characterized by Differentia Scanning Calorimetry (DSC), Polarized Optical Microscopy(POM), Flourier Transmit Infrared(FTIR). etc. The results indicate that PHBHQ shows nematic phase during cooling process between 131℃ and 940C. The curing agents which are chosen in the experiment are 4,4'- diam inodi phenylmethane( DDM ).4,4'-diam inodiphenylsulfone(DDS).4,4'- diaminodiphenylbiphenol A(DDBA) and mixed aromatic diamine 4#(the mol ratio of DDM/DDS/DDE is equal to 5:2:1).The curing reaction characteristic, heat and mechanic properties of cured resin have been studied. It is discovered that DDM, DDBA. mixedaromatic diamine 4# combined with PHBHQ can form low me1 t point system, butDDS can' t form. Tho comprehonsiyc performance of PHBHQ/DDM and PHBHQ/mixcdaromat ic diamine 4# are better. The curing network of PHBHQ/DDM andPHBHQ/mixed aromatic diamine 4# is comprised of oriontdl order mosogcn icdomain and isotropy domain observed by SEM, P0M and Wide--angle X--RayDi ffrac t ion (WAXD).The curing mechanism and kinetics of PHBHQ reacted with DDM are studiedby FTIR. The curing reaction proceeded in auto--acce lerating mechan ism and i saccelerated by the hydroxyl group produced in the curing process. Theisothermal curing processes of PHBHQ/DDM system at different temperature aremoni tored by FTIR. The kinet ics parameters of each step of curing reactionare cal cu1 ated: Ea,=66. 5lKJ/mo1, Ea,=69. 05KJ/moI.'rhe microstructure and curing properties of the PHBHQ toughening EP andPHBHQ toughening BMI system are studied. The four systems arePHBHQ/CYD--l28/DDM,...
Keywords/Search Tags:Liquid Crystalline Epoxy, Nematic Phase, Mesogenic Domain, Toughening mechanism, Epoxy resin, Bismaleimide, Microstructure
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