Preparation, Structure, Properties And Dispersion Behavior Of FRCR/LS Nanocomposites

To improve the performance of the free radical curing resins and broaden their usage, diallyl phthalate (DAP) and vinyl ester resin (VER) were chosen as matrix respectively to prepare polymer layered silicate (PLS) nanocomposites investigated by adding OLS. The following important work and results were emphasized in this dissertation.(1) The Organomontmorillonte (OMMT) and Organorectorite (OREC) were synthesized through a cationic exchange reaction using two kinds of inorganic clays, sodium montmorillonite (Na-MMT) and calcium rectorite (Ca-REC), respectively. The Infrared Spectrum (IR), broadened gallery spacing and improved thermal stability before 200℃of the OLS indicate the insertion of the organic intercalators.(2) The DAP and VER based nanocomposites were manufactured using four OLS respectively through an in situ polymerization. The X-ray Defraction (XRD) and Transmission Electronic Microscopy (TEM) show the nanocomposite forms an orderly interclated, intercalation-dominated and exfoliation-dominated structure for DAP/OMMT, DAP/OREC and VER/OLS, respectively. The structure of long-chain organic intercalators is found to have no effect on the nanocomposite structure in nano-scale, but have an effect on the dimension and distribution of intercalated tactoids in micro-scale.(3) A maximum of flexural and impact strength of DAP nanocomposites can be obtained with the increase of the OLS loading, while the variation of flexural modulus is dependent on the type of inorganic clays. The dynamic storage modulus and glass transition temperature of DAP nanocomposites are also found increased by adding OLS. Flowing a conventional curing method, the flexural modulus increase marginally, while the flexural strength of VER nanocomposites decrease with the increase of OLS loading, with longer gel time, lower insoluble fraction of cured resins and lower glass transmission temperatures of cured materials. These parameters can be enhanced by adding a medium temperature initiator, benzoyl peroxide, and altering the curing condition. Following the latter curing method, the flexural strength and glass transmission temperature is found even higher than that of cured pure VER resin. However, the impact strength of all the VER nonocomposite samples decreases with the increase of OLS loading.(4) The thermal stability of DAP nanocomposites decrease with the increase of OLS loading, while the stability of VER nanocomposites increase with the addition of OLS. The stability of both matrices based nanocomposites are influenced with the interclator structure and the type of inorganic clays.(5) Compared with the pure DAP monomer, the delayed gel time (except for MHAB-MMT reaction system), increased total active energy of the two peaks of Differential Scanning Calorimetry (DSC) scans and decreased curing degree indicate that the OLS have hindered the curing reaction of DAP/OLS system. Nevertheless, the conversion to the gel point, molecular weight and distribution, and iodine number is unaffected by adding OLS, which indicates the curing mechanism of DAP is unchanged in DAP/OLS system.(6) The effect of the intercalator structure, dipole moment of polymers and monomers, crosslinking and polymerization heat on the microstructure of FRCR/LS nanocomposites was studied systematically. It was found that the role of intercalators is to enlarge the gallery spacing to make room for the monomers to penetrate into the gallery of clays during polymerization. In addition, the polarity of polymers and monomers (or liquid resins) was found not essential for the exfoliation of clays in DAP monomers or VER resins. Only can the exfoliated nanocomposite be obtained under the condition that the delamination of clay layers is drived by reaction heat before gel point. Based upon these results, a model was proposed to interpret the dispersion kinetics of LS in FRCR matrix when in situ polymerization is used to prepare FRCR/LS nanocomposites. The key points of this model are:1) the dispersion process can be divided into two ones, i. e. the processes of the first intercalation and the subsequent intercalation.2) The basal spacing of OLS after the first intercalation is controlled by the polarity of monomers (or liquid resins) while the subsequent intercalation, whicth may be affected by the crosslinking, is drived by the chemical reacton.3) An exfoliated nanocomposite can not be prepared unless the subsequent intercalation proceeds successfully till the basal spacing of OLS is more than 8 nm.(7) The DAP based unidirectional laminates modified with OLS were manufactured using conventional hand lay-up techniques. The flexural performance of laminates along the fibers are observed unaffected with the addition of OLS, while the interlaminar shear strength (ILSS) and compressive strength are influenced by the structure of intercalators and the type of inorganic clays. The ILSS and off-axis compressive strength increase evidently with adding the OLS containing reactive intercalator or being able to exfoliate to some extent, which reason can be ascribe to the property improvement of matrix and the enhancement of interfacial adhesion between the fibers and matrix.