Synthesis and Characterization of Segmented Polyurethane/Clay via Poly(ε-caprolactone)/Clay

• Main Authors: Teng-Kuei Chen, 陳燈桂
• Other Authors: Kung-Hwa Wei
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/24762049948134775121

博士 === 國立交通大學 === 材料科學與工程系 === 88 === Montmorillonite is a type of natural clays and consisted of two SiO2 tetrahedrons attached to one Al2O3 octahedron. Through van der Waals force the metallic ions and ionic bonds between crystalline layers provide sites for ion exchange by organic molecules. These silicate layers dimensions were 100 nm x 100 nm x 1 nm, and carried negative charges, causing an absorption of cations such as sodium (Na+) or calcium (Ca+2). The present research is concerned with the preparation of polyurethane/clay nanocomposites with two methods. Additionally, the investigations on the crystalline morphology and the reaction mechanisms of caprolactone monomer in the presence of various types of organoclay were studied. The reaction mechanism of polycaprolactone (PCL) /clay nanocomposites synthesized from organic modified clay (organoclay) and caprolactone (CL) monomers was investigated with differential scanning calorimetry and X-ray diffraction. It was found that the polymerization process of caprolactone in the presence of organoclay proceeded in two stages. The first stage occurred at low temperature, and it involved the initiation of ring-opening of caprolactone in the interlayer gallery of silicates by the functional groups of the swelling agents. The second stage took place at higher temperatures where the propagation of the active polycaprolactone chains progressed by a massive diffusion of caprolactone near the chains as the silicate layers exfoliated in polycaprolactone matrix. The activation energy of the first stage reaction increased, while the activation energy of the second stage reaction propagation decreased with the increasing amount of organoclay. Both of the activation energies depended on the type of swelling agent. The crystal sizes and crystallinity of polycaprolactone decreased with the increasing amount of organoclay, with the shape of growing crystals remained unchanged, as evidenced by X-ray and polarized microscope results. The descriptions of these two processes are as following: (1)Synthetic method: The synthesis of polyurethane/clay nanocomposites involved a reaction of the mixtures of 1, 4-butanediol (1, 4-BG), 4,4''-diphenylmethane diisocyanate (MDI), polycaprolactone diol (Mn~1000) and polycaprolactone/clay (PCL/clay) diol, with PCL/clay first being synthesized following the procedure in the literature. The elongation at break (EB) for polyurethane/clay nanocomposites containing 1.4 mole % PCL/clay had a six-fold increase as compared to that of the pure PU (i.e. 690% vs. 103%). However, the EB for PU/clay containing 4.2 mole % PCL/clay dropped significantly to 57.5%, but the maximum strength of the PU/clay still increased with the amount of PCL/clay. This implied that the properties of PU/clay changed from that of polyurethane elastomer structure to thermoplastic polyurethane structure at high PCL/clay content. (2)Solution blending process: The PU/clay nanocomposites was also synthesized by directly mixing of PU and organoclay such as 12COOH-mont and BZD-mont in DMF, and intercalated 1, 3 wt% clay/PU nanocomposites were formed. It was found that the chemical structures of the PU were not affected by the presence of organoclay from the FT-IR study. By comparing the tensile strength and elongation ratio of 1wt% BZD-mont, the prepared polyurethane/clay nanocomposites with these of polyurethane resin, the increase was twofold for tensile strength from 66.8 kgf/ cm2 to 144 kgf/ cm2, and three-fold for elongation at break for 220% to 680%. The water absorption ratios for both 1wt% 12-COOH-mont/PU and 1 wt% BZD-mont/PU also showed decreasing trend.