| Summary: | 博士 === 國立臺灣科技大學 === 材料科學與工程系 === 107 === The thermoplastic polyurethanes (TPU) is synthesized by stepwise polymerization, during which the molecular weight increases stepwise. As a result, it is difficult to control the molecular weight. When the mechanical strength of TPU increases with molecular weight, the processability (softening point) of TPU increases as well. Therefore, the molecular weight control, mechanical properties and processability of TPU are considered contradictory issues. This study used the concentration of self-developed end-capping agent to control the molecular weight of TPU, and designed the molecular structure of end-capping agent to enhance the hydrogen bond network of TPU, so that the TPU at low molecular weight can have low temperature working properties and good mechanical properties. First, this study synthesized the copolymer of end-capping agents at four N,N-Dimethyl acrylamide (DMAA) concentrations, which are D03 (DMAA 3.0 wt.%), D05 (DMAA 5.0 wt.%), D07 (DMAA 7.0 wt.%) and D10 (DMAA 10 wt.%). The Polytetramethylene Ether Glycol (PTMG) and 4,4-Methylene diphenyl diisocyanate (MDI) were used as raw materials in this study, mixed with end-capping agents D03, D05, D07 and D10 respectively, the TPU was synthesized by using mass polymerization. The TPU showed the characteristic peaks of benzene ring, carbamate and DMAA respectively in the FT-IR spectrum. The absorption peak of -N=C=O- was not shown around 2268 cm-1, proving that the structure of TPU contains end-capping agent, and the molecular structures of PTMG and MDI fully react. The absorption peak of -C=O in the FT-IR spectrum moved towards low wave number and split into double peak. When the DMAA concentration of end-capping agent increased from 3.0 wt.% to 10 wt.%, the -C=O(H-bond) area percent of hydrogen bond increased from 41.7 % to 57.6 %. This result proves that the DMAA increases the number of hydrogen bonds of molecular structure of TPU. The molecular weight of TPU increased from 3.0 wt.% to 10 wt.% with the DMAA concentration of end-capping agent, the molecular weight of TPU increased from 35517 g/mole to 56103 g/mole. This is because the steric hindrance effect generated by the -N(CH3)2 in the molecular structure of DMAA inhibited the end-capping agent -OH and -NCO groups from forming covalent bond. The melting point of TPU refers to the melting point of hard segment (Tmh). As the DMAA concentration in the molecular structure of end-capping agent increased, the Tmh and ΔH of TPU also raised. This is because the increase of hydrogen bonding force between hard segments led to the increase of the Tmh and ΔH of TPU. When the DMAA concentration in the molecular structure of end-capping agent increased from 3.0 wt.% to 10 wt.%, the tensile strength increased from 1.4 kg/cm2 to 1.7 kg/cm2, meaning the DMAA concentration increased gradually, Moreover, as the number of hydrogen bonds increased, the mechanical properties were enhanced. When the DMAA concentration in the molecular structure of end-capping agent increased from 3.0 wt.% to 10 wt.%, the peel strength increased from 0.90 kg/cm to 2.2 kg/cm, and the shear strength increased from 24 kg/cm2 to 30 kg/cm2.
The mechanical properties of the synthetic 5D10, 10D10 and 15D10 of this study and commercially available goods Bemis 3405 after 50 times of water washing are described below. The softening temperature of 5D10, 10D10 and 15D10 was 130°C to 135°C, which are better than the softening temperature 150°C to 170°C of Bemis 3405. The peel strengths of 5D10, 10D10 and 15D10 were 2.1 kg/cm, 1.0 kg/cm and 0.5 kg/cm respectively, which are also better than the peel strength 0.3 kg/cm of Bemis 3405. In terms of the shear strength of TPU, the shear strengths of 5D10, 10D10 and 15D10 were 26 kg/cm2, 23 kg/cm2 and 21 kg/cm2 respectively, which are better than the shear strength 17 kg/ cm2 of Bemis 3405. This study also tested the peel strength and shear strength of the synthetic TPU in the harsh high temperature storage environment and the test in the low temperature storage environment. The results are comparable with the commercially available products.
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