| Poly(ethylene terephthalate)(PET) is a semi-crystalline thermoplastic. The six-sided carbon aromatic benzene ring in PET chain makes it has a good balance of thermal, and mechanical properties, low permeability and chemical resistance. Regarding its advantages, PET has been widely used in the fields of fibers, automotive industry, and for food and beverage packaging. However the bulk PET has low crystallinity because it is a semi-crystalline polymer. Under the common condition, the low crystallinity limits the application of PET in engineering plastic. Therefore improving the crystallization behaviors of PET becomes a big program in polymer modification. In this research, the PET was modified through inner factor and outer factor by precipitation method and solvent-casting method, respectively. Through precipitation, the high crystallization PET can be made without incorporation of any nucleating agent that makes PET has highest purity. Unlike traditional melting method, the solvent-casting method makes the nucleating agents dispersed into polymer homogeneously. The crystallization behaviors, thermal stabilities and mechanical properties of the modified PET were studied.Based on the solvent trifluoroacetic acid(TFA), a poly(ethylene terephthalate)(PET)/allylisobutyl polyhedral oligomeric silsesquioxanes(a-POSS) nanocomposite is prepared by a solvent-casting method and as-received PET(asr-PET) is modified by a precipitation method to yield precipitated PET(p-PET). The crystallization behaviors of PET/a-POSS nanocomposite and p-PET have been studied. Differential scanning calorimetry(DSC) results show these two modification methods improved the crystallization temperatures and crystallinities of PET. The same results are also confirmed by FTIR, where the ester group stretching is shifted in the PET/a-POSS nanocomposite and p-PET samples from its frequency in asr-PET. Both PET/a-POSS nanocomposite and p-PET are subsequently used to further nucleate asr-PET at the levels of 1 and 5 wt% to form the self-nucleated PETs. DSC is used to determine the crystallization behaviors and self-nucleating abilities of these four different self-nucleated PET samples(asr-PET with 1 and 5 wt% of PET/a-POSS nanocomposite; asr-PET with 1 and 5 wt% of p-PET). All of the DSC results show that these four self-nucleated PET samples have higher crystallization temperature and higher crystallinity ratio.PEGs was used as nucleation agents in asr-PET and p-PET. 1, 3, 5 and 7 weight percent of PEGs were added into asr-PET and p-PET respectively to form the PET/PEGs and p-PET/PEGs nanocomposites. The FTIR results show the PEGs affected both of the PET. The DSC was tested with the heating rate of 20 °C/min and cool rate of 50 °C /min. Under this condition, the DSC results show the crystallization temperature of PET/PEGs nanocomposites have been improved from 168.2 °C to 193.5, 187.5, 181.9 and 192.1 °C respectively with the incorporation of 1, 3, 5 and 7% of PEGs. Meanwhile, the crystallization rates of PET/PEGs nanocomposites have been improved from 10.1 % to 25.6, 25.0, 27.7 and 19.6 respectively. TGA shows with the adding of PEGs, the thermal stabilities have been improved as well. Nano-indentation shows the mechanical properties and hardness of increased with increasing of PEGs amount.For p-PET/PEGs nanocomposites, the FTIR was applied to detect the influence of PEGs on p-PET. At the heating rate of 20 °C/min and cool rate of 50 °C /min, the DSC shows that the crystallization temperatures of p-PET/PEGs nanocomposites have been improved after incorporation of PEGs while the rate of crystallization have been improved at large. Both of DSC and TGA show the thermal stabilities have been improved when the PEGs were added into p-PET. From the nano-indentation, the hardness and Young’s modulus have been improved comparing to the pure p-PET. |
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