Double melting behavior of poly(trimethylene terephthalate) (PTT) was studied in detail by means of differential scanning calorimetry (DSC) and optical microscopy. The results indicate that the low-temperature melting...Double melting behavior of poly(trimethylene terephthalate) (PTT) was studied in detail by means of differential scanning calorimetry (DSC) and optical microscopy. The results indicate that the low-temperature melting peak of PTT at ca. 218℃ for the samples crystallized isothermally at 203℃ is associated with the melting of crystals produced by secondary crystallization, while the high-temperature melting peak of it at about 227℃ is related to the melting of the crystals produced by primary crystallization. The results further demonstrate that the PTT crystals growing non-isothermally during cooling process are thermodynamically unstable and can undergo structure reorganization during the DSC heating scan. The reorganized crystals melt at temperature higher than the crystals produced by secondary crystallization at 203 ℃. Consequently, for the non-fully crystallized samples, the crystals grown during cooling also exhibit contribution to the high-temperature melting peak.展开更多
Time-resolved FTIR,WAXD/SAXS and DSC have been used to investigate the structural variation of non-isothermally crystallized poly(trimethylene terephthalate)(PTT) during the heating process.The three-phase model:the l...Time-resolved FTIR,WAXD/SAXS and DSC have been used to investigate the structural variation of non-isothermally crystallized poly(trimethylene terephthalate)(PTT) during the heating process.The three-phase model:the lamellar phase,the mobile amorphous phase(MAP) and the rigid amorphous phase(RAP) between lamellae is suggested to describe the structure of meltcrystallized PTT.According to FTIR results,the conformation of RAP in the constrained state is different from that of MAP.The increased content of amorphous phase in the temperature range from 120 to 192℃ is ascribed to the relaxation of RAP,rather than the melting of defective crystals.When the PTT is heated to a temperature above 192℃,the recrystallization/crystal perfection of original defective lamellae occurs without a pre-melting process,which leads to an increase in lamellar thickness and probably connects two adjacent lamellar stacks.This is responsible for an increase in crystallinity as well as a higher major melting temperature.展开更多
Crystallization behavior and resultant crystalline structure of a series of temperature-rising elu-tion-fractionated specimen of a Ziegler-Natta catalyst-synthesized propylene-ethylene random co-polymer were studied b...Crystallization behavior and resultant crystalline structure of a series of temperature-rising elu-tion-fractionated specimen of a Ziegler-Natta catalyst-synthesized propylene-ethylene random co-polymer were studied by DSC, WAXD and AFM. The experimental results indicate that both crystalliza-tion temperature and propylene sequence length exhibit great influence on the crystallization behavior and crystalline structure of the copolymer. It was found that the ethylene co-monomers acting as point defects inserted into the polypropylene chains play an important role in the formation of γ-iPP. As the co-monomer content increases, the crystallizable sequence length of iPP decreases, which produces an appropriate condition for its γ crystallization. At the same time, the existence of chain defects leads to a lower crystallinity of the copolymer and imperfection of the resultant crystals. For each individual sample with certain propylene sequence length or ethylene content, the increment of γ-iPP crystal content with increasing crystallization temperature demonstrates that higher crystallization tempera-ture is in favor of the γ-iPP crystallization. Pure γ-iPP crystals have been got in samples with propylene sequence length lower than 21 under suitable crystallization conditions.展开更多
The isothermal and non-isothermal crystallization kinetics of LCBPP and linear-iPP was investigated by optical microscopy and differential scanning calorimetry (DSC). The optical microscopy results in the isothermal c...The isothermal and non-isothermal crystallization kinetics of LCBPP and linear-iPP was investigated by optical microscopy and differential scanning calorimetry (DSC). The optical microscopy results in the isothermal crystallization process show that the crystals of LCBPP grow slower than the crystals of the linear-iPP. This originates from the low chain mobility, or in other words, the lower chain diffusion rate of LCBPP due to the existence of long side chains. The DSC results in the isothermal crystallization process show that the LCBPP exhibits, however, a higher overall crystallization rate with respect to the linear-iPP. This is related to the higher nucleation ability of LCBPP since the isothermal crystallization process of both LCBPP and linear-iPP are nucleation-dominated. Avrami analysis indicates that the nucleation nature and crystal growth manner of LCBPP and linear-iPP are about the same. The analy- ses of the non-isothermal crystallization processes indicate an increment in crystallization rate with increasing cooling rate. But at any cooling rate, the linear-iPP crystallizes more quickly than the LCBPP. This implies that the non-isothermal crystallization processes of LCBPP and linear-iPP are diffu- sion-dominated, in which the lower chain diffusion rate of LCBPP results in the slower crystallization of it.展开更多
基金Supported by the Outstanding Youth Fund of China (Grant No. 20425414)National Natural Science Foundation of China (Grant Nos. 50521302, 20574079, 20634050, and 50773088)
文摘Double melting behavior of poly(trimethylene terephthalate) (PTT) was studied in detail by means of differential scanning calorimetry (DSC) and optical microscopy. The results indicate that the low-temperature melting peak of PTT at ca. 218℃ for the samples crystallized isothermally at 203℃ is associated with the melting of crystals produced by secondary crystallization, while the high-temperature melting peak of it at about 227℃ is related to the melting of the crystals produced by primary crystallization. The results further demonstrate that the PTT crystals growing non-isothermally during cooling process are thermodynamically unstable and can undergo structure reorganization during the DSC heating scan. The reorganized crystals melt at temperature higher than the crystals produced by secondary crystallization at 203 ℃. Consequently, for the non-fully crystallized samples, the crystals grown during cooling also exhibit contribution to the high-temperature melting peak.
基金supported by the National Natural Science Foundation of China (50773088)supported by Shanghai Synchrotron Radiation Facility in China (j10sr0008 and 08sr0188)
文摘Time-resolved FTIR,WAXD/SAXS and DSC have been used to investigate the structural variation of non-isothermally crystallized poly(trimethylene terephthalate)(PTT) during the heating process.The three-phase model:the lamellar phase,the mobile amorphous phase(MAP) and the rigid amorphous phase(RAP) between lamellae is suggested to describe the structure of meltcrystallized PTT.According to FTIR results,the conformation of RAP in the constrained state is different from that of MAP.The increased content of amorphous phase in the temperature range from 120 to 192℃ is ascribed to the relaxation of RAP,rather than the melting of defective crystals.When the PTT is heated to a temperature above 192℃,the recrystallization/crystal perfection of original defective lamellae occurs without a pre-melting process,which leads to an increase in lamellar thickness and probably connects two adjacent lamellar stacks.This is responsible for an increase in crystallinity as well as a higher major melting temperature.
基金the Outstanding Youth Fund of the National Natural Science Founda-tion of China (Grant No 20425414)National Natural Science Foundations of China (Grant Nos. 50521302, 20423003, 20574079,and 20604031)State "973" Pro-grams from the Ministry of Science and Technology of China (Grant No.2003CB615602)
文摘Crystallization behavior and resultant crystalline structure of a series of temperature-rising elu-tion-fractionated specimen of a Ziegler-Natta catalyst-synthesized propylene-ethylene random co-polymer were studied by DSC, WAXD and AFM. The experimental results indicate that both crystalliza-tion temperature and propylene sequence length exhibit great influence on the crystallization behavior and crystalline structure of the copolymer. It was found that the ethylene co-monomers acting as point defects inserted into the polypropylene chains play an important role in the formation of γ-iPP. As the co-monomer content increases, the crystallizable sequence length of iPP decreases, which produces an appropriate condition for its γ crystallization. At the same time, the existence of chain defects leads to a lower crystallinity of the copolymer and imperfection of the resultant crystals. For each individual sample with certain propylene sequence length or ethylene content, the increment of γ-iPP crystal content with increasing crystallization temperature demonstrates that higher crystallization tempera-ture is in favor of the γ-iPP crystallization. Pure γ-iPP crystals have been got in samples with propylene sequence length lower than 21 under suitable crystallization conditions.
基金the Outstanding Youth Fund and the National Natural Science Founda-tion of China (Grant Nos. 50521302, 20574079 and 20423003)
文摘The isothermal and non-isothermal crystallization kinetics of LCBPP and linear-iPP was investigated by optical microscopy and differential scanning calorimetry (DSC). The optical microscopy results in the isothermal crystallization process show that the crystals of LCBPP grow slower than the crystals of the linear-iPP. This originates from the low chain mobility, or in other words, the lower chain diffusion rate of LCBPP due to the existence of long side chains. The DSC results in the isothermal crystallization process show that the LCBPP exhibits, however, a higher overall crystallization rate with respect to the linear-iPP. This is related to the higher nucleation ability of LCBPP since the isothermal crystallization process of both LCBPP and linear-iPP are nucleation-dominated. Avrami analysis indicates that the nucleation nature and crystal growth manner of LCBPP and linear-iPP are about the same. The analy- ses of the non-isothermal crystallization processes indicate an increment in crystallization rate with increasing cooling rate. But at any cooling rate, the linear-iPP crystallizes more quickly than the LCBPP. This implies that the non-isothermal crystallization processes of LCBPP and linear-iPP are diffu- sion-dominated, in which the lower chain diffusion rate of LCBPP results in the slower crystallization of it.
