A differential scanning calorimetry study on poly(ethylene terephthalate) isothermally crystallized at stepwise temperatures: multiple melting behavior re-investigated

The multiple melting behavior of poly(ethylene terephthalate) (PET) was investigated with differential scanning calorimetry (DSC) by examining PET samples having been subjected to special schemes of crystallization and annealing treatment at multiple descending temperatures. Upon such step-wise annealing in decreasing temperatures, the existence of doublet melting peaks in addition to a series of multiple minor peaks in the PET has been demonstrated using carefully designed thermal schemes. Using the Hoffman theory, multiple lamellae populations, might be suggested to be simultaneously present in the PET subjected to such thermal treatments. However, direct experimental evidence has yet to be provided. The low-temperature minor crystals simply melt during normal scanning without having time enough to reorganize into higher-melt crystals. Nevertheless, the effect of scanning on non-isothermal crystallization does exist but is primarily confined to the temperature range much below the main melting region where the crystallization of polymer chains can progress at a reasonable rate. At higher temperatures near the main melting region, annealing for extended times is required in order to result in relative changes of the melting endotherms of the upper and lower peaks in the main melting doublet. In all we have shown that interpretations of the multiple melting phenomenon in semicrystalline polymers can be better refined.     

Fiber property and structure development of polyester blend fibers reinforced with a thermotropic liquid‐crystal polymer

Ternary blend fibers (TBFs), based on melt blends of poly(ethylene 2,6‐naphthalate), poly(ethylene terephthalate), and a thermotropic liquid‐crystal polymer (TLCP), were prepared by a process of melt blending and spinning to achieve high‐performance fibers. The reinforcement effect of the polymer matrix by the TLCP component, the fibrillar structure with TLCP fibrils of high aspect ratios, and the development of more ordered and perfect crystalline structures by an annealing process resulted in the improvement of the tensile strength and modulus for the TBFs. An increase in the apparent crystallite size with the spinning speed was attributed to the development of larger crystallites and more ordered crystalline structures in the annealed TBFs. The birefringence and density of the TBFs increased with increasing spinning speed, the TBFs becoming more oriented and the crystal packing becoming more enhanced. The molecular orientation was an important factor in determining the tensile strength and modulus of the TBFs. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 395–403, 2004     

Structural analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fibers prepared by drawing and annealing processes

Structure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fibers prepared by drawing and annealing processes has been analyzed through wide-angle X-ray diffraction (WAXD), density, infrared dichroism, and birefringence measurements. There are three different types of crystalline structure in these fibers: two of these are the two types of orthorhombic with different orientation modes (the ordinary c-axis orientation (c//Z), and the preferential orientation of c-axis to the direction perpendicular to the fiber axis (c⟂Z)); and the third is pseudohexagonal. The weight fractions of the three types of crystals and amorphous phase were analyzed combining the WAXD integrated intensity and density data. The relation between crystalline orientation factors obtained separately from the WAXD measurement and the infrared dichroic ratio is also discussed. The birefringence of these fibers shows negative and positive values, depending on drawing and annealing temperatures. Considering the intrinsic birefringence and weight fraction of the c//Z, c⟂Z, and pseudohexagonal crystals, birefringence of the amorphous phase was evaluated. The amorphous birefringence shows positive values and decreases with an increase in the annealing temperature. From the analyzed fiber structure, it was speculated that the c⟂Z and pseudohexagonal crystals are preferentially formed in the drawing process irrespective of the drawing temperature.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2471–2482, 1998     

Unique morphological and thermal behaviors of reorganized poly(ethylene terephthalates)

Bulk poly(ethylene terephthalate) PET has been reorganized both morphologically and conformationally by processing from its inclusion complex (IC) formed with γ‐cyclodextrin (CD). In the narrow channels of its γ‐CD‐IC crystals the included guest PET chains are isolated from neighboring PET chains and the ethylene glycol (EG) units adopt the highly extended g±tg? kink conformations, whose cross‐sectional diameters are ～80% of the diameter of the fully extended, all‐trans crystalline PET conformer, though they are nearly (～95%) as extended. When the highly extended, unentangled guest PET chains are coalesced from their γ‐CD‐IC crystals by exposure to hot water, host γ‐CDs are removed and the PET chains are presumably consolidated into a bulk sample with a morphology and constituent chain conformations not normally found in PET samples solidified from their randomly coiling, possibly entangled, disordered melts and solutions. Observations by polarized light and atomic force microscopies provide visual evidence for widely different semicrystalline morphologies developed in coalesced and as‐received PETs when crystallized from their melts, with possibly chain extended, small crystals and spherulitic, chain‐folded, large crystals, respectively. DSC observations reveal that coalesced PET is rapidly crystallizable from the melt, while as‐received PET is slow to crystallize and is easily quenched into a totally amorphous sample. Analyses of ¹³C‐NMR data strongly indicate that the PET chains in the noncrystalline regions of the coalesced sample remain predominantly in the highly extended kink conformations, with g±tg? EG units, which are required by their inclusion into PET‐γ‐CD‐IC crystals, while the predominantly amorphous PET chains in the as‐received sample have high concentrations of gauche± ? CH₂? CH₂? and trans ? O? CH₂? ,? CH₂? O? EG bond conformations. ¹³C‐NMR T₁(¹³C) and T_1ρ(¹H) relaxation studies show no evidence of a glass transition for coalesced PET, while the as‐received sample shows abrupt changes in both the MHz [T₁(¹³C)] and kHz [T_1ρ(¹H)] motions at T ～ T_g. Preliminary observations of differences in their macroscopic properties are attributed to the very different morphologies and conformations of the constituent chains in these PET samples. Apparently the kink conformers in the noncrystalline regions of coalesced PET are at least partially retained for extended periods even in the melt and are rapidly crystallized upon cooling. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 386–394, 2004     

Crystallization and melting of cold-crystallized poly(phenylene sulfide)

In this study, we report the melting behavior of poly(phenylene sulfide), PPS, which has been cold-crystallized from the rubbery amorphous state. We find that the crystallization kinetics are faster for cold-crystallized PPS than for melt-crystallized material, due to formation during quenching of a short-range ordered, but noncrystalline, structure. We observe that the endothermic response of cold-crystallized PPS at a large undercooling consists of a low temperature endotherm, followed by an exothermic region, and by the main higher melting endotherm. The lower melting peak temperature of cold-crystallized PPS increases as the crystallization temperature increases, but the main upper melting peak temperature remains almost the same. The size of the exothermic region is strongly related to the degree of undercooling, and must be taken into account in order properly to determine the degree of crystallinity of the material prior to the scan. When the crystallization time is varied, we see a systematic decrease in the size of the main endotherm, and an increase in size of the lower melting endotherm. This suggests that a portion of the main endothermic response is due to reorganization during the scan. Annealing will not only increase the degree of crystallinity but also improve the crystal perfection; therefore the ability of an annealed sample to reorganize decreases as the annealing time increases. However, an additional third melting peak is seen when a cold-crystallized sample is annealed at high temperature for a sufficiently long residence time. The existence of the third melting peak suggests that more than one kind of distribution of crystal perfection may occur when PPS has been cold-crystallized and subsequently annealed.     

Oriented noncrystalline structure in PET fibers prepared with threadline modification process

The development of an oriented noncrystalline phase in a semicrystalline polymer filament has been studied via X-ray scattering. These unique PET fibers contain a relatively high noncrystalline content and also have high tenacity, high modulus, and low breaking elongation. Fiber properties were found to be very responsive to the oriented amorphous phase content. This phase was utilized for interpreting noncrystalline orientation in PET fibers produced by a new extrusion technique. Here, the oriented noncrystalline regions in a series of PET fibers varies from 6% to 63%, depending strongly on the production conditions. In particular, samples produced with a newly developed threadline modification process possess a high content of oriented noncrystalline polymer. Measurements such as dynamic and static mechanical properties have been performed on various samples, and these properties are related to the oriented noncrystalline phase. The results provide direct evidence for the existence of highly oriented noncrystalline material in these unique PET fibers spun with a threadline modification process. © 1996 John Wiley & Sons, Inc.     

Higher order structural analysis of stereocomplex‐type poly(lactic acid) melt‐spun fibers

The higher order structure of stereocomplex‐type poly(lactic acid) melt‐spun fibers of an equimolar blend of poly(L ‐lactic acid) and poly(D ‐lactic acid) was analyzed with wide‐angle X‐ray diffraction (WAXD) and birefringence measurements. Two different crystalline structures were observed in the fibers: α‐form homocrystals and stereocomplex crystals. The weight fractions of the two crystals were estimated with the WAXD integrated intensity data. The crystalline orientation factors were obtained from the WAXD measurements. Well‐oriented homocrystals formed during a drawing process at the crystallization temperature of the homocrystal. Drawing above this temperature caused the stereocomplex crystal to be formed. The crystalline orientation tended to be lower with increasing drawing temperatures. Through the combination of the intrinsic birefringence and the fractions of the α‐form homocrystals and stereocomplex crystals, the birefringence of the amorphous phase was evaluated. The amorphous birefringence stayed positive and decreased with increasing drawing temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 218–228, 2007     

不同后处理条件下聚萘二甲酸乙二酯纤维的结构变化

对不同纺速下制得的聚萘二甲酸乙二酯 (PEN)初生纤维进行了冷拉伸、定长热处理和热拉伸等后处理 .通过WAXS、DSC等测试研究了纤维中结构变化与后处理条件之间的关系 .结果表明 ,较低纺速下所制得的无定形初生纤维在低于Tg 温度下的冷拉伸时发生了应力诱导结晶 ,纤维中生成了α晶体 .同样的初生纤维在定长热处理过程中直至 2 0 0℃仍保持无定形结构 .这些结果说明施加应力相对于升高温度对于α晶体的生成更为重要 .而热拉伸样品中结晶结构的形成与初生纤维的结构有很大关系 ,低纺速下无定形初生纤维在热拉伸后形成α晶体 ,而高纺速下主要含有 β晶体的初生纤维经热拉伸后 β晶体会部分转变为α晶体 ,且 β晶转变为α晶的难易程度取决于初生纤维中 β晶的完善程度 ,初生纤维中 β晶越完善 ,热拉伸时 β晶体越不易转变为α晶体     

Structure development and physical properties achieved in the drawing and/or annealing of PEN fibers

As‐spun poly(ethylene‐2,6‐naphthalate) (PEN) fibers (i.e., precursors) prepared from high molecular weight polymer were drawn and/or annealed under various conditions. Structure and property variations taking place during the treatment process were followed via wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering, differential scanning calorimetry (DSC), and mechanical testing. Both the WAXS and DSC measurements of the cold‐drawn samples stretched from a low‐speed‐spun amorphous fiber indicate that strain‐induced crystallization can occur at a temperature below the glass‐transition temperature and that the resultant crystal is in the α‐form modification. In contrast, when the same precursor was subjected to constrained annealing, its amorphous characteristics remained unchanged even though the annealing was performed at 200 °C. These results may imply that the application of stretching stress is more important than elevated temperatures in producing α‐form crystallization. The crystalline structure of the hot‐drawn samples depends significantly on the morphology of the precursor fibers. When the precursor was wound at a very low speed and in a predominantly amorphous state, hot drawing induced the formation of crystals that were apparently pure α‐form modification. For the β‐form crystallized precursors wound at higher speeds, a partial crystalline transition from the β form to the α form was observed during the hot drawing. In contrast with the mechanical properties of the as‐spun fibers, those of the hot‐drawn products are not improved remarkably because the draw ratio is extremely limited for most as‐spun fibers in which an oriented crystalline structure has already formed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1424–1435, 2000     

Quantitative structural characterization of the melting behavior of isotactic polypropylene

The melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high-temperature endotherm (T_2M) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 220°C, while the lower-temperature endotherm (T_1M) extrapolates to an ultimate melting point of 185°C. Noncrystalline chain orientation influences the endotherm temperature through its changing configurational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.     

Reorganization of the structures,morphologies, and conformations of bulk polymers via coalescence from polymer–cyclodextrin inclusion compounds

Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the γ‐cyclodextrin (CD) host and PET and PC guests, which are reported for the first time. Differential scanning calorimetry, Fourier transform infrared, and X‐ray observations of PET and PC samples coalesced from their crystalline γ‐CD‐ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as‐received PC is generally amorphous with a glass‐transition temperature (T_g) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (T_m) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated T_m value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐CD host lattice are possibly more chain‐extended and certainly more stable than chain‐folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a T_m value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a T_g value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a T_g nor a crystallization exotherm but simply remelts at the as‐coalesced T_m. This behavior is unaffected by the coalesced PET sample being held above T_m for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their γ‐CD‐ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X‐ray observations are described here. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002     

Step‐like melting mechanisms of isothermally crystallized isotactic polypropylene

The complex melting behavior of isotactic polypropylene, after isothermal crystallization, was studied within the context of step‐like melting mechanisms which were previously proposed for high temperature polymers. The morphological characteristics of the melting process were also studied as a function of molecular weight, and close similarities were observed with respect to high temperature polymers. Positive birefringence crystals of low molecular weight samples developed double melting behavior in three steps. The first melting step was assigned to continuous melting of secondary crosshatch reversing lamellae, together with recrystallization of the remaining isothermal crystals. In the second melting step (first melting endotherm), crystals tended to lose their original coarse negative birefringence due to melting of secondary reversing branching. This effect rendered new, finer texture, but still negative birefringence crystals. In the third melting step (second melting endotherm), there was a combination of melting of two crystal populations, one consisting of the remaining fraction of reversing primary crystals, and the other consisting of nonreversing primary crystals. A crosshatch secondary branching model was therefore proposed to explain the overall results. Mixed birefringence spherulites of high molecular weight samples displayed similar, although proportional, behavior under identical crystallization and melting conditions corroborating the proposed melting mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2188–2200, 2008     

Effects of the drawing form and draw ratio on the fiber structure and mechanical properties of CO2-laser-heated-drawn poly(ethylene terephthalate) fibers

The structure, mechanical properties, and thermomechanical properties of poly(ethylene terephthalate) (PET) fibers obtained by laser-heated drawing were investigated in terms of their dependence on the draw ratio and feed speed and the differences between neck-drawn fibers and flow-drawn fibers. The long period at a draw ratio of 6.0 reached 19.0 nm, notably larger than at lower ratios, whereas the tilting angle of the laminar structure was constant at about 60°, regardless of the draw ratio. A maximum value of 15.0 GPa was attained for the initial modulus, and 1.07 GPa was attained for the tensile strength. A higher tensile strength orientation-induced crystallized fiber at the same initial modulus was obtained from higher molecular weight PET. The relationship between the compliance and molecular orientation of the amorphous phase was studied with a series model of crystalline and amorphous phases. The results revealed that, in the high-draw-ratio fibers, the compliance of the amorphous phase decreased with the draw ratio at a higher rate than indicated by extrapolation to intrinsic values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 79–90, 2004     

Crystallization and melting behavior of liquid crystalline copolyesters based on poly(ethylene terephthalate)

A series of copolyesters were prepared by the incorporation of p‐hydroxybenzoic acid (HBA), hydroquinone (HQ), and terephthalic acid (TA) into poly(ethylene terephthalate) (PET). On the basis of viscosity measurements, high molar mass copolyesters were obtained in the syntheses, and ¹H‐NMR analyses indicated the total insertion of comonomers. They exhibit nematic phase above melting temperature, as observed by polarized light microscope (PLM). Their crystallization and melting behaviors were also studied by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Introduction of HQ/TA disrupts longer rigid‐rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization at solid phase polymerization conditions (up to 24 h at 200°C) resulted in increased copolymer randomness (by NMR) and higher melting point, the latter attributed to structural annealing. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 369–377, 1999     

一个低分子量聚氧化乙烯从亚稳态的折叠链片晶向稳态的伸直链片晶转化增厚过程的研究

报道分子量为5000的聚氧化乙烯(PEO)从熔融态淬火到液氮温度后形成的两次链折叠(2-FC)片晶增厚过程的研究结果.在升温和恒温条件下,采用小角X射线散射(SAXS)在位地跟踪了2-FC片晶增厚成一次链折叠(1-FC)和进一步成为伸直链(EC)片晶的增厚过程.通过对SAXS数据以及它们的一维相关函数的数据的分析,发现在52℃以下,2-FC片晶主要增厚为1-FC片晶;在52℃以上,2-FC片晶则主要增厚为EC片晶;在58℃到EC片晶的熔点的温度区域里,已经形成的1-FC片晶还会熔融,完全转化为EC片晶.利用偏光显微镜(PLM)和扫描电子显微镜(SEM)观察晶体的形貌,比如球晶,获得的研究结果表明,没有发生大范围的晶体破坏后再形成的变化,也就是说片晶的增厚过程是一个发生在球晶内部的薄片晶熔融后转化为厚片晶的过程.     

Effects of posttreatment on the properties of modified PLLA/PDLA fibers

Poly(L ‐lactic acid)/poly(D ‐lactic acid) (PLLA/PDLA) blended with plasticizer poly(ethylene glycol) and nucleation agent TMC‐306 as‐spun fibers were prepared by melt spinning. The posttreatment was applied by hot drawing at 70°C and then heat‐treating at different temperatures for 30 minutes. In the process of hot drawing, orientation induced the further formation of the sc crystals and increased the degree of crystallinity of drawn fibers. When the hot drawing ratio reached 3 times, the properties of the fibers were relatively better. The highly oriented fibers containing pure sc crystals with high crystallinity were obtained by heat‐treating at a temperature above the melting point of α crystals. The posttreated PLLA/PDLA fibers with poly(ethylene glycol) and TMC‐306 (LDTP) obtained by hot drawing to 3 times at 70°C and then annealing at 170°C for 30 minutes exhibited the best antioxidative degradation and heat resistance properties. The initial decomposition temperature (T_5%) and heat resistance of posttreated LDTP fiber were about 94°C and 20°C higher than those of the commercial PLLA fiber, respectively.     

Probing multiple melting behaviors in poly(ethylene naphthalene 2,6‐dicarboxylate) with different thermal histories by simultaneous wide‐angle and small‐angle X‐ray scattering

A simultaneous wide‐angle and small‐angle X‐ray scattering study of two poly(ethylene naphthalene 2,6‐dicarboxylate) samples crystallized from the glassy state at different annealing temperatures for different annealing times was carried out with synchrotron radiation. Either single or dual melting was induced in the samples, as confirmed by differential scanning calorimetry (DSC). The correlation function and interface distribution function were calculated to evaluate microstructural parameters such as the long spacing, the thickness of the amorphous and crystalline phases, and the width of the size distributions. The sample with dual melting behavior exhibited an abrupt increase of all microstructural parameters at temperatures above the melting of the lowest endotherm, whereas the sample revealing a single melting endotherm did not show such a sudden change. This finding agrees with the concept that the appearance of two melting peaks in DSC traces can be explained by the dual lamellar stacking model. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 881–894, 2001     

聚对苯二甲酸二甲酯/聚2,5-呋喃二甲酸二甲酯嵌段聚酯的合成与表征

以生物基单体2,5-呋喃二甲酸、乙二醇为原料合成聚2,5-呋喃二甲酸乙二醇酯(PEF)。采用熔融酯交换法以PEF聚酯部分取代聚对苯二甲酸乙二醇酯(PET),制备了系列PET-b-PEF嵌段共聚酯。通过核磁共振仪(NMR)、差示扫描量热仪(DSC)、热失重仪(TGA)、X射线衍射仪(XRD)等技术手段表征了共聚酯的结构和性能。结果表明,该系列共聚酯的玻璃化转变温度(Tg)在75.8~80.3℃之间,且随着PEF链段质量分数的增加,PET-b-PEF嵌段共聚酯的Tg先降低后升高,结晶度和熔融温度逐渐降低。当PEF链段含量高于15%时,共聚酯没有结晶峰。该系列共聚酯具有良好的热稳定性,起始分解温度在392.2~407.9℃之间,与所制备的PET起始分解温度403.3℃接近。且当共聚酯中PEF链段含量低于15%时,起始分解温度均在407℃左右,优于PET的热稳定性。     

Structural features of crystallized poly(ethylene terephthalate) polymers

Polyethylene terephthalate (PET) is a widely used polymeric material. In this work, the microstructural features before and after the solid‐state polymerization (SSP) of several DuPont PET products were investigated by low‐voltage scanning electron microscopy (LV‐SEM) and atomic force microscopy (AFM). The microstructural features on the cross section of various PET samples included crystallites, voids, boundaries, defects, and amorphous phases. The SEM images revealed layered and stepped structural features at the micron and 10‐micron scales that are highly crystallized at the near‐edge region of the cross section for both linear and branched PET samples after the SSP process. The AFM images demonstrate that the degree of crystallization for the linear and branched PET samples increases gradually from the central area to the edge on the cross section. The linear crystallized PET has a higher degree of orientation than the branched crystallized PET in the 10‐micron to micron scales, but their crystalline structures have no significant differences in the submicron to nanometer scales. The PET crystallization process occurs when the molecular chains in the amorphous phase are aligned and folded to form straight molecular chains at the nanometer scale, and small crystallites are formed. The crystallites aggregate and align together into a polygon rod‐like‐shaped crystallites at the submicron scale. Finally, large crystallites at the micron size are formed that appear on the edge area of the cross section. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 245–254, 2002     

涤纶工业丝等温收缩中的结构变化

采用广角X 射线衍射、密度梯度、声速和差示扫描量热等实验方法对 145 5dtex/ 110f成品涤纶工业丝等温收缩的结构变化进行了表征 ,外加张力为 0 3N ,测定温度范围 375～ 494K .结果表明 ,涤纶工业丝的热收缩在宏观上表现为速率不同的两个过程 ,对应两种不同机理 .其中快过程对应非晶区的解取向 ,对收缩的贡献是主要的 ;慢过程对应晶区的变化 ,包含了晶粒的增长 ,新的不完善晶粒的形成和晶区的完善 .晶粒的增长在较短的时间内基本完成 ,再结晶则存在于整个收缩过程 .随温度的升高 ,晶区变化速度明显加快 ,对非晶区解取向的抑制效应因此变大 .