Microstructural modifications in uniaxially hot‐drawn polycyclohexylene terephthalate films

Semi‐aromatic thermoplastic polycyclohexylene terephthalate (PCT), initially wholly amorphous, was uniaxially drawn to study microstructural modifications as the appearance of the strain‐induced (S.I.) crystalline phase. Polyethylene terephthalate (PET) and poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) (PETG) are considered as reference materials in this work. In polycyclohexylene terephthalate (PCT) the presence of a saturated ring (which is not quite as rigid as the aromatic ring) modifies the characteristics of both thermal and S.I. crystallization. Samples with various draw ratios (drawing of PCT films is performed at T > T_g) were analyzed by Modulated Differential Scanning Calorimetry, wide angle X‐ray scattering, and birefringence measurements. In drawn PCT films, an S.I. crystalline phase appears continuously with the draw ratio and reaches 35%. For this polymer and for the highest draw ratio, the “true” amorphous fraction practically disappears. The material is composed only of the S.I. crystalline phase and the “rigid” amorphous phase. Polym. Eng. Sci. 44:509–517, 2004. © 2004 Society of Plastics Engineers.     

Toughening of polyethylene terephthalate/amorphous copolyester blends with a maleated thermoplastic elastomer

The toughening of polyethylene terephthalate (PET)/amorphous copolyester (PETG) blends using a maleic anhydride grafted mixture (TPEg) of polyethylene‐octene elastomer and a semicrystalline polyolefin plastic (60/40 by weight) was examined. The TPEg was more effective in toughening PETG than PET, although the dispersion qualities of the TPEg particles in PET and PETG matrices were very similar. At the fixed TPEg content of 15 wt %, replacing partial PET by PETG resulted in a sharp brittle‐ductile transition when the PETG content exceeded the PET content. Before the transition, PET/PETG blends were not toughened with the TPEg of 15 wt %, whereas after the transition, the PET/PETG blends with 15 wt % of TPEg, similar to the PETG/TPEg (85/15) binary blend, maintained a super‐tough level. The impact‐fractured surfaces of the PET/PETG/TPEg blends were also evaluated. When PETG content was lower than PET content, the ternary blend showed a brittle feature in its impact‐fractured surface, similar to the PET/TPEg (85/15) binary blend. While PETG content exceeded PET content, however, the impact‐fractured surface of the ternary blend was very similar to that of PETG/TPEg (85/15) binary blend, exhibiting intensive cavitation and massive matrix shear yielding, which were believed to be responsible for the super‐tough level of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 797–805, 2003     

Ductility of filled polymers

The ductility of a calcium carbonate-filled amorphous copolyester PETG in a uniaxial tensite test was examined as a fiction other filler volume fraction. A ductile-to-quasibrittle transition occurred as the volume fraction of filler increased. This transition was from propragation of a stable neck through the entire gauge length of the specimen to fracture in the neck without propagation. The draw stress (lower yield stress) did not depend on the filler content and was equal to the draw stress of the unfilled polymer. It was therefore possible to use a simply model to predict the dependence of the fracture strain on the filler volume fraction. It was proposed that when the fracture strain decreases to the draw strain of the polymer the fracture mechanism changes and the fracture strain drops sharply. The critical filler content at which the fracture mode changes is determined primarily by the degree of strain-hardening of the polymer. © 1994 John Wiley & Sons, Inc.     

Poly(ethylene terephthalate)/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate)/clay nanocomposites: Mechanical properties,optical transparency,and barrier properties

Poly(ethylene terephthalate) (PET)/clay, PET/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG), and PET/PETG/clay nanocomposites were fabricated using the twin‐screw extrusion technique. The spherulitic morphologies, thermomechanical, mechanical, and gas‐barrier properties, as well as the effect of clay on the transparency of the resulting nanocomposites were identified. The clay induced the heterogeneous nucleation of the nanocomposites during the cold crystallization process, thereby increasing the crystallinities and melting temperatures of the resulting nanocomposites. The incorporation of clay increased the storage moduli, Young's moduli, impact strengths, and barrier properties of the PET, PETG, and PET/PETG blend. Regarding the optical transparency, the inclusion of clay can make the crystallizable PET matrix crystalline opaque. However, the amorphous PETG maintained its transparency. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39869.     

Poly(ethylene terephthalate)/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate)/clay nanocomposites: Effects of biaxial stretching

In this study, we fabricated poly(ethylene terephthalate) (PET)/clay, PET/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG), and PET/PETG/clay nanocomposite plates and biaxially stretched them into films by using a biaxial film stretching machine. The tensile properties, cold crystallization behavior, optical properties, and gas and water vapor barrier properties of the resulting films were estimated. The biaxial stretching process improved the dispersion of clay platelets in both the PETG and PET/PETG matrices, increased the aspect ratio of the platelets, and made the platelets more oriented. Thus, the tensile, optical, and gas‐barrier properties of the composite films were greatly enhanced. Moreover, strain‐induced crystallization occurred in the PET/PETG blend and in the amorphous PETG matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42207.     

Effects of zone drawing on the structure of metallocene polyethylene

The influence of zone drawing on bulk properties and structure of metallocene polyethylene (m‐PE) is reported. Two different m‐PE materials were subjected to tensile stresses above the yield point by zone drawing in the temperature range from 50 to 100°C. Drawn materials were characterized by using small‐ and wide‐angle X‐ray scattering (SAXS, WAXS), molecular retraction, and small‐angle light scattering (SALS). Structural changes were studied as a function of drawing temperature, engineering stress, and draw ratio. WAXS showed strong crystalline orientation in drawn samples, and only the orthorhombic crystal modification was observed. SAXS showed lamellar orientation in drawn samples. At low drawing temperatures of 50 or 60°C, draw ratio increased as a step function of stress. There is a stress barrier, which must be exceeded before high‐draw ratios can be achieved at these temperatures. At drawing temperatures of 70°C or above, the barrier stress is low enough that draw ratio increases nearly linearly as a function of stress. Below the stress barrier, spherulitic structure is observed by small‐angle light scattering (SALS). Elongation occurs via deformation of the interspherulitic amorphous phase. Molecular retraction was low for these samples, indicating mostly plastic deformation of the amorphous material. Above the stress barrier, SALS showed that spherulites are destroyed. Elongation occurs via deformation of the intraspherulitic amorphous phase. Molecular retraction for these samples was high, indicating elastic deformation of the amorphous material. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3492–3504, 2001     

In situ fibrillar reinforced PET/PA‐6/PA‐66 blend

Ternary fibrillar reinforced blends are obtained by melt‐blending of poly(ethylene terephthalate) (PET), polyamide 6 (PA‐6) and polyamide 66 (PA‐66) (20/60/20 by weight) in the presence of a catalyst, followed by cold drawing of the extruded bristles to a draw ratio of about 3.4 and additional annealing of the drawn blend at 220 or 240°C for 4 or 8 h. The blend samples are studied by DSC, X‐ray diffraction, SEM, and static and dynamic mechanical testing (DMA). SEM and DMA show that PA‐6 and PA‐66 form a homogeneous, continuous matrix in which PET regions are dispersed. X‐ray and DSC measurements of the drawn and annealed at 220°C samples suggest mixed crystallization (solid solubility) of PA‐6 and PA‐66, and cooperative crystallization of PET with the two polyamides. After annealing at 240°C (above the melting point of PA‐6 and below that of PET), the polyamide matrix becomes partially disoriented, while the oriented, fibrillar PET is preserved and plays the role of a reinforcing element. The DSC results for the same samples suggest in situ generation of an additional amount of copolymer. This additional copolymerization, together with that generated during blend mixing in the extruder, improves the compatibility of the blend components (mostly at the PET‐polyamide interface) and alters the chemical composition of the blend.     

Processing of single polymer composites using the concept of constrained fibers

The concept of “overheating” is one of the known methods for manufacturing single polymer composites. This concept is validated on two categories of semi‐crystalline polymers: the drawable, apolar (i.e., isotactic polypropylene [iPP], ultra‐high molecular weight polyethylene [UHMWPE]) and the less drawable, polar ones (i.e., polyethyleneterephalate [PET] and polyamides [PA]). The interchain interactions in apolar polymers are relatively weak and therefore a high degree of drawability can be obtained. Polar polymers on the other hand have relative strong interchain interactions, they are therefore less drawable. A shift higher than 20°C of the melting temperature can be obtained in case of highly extended iPP (draw ratios >14). Ultra‐drawn PE shows only 10°C overheating upon constraining and this is mainly due to the change in chain mobility for PE in the hexagonal phase. In case of PET and PA6, only draw ratios of 4 could be reached; however, temperature shifts of about 10°C for constrained fibers compared to unconstrained fibers could be measured. A proof of principle of the potential of the constraining concept for the manufacturing of single polymer composites is obtained by the preparation of single fiber model composites. The effect of the post‐drawing conditions on overheating is examined in details on the example of iPP. It is concluded that both post‐drawing temperature and ultimate draw ratio have a significant influence on the degree of overheating. POLYM. COMPOS., 26:114–120, 2005. © 2004 Society of Plastics Engineers     

Molecular structures and physical properties of heat‐drawn conjugate fibers

As‐spun poly(trimethylene terephthalate) (PTT)/poly(ethylene terephthalate) (PET) side‐by‐side conjugate fibers were drawn to investigate the effects of drawing conditions on structure development and physical properties. Effects of draw ratio and heat‐set temperature were observed. In the state of an as‐spun fiber, the molecular orientation of PTT was higher than PET, whereas PET molecular orientation increased remarkably over PTT with increasing draw ratio. Crimp contraction increased sharply at a draw ratio over 2.0, where the crystalline structure of the PET developed sufficiently. A heat‐set temperature of at least 140°C was required to develop sufficient crimp contraction. The crystallinity and orientation of the PET were attributed mainly to the crimp contraction of the drawn fiber. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effect of water molecules on crystallization during unixial drawing of poly(ethylene terephthalate) films

The role played by sorbed water molecules present within poly(ethylene terephthalate) film at the moment of uniaxial drawing on the appearance and the percentage of the strain‐induced crystalline (SIC) phase is investigated by birefringence, X‐ray diffraction, and differential scanning calorimetry measurements. We show that, for law draw ratio, water play its traditional plasticizer effects. The SIC phase appears for a draw ratio, which depends weakly on the relative humidity. The water does not modify the degree of crystallinity of drawn films but impedes the growth of a part of the crystallites and modify their crystalline size. For high draw ratio, water impedes the orientation of the amorphous phase. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1056–1066, 2000     

Formation of porous poly(ethylene‐co‐vinyl alcohol) membrane via thermally induced phase separation

Crystalline poly(ethylene‐co‐vinyl alcohol) (EVOH) membranes were prepared by a thermally induced phase separation (TIPS) process. The diluents used were 1,3‐propanediol and 1,3‐butanediol. The dynamic crystallization temperature was determined by DSC measurement. No structure was detected by an optical microscope in the temperature region higher than the crystallization temperature. This means that porous membrane structures were formed by solid–liquid phase separation (polymer crystallization) rather than by liquid–liquid phase separation. The EVOH/butanediol system showed a higher dynamic crystallization temperature and equilibrium melting temperature than those of the EVOH/propanediol system. SEM observation showed that the sizes of the crystalline particles in the membranes depended on the polymer concentration, cooling rate, and kinds of diluents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2449–2455, 2001     

Preparation and properties of a liquid crystalline segmented block copolyester

A segmented block copolyester with a liquid crystalline (LC) “hard block” and poly(tetramethylene glycol) (PTMG) “soft block” was prepared and characterized by intrinsic viscosity [η], by gel permeation chromatography (GPC) for number average molecular weight and molecular weight distribution, by differential scanning calorimetry (DSC), and by dynamic mechanical thermal analysis (DMTA). The “soft block” had a melting transition at about ?30°C and the hard block had a glass transition at about 70°C and a nematic-to-isotropic transition at 260°C. Mechanical testing, which included tensile testing, hysteresis analysis and stress relaxation at small strains, revealed that the block copolyester was a flexible rubbery material with an elongation at break of about 1000% and showed reversible extension below 50% strain.     

Characterization of polyethylene terephthalate films drawn in hot water

Sorbed water molecules in PET (around 1% in mass) lead to classic plasticizing effects, basically evidenced by a decrease of the glass transition (T_g) and of the cold crystallisation (T_c) temperatures with increasing water content. During drawing of dry PET film and depending on the draw ratio, the initial amorphous phase is oriented at first, then a strain‐induced crystallisation appears. This work deals with the conjugate effects of drawing and water sorption in PET films drawn in hot water. Differential scanning calorimetry and birefringence measurements shown that drawing performed in hot water leads to modifications of T_g and T_c without modification of the degree of crystallinity. Moreover, the formation of water clusters is observed when the strain‐induced crystalline phase occurs.     

Blends of poly(ethylene terephthalate) with co[poly(ethylene terephthalate-p-oxybenzoate)]. II. Composition effect on the rate of crystallization

Poly(ethylene terephthalate) (PET) was blended with four different kinds of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, designated P28, P46, P64, and P82, with the level of copolyester varing from 1 to 15 wt %. All samples were prepared by melt-mixing in a Brabender Plasticorder for 8 min. The crystallization behavior of samples were then studied via DSC. The results indicate that these four copolyesters accelerate the crystallization rate of PET in a manner similar to that of a nucleating agent. The acceleration of the PET crystallization rate was most pronounced in the PET/P28 blends with a maximum level at 10 wt % of P28, and in the PET/P28 blends, at 5 wt % of P82. The melting endotherm onset temperatures and the melting peak widths for the blends are comparable with those of neat PET. These results imply that the stability of PET crystalline phase in the blends does not change by blending. The observed changes in crystallization behavior, however, are explained by the effect of the physical state of the copolyester during PET crystallization as well as the content of the p-oxybenzoate (POB) moiety in corporated into the blends. © 1995 John Wiley & Sons, Inc.     

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

This study was devoted to the effect of extensional flow during film extrusion on the formation of the β‐crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two‐channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two‐channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum β‐phase content were determined as follows: temperature = 90°C, strain = 500%, and strain rate = 0.083 s^?1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their β‐phase content and piezoelectric strain coefficient (d₃₃) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% β‐phase content was obtained for the samples prepared with the two‐channel die, which was 7% higher than that of the samples prepared by the slit die. The d₃₃ value of the two‐channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mobile amorphous phase fragility in semi-crystalline polymers: Comparison of PET and PLLA

PET and PLLA were cold crystallised at various times and the two polymers were studied by differential scanning calorimetry (DSC), dielectric spectroscopy (DS) and thermally stimulated depolarisation currents (TSDC). The crystalline, the amorphous and the rigid amorphous fraction were quantified. The percentage of rigid amorphous fraction is very large in semi-crystalline PET and very low in semi-crystalline PLLA. From DSC, DS and TSDC data, the values of the relaxation times of four samples were obtained above and below the glass transition. The “strong-fragile” glass former liquid concept was used and the fragility of polymers was obtained. The presence of the crystalline phase and of a rigid amorphous fraction does not significantly modify PLLA fragility parameters and the polymer remains “fragile”, while for PET the semi-crystalline material goes towards a “strong character”. The coupling between phases is much weaker in PLLA than in PET.     

HBA／PET／HQ—TPA液晶共聚芳酯的合成与表征

采用熔融缩聚方法合成了ＨＢＡ／ＰＥＴ及ＨＢＡ／ＰＥＴ／Ｈ１－ＴＰＡ液晶共聚酯。应用ＤＳＣ，偏光显微镜等对共聚酯性能进行了表征。结果表明：加入第三单体后，可以改善二元聚酯ＨＢＡ／ＰＥＴ的共聚反应条件，并且所有样品匀具有较大的特性粘度，较小的熔融热焓，二元体系的玻璃化转变较明显，加入第三单体后的三元共聚体系玻璃化转变消失，并且随着第三单体含量的增加，共聚酯熔点上升。     

Syntheses and characterization of poly(butylene terephthalate) copolyesters modified with p‐acetoxybenzoic acid

Poly(butylene terephthalate) (PBT) copolyesters modified with seven compositions of p‐acetoxybenzoic acid (PABA) ranging from 10 to 70 mol % were prepared. The X‐ray diffraction patterns, the polarizing microscopy behaviors, and thermal analysis showed that the modified PBT contained more PABA homopolymer units (PABA–PABA) than PBT–PABA units in the copolyesters. On increasing PABA mole percenage, PBT crystallinity decreased and thermal stability increased. It was found that although the PBT copolyesters did not exhibit a clear liquid crystalline texture like the copolyester of poly(ethylene terephthalate) modified with PABA did, the PBT copolyester containing 70 mol % of PABA exhibited the typical shear thinning behavior of a liquid crystalline polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1085–1095, 2001     

Pyrolysis of an amorphous copolyester

The pyrolysis of the amorphous copolyester poly(ethylene glycol‐co‐cyclohexane 1,4‐dimethanol terephthalate) (PETG) was investigated. The applied technique was thermogravimetry/differential scanning calorimetry/mass spectrometry analysis. The pyrolysis products of PETG were ascertained. The results showed that the PETG mass loss was 90.36% from room temperature to 650°C, its thermal decomposition was mainly completed in one step at 425.2°C, and the aliphatic backbone of PETG played a dominant role in controlling the behavior of the pyrolysis. The pyrolysis mechanism was also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2793–2797, 2006     

Conformational development of polylactide films induced by uniaxial drawing

Uniaxially drawn polylactide (PLA) films were prepared using various draw ratios (2, 3, 4 and 4.5) at a constant draw rate and temperature. It was confirmed that the conformational structure of the PLA films prepared using the uniaxial drawing process was composed of the α′‐phase form. The conformational structure deformation of α′‐phase PLA films, according to the various draw ratios used, was investigated in terms of strain‐induced crystalline behavior and molecular orientation analysis. It is of utmost importance to confirm the α′‐phase structural deformation caused by the uniaxial drawing process because it directly relates to the characteristics of PLA films. The conformational structure deformations of the α′‐phase, created by uniaxial drawing, led to improved mechanical properties, as evident from mechanical testing and dynamic mechanical analyses results. © 2013 Society of Chemical Industry