Fracture behaviour of polyethylene naphthalate (PEN)

Fracture toughness of a semi-crystalline polyethylene naphthalate (PEN) film of thicknesses 0.050, 0.075 and 0.125 mm was measured as a function of temperature and loading rate using both double edge notched tension (DENT) and single edge notched tension (SENT) specimens. The specific essential work of fracture (EWF) and the multi-specimen J-integral methods were used to evaluate fracture toughness. The variation of the specific total work of fracture (w_f) with ligament length (L) was linear for ligament lengths between 5 and 15 mm. Within this range, w_f versus L was independent of thickness at all temperatures but was dependent on both temperature and loading rate. The specific EWF (w_e) was found to be independent of thickness and loading rate but showed three regions of varying temperature dependence. Between 23 and 80°C (region I) w_e was essentially independent of temperature but increased with temperature between 80 and 120°C (region II) and decreased with temperature thereafter (region III). At glass transition temperature (i.e. 120°C), w_e reached a maximum value of 75 kJ/m². The specific non-EWF (βw_p) increased with both loading rate and temperature. The greatest change in βw_p value with respect to temperature was obtained in region II.The plot of J-integral versus crack extension (Δa) was independent of thickness but was dependent upon temperature. w_e was found to be equivalent to both J_0.2 and J₀.     

Structure development during melt spinning of linear polyethylene fibers

Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.     

Structure formation in high-speed spinning of polyethylene terephthalate

Conclusions Commonness and differences in yarn structure formation by high-temperature and low-temperature stretching have been shown.Model concepts on the development of structure in high-temperature deformation during the process of high-speed yarn spinning have been examined.It has been found that, on changing the linear density of elementary filaments, the spinning speed, or the position of the lubricating device, the proportion of effective high-temperature and low-temperature deformations changes.Translated from Khimicheskie Volokna, No. 3, pp. 16–19, May–June, 1988.     

Structure development in melt spinning poly(vinylidene fluoride) fibers and tapes

A series of poly(vinylidene fluoride)s of varying molecular weight have been melt spun to form fibers and tapes. These have been characterized with wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), birefringence, and small angle light scattering (SALS). WAXD and DSC have detected both the α and β crystal structures in melt spun fibers with the relative amount of β increasing with drawdown stress. WAXD and birefringence have been used to detect orientation in the fibers. Hermans–Stein orientation factors have been computed for the α-phase as a function of drawdown stress. Superstructure has been investigated using SALS. The mechanical properties of fibers have been determined with a tensile testing machine and correlated with orientation and spinline stress.     

聚萘二甲酸乙二酯的研究及发展

简要回顾了PEN的发展 ,并对PEN的性能、合成和影响因素及应用进行了介绍。由于萘环代替苯环 ,其强度、尺寸稳定性 ,热稳定性 ,耐化学性 ,耐水解性 ,气隔性比PET更优良。合成方法与PET相似。主要用项是化学薄膜 ,纤维、容器等 ,采取改性方法 ,可降低使用成本     

Single and double bubble tubular film extrusion of polyethylene 2, 6‐naphthalate (PEN)

An experimental study of film formation and structure development of polyethylene 2,6‐naphthalate (PEN) in single and double bubble tubular film extrusion is presented. PEN was largely stable in film blowing. The films produced were characterized with wide angle X‐ray diffraction, DSC, and Abbe refractometer techniques. The structure and orientation in the films varied substantially with process and film formation history. Single bubbles exhibited polymorphs with considerable levels of orientation, while double bubbles possessed only the extended α‐modification. With increasing planar strain, the naphthyl rings on the chain backbone became increasingly aligned parallel to the film surface. The mechanism of structure evolution in PEN was related to its behavior during the inflation period and compared with that found in polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).     

Structure development during polymer processing: Studies of the melt spinning of polyethylene and polypropylene fibers

Experimental studies of structure development in melt spinning of polyethylene and polypropylene fibers are described. Emphasis is given to the influence of applied stresses on the rates of crystallization and on the development of crystalline morphology. The relationship of fiber morphology to mechanical properties, especially “hard elastic fibers” is considered. The relevance of such studies to other polymer processing operations such as film extrusion is discussed.     

Novel impacts of glycol-modified poly(ethylene terephthalate)(PETG) to crystallization behavior of polyethylene naphthalate (PEN) within stretched miscible blends

For studied blends of amorphous glycol-modified poly(ethylene terephthalate) (PETG) and semicrystalline polyethylene naphthalate (PEN), melt miscibility is understood from the linear variation of a single glass transition temperature (T_g) over the entire composition range. The diluent effect of PETG component severely retarded the crystallization of PEN component within blends. Nevertheless, after being through isothermal stretching at 120 °C, crystallization was able to progress efficiently during heating in a continuous manner. Instead of being thermally relaxed back to amorphous state, parallel sliding motions of stretched PEN segments toward crystallization appear rather dominant. Within stretched blends, the PETG content emerged as a critical factor to the crystallinity increase of PEN fraction and the absence of lattice defect, instead of behaving as a diluent component. Furthermore, as being indicated by in-situ small-angle X-ray experiments, regular lamellar stacking gradually developed within stretched blends through heating, which indicates the involvement of thermally activated self-association of randomly distributed crystalline lamellae. With including a higher fraction of PETG component, these secondary ordering processes including lamellar thickening can be activated at lower temperature. Hence, the accompanied thermal relaxation of flexible PETG segment is inferred able to lubricate the sliding of stretched PEN segments in amorphous regions via lowering encountered frictional hindrance, and thus enhance both primary and secondary ordering processes within stretched blends.     

Biodegradable fibers of poly(L-lactide) produced by high-speed melt spinning and spin drawing

A polylactide (PLA type LA 0200 K) was spun in high-speed melt spinning and spin drawing processes. The fibers were characterized with regard to the degree of crystallinity, the orientation, and the textile physical properties. The polymer was produced by a reactive extrusion polymerization process, and its hydrolytic degradation during the processes of drying and spinning and its thermal and rheological properties were characterized. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2785–2797, 1999     

Processing characteristics,structure development,and properties of uni and biaxially stretched poly(ethylene 2,6 naphthalate) (PEN) films

Poly(ethylene 2,6, naphthalene dicarboxilate), PEN, is very similar to poly(ethylene terephthalate), PET, in its chemical structure and was, therefore, expected to exhibit similar processing characteristics. We, however, observed a few problems during stretching of PEN, the most important of which was necking behavior at 145°C, which is between T_g (117°C) and T^cc (195°C). This is usually observed in PET only when it is stretched close to or below T_g. At temperatures between T_g and T_cc (cold crystallization temperature) PET stretches rather uniformly. The temperature window for film stretching appears to be rather wide, but our results indicate that this is not the case. Films stretched to high stretch ratios become uniform due to propagation and final disappearance of necks as a result of stress hardening. Our attempts at stretching these films at higher temperatures indicated that necking is eliminated, but so is stress induced crystallization, which causes stress hardening (unless high stretching rates are employed). The presence of stress hardening is essential for obtaining high quality, uniform films of these polymers. In addition, at high temperatures thermally activated crystallization which starts dominating the structure development, detrimentally affects the general appearance of the films. In brief, the PEN films we investigated have a narrower processing window than was anticipated based on their thermal behavior alone. At elevated temperatures the films are sensitive to the rate of stretching even more than typical PET processed at comparable conditions. The uniformity of the films depends on the stretch ratio, stretching mode, ratio(s) and rates and temperature. WAXS studies on the films indicate that the macromolecules packed into the low temperature crystal modification. In addition, WAXS pole figure studies suggest that naphthalene planes preferentially orient parallel to the film surface during biaxial stretching. The biaxially stretched films were observed to exhibit a bimodal chain orientation as evidenced by pole figure analysis of the (010) planes.     

Structure development of poly(L‐lactic acid) fibers processed at various spinning conditions

Poly(L ‐lactic acid) (PLA) filaments were spun by melt‐spinning at 500 and 1850 mm^?1, and further drawn and heat‐set to modify the morphology of these PLA filaments. PLA yarns were characterized by wide‐angle X‐ray diffraction (WAXD) and sonic method. WAXD reveals that PLA yarns spun at 500 mm^?1 are almost amorphous while the PLA filaments spun at 1850 mm^?1 have about 6% crystallinity. This is different from PET filaments spun at the same speed that have almost no crystallinity. Both drawn‐ and heat‐set PLA filaments showed much higher crystallinity (60%) than do as‐spun fibers produced at 500 and 1850 mm^?1 speed, which is also higher than the usual heat‐set PET yarns. It appears that crystalline orientation rapidly reaches a value in the order of 0.95 at 1850 mm^?1 and that drawn‐ and heat‐set yarns have almost the same crystalline orientation values. Molecular orientation is relatively low for as‐spun PLA yarn, and molecular orientation increased to ～0.5 after drawing or heat–setting or both. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1210–1216, 2006     

Hot compaction of polyethylene naphthalate

In this article, we describe the production of single polymer composites from polyethylene naphthalate (PEN) multifilaments by using the hot compaction process. In this process, developed at Leeds University, highly oriented tapes or fibers are processed at a critical temperature such that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the composite. This process is, therefore, a way to produce novel high‐volume fraction polymer/polymer composites where the two phases are chemically the same material. A variety of experimental techniques, including mechanical tests and differential scanning calorimetry, were used to examine the mechanical properties and morphology of the compacted PEN sheets. Bidirectional (0/90) samples were made at a range of compaction temperatures chosen to span the melting range of the PEN multifilaments (268–276°C). Measurement of the mechanical properties of these samples, specifically the in‐plane modulus and strength, allowed the optimum compaction temperature to be ascertained (～ 271°C), and hence, the optimum mechanical properties. The optimum compacted PEN sheets were found to have an initial modulus close to 10 GPa and a strength of just over 200 MPa. The glass transition temperature of the optimum compacted sheets was measured to be 150°C, nearly 40°C higher than compacted poly(ethylene terephthalate) (PET) sheets. In previous work on polypropylene and PET hot compacted materials, it proved instructive to envisage these materials as a composite where the original oriented multifilaments are regarded as the reinforcing phase, and the melted and recrystallized material are regarded as the matrix phase. Dynamic mechanical bending tests (DMTA) were used here to confirm this for PEN. DMTA tests were carried out on the original fibers and on a sample of completely melted material to determine the fiber and matrix properties, respectively. The composite properties were then predicted by using a simple rule of mixtures and this was found to be in excellent agreement with the magnitude and measured temperature dependence of the hot compacted PEN material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 796–802, 2004     

Structure and property development of aromatic copolysulfonamide fibers during wet spinning process

The structure and performance changes of aromatic copolysulfonamide (co‐PSA) fibers that occurred during wet spinning process have been studied. While using different length scale characterization, including scan electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), and small‐angle X‐ray scattering (SAXS), it was found that the molecular chains of co‐PSA formed an isotropic network during coagulation which further lead to extension and orientation of these chains during the subsequent stretching. As a result, only after heat stretching and heat setting the molecular chains tended to pack into crystal lattice in the fibrils. This gave rise to a much denser structure along the spinning line and the glass transition temperature of co‐PSA fibers increased a little after heat setting. Before heat stretching, the co‐PSA fibers were in amorphous state, and only the amorphous orientation was observed within the fibers. After heat stretching at the temperature higher than T_g, the fraction of amorphous region decreased, and the crystal structure formed in the fibers, which became more perfect during heat setting. The structure development during spinning process contributed toward the improvement of thermo‐mechanical stability, tenacity and modulus of the co‐PSA fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42343.     

Studies on melt spinning process of hollow polyethylene terephthalate fibers

Dimensional change and profile development in the melt spinning process of polyethylene terephthalate hollow fibers were studied through the numerical simulations and experimental results. The simulation predicts the final dimensions and profiles development of the hollow fibers at various positions from the die. Experimental results show that the melt extruded from the spinneret coalesces initially to form a hollow inner core and the cross‐sectional shape holds for over the whole spinline with only variation in the hollow portion. Analysis of the effect of spinning parameters on hollow portion shows that the spinning temperature, mass throughput rate, and take‐up speed are the most critical variables in controlling the hollow portion followed by quench air velocity. The quench air temperature has relatively less effect than the other variables. As the mass throughput rate and quench air velocity increase and the take‐up speed and spinning temperature decrease, the hollow portion increases. To investigate the effect of die geometry, die having a different ratio of inner to outer diameter was used. The effect of change of process variables decreases as the die gap becomes narrow. POLYM. ENG. SCI. 46:609–616, 2006. © 2006 Society of Plastics Engineers     

Structure evolution of ultra high molecular weight polyethylene/montmorillonite nanocomposite fibers prepared by melt spinning

Nanocomposite fibers of ultra high molecular weight polyethylene (UHMWPE) and organic montmorillonite (OMMT) were successfully prepared by a melt‐spinning process. The evolution of the microstructures of the nanocomposite fibers in the drawing process was preliminarily studied by X‐ray diffraction (XRD), differential scanning calorimetry, and small‐angle X‐ray scatters. With the increase of draw ratio values, the crystallinity of the nanocomposite fibers increased, the grain size decreased, and the folded chain crystals gradually transformed into extended chain crystals. The results suggested the evolution of the nanocomposite fibers was similar with that of the fibers made by gel‐spun drawing process. The addition of OMMT in UHMWPE improved the fluidity of the composites yet without affecting the crystal structure of UHMWPE in the drawing process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3930–3936, 2013     

Necking mechanism and its elimination in uniaxially drawn films of poly(ethylene naphthalate) (PEN)/polyetherimide (PEI) blends

The influence of blend composition on the deformation behavior of cast amorphous PEN/PEI blends were investigated above their respected glass transition temperatures. PEN inherently shows a sharp necking phenomenon when stretched at temperatures as high as 20°C above its glass transition temperature. This was attributed to highly localized rapid alignment of naphthalene planes parallel to the surface of the films. The addition of PEI was observed to reduce this necking behavior. The neck formation completely disappears when the PEI fraction exceeds 10% in the blend. X-ray studies indicate that the increase of PEI hinders the rapid alignment of naphthalene planes parallel to the surface of the films. The presence of PEI chains in the blend was found to increase the overall friction between the polymer chains in the system and this was found to prevent the formation of highly localized necks. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2059–2074, 1997     

聚萘二甲酸乙二酯的生产和应用

综述了聚萘二甲酸乙二酯(PEN)及其原料2,6-二甲基萘(2,6-DMN)的生产工艺,对比分析了2,6-DMN的各种分离和提纯技术,并介绍了PEN的主要用途及发展前景。生产PEN的2,6-DMN的纯度必须达到98.0%,2,6-DMN的合成、分离与提纯是制约PEN生产的瓶颈。采用络合结晶法及乳化结晶法分离和提纯2,6-DMN的工艺较简单,产品收率及纯度均较高,工业化可能性较大。随着环保要求的提高,可再生或可重复使用的PEN制品必将受到重视。因此,国内应加大这方面的科研力度,以实现PEN在国内的工业化生产。     

Structure and property studies of poly(trimethylene terephthalate) high-speed melt spun fibers

Poly(trimethylene terephthalate) has been melt spun at various take-up velocities from 0.5 to 8 km/min to prepare fiber samples. The effect of take-up velocity on the structure and properties of as-spun fibers has been characterized through measurements of birefringence, density, wide-angle X-ray scattering, DSC melting behavior, tensile properties and boiling water shrinkage (BWS). The birefringence exhibits a maximum at take-up velocities between 3 and 4 km/min. The fiber samples spun at the lower take-up speeds have essentially amorphous structures, while the filaments prepared at a velocity range higher than 4 km/min all possess an obvious crystalline structure. With increasing take-up speed, a steady improvement in tensile strength, elongation to break, and BWS is found, whereas the initial modulus remains almost constant within the measurement error, over the entire take-up speed range between 0.5 and 8 km/min.     

Structure development in the melt spinning of nylon 66 fibers and comparison to nylon 6

The development of crystallinity and orientation during the melt spinning of nylon 66 was investigated. Nylon 66 was found to crystallize in the spinline to form the Bunn-Garner α-triclinic structure. This behavior differs from that of nylon 6. Nylon 66 was found to develop lower crystalline orientation than nylon 6 under comparable spinning conditions.     

Structure development and properties of high-speed melt spun poly(butylene terephthalate)/poly(butylene adipate-co-terephthalate) bicomponent fibers

Ultra-high-speed bicomponent spinning of poly(butylene terephthalate) (PBT) as sheath and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) as core was accomplished with the take-up velocity up to 10 km/min. The structure development of the individual component and the properties of PBT/PBAT fibers were investigated through the measurements on differential scanning calorimetry, wide-angle X-ray diffraction, birefringence and tensile test. Due to the mutual interaction between two polymer-melts along the spinline, the processability of both components in PBT/PBAT bicomponent spinning was improved compared with those of corresponding single component spinnings. Furthermore, in PBT/PBAT fibers, the structure development of PBT component was found to be greatly enhanced, which led to the improvement in its thermal and mechanical properties; whereas the structure development of PBAT component was significantly suppressed, in which nearly non-oriented structure was observed in both crystalline and amorphous phases.