Molecular PET Research Articles

Mechanical properties of poly(ethylene terephthalate) modified with functionalized polymers

This study examined the effect of blending poly(ethylene terephthalate) (PET) with 5% of a functionalized polymer. The blends were characterized by particle size and size distribution, unnotched tensile behavior, toughness, and notch sensitivity. The improved properties of blends that incorporated a functionalized elastomer were consistent with in situ formation of a graft copolymer by reaction with PET end groups. Triblock copolymers were examined that had styrene end blocks and an ethylene/butylene midblock (SEBS) with grafted maleic anhydride. The present study extended previous investigations that focused on level of grafting to examine the effects of component molecular weight and PET hydroxyl-to-carboxyl end-group ratio. Increasing the molecular weight of the SEBS and decreasing the hydroxyl-to-carboxyl ratio of the PET increased the effectiveness of the SEBS. In addition, a mix of an unfunctionalized SEBS with a functionalized SEBS was more effective than a single SEBS with the same total anhydride content. The same elastomers were the most effective for modifying a lower molecular weight PET (intrinsic viscosity 0.73) and a higher molecular weight PET (intrinsic viscosity 0.95). Some functionalized polypropylenes included in the study did not enhance the properties of PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 203–219, 1999

Properties of high-speed spun high molecular weight poly(ethylene terephthalate) filaments

High-speed spinning of high molecular weight poly(ethylene terephthalate) (PET) having an intrinsic viscosity of 0.98 dL/g was performed at the take-up velocity range of 2.5–5.5 km/min. The structure of the as-spun filaments was analyzed by density, birefringence, WAXS, DSC, boiling water shrinkage, and tensile properties. Stress-induced crystallization takes place above 3 km/min, which is confirmed by the steep increase in density, the growth of the crystal size, melting point increase, and the decrease in boiling water shrinkage. The plot of crystallinity versus birefringence shows that crystallinity increases drastically after birefringence reaches the value of about 0.075. A comparison with the data of other researchers will clearly present the effects of molecular weight on the properties of PET filaments spun at high speed, for example, the take-up velocity range of the steep increase in density for high molecular weight PET is lower than that for low molecular weight PET by about 1 km/min. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1283–1291, 1999

Effects of Molecular Weight on Melt Spinning and Mechanical Properties of High-Performance Poly(ethylene Terephthalate) Fibers

Effects of the molecular weight (intrinsic viscosity) of poly(ethylene terephthalate) on the formation of fibers and their properties are analyzed. Correlations between molecular weight and various viscosity characteristics are compared. Because of high melt viscosity, effective melt spinning is limited to polymers with intrinsic viscosities [η] not higher than 0.8-0.9 dl/g. High molecular weight polymers ([η] = 2.0-4.9 dl/ g) have been used for solution (gel) spinning. Molecular weight is not a primary characteristic responsible for mechanical properties, but it may affect tenacity and modulus indirectly. The tenacity of industrial PET fibers manufactured by a variety of processes exhibits positive correlation with intrinsic viscosity; the correlation of the modulus is less evident. Melt spun and drawn fibers exhibit tenacities of up to 12 g/ den and moduli of up to 220 g/den, while fibers solution spun from high molecular weight PET ([η] = 2.6 dl/g) subjected to deep drawing (total draw ratio = 16.4) reach a tenacity of 18.5 g/den and a modulus of 313.2 g/den. A new zone drawing and annealing process, apparently insensitive to molecular weight, yields PET fibers with a tenacity of 14 g/den and a modulus of 246 g/den. The role of molecular weight in obtaining high mechanical performance is discussed.

UV Stabilization of PET Fibers: Microscopy Study

Ultraviolet microspectrophotometry is used to monitor the radial diffusion of three uv stabilizers in high molecular weight PET fibers. Under identical application con ditions, the benzotriazole and benzotriazine derivative stabilizers show peripheral penetration only, whereas the benzophenone derivative stabilizer diffuses throughout the fiber cross section. Peripheral penetration of the benzotriazole and benzotriazine derivatives does not prevent polymer photodegradation in the unprotected interior, whereas all regions of the fiber are protected by the more uniformly distributed ben zophenone stabilizer. Heavy peripheral deposition of the benzotriazole stabilizer pre vents these highly protected regions from polymer photodegradation.

Liquid crystalline block copolymers containing rigid units and flexible ethylene terephthalate segments

AbstractLiquid crystalline block copolymers containing different compositions of terephthaloyl bis(4‐oxybenzoyl) (triad) mesogen and flexible ethylene terephthalate (ET) units, were synthesized in tetrachloroethane/pyridine (TCE/Py) at 150°C and in 1‐chloronaphthalene (1‐CN) at elevated temperatures. Inherent viscosities of the PET block copolymers were always lower than 0.25 dL/g. By replacing the ET blocks with butylene terephthalate (BT) blocks, a copolymer of higher inherent viscosity (> 0.8 dL/g) was synthesized in 1‐CN at 220°C. Formation of low molecular weight PET copolymers was attributed to: (1) insolubility of the block copolymer in TCE/Py and (2) formation of side products which alter the stoichiometry of the reactants when the reaction was carried out in 1‐CN. The block copolymers were characterized by 1H and 13C‐NMR spectroscopy. Copolymer compositions were calculated from 1H and 13C‐NMR data. Thermal behavior of these copolymers was analyzed by DSC and polarizing optical microscopy. All copolymers exhibited a nematic liquid crystalline texture. © 1995 John Wiley & Sons, Inc.

Studies on co[poly(ethylene terephthalate- p-oxybenzoate)] thermotropic copolyester: sequence distribution evaluated from TSC measurements

Relaxation/transition behaviours for copolyesters made from poly(ethylene terephthalate) (PET) and p -acetoxybenzoic acid (POB) have been characterized by thermally stimulated current (TSC) measurement. The sequence distribution, in terms of the degree of blockiness, in dual chemidomains of POB/PET copolyester is simulated from a model developed by us to predict the probability between block sequence and random sequence under a given composition and measuring condition. It is found that the degree of blockiness, a measure of sequence distribution, under the same polarization temperature generally increases with increasing POB content in the POB/PET copolyester. For copolyesters of the same composition, the degree of blockiness shows a large decrease after solid-state polymerization when high molecular weight PET is used, whereas it shows only a small decrease or an increase after solid-state polymerization when PET of lower molecular weight is used. It is concluded that the change in the degree of blockiness caused by the solid-state polymerization of copolyesters is dependent on the molecular weight of sequences of the PET moiety in the structure.

The onset of orientational crystallization in poly(ethylene terephthalate) during low temperature drawing

AbstractIt is well known that crystallization can be induced in amorphous poly(ethylene terephthalate) (PET) by orientation below the isotropic crystallization temperature. The magnitude of the strain necessary for crystallization varies inversely with molecular weight because of relaxation. However, lower molecular weight PET might be expected to, crystallize at a lower extent of molecular orientation, since the crystallization rate also varies inversely with molecular weight. Chain conformations were measured during low temperature drawing of PET of various molecular weights. The molecular configuration associated with strain induced crystallization was found to be independent of chain length. The onset of orientational crystallization was associated with a particular conformation, and this critical trans/gauche ratio was equivalent for PETs of various molecular weights. The drawing behavior is thus in accord with theory concerning the transition of flexible chain polymes from isotropy to an ordered state. This result is congruent with previous studies suggesting the presence of extended chain crystallinity in amorphous PET after low temperature drawing.

Viscosity–molecular weight relationships for poly(ethylene terephthalate) in hexafluoroisopropanol–pentafluorophenol using SEC–LALLS

AbstractViscosity–molecular weight characterization of poly(ethylene terephthalate) (PET) in hexafluoroisopropanol (HFIP), pentafluorophenol (PFP), and HFIP/PFP is reported for the first time using size exclusion chromatography‐low angle laser light scattering (SEC–LALLS) measurements. These strong solvents are capable of dissolving PET under very mild conditions and therefore minimize polymer degradation. In addition these solvents are capable of dissolving PET samples which have poor solubility in more traditional PET solvents such as orthochlorophenol (OCP) and phenol/tetrachloroethane (PTCE). By combining molecular weight information, obtained without the need of any SEC calibration curves, with intrinsic viscosity measurements, on several broad molecular weight PET samples, the Mark–Houwink coefficients for the five PET–solvent systems mentioned above have been determined. The coefficients correspond to those which would be obtained by using a large number of relatively monodisperse samples of PET covering a molecular weight range of about 2 × 103 to 2 × 105. Data is also provided which shows that intrinsic viscosities for PET in HFIP, PFP, HFIP/PFP, OCP, and PTCE can be determined from a single viscosity measurement at a finite concentration. Data for interconverting intrinsic viscosities determined in any of these five solvents is also given.

HIGH SPEED MELT SPINNING OF POLYETHYLENETEREPHTHALATE (PET); EFFECT OF MOLECULAR WEIGHT

PET filaments have been produced by the high speed melt spinning method in the range of take-up velocity, 1, 000-8, 000m/min for the three different molecular weight PET (_??_η=18, 400, 20, 500, 29, 800).The physical and mechanical properties of these filaments were studied as a function of molecular weight. The following results were obtained.(1) Until the take-up velocity reaches 4, 000-5, 000m/min, the fiber structure formation by oriented crystallization develops at lower take-up velocity for the higher molecular weight sample. It is suggested that the elongational viscosity varied by the molecular weight affects the crystallization of PET under the orientation in the high speed melt spinning.(2) The degree of molecular orientation and the degree of crystallization show levelling off after the spinning velocity reaches 4, 000-5, 000m/min. The values of these levels are lower for the higher molecular weight sample, indicating that the increase in the molecular weight does not lead to the development of the fiber structure in the melt spinning. Decreased molecular motion of the higher molecular weight PET may give rise to this fact.(3) For the fibers spun at the take up velocity near the critical spinnability, the decrease in the densities, the reduction of the birefringences, the development of crimps and the appearance of a shoulder melting peak in the DSC thermograms, were found. These may be due to the sliding or the scission of the chain molecules or to the increase in the void content. Further investigations are aimed at these problems.

Formation of diethylene glycol as a side reaction during production of polyethylene terephthalate

AbstractPolymers of poly(ethylene terephthalate) (PET) always contain a certain amount of incorporated diethylene glycol (DEG), substituting the incorporated glycol. DEG is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with ethylene glycol or during direct esterification of terephthalic acid with ethylene glycol, and to a smaller extent during the polycondensation of the low‐molecular material. DEG is formed via an unusual type of reaction: ester + alcohol → ether + acid. Some evidence of this type of reaction is given by the formation of dioxane in low molecular PET and of methyl Cellosolve and methyl carbitol during the ester interchange of DMT with ethylene glycol and diethylene glycol, respectively. The strongest support for this type of reaction, however, was obtained from kinetic data. Polyesters of low molecular weight with OH group contents ranging from 3 to 0.5 mole/kg were heated at 270°C in sealed tubes for 1–7 hr. The kinetic equation for the proposed reaction is: d[DEG]/dt = k[OH] [ester]. With the aid of one rate constant the formation of DEG in all esters could be described.