Kinetics of drying polybutylene terephthalate and polyethylene terephthalate granulate

In studying the dynamics of drying of PBT and PET granulate, the parameters of the process that ensure sufficient process stability of their melts were determined. It was found that the rate of self-ordering of structural elements in the polymer substrate in drying is higher in PBT than in PET due to the greater flexibility of the macromolecules. __________ Translated from Khimicheskie Volokna, No. 1, pp. 7–10, January–February, 2006.     

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).     

Action of alkali on polybutylene terephthalate and polyethylene terephthalate polyesters

The two polyesters (polybutylene terephthalate and polyethylene terephthalate) were treated with aqueous as well as alcoholic solutions of sodium hydroxide at varying temperatures for different durations of time. The results were evaluated in terms of the loss in weight of the samples. The fabric samples of polyethylene terephthalate showed a greater degree of weight loss as compared to those of polybutylene terephthalate. The mechanism for the differences in the action of alkali on these two polyesters is explained. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1097–1102, 2000     

Melt rheology of polyarylate/polybutylene terephthalate blends

The viscosity, the activation energy of flow, and the exchange reactions of bisphenol A 50/50 isophthalic/terephthalic acid and poly(butylene terephthalate) blends are studied by means of an extrusion capillary rheometer, covering a range of 10 s^?1 to 300 s^?1 shear rate and 280°C to 300°C temperature. The results are interpreted in terms of compatibility and free volume additivity. The decrease in viscosity with time is explained as a result of transesterification rather than degradation.     

Investigation of double bubble tubular film extrusion of polyamide 6 and film structural characteristics

Biaxially oriented polyamide 6 films were made by double bubble tubular film extrusion. The crystalline character and biaxial orientation of the films were investigated by measuring (in plane and out of plane) birefringences, IR (infrared) spectroscopy, and wide angle X-ray diffraction (WAXS) flat film patterns and pole figures. The samples were also examined by tensile stretching tests in different sampling directions.     

Fracture of polybutylene terephthalate (PBT) film

Combined effects of thickness and temperature on essential work of fracture (EWF) of polybutylene terephthalate (PBT) film were studied using single edge notched tension (SENT) and double edge notched tension specimens. It is found that specific essential work of fracture (w_e) for PBT is independent of temperature below T_g (≈80 °C), but decreases above T_g. Between temperatures 25 and 100 °C, w_e was independent of film thickness in the range 0.125-0.375 mm. The specific non-essential work of fracture (βw_p) was temperature and thickness dependent, being greater for the SENT type specimens. Specimen orientation had no influence on w_e but strongly affected βw_p. It was found that βw_p is greater for cracks propagating normal to the extrusion direction as compared to the parallel direction.     

Effect of processing parameters on the mechanical properties of in situ compatibilized polybutylene terephthalate/acrylonitrile–butadiene–styrene blends

To evaluate mechanical properties of blends prepared by intermeshing corotating twin‐screw extrusion (ICTSE), it is usually necessary to injection mold specimens after the extrusion mixing process. At this study an alternative method is used to obtain testing specimens from ribbons extruded polybutylene terephthalate/acrylonitrile–butadiene–styrene blends, (PBT/ABS), compatibilized with methyl methacrylate–glycidyl methacrylate‐ethyl acrylate (MGE) by ICTSE, and then to correlate their mechanical properties with the processing parameters. Regarding to the extrusion process parameters, it has been noted that higher feed rates, lower screw speeds and narrower kneading blocks have reduced the ductile‐brittle transition temperature (DBTT) of the compatibilized PBT/ABS blends, thereby suggesting that the molecule integrity of blend polymeric components has been preserved and that a good dispersion of the ABS domains in the PBT matrix has been achieved. Injection molded PBT/ABS blends were obtained to compare to the extruded ribbons. The mechanical tests for both specimens have shown the same trends. The injection molded samples have presented poorer impact strength, tensile strain at break and tensile strength, when compared to the respective extruded samples. That behavior has been attributed to the high level of molecular orientation resulting from the injection molding process and mainly to PBT degradation during process. The PBT degradation could have increased its degree of crystallinity, which has been confirmed by DSC measurements. As result, the blend became more brittle, decreasing its Izod impact strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polystyrene/polyethylene terephthalate/polystyrene-block–polycaprolactone blends: Emulsification and mechanical performance

A polystyrene-polycaprolactone diblock copolymer was extrusion blended with polystyrene and polyethylene terephthalate. The morphologies of the resultant blends were studied using differential scanning calorimetry and scanning electron microscopy. In all compositions studied, the polystyrene and polyethylene terephthalate phases exhibited discrete glass transitions indicative of the immiscibility of these components. However, addition of the copolymer increased the extent of dispersion of the homopolymer components within one another quite effectively. Blend specimens were tested with respect to tensile, flexural, impact, and thermal performance characteristics to study the effects of morphology and composition on these factors. In general, the blends were rigid, brittle materials with some-what enhanced thermal characteristics. Addition of polystyrene-block-polycaprolactone polymer to the blends resulted in increased brittleness, slightly reduced thermal performance, and, in some instances, greatly increased rigidity.     

Effects of hybrid nucleating agents on glass fiber‐reinforced polyethylene terephthalate/polybutylene terephthalate alloy crystallization

In this article, the Surlyn® 8920 and AX 8900 were mixed as hybrid nucleating agents for glass fiber (GF)‐reinforced polyethylene terephthalate (PET)/polybutylene terephthalate (PBT) alloy. The crystallization behaviors on GF‐reinforced PET/PBT alloy with compound nucleating agents of Surlyn® 8920 and AX 8900 were studied by differential scanning calorimeter. The Jeziorny method, Mo method, and Kissinger method were used for studying the non‐isothermal crystallization process of the composite alloys. While single AX 8900 cannot further improve the crystallization properties of the alloy and reduced the crystallization rate, the introduction of Surlyn® 8920 can effectively ameliorate the condition. The results demonstrated the hybrid nucleating agents of Surlyn® 8920 and AX 8900 not only can accelerate crystal growth, but also can significantly reduce the energy barrier, and it has a good effect in the alloy to the nucleation. POLYM. COMPOS. 37:1167–1172, 2016. © 2014 Society of Plastics Engineers     

Rheology-processing-property relationships in tubular blown film extrusion. I. High-pressure low-density polyethylene

Three different grades of high-pressure low-density polyethylene resin were used to establish relationships between tubular film blowability and the molecular parameters, namely, the molecular weight distribution (MWD) and the degree of long-chain branching (LCB), and also between the processing conditions and the mechanical properties of the tubular blown films produced. For the study, both the shearing and elongational flow properties of the resins were determined. During the tubular film blowing experiment we measured the freeze-line position, the tubular bubble diameter, the takeup speed, the axial tension, the pressure inside the tubular bubble, and the mass flow rate of the resin. The thickness of the tubular blown films was measured from the samples collected. In order to determine the tubular film blowability, we measured the maximum takeup speed at which the tubular blown bubble broke, for various blowup ratios. The measurements described above permitted us to calculate the tensile stresses at the freeze line, in both the machine and transverse directions, and they were found to be correlatable to the processing conditions employed. It has been found that the tubular film blowability is increased as the resin's MWD becomes narrower and the degree of LCB is less. It has been found further that a resin having lower elongational viscosity tends to give a greater draw-down ratio, indicating a better tubular film blowability. Finally, the tensile properties of the tubular blown films were found correlatable to the processing variables, namely, blowup and takeup ratios.     

Rheology-processing-property relationships in tubular blown film extrusion. II. Low-pressure low-density polyethylene

An experimental investigation was undertaken to establish rheology-processing-property relationships in the tubular blown film extrusion of low-pressure low-density polyethylene (LP-LDPE). For the study, three commercial LP-LDPE resins, each from a different resin manufacturer, were used in producing tubular films, by employing the apparatus described in Paper I of this series. Both molecular and rheological characterizations of the resin were conducted, enabling us to interpret the tubular film blowing characteristics of the resins. Correlations were obtained between the processing variables (namely, blowup and takeup ratios) and the tensile properties of the films. The tubular film blowing characteristics of LP-LDPE and HP-LDPE resins are compared. Differences in the rheological properties (namely, elongational viscosity) of the two types of resin are used in explaining the experimentally observed differences in their tubular film blowability.     

Effect of various added compatibilizers on the crystalline structure of polypropylene homopolymer/polybutylene terephthalate and polypropylene copolymer/polybutylene terephthalate polymer blends

Blends of semicrystalline isotactic polypropylene homopolymer and polypropylene copolymer with polybutylene terephthalate with different compatibilizers [i.e., styrene acrylonitrile, Surlyn, styrene–ethylene–butadiene styrene (SEBS), block copolymer and SEBS block copolymer grafted with maleic anhydride] were prepared by melt blending. Wide angle‐X‐ray scattering patterns of injection moldings were obtained. The crystallinity index and d‐spacing were calculated with different concentrations of different compatibilizers. X‐ray results in the structural investigation of the compatibilized blends correlated well with the different compatibilizer concentrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1190–1193, 2003     

Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

Studies on blends of a thermotropic liquid crystalline polymer and polybutylene terephthalate

Summary Structure-property relationships of blends of a thermotropic polyester-type main-chain LCP and polybutylene terephthalate (PBT) were investigated. LCP was melt blended with three different PBTs and the blends were processed by injection moulding or extrusion. Mechanical and thermal properties of the blends were determined and the blend structure was characterized by scanning electron microscopy (SEM). LCP acted as mechanical reinforcement for PBT and improved also its dimensional and thermal stability. The stiffness of PBT increased with increasing LCP content, but at the same time the blends became more brittle. In extrusion the orientation of LCP phases could be further enhanced by additional drawing, which led to significant improvements in strength and stiffness at LCP contents of 20–30 wt.-%.     

Rheology and sheet extrusion of Novatein thermoplastic protein/polybutylene adipate-co-terephthalate blends

Novatein is a thermoplastic polymer made from blood meal proteins, but it has rheological properties very different from commodity thermoplastics. Capillary rheometry revealed an apparent time dependent shear viscosity for Novatein, evident from a decreasing pressure drop over time, measured at constant shear rate. However, blending with polybutylene adipate-co-terephthalate (PBAT) reduced the time dependence for uncompatibilized blends and virtually eliminated time dependence for compatibilized blends containing 30 wt % PBAT. Novatein's extensional viscosity is three orders of magnitude more than its shear viscosity and explained the difficulty in sheet extrusion. In contrast, 30% compatibilized blends had an extensional viscosity similar to neat PBAT and was also the only blend that could be successfully sheet extruded. Although uncompatibilized blends at the same or lower PBAT content also had a lower extensional viscosity, they could not be sheet extruded and the difference was the 30% compatibilized blends had a fine PBAT phase structure (co-continuous in this case), which was sufficiently adhered to the Novatein phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47977.     

Reactive compatibilization of polypropylene/polyethylene terephthalate blends

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP-g-GMA) was studied. Two PP-g-GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20-fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub-micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10–20 μm wide. The low-GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifiying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated.     

Compatibilization of polyethylene terephthalate/polypropylene blends with styrene–ethylene/butylene–styrene (SEBS) block copolymers

Blends of polyethylene terephthalate (PET) and polypropylene (PP) at compositions 20/80 and 80/20 were modified with three different styrene–ethylene/butyl–ene-styrene (SEBS) triblock copolymers with the aim of improving the compatibility and in particular the toughness of the blends. The compatibilizers involved an unfunctionalized SEBS and two functionalized grades containing either maleic anhydride (SEBS-g-MAH) or glycidyl methacrylate (SEBS-g-GMA) grafted to the midblock. The effects of the compatibilizers were evaluated by studies on morphology and mechanical, thermal and rheological properties of the blends. The additon of 5 wt % of a SEBS copolymer was found to stabilize the blend morphology and to improve the impact strength. The effect was, however, far more pronounced with the functionalized copolymers. Particularly high toughness combined with rather high stiffness was achieved with SEBS-g-GMA for the PET-rich composition. Addition of the functionalized SEBS copolymers resulted in a finer dispersion of the minor phase and clearly improved interfacial adhesion. Shifts in the glass transition temperature of the PET phase and increase in the melt viscosity of the compatibilized blends indicated enhanced interactions between the discrete PET and PP phases induced by the functionalized compatibilizer, in particular SEBS-g-GMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:241–249, 1997     

Polypropylene/polyethylene terephthalate blends compatibilized through functionalization

In attempts to improve the compatibility of polypropylene with polyethylene terephthalate, an acrylic acid functionalized polypropylene was evaluated as the blend component in polyblends containing 40 percent by weight polyethylene terephthalate and compared with an unmodified polypropylene. The preliminary experiments in a batch laboratory mixer were followed by compounding in a co-rotating twin-screw extruder. Additives such as magnesium acetate and p-toluenesulfonic acid were evaluated as catalysts for potential interchange or esterification reactions that could occur in the melt. The blends were characterized through scanning electron microscopy, infrared spectroscopy, differential scanning calorimetry, and for mechanical properties. The results show that the functionalized polypropylene promotes a fine dispersed phase morphology, improves processability and mechanical properties, and modifies the crystallization behavior of the polyester component. These effects are attributed to enhanced phase interactions resulting in reduced interfacial tension (calculated as a 4-fold decrease). The presence of the additives does not, in general, improve any further the blend morphology and properties, or its processability.     

The reactive extrusion of polyethylene/polypropylene blends

The objective of this work was to investigate the compatibilization of a blend of linear low density polyethylene with polypropylene by Injection of a free radical initiator during extrusion. The reactive extrusion process utilized a single screw extruder equipped with two static mixers. The initiator was injected into the extruder feedport and temperature programming used to cause most reaction to occur within the static mixers. Although elongation at yield was increased by 37 percent, impact strength and yield strength decreased by 17 and 54 percent, respectively. Scanning electron microscopy showed that the maximum size of the dispersed phase decreased from a maximum size of four microns to less than two microns upon addition of initiator. Size exclusion chromatography (SEC), temperature rising elution chromatography (TREF), and differential scanning calorimetry showed that the polypropylene in the blend was degrading while the polyethylene was increasing in molecular size. The combination of SEC and TREF was particularly useful in elucidating this result. No copolymer was discerned by any of the methods used.