PBT Content Research Articles

Influence of processing method on the fracture toughness of thermoplastic-modified, carbon-fiber-reinforced epoxy composites

The influence of processing method on the fracture toughness of thermoplastic-modified, carbon-fiber-reinforced epoxy composites has been investigated. The composites used in this work were prepared from toughened epoxy (176°C cure) prepregs with carbon fiber reinforcement. Tetraglycidyl-4,4 ′-diaminodiphenyl methane (TGDDM) type epoxy resin was used as a matrix material and the polyacrylonitrile based T-300 (12 K) type was used as a carbon fiber. The prepregs had 37 wt.% of resin and a fiber areal weight of 145 ± 3 g/m 2. Poly(butylene terephthalate) (PBT) was used as a dispersed phase. Nylon 6 was also tried as a dispersed phase. In order to optimize the preparation and the toughness of the prepreg, three different processes were attempted; spray-up, double pass, and general types. The mode-II interlaminar fracture toughness was determined in terms of G IIc by using the end-notch-flexure (ENF) test. The toughness of the composite was investigated as a function of the prepreg preparation method, resin formulation, and the kinds and contents of a dispersed phase. It was found that the double-pass impregnation produces composites with higher toughness, compared with the general type of preparation process. Prepregs with an epoxy formulation with lower TGDDM content exhibited higher toughness. The prepregs toughened with Nylon 6 always showed higher G IIC, glass-transition temperatures, as compared with those with PBT, regardless of the preparation methods and the formulation. Finally, it was concluded that the toughness of composites made from prepreg prepared by the spray-up preparation method shows a maximum when the PBT content was 15 phr.

Microhardness of condensation polymers and copolymers. 2. Poly(ester ether carbonate) thermoplastic terpolymers

The number of phases, transition temperatures, and microhardness of a series of poly(ester ether carbonate) (PEEC) multiblock terpolymers with poly(butylene terephthalate) (PBT) hard segments have been investigated as a function of ether/carbonate (EC) soft-segment composition at constant PBT content. The polymerization degree of PBT and the intrinsic viscosity of the terpolymers were determined by viscosimetry. The degree of crystal-Unity, long spacing, glass transitions Tg , and melting temperature were derived by means of x-ray diffraction, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) measurements. Surface mechanical properties were studied by microindentation tests. It was found that the terpolymer consists of two amorphous (EC and PBT) phases and one crystalline (PBT) phase. The Tg value of PBT does not depend on the chemical composition of the soft segments, in the contrast to the Tg of the soft-segment amorphous phase. Introduction of polycarbonate moities in the soft segments induces an increase of Tg by 50°C without formation of an additional (third) amorphous phase. The reduced crystallizability of PBT hard segments (by a factor of 3) is explained by this decrease of flexibility of the soft segments, which also causes a twofold reduction in the microhardness values. The dominating contribution of crystallinity to the microhardness is shown. However, the much lower measured overall microhardness in contrast to the one calculated by means of the additive law is explained by the plasticizing effect of the soft amorphous phase. This assumption is in agreement with the structure model derived from the small-angle x-ray (SAXS) and wide-angle x-ray (WAXS) data.

Functionalization of polypropylene with oxazoline and reactive blending of PP with PBT in a corotating twin‐screw extruder

The aim of this study was to prepare a compatibilized PP/PBT blend in a twin-screw extruder, using oxazoline-functionalized PP. First we prepared the functionalized PP (PP-g-OXA), and then we used it as a compatibilizer in the subsequent reactive blending stage. Polypropylene was successfully functionalized by ricinoloxazoline maleinate in a corotating twin-screw extruder using a melt free radical grafting technique. Grafting yields up to 2.1 phr were achieved. This functionalized PP used as a compatibilizer markedly improved the mechanical properties of the uncompatibilized PP/PBT (PBT content 30 wt %) blend. Significant improvements were observed, especially in impact strength (Charpy) and elongation at break of the compatibilized blends. The increased interactions between the phases were characterized by SEM analysis, DMTA, and DSC experiments. The properties of the blend greatly depended on the degradation of the PP during grafting. An optimal content of compatibilizer exists, which is dependent on the degradation of PP, grafting yield of oxazoline monomer, and on the amount of free, ungrafted monomer present in the compatibilizer. These factors can be adjusted by properly choosing the processing conditions and chemical parameters. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 883–894, 1997

Functionalization of polypropylene with oxazoline and reactive blending of PP with PBT in a corotating twin-screw extruder

The aim of this study was to prepare a compatibilized PP/PBT blend in a twin-screw extruder, using oxazoline-functionalized PP. First we prepared the functionalized PP (PP-g-OXA), and then we used it as a compatibilizer in the subsequent reactive blending stage. Polypropylene was successfully functionalized by ricinoloxazoline maleinate in a corotating twin-screw extruder using a melt free radical grafting technique. Grafting yields up to 2.1 phr were achieved. This functionalized PP used as a compatibilizer markedly improved the mechanical properties of the uncompatibilized PP/PBT (PBT content 30 wt %) blend. Significant improvements were observed, especially in impact strength (Charpy) and elongation at break of the compatibilized blends. The increased interactions between the phases were characterized by SEM analysis, DMTA, and DSC experiments. The properties of the blend greatly depended on the degradation of the PP during grafting. An optimal content of compatibilizer exists, which is dependent on the degradation of PP, grafting yield of oxazoline monomer, and on the amount of free, ungrafted monomer present in the compatibilizer. These factors can be adjusted by properly choosing the processing conditions and chemical parameters. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 883–894, 1997

Hot drawing of partially miscible blends of polycarbonate and poly(butylene terephthalate)

Samples of PC-PBT blends over the entire composition range were drawn at 160°C to high extensions, 2.1–5.8, to study the mechanical reinforcement and the molecular structure development upon deformation. Elastic modulus E' increases with extension ratio for all compositions and temperatures. Blends with 25 and 40 wt% of PC show higher E' at low temperature than pure PBT blends do. Crystallinity increases with extension ratio and is relatively smaller with increasing PC content. The influence of the reversible α to β crystal form transformation was also studied. The second moment of the orientation function f for both crystal forms increases to high values > 0.9 at relatively low extensions. f decreases with PC content for α crystals but decreases for β crystals. The α fraction is high for PBT and decreases with PC content and extension ratio in the blends. Strain recovery experiments show that the α to β transformation is also elastic in nature at high extension ratios and that the reinforcing effect in high PBT content blends is not due to the α/β ratio. © 1996 John Wiley & Sons, Inc.

Steady-state permeation of carbon dioxide through a miscible, glassy polymer blend

Steady-state permeation measurements are reported for carbon dioxide (CO 2 ) through quenched, amorphous films of a miscible blend of poly(butylene terephthalate) (PBT) and a random copolyester of bisphenol-A and iso/terephthalate acids (PAr). Permeabilities were determined at 35°C on blends with up to 60 wt % PBT and for CO 2 pressures up to 300 psi (2.06 MPa). At a fixed blend composition, the permeability, P, decays with driving pressure, p, as described by dual-mode models for gas transport in glassy polymers. From regression fits of the data to dual-mode model predictions for P(p), high- and low-pressure limiting permeabilities are determined. These decrease with PBT content in a manner indicating strong, favorable energetic interactions between the PBT and PAr components in the blend.

Compatibilization of PP/PBT and PP/PA6 blends with a new oxazoline-functionalized polypropylene

Aim of this work was to study the effectiveness of a novel oxazoline-functionalized polypropylene as a compatibilizer for PP/PBT and PP/PA6 blends. This polypropylene-based compatibilizer mixes well with the polypropylene and is capable of reacting with the carboxylic and amine end groups of PBT and PA6. Significant improvements in blend toughness were achieved without reduction in strength and stiffness. These effects were related to stabilized morphology of finely dispersed minor phase well attached to the matrix. The enhanced interfacial interactions between the two phases, in particular at high PBT content were evidenced by increased melt viscosity.

Histological evaluation of a biodegradable polyactive ®/ hydroxyapatite membrane

Guided tissue regeneration (GTR) is a technique which is used for the treatment of bone defects associated with periodontal disease or enossal dental implants. In most experimental studies on GTR, non-degradable membranes are used. A drawback inherent to such devices is that at the end or in the course of the wound healing they have to be removed. Therefore, the aim of the present study was to investigate a new biodegradable membrane material for use in GTR, which also has excellent mechanical properties and is biocompatible. The material is a composite consisting of poly(ethyleneglycol terephthalate) and poly(butylene terephthalate) segmented copolymer (PEG/PBT), which for the experiments was used in pure form and also mixed with hydroxyapatite (HA) grains. Subcutaneous and subgingival implantation studies in goats were performed to determine the biocompatibility and biodegradability characteristics of several of these materials. Differences between materials were introduced in the production process, PEG PBT ratio, material thickness and presence of HA. Implantation periods were 3, 6 and 12 wk. The histological results indicated that all investigated materials were biocompatible with the surrounding tissue. Degradation of the membranes was attended by a mild cellular reaction. The degradation process was mainly influenced by the PEG PBT ratio. A higher PBT content resulted in a decreased degradation.

Synthesis and properties of poly(butylene terephthalate)- b-polyisobutylene segmented block copolymers

Segmented block copolymers of polyisobutylene (PIB) and poly(butylene terephthalate) (PBT) were made by condensation polymerization of α,θ-di-anhydride telechelic PIB, with 1,4-butanediol and dimethyl terephthalate. The inherent viscosity of the polymers was between 0.35 and 2.0 dl g −1. The extractability of the polymers with hexane was studied. The thermal behaviour of these polymers was studied by differential scanning calorimetry and dynamic mechanical thermal analysis. PBT- b-PIB had a glass transition temperature of −62°C and a melting temperature of 200–220°C. A shear modulus was found which, at room temperature, increased from 0.4 to 900 MPa with increasing PBT content in the block copolymer. The degradation was followed by measuring the change of inherent viscosity during thermal and hydrolytic treatment. The PBT- b-PIB showed good resistance to thermal and hydrolytic degradation.

Phase behavior of ternary PBT–PC/phenoxy blends

AbstractTernary polymer blends were obtained by melt mixing, mixing up to 30% poly(butylene terephthalate) (PBT) with polycarbonate (PC) and phenoxy in an attempt to improve the miscibility of the PC/phenoxy binary blend. Although most of the blends with a PBT content higher than 10% appear as transparent, two Tg's appeared at all the blend compositions. These Tg's correspond to PC‐rich and phenoxy‐rich phases where a low amount of the main component of the other phase and all PBT are dissolved in amounts that are a function of the PC/phenoxy ratio of the blend. Increasing the PBT contents in the blends closes to linearity the torque versus composition plot, so that a relationship between miscibility level and viscosity exists in these blends.

Surface studies of polyether–polyester copolymers and blends

The surface composition and morphology of a series of thermoplastic elastomers based on polyester (PBT)–polyether (PPG) copolymers have been studied using x-ray photospectroscopy (XPS) and static secondary-ion-mass spectroscopy (SIMS). In all cases, an enrichment of the polyether soft block at the surface is observed. The degree of preferential surface adsorption is greater for molded specimens compared ot the solvent cast films. The enrichment factor (surface content/bulk content) is greater for speciment of highest PBT content. Angle-dependent XPS measurements are fit with an enriched overlayer model and a continuous profile model. Static SIMS measurements are consistent with the XPS results for molded versus solvent cast films, but indicate that some PBT is present at the outer surface of all specimens analyzed.

Thermal behavior, morphology and the determination of the polymer‐polymer interaction parameter of polycarbonate‐poly(butylene terephthalate) blends

AbstractBlends of bisphenol‐A polycarbonate (PC, poly(oxycarbonyloxy‐1,4‐phenylene‐2‐isopropylidene‐1,4‐phenylene)) and poly(butylene terephthalate) (PBT, poly(oxytetramethyleneoxy‐terephthaloyl)) have been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were prepared by screw extrusion and solution casting with mass fractions of PC in the blends varying from 0,90 to 0,10. From the measured glass transition temperature (Tg) and apparent mass fractions of PC and PBT dissolved in each phase, it appears that the PBT dissolves more in the PC‐rich phase than does the PC in the PBT‐rich phase. Also, compatibility is greater in the case of extruded blends than in the case of solutioncast blends. The values of the Flory‐Huggins polymer‐polymer interaction parameter (χ12) were determined and found to range from 0,042 to 0,033 for extruded blends at 250°C and from 0,054 to 0,039 for solution casting at 25°C. The χ12 decreases with increase of PBT content throughout the investigated composition range. From the Tg's, the microscopy study and the extrudate swell ratios, it is concluded that compatibility is achieved in the blends having mass fractions 0,90, 0,20 and 0,10 of PC, but that these blends are not microscopically homogeneous.

Processing of bulk [formula omitted] molecular composites

A novel process for the fabrication of rigid-rod polymer reinforced thermoplastic molecular composites into bulk articles is presented. The as-processed poly( p-phenylene benzobisthiazole) (PBT)/nylon-6,6 molecular composites, depending on their PBT content, showed significantly higher tensile properties than nylon-6,6 and maintained an excellent bulk integrity even above the melting temperature of nylon. The Young's moduli of these molecular composites were compared to those predicted from the rule of mixtures for three-dimensionally isotropic fibre composites. By assuming PBT/nylon-6,6 molecular composites to be stiff fibre composites, the reinforcement efficiency of PBT was estimated to achieve 50–70% that of the maximum.

Block copolymers of poly(ethylene terephthalate)‐poly(butylene terephthalate). II. Small‐angle light‐scattering studies

AbstractSmall‐angle light‐scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusual Hv patterns with the four lobes along the polarizer directions, while at later stages they showed the usual Hv patterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster‐crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superstructure.

Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior

AbstractBlock copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end‐group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster‐crystallizing PBT blocks crystallized first and provided built‐in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast‐crystallizing copolyester.

Crystallization behaviour of poly(ethylene terephthalate) and poly(tetramethylene terephthalate) blends

AbstractThe isothermal and non‐isothermal crystallization behaviour of blends of poly(ethylene terephthalate) (PET) and poly(tetramethylene terephthalate) (PBT) is investigated at low percentage of the second component. The melting behaviour of the isothermally crystallized sample shows that the crystallization behaviour in the blend is governed by the mobility of PBT. Below 200°C the crystallization process is hindered, whereas above 200°C the PET crystals are larger in case of added PBT. The non‐isothermal crystallization behaviour shows that the crystallization process is hindered when the PBT content in the blend is less or higher than 6 wt.‐%.