PBT Chains Research Articles

Influence of Molecular Weight on the Bead Foaming and Bead Fusion Behavior of Poly(butylene terephthalate) (PBT)

A current trend in the progress of bead foams is the use of engineering polymers (i.e., poly(butylene terephthalate) (PBT)), which are more temperature resistant than commodity polymers and thus offer new areas of application. Currently, foaming and molding of PBT bead foams seem to be possible only with an epoxy-based chain extender. This modification leads not only to an increase in molecular weight but also to a changed PBT chain architecture (i.e., branching or even cross-linking). Thereby, the crystallization behavior is considerably slowed down so that the time for chain interdiffusion across neighboring bead surfaces is prolonged. This study investigates the molecular weight influence separately. The crystallization behavior is controlled by varying the length of linear PBTs in such a way that different bead fusion phenomena result. With increasing molecular weight, a lower open cell content (OCC), and therefore a higher expansion behavior during thermomechanical analysis, was observed, which increases the contact area between the beads in the cavity during the steam chest molding process. Adding to the literature shown so far, this study shows that linear chemically unmodified PBT can also be processed into bead foam components using PBTs having a higher molecular weight.

High-performance and functional PBT/EVMG/CNTs nanocomposites from recycled sources by in situ multistep reaction-induced interfacial control

Super-tough and antistatic poly (butylene terephthalate) (PBT) composites from recycled sources with carbon nanotubes were prepared by a multistep reactive compounding process. The PBT-modification was accomplished using epoxidized elastomers (EVMG), epoxidized multi-walled carbon nanotubes (e-CNTs) and epoxidized rheology modifiers (ADR). The reaction between epoxy and PBT-COOH (or –OH) groups enhanced the interfacial bonding between the PBT matrix and the dispersed EVMG and CNTs phases. Moreover, the distribution of CNTs is exclusively in the PBT phase. The presence of ADR resulted in a larger viscosity ratio of the PBT phase to the EVMG phase due to the PBT chain extension and branching, which led to a smaller EVMG particle size and a shorter inter-particle distance. Consequently, both the mechanical properties and the electrical conductivity of the PBT composites were considerably improved due to a synergistic effect of the EVMG and the ADR, e.g., the notched impact strength of the PBT composites reached up to 88 kJ/m2 and the percolation threshold value for conductive network was reduced by 27%. The super-tough and antistatic PBT composites designed in this study may broaden the application range of PBT in automotive and electrical applications.

Evaluation of thermal transitions in Poly (butylene terephthalate)/15A MMT nanocomposites: Nonisothermal experiments and modelling using isoconversional methods

Friedman’s differential isoconversional approach is applied to obtain effective activation energy (Eα) for Poly (butylene terephthalate) and PBT/15AMMT nanocomposites. The presence of 15AMMT content has largely affected Eα values. Further Vyazovkin and Sbirrazzuoli’s approach is used to determine Hoffman-Lauritzen parameters (Kg &U*). The crystallization regime transition (II–III) occurs for neat PBT at 189 °C and its nanocomposites is at 189–192 °C. Kg(III)/Kg(II) ratios are closer to theoretical value of 2. However the corresponding value of U* is inappropriately too low with negative sign (Correlation coefficient R2 = 0.9–0.99) and which is however highly anomalous when compared to other polymers. Setting U* to 6300 J/mol, 4300 J/mol and 0 J/mol, resulted in poor Kg(III)/Kg(II) ratios and R2. This imply that there is a considerable chain mobility during regime II crystallization which is explained in terms of rapid extraction of PBT chain segments by the force of crystallization, following the tube-reptation postulate.

Effects of size and shape of dispersed poly(butylene terephthalate) on isothermal crystallization kinetics and morphology of poly(lactic acid) blends

The isothermal crystallization kinetics and morphology of the poly(lactic acid) (PLA) blends containing three different sizes of both spherical and fibrous poly(butylene terephthalate) (PBT) domains have been comparatively investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The dynamic DSC measurement reveals that PBT domains significantly increase the degree of crystallinity of the PLA. Furthermore, the Avrami model is employed to evaluate the crystallization kinetics under isothermal conditions and it is found that PBT acts as nucleating agent, leading to a high overall crystallization rate constant k and shortened crystallization half time t1/2. Furthermore, the crystallization rate of PLA is promoted with the incorporation of PBT with a large specific surface area. The average Avrami index n of all samples lies within the range of 3.3 − 4.0, suggesting that morphologies of PBT do not affect the nucleation mechanism; however, the depression of equilibrium melting temperature in the blends ascribes the reductions of perfectness and size of the PLA crystallites. Besides, the nucleation of PLA crystallites around PBT fibers is probably faster than those around PBT spheres because the PBT chains oriented at the fiber surface as a result of flow‐induced crystallization during melt stretching may serve as the primary nuclei for PLA chains to drastically crystallize at the fiber surface. POLYM. ENG. SCI., 56:258–268, 2016. © 2015 Society of Plastics Engineers

Inhibited transesterification on the properties of reactive core-shell particles toughened poly(butylene terephthalate) and polycarbonate blends

Reactive core-shell particles with polybutadiene as core (297 nm) and methyl methacrylate-co-styrene-co-glycidyl methacrylate terpolymer as shell (PB-g-MSG) were prepared to toughen poly(butylene terephthalate) (PBT) and polycarbonate (PC) blends. Sodium pyrophosphate (SPP) was used to modify the transesterification between PBT and PC. FTIR results proved the occurrence of the transesterification and the addition of SPP inhibited the exchange reactions. SEM displayed the PB-g-MSG particles dispersed in PBT/PC matrix uniformly and the addition of SPP had no negative influence on the uniform dispersion. The crystallization temperature of PBT increased with the addition of SPP which indicated the constraint of PC block on the crystallization of PBT chain became poor. At the same time, with the addition of SPP into the PBT/PC/PB-g-MSG blend, the Tg of PC phase further shifted to higher temperature. PB-g-MSG was an effective toughener for PBT/PC blends, however, SPP decreased the toughening efficiency of PB-g-MSG particles for the PBT/PC blends. The yield strength and tensile modulus of PBT/PC blends increased first and then deceased with the increase of SPP content in the blends. Fracture mechanisms results showed the addition of SPP was not beneficial to the cavitation of the core-shell particles and shear yielding of the matrix and led to the decreased impact toughness.

Synthesis of Poly(butylene terephthalate)/Attapulgite Nanocomposites by In-Situ Polymerization and Its Crystallization Behavior

Poly(butylene terephthalate) (PBT)/attapulgite (AT) nanocomposites were prepared via in-situ polymerization without pre-modification of AT. By this method, PBT chains were successfully grafted onto the surface of AT, which was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Scanning electron microscope examination indicated the uniform dispersion of AT nanoparticles in PBT matrix. The crystallization behavior of PBT/AT nanocomposites was investigated by X-ray diffraction patterns, differential scanning calorimetry, and step-scan differential scanning calorimetry. The non-isothermal crystallization processes were analyzed with the Avrami, Ozawa, and Mo methods. Crystallization activation energies of the samples were also determined by the Kissinger method. The results indicated that AT could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization, while AT also acted as a physical hindrance to retard the transport of polymer chains to the growing crystals.

Toughening of Poly (Butylene Terephthalate) with Epoxy-Filled Poly (Ethylene–Octene) Copolymer

Toughened poly (butylene terephthalate) (PBT) with triglycidyl isocyanurate (TGIC)-filled poly (ethylene–octene) (POE) was prepared by melt reaction extrusion. For retarding the reaction extent between PBT and the epoxy component, the TGIC was first blended with POE to enwrap its reactive epoxy groups. Then, the TGIC-filled POE was used to melt blend with PBT. The Fourier transform infrared (FTIR) spectra showed that no other peaks appeared in the POE/TGIC specimens except for those originally existing in pure POE and TGIC. The rheological results further confirmed that no reaction occurred between the epoxy and the POE matrix. When the POE/TGIC was blended with PBT, a distinct increase of the viscosity suggested that the migration of the TGIC from POE to PBT during the melt processing induced chain extension reactions of PBT. The results obtained from DSC and DMA revealed that the chain extension of PBT induced by the reaction with TGIC restricted the mobility of PBT chains leading to a limitation of the recrystallization-remelting process and an increase of the glass transition temperature of PBT. The mechanical tests showed that the presence of TGIC in the POE phase distinctly improved the toughness of PBT. Compared to the case of a PBT/POE (80/20, wt%/wt%) blend, the elongation at break and impact strength of the system filled with 5 phr TGIC were increased more than three and six times, respectively.

Influences of exfoliated graphite on structures, thermal stability, mechanical modulus, and electrical resistivity of poly(butylene terephthalate)

AbstractWe report structural features and multifunctional properties of nanocomposites based on poly(butylene terephthalate) (PBT) and exfoliated graphite (EG), which are manufactured by melt‐compounding technique. Scanning electron microscope and X‐ray diffraction data exhibit that graphene platelets of EG are well dispersed and exfoliated in the PBT matrix even at high EG content of 7.0 wt %. Raman spectra support that graphene platelets of EG are interacted specifically with phenyl rings of PBT chains at nanocomposite interfaces. DSC cooling and following heating thermograms of the nanocomposites demonstrate that graphene platelets of EG play a role as effective nucleating agents for PBT α‐phase crystals and thus lead to accelerating the overall crystallization of the nanocomposites. Thermal stability of PBT/EG nanocomposites is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the PBT matrix, especially at the active oxygen gas condition. Dynamic mechanical modulus of the nanocomposites is also enhanced significantly with increasing the EG content. The electrical volume resistivity of the nanocomposites is decreased dramatically from ∼ 1018 to ∼ 106 Ω cm by forming the electrical conduction path at a certain EG content between 3 and 5 wt %. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effects of filler type on the nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT) composites

AbstractIn this study, melt‐crystallization behaviors of poly(butylene terephthalate) (PBT) composites including different types of inorganic fillers were investigated. Composite samples having 5 wt % of fillers were prepared by melt processing in a twin screw extruder using commercial grades of calcite (CA), halloysite (HL), and organo‐montmorillonite (OM) as filler. Depending on the filler type and geometry, crystallization kinetics of the samples was studied by differential scanning calorimetry (DSC) methods. Effect of filler type on the nonisothermal melt‐crystallization kinetics of the PBT was analyzed with various kinetic models, namely, the Ozawa, Avrami modified by Jeziorny and Liu‐Mo. Crystallization activation energies of the samples were also determined by the Kissinger, Takhor, and Augis–Bennett models. From the kinetics study, it was found that the melt‐crystallization rates of the samples including CA and HL‐nanotube were higher than PBT at a given cooling rate. On the other hand, it was also found that organo‐montmorillonite reduced the melt‐crystallization rate of PBT. It can be concluded that organic ammonium groups in the OM decelerate the crystallization rate of PBT chains possibly due to affecting the chain diffusion through growing crystal face and folding. This study shows that introducing organically modified alumina‐silicate layers into the PBT‐based composites could significantly reduce the production rate of the injection molded parts during the processing operations. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Preparation of polybutylene terephthalate/silica nanocomposites by melt compounding: Evaluation of surface properties

Influence of nanosilica on surface properties of poly(butylene terephthalate) was investigated by the use of Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), contact angle measurement (CAM), scanning electron microscopy (SEM) and reflectance spectroscopy (RS). FTIR results indicated that surface groups of silica have some interfacial interactions and bonding with carboxyl or hydroxyl end groups of PBT chains. AFM and SEM figures of the resultant nanocomposites illustrated increased surface roughness compared to pure PBT. Optical properties of nanocomposite films were finally determined by the aid of reflectance spectrophotometer.

Study of the Preparation and Properties of PBT/Epoxy/SiO2 Nanocomposites

Poly (butylene terephthalate) (PBT)/SiO2 nanocomposites, with epoxy resin as a compatibilizer, were prepared by melt blending in a twin-screw extruder. The phase morphology, crystallization behavior, and mechanical properties of the hybrid nanocomposites were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and mechanical tests. The addition of epoxy resin improves the dispersion of SiO2 particles with size of about 70–100 nm and the interfacial interaction between SiO2 and PBT matrix is enhanced due to the reaction between the epoxy groups of the epoxy resin and the hydroxyl groups of the SiO2 surfaces and PBT chains. As a result, the tensile strength, modulus, and flexural strength of the nanocomposites were improved by the presence of 1 wt% epoxy with unchanged notched impact strength.

Synthesis and thermal characterization of random poly(butylene terephthalate‐co‐2‐methyl‐ethylene terephthalate) copolyesters

AbstractPoly(butylene terephthalate‐co‐2‐methyl‐ethylene terephthalate) (PBT/MET) was synthesized by incorporating 1,2‐propandiol(1,2‐PDO) into PBT chains. The molar composition and chemical structure of PBT/MET copolyesters were confirmed by means of FT‐IR and 1H‐NMR. To investigate the effect of 1,2‐PDO on the thermal properties of PBT/MET copolyesters, the copolymerizations were carried out by varying various contents of MET units, and the prepared materials were evaluated by differential scanning calorimetry and thermogravimetric analysis. Results suggested that with the increase of the content of 1,2‐PDO, the amount of crystallinity and the melting temperature decline, while the glass transition temperature increases and the copolyesters become more transparent and brittle with respect to PBT homopolymer. In addition, the Tg‐composition and Tm‐composition data are well subjected to the Wood equation and Flory's equation, respectively. All these copolyesters are found to consist of the general trend displayed by copolymers reported elsewhere. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Surface modification effects of core–shell rubber particles on the toughening of poly(butylene terephthalate)

AbstractWe toughened poly(butylene terephthalate) (PBT) by loading core–shell rubber (CSR) type impact modifiers, consisting of a rubbery poly(n‐butyl acrylate) core and a rigid poly(methyl methacrylate) shell. To optimize the dispersion of CSR particles into the PBT matrix during melt compounding, the shell surface was modified with different grafting ratios of glycidyl methacrylate (GMA) reactive with PBT chain ends. In PBT blends with a 20 wt % CSR loading, the dispersed rubbery phases showed discernible shapes depending on the grafted GMA content, from predetermined spheres with 0.25 ± 0.05 μm diameters to their aggregates in the 2–3 μm diameter range. As a result, the interparticle spacing (τ) could be controlled from 0.25 to 4.0 μm in the PBT blends containing the fixed rubber loading. The Izod impact strengths of these samples increased significantly below τ = 0.4 μm. Additional thermal and morphological analyses strongly supported the hypothesis that the marked increase in toughness of the blends was related to less ordered lamellar formation of the PBT matrix under the confined geometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and characterization of poly(butylene terephthalate)/silica nanocomposites

AbstractIn this study, we presented a convenient, in situ polymerization route for the preparation of Poly (butylene terephthalate) (PBT)/silica nanocomposites, in which silica was not premodified. The nanocomposites were synthesized by in situ polymerization of terephthalic acid (TPA), 1,4‐butanediol (BD) and silica. The structure of these nanocomposites were investigated by Fourier transform infrared (FTIR) and thermogravimetric analyses (TGA). The results show that PBT chains were successfully grafted onto the surface of silica. Transmission electron microscope (TEM) micrographs revealed that silica were homogeneously dispersed in PBT matrix at a size level of 10–20 nm. The isothermal crystallization kinetics of pure PBT and PBT/silica nanocomposites were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. The existence of silica could lead to an acceleration of crystallization and enhance the thermal stability of PBT. According to dynamic mechanical analysis (DMA), the storage modulus of PBT/silica nanocomposites were markedly improved compared with pure PBT. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The incorporation of rigid diol monomers into poly(butylene terephthalate) via solid‐state copolymerization and melt copolymerization

AbstractIncorporation of 2,2‐bis[4‐(2‐hydroxyethoxy)phenyl]propane (Dianol 220®) into poly(butylene terephthalate) (PBT) via solid‐state copolymerization (SSP) showed that Dianol, besides being the reactant, also acts as a swelling agent for rigid amorphous PBT chain segments. Being swollen, these amorphous chain segments become sufficiently mobile to contribute to the SSP process. The thermal behavior of the resulting copolyesters is comparable with melt copolymerized copolymers, although having a different chemical microstructure. The main reason is a full miscibility in the melt of unmodified PBT chain segments and modified chain segments, which eliminates the advantages of a blocky microstructure for the SSP copolyesters. However, incorporation of 2,2′‐biphenyldimethanol (BDM) into PBT resulted in a higher crystallization temperature compared with PBT–Dianol copolymers of equal composition. Preordering of polymer chains in the melt by incorporating rigid, phase separating BDM‐moieties, preferably via SSP to obtain a non‐random distribution, may be the origin of the enhanced crystallization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1203–1217, 2008

Preparation and characterization of poly(butylene terephthalate)/poly(ethylene terephthalate) copolymers via solid‐state and melt polymerization

AbstractTo increase the Tg in combination with a retained crystallization rate, bis(2‐hydroxyethyl)terephthalate (BHET) was incorporated into poly(butylene terephthalate) (PBT) via solid‐state copolymerization (SSP). The incorporated BHET fraction depends on the miscibility of BHET in the amorphous phase of PBT prior to SSP. DSC measurements showed that BHET is only partially miscible. During SSP, the miscible BHET fraction reacts via transesterification reactions with the mobile amorphous PBT segments. The immiscible BHET fraction reacts by self‐condensation, resulting in the formation of poly(ethylene terephthalate) (PET) homopolymer. 1H‐NMR sequence distribution analysis showed that self‐condensation of BHET proceeded faster than the transesterification with PBT. SAXS measurements showed an increase in the long period with increasing fraction BHET present in the mixtures used for SSP followed by a decrease due to the formation of small PET crystals. DSC confirmed the presence of separate PET crystals. Furthermore, the incorporation of BHET via SSP resulted in PBT‐PET copolymers with an increased Tg compared to PBT. However, these copolymers showed a poorer crystallization behavior. The modified copolymer chain segments are apparently fully miscible with the unmodified PBT chains in the molten state. Consequently, the crystal growth process is retarded resulting in a decreased crystallization rate and crystallinity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 882–899, 2007.

Processing, rheology and structure of melt compounded PBTclay nanocomposites having different chemical composition.

AbstractIn this study the melt flow behavior of poly(butylene terephthalate)-clay nanocomposites produced by melt compounding was investigated. Four commercial organo-modified montmorillonites, differing mainly by the organic treatment used in the modification, were employed as nanometric fillers and blended with the poly(butylene terephthalate) (PBT) at two weight percentages each (6 and 9wt%). The process was carried out using a laboratory-scale twin-screw extruder at two different extrusion rates, in order to evaluate the effect of the shear rate during the process on microstructure and flow properties. In this regard, the nanocomposite samples were submitted to morphological analyses and rheological measurements in the dynamic regime. The effect of temperature on the flow behavior of the hybrids with respect to the neat PBT matrix was also investigated. The obtained data were related to the hybrid compositions and then to the chemical affinity between polymer and clay type. All the reported results have shown a gradual transition from a pseudo-Newtonian trend towards a pseudo-solid-like flow behavior with the increase of the clay loading and the dispersion/exfoliation level of the clay particles, due to the corresponding increase of the polymer-silicate interactions that slow the relaxation times of the PBT chains. Moreover, it was also evident that for the fillers having the higher affinity towards the PBT the nano-scale dispersion benefit from higher residence times, and therefore slower extrusion rates; on the contrary, for the fillers having poor interaction with the polymer, higher shear stress, and therefore higher extrusion rates, are needed to disrupt the clay tactoids in smaller particles. In the last part of the work, in order to verify if a relationship between flow properties and degree of exfoliation does actually exist, the rheological data were also processed using a simple semi-quantitative empirical method proposed in literature. The method failed for our systems, thus underlining the insufficiency of the rheological response alone in quantifying the exfoliation degree of an organoclay in the matrix.

Poly(butylene terephthalate) Copolymers Obtained via Solid-State Polymerization and Melt Polymerization. A Study on the Microstructure via 13C NMR Sequence Distribution

The chemical microstructure of poly(butylene terephthalate) (PBT) copolymers obtained by incorporation of a rigid diol, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (Dianol 220), into PBT using solid-state polymerization (SSP) and melt polymerization (MP) was analyzed. 13C NMR sequence distribution analysis showed that Dianol was randomly incorporated in the PBT−Dianol copolymers obtained by MP. However, the used 13C NMR sequence distribution analysis method was based on solution NMR. As a consequence, the obtained chemical microstructure reflects both the crystalline and amorphous part. For PBT−Dianol copolymers obtained by SSP, the modification only took place in the amorphous phase of PBT. Hence, knowledge of the chemical microstructure of the amorphous phase is important for tailoring the final properties of these copolymers obtained by SSP. Therefore, a calculation method was developed to adjust the solution 13C NMR peak integral values of the dyad sequences in such a way that only the amorphous fraction, which participates in the transesterification process, was taken into consideration for calculating the degree of randomness. The semicrystalline PBT−Dianol copolymers as obtained by SSP were initially represented by the often-used two-phase (crystalline/amorphous) model. The resulting chemical microstructure of the amorphous phase gave a strong indication that part of the amorphous phase was not accessible for incorporation of Dianol by SSP. Therefore, a three-phase (crystalline, rigid amorphous and mobile amorphous) model was used to represent the morphology of the PBT−Dianol copolymers. Crystalline, mobile amorphous, and rigid amorphous fractions were determined by DSC. Using this three-phase model, the calculation method showed that only the mobile amorphous fraction was accessible for incorporation of Dianol by SSP. At the used solid-state polymerization temperature of 180 °C, the PBT chains in the rigid amorphous and crystalline phase are not mobile enough to participate in the transesterification reaction. Furthermore, determination of the chemical microstructure of the mobile amorphous fraction showed that Dianol was fully randomly incorporated in this fraction.

A rheological study on kinetics of poly(butylene terephthalate) melt intercalation

A multilayered sample with alternatively superposed poly(butylene terephthalate) (PBT) and nonpolar polymer/clay sheets was elaborately prepared to investigate the whole hybridization process of polar polymer. The kinetics of PBT melt intercalation was studied by a rheological approach. The whole intercalation process was demonstrated by the changes of the low-frequencies viscoelastic response with annealing time. The results of the apparent diffusivities and the calculated activation energy indicate that the PBT/clay hybrid formation presents a molecular weight dependence, which may result from the enhancement of interactions between polar groups on PBT chains and the silicate surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1865–1871, 2006

Deformation behavior and nucleation activity of a thermotropic liquid-crystalline polymer in poly(butylene terephthalate)-based composites

Polymer composites based on a thermotropic liquid-crystalline polymer (TLCP) and poly(butylene terephthalate) (PBT) were prepared using a melt blending process. Polymer composites consisting of bulk cheap polyester with a small quantity of expensive TLCP are of interest from a commercial perspective. The interactions between the PBT chains and the flexible poly(ethylene terephthalate) (PET) units in the TLCP phase resulted in an improvement in the compatibility of PBT/TLCP composites. TLCP droplets deformed and fragmented into smaller droplets in the PBT/TLCP composites, which resulted in TLCP fibrillation through the effective deformation of the TLCP droplets. The nucleation activities of the PBT/TLCP composites increased by adding even a small amount of the TLCP component.