Cyclic Butylene Terephthalate Research Articles

Poly(butylene terephthalate)‐functionalized MWNTs by in situ ring‐opening polymerization of cyclic butylene terephthalate oligomers

Poly(butylene terephthalate) (PBT) had been covalently attached onto the surface of multiwalled carbon nanotubes (MWNTs) by a “grafting from” method based on in situ ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) using MWNT‐supported initiator (MWNT‐g‐Sn). The SnO bond grafted on the surface of MWNTs, which was confirmed by X‐ray photoelectron spectroscopy, provided the initiating sites for ROP of CBT. Fourier transformed infrared spectroscopy and nuclear magnetic resonance were used to confirm the chemical structure of MWNT‐graft‐PBT copolymer and emission transmission electron microscope was utilized to observe the nanostructure of the PBT functionalized MWNTs. A distinct core–shell structure with PBT layer as the shell could be observed after functionalization of PBT despite it was not uniform. The results of thermogravimetric analysis indicated that the grafting ratio of PBT was about 59.3%. Furthermore, the solubility of the PBT functionalized MWNTs in phenol/tetrachloroethane had also been investigated. Copyright © 2010 John Wiley & Sons, Ltd.

Entropically-driven ring-opening polymerization of cyclic butylene terephthalate: Rheology and kinetics

Cyclic butylene terephthalate oligomers (CBT) with ultra-low melt viscosity can be polymerized into poly (butylene terephthalate) (pCBT) via entropically-driven ring-opening polymerization (ED-ROP) in a short time (ranging from several seconds to 10 min) with no chemical emission and no heat generation during the polymerization process. Due to no heat generation, dynamic rheological measurements were used to monitor the polymerization of CBT from 220 to 250°C. The polymerization was accompanied by a steep increase of the melt viscosity and modulus in isothermal rheological tests, and much faster at higher temperature. With rheological results, reptation theory and Double reptation model were adopted to determine the variation of the molecular weight and concentration with time for pCBT. According to the ED-ROP mechanism of CBT, kinetics equations were also established to simulate the polymerization process. Furthermore, using the results of variation of molecular weight with time for pCBT and kinetics equations, the polymerization rate constants for initiation and propagation steps were evaluated, and the activation energy was also obtained. It was proved that rheological method is a convenient and reliable way to investigate the kinetics of ED-ROP of CBT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Melting and crystallization behavior of copolymer from cyclic butylene terephthalate and polycaprolactone

In this study, we investigated the nonisothermal crystallization kinetics, crystallization morphology, and melting behavior of polymerized cyclic butylene terephthalate (pCBT) copolymerized with polycaprolactone (PCL). The results of this experiment indicated that the Ozawa exponent varied between 2 and 3 for pCBT, but between 1 and 2 for blends of pCBT/PCL. At the same temperature (185°C), the crystallization rate constant KT for pCBT/PCL blend was much lower than for pCBT homopolymer. These results indicated a strong hindrance on the crystallization of pCBT/PCL blends. The pCBT and pCBT/PCL samples exhibited no visible difference in morphology or microstructure. However, the crystallization and melting peak temperature of pCBT/PCL blends was ∼20°C lower than that of pCBT homopolymer. Crystal morphology confirmed that the mechanism of simultaneous polymerization and crystallization found applicable to pCBT homopolymer did not apply for blends of pCBT/PCL. It therefore appears that crystallization should be delayed until after the completion of pCBT/PCL copolymerization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Toughening of in situ polymerized cyclic butylene terephthalate by addition of tetrahydrofuran

AbstractA new method of toughening polymerized cyclic butylene terephthalate (pCBT) with tetrahydrofuran (THF) is proposed. The pCBT was prepared by in situ ring‐opening polymerization of a commercial cyclic butylene terephthalate, a cyclic form of poly(butylene terephthalate), in the presence of THF. In comparison to conventionally polymerized pCBT, the resultant material was found to be ductile, showing a strain at break of well above 100% in tensile tests. Other matrix properties, such as tensile modulus, tensile strength and glass transition temperature, were not significantly altered by the addition of THF. It was found that the presence of THF enhanced the polymerization reaction, resulting in an increased molecular weight and a narrowed molecular weight distribution. Moreover, remaining oligomers after polymerization were extracted by the THF and a toughened oligomer‐free pCBT was obtained. The influence of time and temperature on the long‐time toughening action of THF was studied. The results showed that samples became brittle after 3 months when subjected to a temperature of 80 °C, resulting in a reduction of the toughening action. Copyright © 2010 Society of Chemical Industry

Synthesis and properties of poly(butylene terephthalate)/multiwalled carbon nanotube nanocomposites prepared by in situ polymerization and in situ compatibilization

AbstractA novel cyclic initiator was synthesized from dibutyl tin(IV) oxide and hydroxyl‐functionalized multiwalled carbon nanotubes (MWNTs) and was used to initiate the ring‐opening polymerization of cyclic butylene terephthalate oligomers to prepare poly(butylene terephthalate) (PBT)/MWNT nanocomposites. The results of Fourier transform infrared and NMR spectroscopy confirmed that a graft structure of PBT on the MWNTs was formed during the in situ polymerization; this structure acted as an in situ compatibilizer in the nanocomposites. The PBT covalently attached to the MWNT surface enhanced the interface adhesion between the MWNTs and PBT matrix and, thus, improved the compatibility. The morphologies of the nanocomposites were observed by field emission scanning electron microscopy and transmission electron microscopy, which showed that the nanotubes were homogeneously dispersed in the PBT matrix when the MWNT content was lower than 0.75 wt %. Differential scanning calorimetry and thermogravimetric analysis were used to investigate the thermal properties of the nanocomposites. The results indicate that the MWNTs acted as nucleation sites in the matrix, and the efficiency of nucleation was closely related to the dispersion of the MWNTs in the matrix. Additionally, the thermal stability of PBT was improved by the addition of the MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Toughening of basalt fiber‐reinforced composites with a cyclic butylene terephthalate matrix by a nonisothermal production method

AbstractThe interest in thermoplastic composites is growing because of their advantages over thermosets, as well as their recyclability and higher toughness. The melt viscosity of thermoplastic polymers is very high, which makes fiber impregnation difficult. This difficulty can be overcome by the in situ polymerization with cyclic butylene terephthalate (CBT). However, this leads to a brittle polybutyleneterephthalate when isothermal RTM‐production is applied. To solve this problem, a nonisothermal production process for composites with CBT as matrix material was developed and the influence on the toughness was investigated. In the nonisothermal production process, different cooling rates were applied to examine their influence on the toughness of the produced composites. The difference in composites properties was related to the difference in the degree of crystal perfection, which was investigated by differential scanning calorimetry. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:70–79, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20176

Crystallization and morphology of polymerized cyclic butylene terephthalate

AbstractThe crystallization behavior and morphology of polymerized cyclic butylene terephthalate (pCBT) were investigated by thermal differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The spherulite growth rate was analyzed based on the Hoffman and Lauritzen theory to better understand the crystallization behavior. We found four typical morphologic features of pCBT corresponding to the crystallization temperature spectrum: usual negative spherulite, unusual spherulite, mixed birefringence spherulite coexisting with boundary crystals, and highly disordered spherulitic crystallites. The Avrami crystallization kinetics confirmed the occurrence of combined heterogeneous nucleation accompanied by a change in the spherulitic shape of pCBT, which also agreed with the PLM results. The equilibrium melting temperature and glass transition temperature of pCBT were 257.8 °C and 41.1 °C, respectively. A regime II–III transition occurred at 200.9 °C, which was 10 °C lower than that reported for poly(butylene terephthalate) (PBT). Coinciding with and attributed to the regime transition, the boundary crystal disappeared at temperatures above 200 °C and the morphology changed from the mixed type to highly disordered spherulitic crystallites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1127–1134, 2010

Toughening of isothermally polymerized cyclic butylene terephthalate for use in composites

Interest in thermoplastic composites is growing because of their advantages over thermosets in recyclability and in toughness. The melt viscosity of thermoplastic polymers is very high, which makes fibre impregnation difficult. This can be solved by using in-situ polymerization with cyclic butylene terephthalate (CBT). However this leads to a brittle PBT. To solve this problem physical and chemical modification of the polymerized CBT (pCBT) was performed, to disturb the crystallization. Chemical modification with PC and with PTHF has an embrittling effect because of a bad chemical interaction. When polycaprolactone is added to the CBT a copolymer is formed which leads to a lower crystallinity, resulting in a higher toughness of the pCBT. This tougher matrix material was used in composites and a two times tougher composite is produced when only 7 wt% PCL is added to the CBT. The physical modification evaluated was the addition of carbon nanotubes (CNT). Although an increase in stiffness and strength of the pCBT is seen when CNTs are added up to 0.1 wt%, the failure strain decreases.

Rolling and sliding wear properties of hybrid systems composed of uncured/cured HNBR and partly polymerized cyclic butylene terephthalate (CBT)

The phase structure, rolling and sliding wear properties of the hybrids composed of uncured/cured hydrogenated acrylonitrile/butadiene rubber (HNBR) and partly polymerized cyclic butylene terephthalate oligomers (CBT) were investigated. The ratio between HNBR and CBT was varied in the hybrids between 1:0.5 and 1:2. The CBT conversion and phase structure were studied by extraction, differential scanning calorimetry, and dynamic-mechanical thermal analysis.The rolling and sliding wear behaviors of the hybrids under unlubricated condition were determined by using various wear test rigs. It was found that the partly polymerized CBT worked as reinforcement in the HNBR matrix. The specific wear rate of the compounds usually decreased with increasing amount of CBT in both rolling and sliding wear tests. The coefficient of friction (COF) of the hybrids strongly depended on the type and configuration of the wear tests. Dynamic vulcanization of the HNBR in the HNBR/CBT mixes mostly improved the tribological performance. The wear mechanisms were studied as a function of CBT content and discussed.

Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites. It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer ( T m 0 ). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the T m 0 of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer T m 0 .

EVA/PBT nanostructured blends synthesized by in situ polymerization of cyclic cBT (cyclic butylene terephthalate) in molten EVA

Poly(ethylene-co-vinyl acetate) (EVA)/poly(butylene terephthalate) copolymers were synthesized by the in situ polymerization of cyclic butylene terephthalate monomer (cBT) in the presence of molten EVA copolymer. Titanium phenoxide Ti(OPh) 4 which leads to the highest degree of grafting compared to the more classical titanium system was used as the initiator for the ring-opening polymerization of the cBT monomer. The corresponding copolymer was characterized fully by 1H NMR after selective extraction from the blend. As a result, a maximum of 11.3 wt% of EVA-g-PBT copolymer was synthesized by this method. Examination of morphology by transmission electronic microscopy (TEM) showed a fine dispersion of PBT phase with size ranging from 100 to 500 nm in diameter. This gave evidence for a crown structure of the PBT phase that is coated by EVA-g-PBT copolymer. Finally, rheological and mechanical studies highlighted a specific behaviour of this material with improved mechanical properties at room temperature.

Industrial cure monitoring of CBT using DEA for wind energy

Dielectric Analysis (DEA) is a widely used method to measure the cure of many common thermosetting resins systems such as epoxies, polyesters, polyurethanes, polyimides, silicones, bismaleimides and phenolics. The objective of this work is to investigate the curing characteristics of a thermoplastic, Cyclic Butylene Terephthalate (CBT) (supplied by Cyclics Corporation) which polymerises to form Polybutylene Terephthalate (PBT). This paper reports on the results of ongoing experimental investigations in which DEA is used to relate the curing cycle to composite structural features and mechanical performance of a complex composite part. Through adjustments in curing parameters, the significant processing parameters have been identified which optimise the production cycle for thermoplastic PBT composite parts. The recorded ion viscosity is used to determine change in material viscosity, cure rate and cure time. These results have been analysed and presented as a processing guide for correct process control.

Poly (butylene terephthalate)/silica nanocomposites prepared from cyclic butylene terephthalate

Poly (butylene terephthalate) (PBT)/silica nanocomposites were compounded from cyclic butylene terephthalate (CBT) resin with very low melt viscosity via high-speed stirring and subsequent in situ polymerization. The effect of silica nanoparticles on the properties of CBT and its polymer composites has been studied. It was shown that the well-dispersed silica nanoparticles, even in small content (1–2 wt.%), result in the dramatic extension of the polymerization process of CBT resin. The flexural properties of polymerized PBT nanocomposites, including modulus, yield strength and failure strain, was improved significantly with the incorporation of silica nanoparticles.

Novel conductive polymer composites based on poly(butylene terephtalate) filled with carbon fibers

AbstractPoly(butylene terephthalate) (cPBT) synthesized from cyclic Butylene Terephthalate oligomers (CBT) was used as a matrix for carbon fibre (CF) conducting polymer composites (CPC). DSC, rheological studies and measurements of torque of CBT/CF were performed in order to optimise the processing conditions of CPC. DC and AC measurements were carried out for these composites and have shown a low percolation threshold for cPBT/CF.

Hybrids from HNBR and in situ polymerizable cyclic butylene terephthalate (CBT): Structure and rolling wear properties

Hybrids composed of peroxide-curable hydrogenated acrylonitrile-butadiene rubber (HNBR) and cyclic butylene terephthalate oligomers (CBT) were produced. CBT was expected to polymerize in situ when curing the HNBR. Extraction, differential scanning calorimetry (DSC), dynamic-mechanical thermal analysis (DMTA), wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM) were adopted to investigate the CBT conversion and the phase structure of the hybrids before ( T = 190 °C; HNBR-(p)CBT) and after annealing ( T = 250 °C; HNBR-pCBT). Unlubricated rolling wear properties of the related compounds with different CBT contents were assessed in orbital rolling ball (steel)-on-plate (rubber) test rig (Orbital-RBOP). The dynamic coefficient of friction and the specific wear rate were determined. Both (p)CBT and pCBT improved the rolling wear resistance of the hybrids compared to plain HNBR. However, the polymerized CBT (pCBT) improved the wear properties more than the unpolymerized CBT ((p)CBT). The wear mechanisms were identified by inspecting the worn surfaces in scanning electron microscope (SEM) and are discussed as a function of (p)CBT/pCBT modification. Changes in the structure and properties of the hybrids caused by the annealing-induced polymerization of CBT were analyzed.

Toughening of polymerized cyclic butylene terephthalate with carbon nanotubes for use in composites

Low viscosity cyclic butyleneterephthalate (CBT) is a promising material for thermoplastic composites, however after isothermal polymerization (to PBT) and crystallization the material is rather brittle. In the present work, high aspect ratio nanofiller, carbon nanotubes (CNTs), are added to improve ductility. The dispersion of CNTs in CBT is achieved by rotational mixing and appears optimal. Concentrations up to 0.1 wt.%CNT are added to investigate their influence on the mechanical behavior. The addition leads to an increase in stiffness, strength and energy to failure, however, the failure strain slightly decreases. Thermal measurements indicate that the CNTs have no influence on the crystallinity. However, when the mixture of CBT and CNTs is processed in fiber reinforced composites processed by vacuum infusion, the CNTs show a tendency of filtration through the fabric.

Surface Characteristics of Polyhedral Oligomeric Silsesquioxane Modified Clay and Its Application in Polymerization of Macrocyclic Polyester Oligomers

Novel porous aminopropyllsooctyl polyhedral oligomeric silsesquioxane (POSS) modified montmorillonite clay complexes (POSS-Mts) with large interlayer distance and specific surface area have been successfully prepared via ion-exchange reaction and followed by freeze-drying treatment. The morphology of the POSS-Mts is highly influenced by the POSS concentration, pH of the suspension and drying procedure, but the interlayer distance of the POSS-Mts does not change much when the POSS concentration is above 0.4 CEC. The POSS-Mts were used as Sn-catalyst supporters to initiate the ring-opening polymerization of cyclic butylene terephthalate oligomers (CBT) for the first time. No diffraction peak was detected by wide-angle X-ray diffraction for the polymerized composites (pCBT/POSS-Mt), even at 10 wt % loading of POSS-Mt. A clay network rather than exfoliation structure was observed unexpectedly in the composites by transmission electron microscopy. The pCBT/POSS-Mt composite with 10 wt % POSS-Mt was further melt-compounded with commercial PBT resin as a master batch. The tensile properties of the resultant PBT/POSS-Mt composites were highly improved as compared to the pristine PBT due to the homogeneous dispersion of POSS-Mt in the PBT matrix.

Monitoring the Degree of Conversion of Cyclic Butylene Terephthalate Using Dielectric Analysis

Dielectric analysis (DEA) is the most common technique used to determine the state of cure in-process for many thermosetting resins systems such as epoxies, polyesters, polyurethanes, polyimides, silicones, bismaleimides, and phenolics. The objective of this work is to investigate the processing characteristics of cyclic butylene terephthalate (CBT) (supplied by Cyclics Corporation) which polymerises to form a thermoplastic, polybutylene terephthalate (PBT). This paper reports on the interim results of ongoing experimental investigations in which DEA is used to correlate the process cycle to composite structural features and mechanical performance of a complex composite part. Through adjustments in process cycle, the significant processing parameters have been identified which optimise the production of thermoplastic PBT composite parts. The recorded ion viscosity is used to indicate change in material viscosity, conversion rate and process time. These results have been analysed and presented as a guide for correct process control.

Crystallization‐induced shrinkage, crystalline, and thermomechanical properties of in situ polymerized cyclic butylene terephthalate

AbstractThe polymerization and crystallization of cyclic butylene terephthalate oligomers (CBT) were followed by fiber Bragg grating (FBG) and normal force measurements under isothermal conditions at T = 170 and 190°C, respectively. It was found that the FBG and normal force sense only the crystallization‐induced shrinkage. The course of the FBG signal and the normal force as a function of time suggested that crystallization of the polymerized CBT (pCBT) occurs in two steps. The primary crystallization‐induced shrinkage is several hundreds by contrast to the secondary one showing several tens in ppm/min unit according to the FBG results. The two‐step crystallization was confirmed by normal force measurements. The crystallinity and crystalline structure of the pCBTs were studied by differential scanning calorimetry and wide‐angle X‐ray scattering. It was found that the crystallinity and the crystalline parameters slightly differ for the pCBTs formed at T = 170 and 190°C, respectively. The pCBT produced at T = 190°C had slightly higher crystallinity and more perfect crystals than the pCBT formed at T = 170°C. The reliability of the FBG sensing was checked by thermomechanical analysis (TMA). A fair agreement was established between the thermal contraction and thermal expansion measured by FBG and TMA, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Hybrids of HNBR and in situ polymerizable cyclic butylene terephthalate (CBT) oligomers: properties and dry sliding behavior

A peroxide curable hydrogenated nitrile rubber (HNBR) was modified by cyclic butylene terephthalate oligomer (CBT), added in 100 parts per hundred rubber (phr). CBT polymerization was expected to occur simultaneously with that of the curing of the HNBR rubber (T = 190°C, t =2 5 min). Differential scanning calorimetry (DSC) indicated that only a minor part of CBT has been polymerized (pCBT) in the hybrid. Dynamic mechanical thermal analysis (DMTA) revealed that HNBR formed the continuous whereas (p)CBT the dispersed phase. Mechanical properties (hardness, tensile modulus, ultimate tensile strength and strain, tear strength) of the HNBR and HNBR/CBT were determined and collated. Tribological properties were investigated with pin(steel)-on- plate(rubber) (POP), with roller(steel)-on-plate (rubber) (ROP), with oscillating steel cylinder on rubber plate (Fretting) test configurations. Coefficient of friction (COF) and specific wear rate of the HNBR-based systems were determined. It was found that the resistance to wear increases with CBT hybridization. On the other hand, COF did not change much with CBT content. The friction and wear characteristics strongly depended on the test configurations. The worn surface of the HNBR systems was inspected in scanning electron microscope (SEM) to conclude the typical wear mechanisms. SEM investiga- tion showed that the CBT was predominantly recrystallized from its molten state under the curing conditions set. The well developed prism- and platy-like, micron-scaled CBT crystals were made responsible for the reinforcing effect observed.