Cyclic Butylene Terephthalate Research Articles

The Study of Volume Electrical Resistivity and Mechanical Property of CBT/Carbon Black/Aluminum Composites

Cyclic Butylene Terephthalate (CBT)/carbon black (CB)/aluminum composites were prepared by melting blend method and their conductivity and mechanical property were studied by Milliohmmeter and material testing machine. The results showed that at below 1.6 wt% of flake aluminum（Al）, volume electrical resistivity and flexural strength of composites increased with Al content increases and reached the maximum value at 1.6 wt% of Al. Composites containing 18.4 wt% of CB and 1.6 wt% of aluminum exhibited excellent comprehensive performance (electrical resistivity, 20.3 Ω.cm; flexural strength, 40.0 MPa).

Enhanced dispersion for electrical percolation behavior of multi-walled carbon nanotubes in polymer nanocomposites using simple powder mixing and in situ polymerization with surface treatment of the fillers

The electrical conductivity of nanocomposites with a Cyclic Butylene Terephthalate (CBT) matrix and multi-walled carbon nanotubes (MWCNTs) was investigated. Uniform dispersion of the incorporated MWCNTs in the nanocomposites was achieved using a novel preparation method that involved powder mixing and in situ polymerization. Promoted and retarded results at the percolation threshold were observed, and the trend strongly depended on the surface treatment of the MWCNTs, such as acid, hydrogen peroxide and heat treatments. The electrical percolation behavior of nanocomposites with surface treated MWCNTs has been a controversial topic in the literature. The defect and resistivity of MWCNTs, which were expected to be important physical factors that influence the electrical conductivity of the nanocomposites, were found to have only a minor influence. Different functionalities of the MWCNTs after surface treatments altered the dispersion state of the incorporated MWCNTs in the nanocomposites, and the dispersion state was the dominant physical factor that governed the electrical percolation behavior of the nanocomposites.

Improved tensile strength and thermal stability of thermoplastic carbon fiber fabric composites by heat induced crystallization of in situ polymerizable cyclic butylene terephthalate oligomers

Thermoplastic carbon fiber fabric reinforced composites (CFFRCs) were prepared using a novel fast manufacturing process with a low viscosity polymerizable cyclic butylene terephthalate (CBT) resin. Structure and properties of the composites altered by thermal annealing were investigated to develop appropriate post processing of the CFFRCs for fast production and lowering the processing cost. Annealing at 200°C for 120 min resulted in improved mechanical properties and thermal stability of the polymerized CBT (pCBT) based on differential scanning calorimetry, wide‐angle X‐ray diffraction, and thermo gravimetric analysis. The tensile strength of the CFFRC compression molded at 250°C for 2 min was 440 MPa and that of the CFFRC annealed at 200°C for 120 min after compression molding was 500 MPa, which is an improvement of 550 and 625% relative to the pCBT matrix, respectively. In addition, the thermal stability of the CFFRC annealed at 250°C for 120 min improved by 10°C. Therefore, tensile strength and thermal stability of the manufactured CFFRC can be improved by using the appropriate annealing conditions. POLYM. ENG. SCI., 54:2161–2169, 2014. © 2013 Society of Plastics Engineers

A novel process for cost effective manufacturing of fiber metal laminate with textile reinforced pCBT composites and aluminum alloy

A novel process is proposed for cost effective manufacturing of Fiber Metal Laminate (FML) with textile reinforced pCBT composites and aluminum alloy. To improve the adhesive bonding, prepregs with excellent impregnation quality and highly adhesive resin was introduced as interlayer for a 2/1 preform configuration, which is composed of two layers of dry carbon fabrics and one layer of aluminum alloy in between. The preform is impregnated by cyclic butylene terephthalate (CBT) resin melt in resin infusion process under isothermal molding conditions. After manufacturing, the FML was subjected to mechanical characterizations, including interlaminar shear test and Charpy impact test. The influence of various surface treatment methods on the Interlaminar Shear Strength (ILSS) was investigated for evaluation and enhancement of the novel process. Several comparisons between the novel process and the traditional autoclave process were performed to assess the performance of the novel process. The results indicate that the mechanical performance of the FML manufactured with the novel process could be even better than the one fabricated with traditional autoclave process, when the appropriate surface treatment and molding conditions were applied.

Temperature-dependent decyclopolymerization of cyclic oligomers and the implication on destructuring layered nanosheets for nanocomposite reinforcement

Abstract Taking advantages of low viscosity, self-consistent stoichiometry and explosive decyclopolymerization of cyclic butylene terephthalate oligomers (CBTs), the destruction of multi-layered silicate nanosheets of organically modified montmorillonite (OMMT) has been attempted to explore the reinforcing effect on polymer matrix. Because of the molecular weight and the viscosity imparted by cyclic structure, CBTs were successfully embedded into OMMT galleries, as evidenced by XRD presenting a large down-shift of basal plane peak along with decrease of peak intensity. Subsequent decyclopolymerization of CBTs in-between silicate nanosheets of OMMT has been found governed by polymerization temperature; when a poly(CBT) of high molecular weight is obtainable, efficient dissociation of OMMT to silicate nanosheets and their homogeneous dispersion allowing a notable increase of energy absorption for failure are yielded. A dissociation of OMMT mediated by the temperature-dependent decyclopolymerization presents the usability of cyclic oligomers in the formation of thermoplastic polymer-based nanocomposites exhibiting effective reinforcement which can be hardly accomplished through a conventional process.

Influence of textile preforming binder on the thermal and rheological properties of the catalyzed cyclic butylene terephthalate oligomers

The influence of an epoxy resin textile preforming binder on the thermal and rheological properties of the catalyzed Cyclic Butylene Terephthalate (CBT) oligomers was studied for the manufacturing of textile reinforced pCBT composites with bindered textile preforms. Thermal and rheological investigations were conducted with Differential Scanning Calorimetry (DSC) and plate-plate rheometry, respectively. Significant influences on both non-isothermal und isothermal crystallization of in situ polymerized Cyclic Butylene Terephthalate (pCBT) were observed due to the presence of preforming binder. The crystallization temperature and the crystallinity of pCBT polymer during cooling are both found to decrease with increasing filling fraction of preforming binder. The isothermal polymerization and crystallization process was confirmed to be influenced in the aspect of the starting time of crystallization, the crystallization rate and the crystal structures due to the addition of preforming binder. Furthermore, the processing time was found to be prolonged by adding the preforming binder.

The equilibrium melting temperature and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) and styrene maleimide (c-PBT/SMI) blends

The equilibrium melting point (\( T_{\text{m}}^{0} \)) and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) (c-PBT) and styrene maleimide (SMI) blends prepared by solid dispersion and in situ polymerisation of cyclic butylene terephthalate oligomers (CBT) within SMI were investigated. This c-PBT/SMI blend is a miscible semicrystalline–amorphous blend system. The \( T_{\text{m}}^{0} \) of c-PBT/SMI blends was determined using the Hoffman and Weeks method, while Avrami crystallisation kinetic model have been applied to study their isothermal crystallisation kinetics. It was found that \( T_{\text{m}}^{0} \) decreased with increasing SMI content in the blend compositions. All the crystallisation exotherms were obtained from differential scanning calorimetry under isothermal experimental conditions. The average value of Avrami exponent, n, is in the range of 2.4–2.8 for the primary crystallisation process for c-PBT and its blends, which suggest that heterogeneous nucleation of spherulites occurred and growth of spherulites was between two-dimensional and three-dimensional.

Effect of thermally reduced graphite oxide (TrGO) on the polymerization kinetics of poly(butylene terephthalate) (pCBT)/TrGO nanocomposites prepared by in situ ring-opening polymerization of cyclic butylene terephthalate

Thermally reduced graphite oxide (TrGO) was prepared by thermal exfoliation and reduction of highly oxidized graphite. The pCBT/TrGO nanocomposites were prepared by in situ ring-opening polymerization (ROP) of cyclic butylene terephthalate (CBT). The polymerization kinetics of pCBT/TrGO was monitored by dynamic time sweep in a parallel-plate rheometer. It was found that the increasing TrGO content depressed the rate and degree of CBT polymerization, which is ascribed to the reaction between the growing pCBT chains terminated with carboxyl groups and TrGO surface groups such as hydroxyl and epoxy groups at the initial polymerization stage. The grafted pCBT chains were confirmed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) measurements, and the grafting content was up to 53 wt%. Small amplitude oscillation shear (SAOS) was applied to investigate the rheological properties of pCBT/TrGO and the critical loading to form percolation network was determined as 0.47 vol%, which confirmed the good dispersion of TrGO in matrix. The grafting reaction was also justified from nonlinear rheology and the fractal dimension analysis.

Effects of vacuum infusion processing parameters on the impact behavior of carbon fiber reinforced cyclic butylene terephthalate composites

Carbon fiber reinforced cyclic butylene terephthalate composites have been processed by vacuum infusion under two different non-isothermal processing routes starting from a one-component cyclic butylene terephthalate resin system. One of them was processed under a short cycle with fast cooling, and another one was processed under a long cycle with slow cooling. Both the micro-structure and low-energy impact properties of the composites have been investigated. On one hand, the fast cooling generates randomly dispersed voids and porosities in the resin-rich regions during the crystallization-induced shrinkage. On the other hand, the slow cooling generates a highly crystalline and brittle matrix without porosity. However, many micro-cracks appear in the resin-rich regions due to the combination of the brittleness and longitudinal shrinkage of the matrix. The critical delamination energy of the slow cooled composite is slightly higher than that of the fast cooled one, whereas this latter absorbs over 25% more energy before being penetrated, as well as performing in a less brittle way. The lower interlaminar shear strength of the fast cooled composite is suggested to be the origin of its higher energy absorbing capability and less brittle behavior.

Isocyanate toughened pCBT: Reactive blending and tensile properties

Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymer- ized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear struc- ture for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals.

Living lamellar crystal initiating polymerization and brittleness mechanism investigations based on crystallization during the ring-opening of cyclic butylene terephthalate oligomers

The brittleness of polymerized cyclic butylene terephthalate (pCBT) is generally ascribed to its high crystallization degree and perfect crystal structure. Herein, a simple and effective method for improving the brittleness of pCBT is presented. Unlike other published toughening methods, this method did not decrease or destroy any of the natural advantages of cyclic butylene terephthalate oligomers (CBT) and its ring-opening polymerization (ROP). The melting behaviour and crystallization of CBT demonstrated that some CBT crystals were unable to melt completely during ROP. These un-melted crystals served as self-compatible nucleators and reduced the crystallization induction time of pCBT during ROP, they also plant many stress concentration points which result in the brittleness of pCBT, according to mechanical tests and crystallization kinetics. Finally, the “living lamellar crystal” initiating ROP and new brittleness mechanisms were proposed.

Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites

Graphene-reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry, dynamical mechanical analysis, thermogravimetrical analysis, and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy. It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89 % by incorporating 1- and 5-wt% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behavior, except the ash content, due to the not proper exfoliation except the ash content.

Improved Electrical Conductivity of a Carbon Nanotube Mat Composite Prepared by In-Situ Polymerization and Compression Molding with Compression Pressure

A fabrication method to improve the processability of thermoplastic carbon nanotube (CNT) mat composites was investigated by using in-situ polymerizable and low viscous cyclic butylene terephthalate oligomers. The electrical conductivity of the CNT mat composites strongly depended on the compression pressure, and the trend can be explained in terms of two cases, low and high compression pressure, respectively. High CNT mat content in the CNT mat composites and the surface of the CNT mat composites with fully contacted CNTs was achieved under high compression pressure, and direct contact between four probes and the surface of the CNT mat composites with fully contacted CNTs gave resistance of <TEX>$2.1{\Omega}$</TEX>. In this study the maximum electrical conductivity of the CNT mat composites, obtained under a maximum applied compression pressure of 27 MPa, was 11 904 S <TEX>$m^{-1}$</TEX>, where the weight fraction of the CNT mat was 36.5%.

An investigation into thermoplastic matrix 3D woven carbon fibre composites

Three-dimensional woven textile reinforced composites allow the optimisation and tailoring of specific material properties into the final component. The objective of this work is to investigate the processing characteristics of Cyclic Butylene Terephthalate (supplied by Cyclics Corporation) that polymerises to form a thermoplastic, Polybutylene terephthalate, and to impregnate a multi-layer carbon fibre three-dimensional woven angle interlock fabric to produce a three-dimensional woven thermoplastic composite. Through adjustments in process cycle, the significant processing parameters have been identified, which optimise the production of thermoplastic Polybutylene terephthalate composite parts. Three-dimensional multi-layer reinforcements were manufactured on a modified textile loom to produce fabrics with fibres orientated in the warp, weft and through-the-thickness directions. Thermal and mechanical tests were conducted on the thermoplastic composite and comparisons were made to an epoxy composite with the same weave architecture. It was discovered from thermal analysis and optical microscopy that a highly crystalline matrix was developed as a result of the standard fabrication process with microcracks formed throughout the matrix. Reprocessing and annealing of the 3DCFCBT laminate reduced the crystallinity of the polymer structure.

Polyvinylidene fluoride/poly(ethylene terephthalate) conductive composites for proton exchange membrane fuel cell bipolar plates: Crystallization, structure, and through‐plane electrical resistivity

AbstractPolyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET)‐based composites for proton exchange membrane fuel cell bipolar plates (BPs) were prepared at different crystallization temperatures and characterized by X‐ray diffraction, differential scanning calorimetry, and resistivity setup. Composite conductivity was made possible by using a mixture of carbon black (CB) and graphite (GR). To improve composite processability, its viscosity was reduced by adding a small amount of cyclic butylene terephthalate (c‐BT) oligomer and thermoplastic polyolefin elastomer. In the PVDF/PET‐based composite, it was found that PVDF phase could crystallize easily but PET crystallization was difficult. Because of the CB/GR additives, the formed crystals in PVDF/PET phases had a poor perfection degree and showed a lower melting temperature when compared with pure PVDF and PET. It was observed that PET nucleation was accelerated but not that of PVDF. According to through‐plane resistivity results, composite crystallization temperature range was divided into two parts (below/above 170°C), in which a different variation behavior of through‐plane resistivity was observed. It has been proved that the resistivity was mainly governed by the network of CB/GR developed inside the PET phase, and decreasing the crystallinity of PET led to a decrease of through‐plane resistivity, which is desirable for BPs. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Impact behaviour of carbon fibre reinforced epoxy and non-isothermal cyclic butylene terephthalate composites manufactured by vacuum infusion

Carbon fibre reinforced cyclic butylene terephthalate (CF-pCBT) composites non-isothermally processed by vacuum infusion starting from a one-component system have been successfully manufactured. Both the micro-structure and low-energy impact properties of the CF-pCBT have been investigated and compared with an epoxy system (CF-epoxy). The CF-pCBT composite presents higher solidification shrinkage than the CF-epoxy one, and its void content doubles that of the CF-epoxy. The CF-epoxy composite’s critical delamination threshold energy is slightly higher than that of the CF-pCBT, whereas the CF-pCBT composite absorbs twice as much energy before being penetrated. The lower interlaminar shear strength of the CF-pCBT composite is suggested to be the origin of its higher energy absorbing capability and less brittle behaviour.

Miscibility in cyclic poly(butylene terephthalate) and styrene maleimide blends prepared by solid‐dispersion and in situ polymerization of cyclic butylene terephthalate oligomers within styrene maleimide

AbstractBlends of cyclic butylene terephthalate oligomers (CBT) and styrene maleimide (SMI) were prepared by a solid dispersion technique in various compositions ranging from 90 to 10 wt % of CBT. In situ polymerization of the oligomers in the blend at 190°C produced a blend of cyclic poly(butylene terephthalate) (c‐PBT) and SMI. The blends were characterized by a variety of techniques including differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that the presence of 30 wt % and above of SMI impeded the crystallization of c‐PBT to such an extent that crystallization could not be detected under the conditions of the DSC experiment. The blend system exhibited a single composition‐dependent glass transition temperature (Tg), which indicated the presence of miscibility. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and characterization of poly (butylene terephthalate)/graphene composites by in-situ polymerization of cyclic butylene terephthalate

The ultra-low viscosity of cyclic butylene terephthalate oligomers has been exploited to perform their in-situ ring-opening polymerization in the presence of graphene, to obtain homogeneously dispersed poly(butylene terephthalate)/graphene (PBT/G) composites containing 0.5 to 1.0 %wt of graphene. The results of gel permeation chromatography show that increasing amounts of graphene causes a decrease in the average molecular weight of PBT if the time of polymerization is kept constant, and morphological investigations performed by electron microscopy and x-rays diffraction show that high levels of dispersion of the G sheets are easily obtained by this method of composites processing. Thermal properties of the composites were studied by differential scanning calorimetry and thermogravimetric analysis; results indicate that increasing amounts of G do not strongly influence the degree of crystallinity and the crystallization temperature of PBT, while its thermal stability is significantly increased by the presence of G. All the PBT/G composites demonstrated to be electrically conductive; we found that the electric field assisted thermal annealing of the PBT/G composites induces an increase in conductivity.

Effects of crystalline morphologies on the mechanical properties of carbon fiber reinforcing polymerized cyclic butylene terephthalate composites

Carbon/polymerized cyclic butylene terephthalate (pCBT) composites were prepared through a modified film stacking technique. Three crystalline morphologies of carbon/pCBT composites were obtained at different crystallization temperatures. Tensile, flexural, short beam shear and impact tests were conducted. The low crystallinity carbon/pCBT sam- ples were crystallized at 185°C with spherulitic structure which leads to form the large area spherulite/transcrystalline boundary regions. Consequently, the crack initiated and propagated along with 'weak' spherulite/transcrystalline boundary regions, which were resulted low mechanical properties. Carbon/pCBT sample crystallized at 210°C with high crystallinity and highly disordered spherulitic crystallites without spherulite/transcrystalline boundary lines or boundary crystals exhibits the highest mechanical properties.

Toughening of in situ polymerized cyclic butylene terephthalate by chain extension with a bifunctional epoxy resin

Cyclic butylene terephthalate (CBT) was polymerized in the presence of a low molecular weight bifunctional epoxy resin. The resultant chain extended polymerized CBT (pCBT) showed an increased ductility compared to that of conventionally polymerized pCBT for all analyzed epoxy concentrations (1–4 wt.%). The best results were obtained with 2 wt.% of epoxy resin. Other mechanical properties remained relatively unaffected by the epoxy resin. 1H NMR analysis suggested an esterification reaction of the carboxyl end groups of pCBT and the glycidyl functional groups of the diepoxide. With increasing epoxy content, the chain extended pCBT showed an increasing molecular weight and a decreasing glass transition. Crystallization and melting temperatures as well as crystallinity also decreased with increasing epoxy concentration.