Polymerized Cyclic Butylene Terephthalate Research Articles

A General and Efficient Approach for the Dual-Scale Infiltration Flow Balancing in In Situ Injection Molding of Continuous Fiber Reinforced Thermoplastic Composites.

In situ injection molding of continuous fiber reinforced thermoplastic composites is challenged by unbalanced dual-scale infiltration flow due to the pronounced capillary effect. In this paper, a general and efficient approach was proposed for dual-scale infiltration flow balancing based on numerical simulation. Specifically, Stokes and Brinkman equations were used to describe the infiltration flow in inter- and intra-fiber bundles. In particular, capillary pressure drop was integrated in the Brinkmann equation to consider the capillary effect. The infiltration flow front is tracked by the level set method. Numerical simulation and experimental results indicate that the numerical model can accurately demonstrate the unbalanced infiltration flow in inter- and intra-fiber bundles caused by the changes of the injection rate, the resin viscosity, the injection rate, the fiber volume fraction and the capillary number. In addition, the infiltration flow velocity in inter- and intra-fiber bundles can be efficiently tuned by the capillary number, which is mainly determined by the injection rate for a specified resin system. The optimal capillary numbers obtained by simulation and experiment are 0.022 and 0.026, which are very close to each other. Finally, one-dimensional in situ injection molding experiments with constant injection pressure were conducted to prepare fiber reinforced polymerized cyclic butylene terephthalate composite laminate with various flow rates along the infiltration direction. The experimental results confirmed that the lowest porosity and the highest interlaminar shear strength of the composite can only be obtained with the optimized capillary number, which is basically consistent with the simulation results.

Swarm intelligence integrated micromechanical model to investigate thermal conductivity of multi-walled carbon nanotube-embedded cyclic butylene terephthalate thermoplastic nanocomposites

With the recent demand for miniaturization and integration of electronic devices, there has been a growing interest in device malfunction due to high temperature. In this study, a experimental and theoretical study on the composites with improved thermal conductivity by dispersing multi-walled carbon nanotubes (MWCNTs) in the thermoplastic resin was carried out. A micromechanical model was derived based on the ensemble volume-averaging method and the modified Eshelby’s tensor reflecting the interface properties. The effects of the waviness, interface, and orientation of fillers on the thermal conductivity of composites were numerically analyzed. A computational intelligence-based particle swarm optimization (PSO) algorithm was adopted to the proposed model for optimizing the model constants. The thermal conductivity of the polymerized cyclic butylene terephthalate (pCBT)/MWCNT composites was experimentally measured according to the content of MWCNT. Finally, the experimentally measured data were utilized in the PSO to improve the predictive capability of the proposed model.

Properties of polymerized cyclic butylene terephthalate and its composites via ring-opening polymerization

Continuous glass fiber (GF)-reinforced polymerized cyclic butylene terephthalate (pCBT) composites were prepared via vacuum-assisted resin transfer molding using butyltin tris(2-ethylhexanoate) as the catalyst. The relationship between melt viscosity and polymerization time was examined in the ring-opening polymerization of CBT resin. The effects of polymerization conditions such as catalyst content and polymerization temperature on viscosity average molar mass ( Mv), crystallization, mechanical properties, and microstructure of GF/pCBT composites were also investigated in detail. It is found that both high molecular weight and high degree of crystallinity of resin matrix can lead to high mechanical properties of composites. The composites prepared with 0.5% catalyst at 190°C show the best mechanical properties with tensile strength of 549 MPa, flexural strength of 585.2 MPa, and interlaminar shear strength of 47.1 MPa. The scanning electron microscopy analysis also demonstrates that good interfacial adhesion exists between fiber and resin, which agrees very well with experimental results.

Preparation and Characterization of Multiwalled Carbon Nanotubes-Reinforced pCBT by Ring-Opening Polymerization of Cyclic Butylene Terephthalate

Multiwalled carbon nanotubes (MWCNT)-reinforced polymerized cyclic butylene terephthalate (pCBT) nanocomposites were prepared by in situ ring opening polymerization of cyclic butylene terephthalate oligomers (CBT). The results of differential scanning calorimetry (DSC) indicated that the melting peak located at the low temperature (Tm1) increased and that at higher temperature (Tm2) decreased with the increasing of content of the MWCNT. During the cooling the MWCNT served as nucleation points from where crystallization can start. The more the MWCNT in the system the earlier the crystallization starts. The Morphological investigations performed by scanning electron microscopy (SEM) shown that the MWCNT were embedded in the matrix and held tightly by the matrix. The modulus and strength increased with MWCNT concentration in the nanocomposites, however, the elongation at break, absorbed energy at break and impact strength were decreased with the increasing of MWCNT content.

Effect of hard segment length on the properties of poly(ether ester) elastomer prepared by one pot copolymerization of poly(ethylene glycol) and cyclic butylene terephthalate

A series of poly(ether ester) thermoplastic elastomer were synthesized by a novel single step of cyclic butylene terephthalate (CBT) and poly(ethylene glycol) (PEG) in the presence of stannoxane catalyst at an elevated temperature. The resultant copolymers (pCBT–PEG) based on polymerized cyclic butylene terephthalate (pCBT) as the hard segment and PEG as the soft segment were characterized by means of fourier transform infrared spectrometer (FI-IR), proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) testing. The influence of hard segment length on the properties of the copolymer was investigated in the case of the soft segment length remaining constant. It is found that the pCBT segment length calculated from 1H NMR spectra was decreased with the increase of PEG content. The glass transition, melting and crystallization temperatures and the degree of crystallinity of hard segments were increased with the increase of the pCBT segment length. Thermogravimetry (TG) and derivative TG (DTG) results revealed that the thermal degradation of copolymers was slower than that of the pCBT homopolymer. Mechanical properties of polymers were also reported and the stiffness of the copolymer was improved with the increase of hard segment length.

Effect of fiber surface modification on the lifetime of glass fiber reinforced polymerized cyclic butylene terephthalate composites in hygrothermal conditions

Abstract Mechanical performances of polymerized cyclic butylene terephthalate (pCBT) matrix, glass fiber reinforced pCBT (GF/pCBT), and nano-silica modified glass fiber/pCBT composites (nano-GF/pCBT) in hygrothermal condition were investigated. All the materials were aged in hygrothermal environments for up to three months, and then their mechanical strength degeneration ratio (SDR) was calculated. To study the aging effect of temperature, specimens with and without nano-silica modification were tested in temperatures ranging from 298 to 500 K. Differential scanning calorimeter (DSC) test, dynamic mechanical analysis (DMA), and fiber pull-out test were adopted to complement the experimental results. It is found that all the SDR-time curves follow the linear relationship in hygrothermal environment, while SDR-temperature curves follow a bilinear relationship due to the effect of glass transition temperature (Tg) of the matrix. Fibers modified by coating nano-silica on the surface could decrease SDR of the composites. This is due to the fact that the fillers on the fiber surface could resist the movement of pCBT molecular chain and diffusion of water molecules in aging conditions. The fiber pull-out test verifies that the interface strength between fiber and matrix is enhanced by the modification.

Correlation between polymerization of cyclic butylene terephthalate (CBT) and crystallization of polymerized CBT

The correlation between ring-opening polymerization (ROP) of cyclic butylene terephthalate (CBT) and crystallization of polymerized CBT (pCBT) strongly affected the final properties of pCBT and its composites. The major objective of this contribution is to pinpoint the threshold temperature between them and the interrelation is successfully disclosed. That is, crystallization during polymerization occurs below 204 °C and the crystallization properties of pCBT are determined by this isothermal ROP stage; polymerization and crystallization are gradually separated with the increase of temperature of ROP (T P) from 204 °C, and the crystallization properties of pCBT are dominated by cooling stage; only polymerization is performed above 212 °C. Moreover, quantitative analysis suggests that uniform crystal size distributions and thicker lamellar crystals derive from the stage of crystallization during polymerization. On the contrary, the crystal size distributions become wider above 204 °C of T P and lead to obvious double melting peaks during heating scan. These efforts provide a very useful guide for the related investigation and application of CBT.

Electrical and Mechanical Properties of Short-Carbon-Fiber Reinforced Polymerized Cyclic Butylene Terephthalate Composites

Polymerized cyclic butylene terephthalate (pCBT) resin casts filled with short carbon fibers were prepared by the melt-mixing approach. The electrical conductivity of short-carbon-fiber (SCF) reinforced thermoplastic pCBT resin casts were investigated with a special attention paid to the properties in the percolation threshold region and the mechanical properties of the composites were also studied. The percolation threshold value of the novel material system was determined which was also verified by SEM images and the thermoelectric behavior of the specimens. Even though the electrical properties of SCF/pCBT composites enhanced significantly, the material becomes more brittle than neat pCBT and all the specimens appear brittle fracture during the mechanical test. Moreover, fiber pull-out is the main damage form in three-point-bending test.

Preparation, Mechanical and Thermal Properties of Poly(Butylene Terephthalate) and Its Nanocomposites Prepared from Cyclic Butylene Terephthalate

Polymerized cyclic butylene terephthalate (pCBT) casts and pCBT/nano-silica composites generated from cyclic butylene terephthalate (CBT) were manufactured. The mechanical properties of pCBT casts with various ratio of catalyst were investigated through three-point bending test, and the thermal properties of the samples were tested by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). Moreover, the fracture morphologies of pCBT as well as its nano-silica composites were observed by SEM. From the study, suitable catalyst content for CBT resin was determined and pCBT/nano-silica composites were found to have better thermal performances compared with neat pCBT.

Effect of Nano-fillers on the Thermal Performance of pCBT Resin

In this paper, the influence of nano-graphite and nano-TiO2 with the content of 0.5wt.% to 2wt.% on the thermal properties of polymerized cyclic butylene terephthalate (pCBT) resin was investigated by Differential scanning calorimetry (DSC) and Thermo gravimetric analysis (TGA), respectively. The experiment results show that the degree of crystallinity of the material decreases with the increasing of nano-particles content. Furthermore, it is found that two melting peaks appearing during the second heating in DSC curves. Meanwhile, with the increasing of nano-TiO2 content, the decomposition rate of the resin decreases slightly in TGA curves.

Toughened carbon fiber fabric‐reinforced pCBT composites

Toughened carbon fiber‐fabric reinforced polymerized cyclic butylene terephthalate (pCBT) composites were obtained by chemical modification of cyclic butylene terephthalate (CBT) with small amounts of epoxy resin and isocyanates as chain extenders. Homogeneous CBT/epoxy and CBT/isocyanate blends were prepared by melt blending the components in a lab‐scale batch mixer at low temperatures and high shear rate. Melt blending was stopped before the ring‐opening polymerization of CBT could start. The modified CBT was the starting material for carbon fiber fabric‐reinforced pCBT composites (fiber content at about 65 wt%) which were prepared by ring‐opening polymerization during compression molding using a simple powder prepreg method. Interlaminar shear strength, flexural strength, and failure strain of the chemically modified composites increased up to 60% with respect to unmodified pCBT composites. Nevertheless, the flexural moduli slightly decreased due to the toughening effect of the chain extender on the pCBT matrix. Drop weight impact tests revealed that the energy absorption of the modified composites was relatively higher as compared to unmodified pCBT composites. POLYM. COMPOS., 37:1453–1460, 2016. © 2014 Society of Plastics Engineers

Prediction and experimental validation of electrical percolation by applying a modified micromechanics model considering multiple heterogeneous inclusions

Classical micromechanics modeling cannot capture the effect of percolation threshold at a low volume fraction of conductive fillers, even though multiple heterogeneities are considered in the modeling to investigate the effect of reinforcement dispersion, electrical tunneling behavior, and conductive networks. In this study, an analytical homogenization approach for composites containing multiple heterogeneities with conductive coated layers was developed in order to predict the percolation threshold effect, the tunneling effect using hard/soft core concept, and the effective electrical conductivity of polymer matrix composites (PMCs) containing randomly oriented ellipsoidal inclusions coated by conductive layers. The electrical conductivities of polymerized cyclic butylene terephthalate (pCBT)-based composites containing nanofillers such as carbon blacks (CBs), graphene nanoplatelets (GNPs), and carbon nanotubes (CNTs) were prepared by the recently developed composite manufacturing processing using solvent-free powder mixing and in-situ polymerization for inducing uniform dispersion of nanofillers of various shapes and dimensions within a polymer matrix. When comparing the experimentally measured electrical conductivities of those composites with the predicted values obtained from the developed micromechanics models, it is confirmed that the developed approach successfully captures the percolation threshold and the tunneling effect of reinforcements on the effective electrical conductivities of composites containing various shapes of reinforcements.

Design of microwave plasma and enhanced mechanical properties of thermoplastic composites reinforced with microwave plasma-treated carbon fiber fabric

Microwave plasma equipment was designed and manufactured to improve the interfacial bonding and mechanical interlocking between carbon fiber fabric (CFF) and the polymer matrix. Tensile specimens for the composites reinforced with the as-received and microwave plasma-treated CFFs were prepared using high-speed fabrication with a polymerizable and low-viscosity cyclic butylene terephthalate (CBT) oligomer matrix. Compared with the polymerized CBT (pCBT) matrix, the tensile strengths of the as-received and plasma-treated CFF reinforced composites (CFFRCs) were enhanced by approximately 362.5% and 436.3%, respectively. A high carbon fiber content of 70vol.% was achieved without introducing pores and/or defects into the CFFRC due to the low viscosity and high impregnation characteristics of the CBT resin. It was confirmed that the microwave plasma can increase the surface roughness of the tested CFF without varying the chemical composition and defect level of the CFF. In addition, the interfacial bonding and mechanical interlocking between the CFF and polymer matrix were improved.

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

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.

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.

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.

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