Carboxyl-terminated Polybutadiene Research Articles

Isocyanate-free Carboxyl-terminated Polybutadiene and Epoxidised Hydroxyl-terminated Polybutadiene Cross-linking System as a Binder in Solid Heterogeneous Propellants

Isocyanate-free Carboxyl-terminated Polybutadiene and Epoxidised Hydroxyl-terminated Polybutadiene Cross-linking System as a Binder in Solid Heterogeneous Propellants

A Metal Coordination-Based Supramolecular Elastomer with Shape Memory-Assisted Self-Healing Effect.

Rubber materials are widely used in aerospace, automotive, smart devices and artificial skin. It is significant to address the aging susceptibility of conventional vulcanized rubber and to impart it rapid self-healing performance for destructive crack damage. Herein, a novel supramolecular rubber elastomer is prepared by introducing metal coordination between carboxyl-terminated polybutadiene and polystyrene-vinylpyridine copolymer. Based on the metal coordination interaction, the elastomer exhibits shape memory and self-healing properties. Moreover, a rapid closure-repair process of destructive cracks is achieved by presetting temporary shapes. This shape memory-assisted self-repair model is shown to be an effective means for rapid repair of severe cracks. An approach to enhance the mechanical and self-healing properties of elastomer was demonstrated by adding appropriate amounts of oxidized carbon nano-onions (O-CNO) into the system. The tensile strength of the elastomer with an O-CNOs content of 0.5 wt% was restored to 83 ± 10% of the original sample after being repaired at 85 °C for 6 h. This study confirms that metal coordination interaction is an effective method for designing shape memory self-healing rubber elastomer. The shape memory-assisted self-healing effect provides a reference for the rapid self-repairing of severe cracks.

Evaluation of the structural integrity of solid rocket propellant by means of the viscoelastic fracture mechanics approach at low and medium strain rates

This work analyzes the influence of the displacement rate on the tensile properties and the fracture parameters, determined through a viscoelastic Fracture Mechanics approach, of carboxyl-terminated polybutadiene (CTPB) based solid composite propellants. Low and medium displacement rates attained in an electromechanical testing machine were inspected. From the true stress-true pseudo strain curves, the Young’s modulus was not influenced by the displacement rate with value almost identical to the instantaneous modulus obtained from stress relaxation tests. The same trend was achieved for the Poisson’s ratio, with a behavior close to incompressibility. On the other hand, the yield stress increased with the displacement rate rise. Regarding the fracture behavior, a strong dependency of the resistance curves in terms of both the viscoelasic J-integral and the viscoelastic crack tip opening displacement, CTOD, on the displacement rate was proved, being greater the fracture resistance as the displacement rate increases. Moreover, a linear relationship between the viscoelasic J-integral and the viscoelastic crack tip opening displacement was demonstrated. These results were confirmed by the fracture surfaces analysis. At low displacement rate, the damage nucleation and propagation occurred in the matrix while at high displacement rates, dewetting phenomena gave rise to rougher surfaces with damage initiation and growth mainly through the matrix – particle oxidizer interface.

Fatigue crack propagation behaviour of carboxyl-terminated polybutadiene solid rocket propellants

The fatigue crack growth behavior of composite solid carboxyl-terminated polybutadiene (CTPB) base propellants from a two stage-rocket has been analyzed. Both motors presented similar compositional percentage of the different constituents but while the booster motor presented aluminum as fuel and fine oxidizer particles, the sustainer motor presented nitroguanidine as fuel and coarse rigid inorganic particles. The fracture characterization revealed that the critical energy release rate values obtained from the grains of the booster motor were higher than those computed from the sustainer motor. The fatigue crack growth behavior of the propellant grains under study was comparable to that shown in rubber and the fatigue crack growth curves obtained from the booster motor were below those from the sustainer motor. The micromechanism of failure in both motors was microvoid nucleation and growth till the formation of a macro-crack capable of subcritical advancement. In the grains from the booster motor, the nucleation and progression of damage occurred through the matrix with fracture surfaces plain and with no trace of oxidizer particles. Instead, in the propellant grains from the sustainer motor, the damage was generated in the particle–binder interface and the progression occurred along these interfaces leading to an abrupt fracture surface with discernible oxidizer particles. The mechanism of failure in the booster motor led to a better fatigue crack growth behavior and the irregular crack advancement in the sustainer motor implied a lower exponent of the crack growth rate to the energy release rate power law.

Toughening mechanism of rubber reinforced epoxy composites by thermal and microwave curing

ABSTRACTThe carboxyl terminated polybutadiene (CTBN) is utilized to improve the toughness of diglycidylether of bisphenol A epoxy cured by heat and microwave. The change of viscosity, chemical groups, and the glass transition temperature (Tg) of system are analyzed. The impact performance is characterized to evaluate the fracture toughness, and tensile properties also are investigated. The fracture morphologies are observed by the scanning electron microscopy for exploring toughening mechanism. The viscosity results indicate that viscosity of system increases with increasing of CTBN, demonstrating the formation of precrosslinking and interpenetrating network structure of two phases. The Fourier transform infrared spectrometer results show that effective chemical bonds are formed between CTBN and epoxy resins. The Tg decreases with introducing CTBN, indicating the decline of crosslinking density, which further suggests inherent three‐dimensional structure have been changed. The impact strength and energy increase with increasing of CTBN, and reach a maximum value of 5.92 kJ/m2 and 0.13 kJ at 15% for thermal curing, respectively, increased by 36.8% and 23.1% relative to microwave curing system, while tensile strength and modulus reach the optimum at 5%. Scanning electron microscopy observation finds that “plastic tensile” and “microvoid” deriving from “sea‐island” structure exist, presenting the ductile fracture features. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45767.

Heat conductive h‐BN/CTPB/epoxy with enhanced dielectric properties for potential high‐voltage applications

To enhance the toughness and electrical insulation properties of cured epoxy, carboxyl-terminated polybutadiene (CTPB) liquid rubber was used to modify epoxy in this study, and the thermal conductivity, mechanical and dielectric properties of modified epoxy were investigated. The results indicate that the CTPB-epoxy exhibits higher impact strength and lower dielectric constant and loss compared with pure epoxy. Further, hexagonal boron nitride (hBN) was used to reinforce epoxy modified with 20 phr CTPB. It is found that compared with the hBN/epoxy under the same filler loading, the heat conductive hBN/CTPB/epoxy possesses a lower dielectric permittivity and dissipation factor in all frequency ranging from 10 2 –10 7 Hz, a higher electrical resistivity and dielectric breakdown strength, and improved mechanical toughness. Therefore, the prepared hBN/CTPB/epoxy composites are potentially useful in practical electrical insulation applications.

Carboxyl-Terminated Polybutadiene–Poly(styrene-co-4-vinylpyridine) Supramolecular Thermoplastic Elastomers and Their Shape Memory Behavior

Aiming at an easy-processing metallo-supramolecular polymer which possesses the shape memory property and large deformation ability, we designed a simple metal coordination complex: the blends of zinc-neutralized carboxyl-terminated polybutadiene and poly(styrene-co-4-vinylpyridine) (PSVP). The two polymers are tightly bound due to the metal coordination interactions between Zn2+ ions from carboxyl-terminated polybutadiene and the pyridine group of the PSVP. The elastomer had reasonably good mechanical properties and was thermoplastic. Improvements in mechanical properties of the blends were realized in the rheology analysis compared with a blend without the introduction of the zinc salt. Small-angle X-ray scattering characterization showed that the microstructure of the elastomeric blend consisted of microphase-separated glassy nanodomains of principally PSVP, which served as cross-link junctions that were connected with polybutadiene chains. The elastomer exhibited good shape memory properties for large...

Thermal, mechanical, and dielectric properties of epoxy resin modified using carboxyl-terminated polybutadiene liquid rubber

Epoxy (Ep) resin modified with carboxyl-terminated polybutadiene (CTPB) liquid rubber was investigated in this study. Fourier transform infrared verified the chemical reactions between oxirane ring of Ep and carboxyl groups of CTPB using benzyldimethylamine as a catalyst. The decrease of the thermal stability could be due to the lower thermal stability of CTPB compared with that of pure Ep. The mechanical results showed that CTPB-modified Ep was superior to that of the pure Ep, and the best overall mechanical properties were normally achieved with 20 phr of CTPB content. The impact strength of the system containing 20 phr CTPB increased by 193% due to the two-phase nature of the system. The dielectric constant and dissipation factor of the modified Ep obviously declined with the CTPB content compared with pure Ep, for instance, the dissipation factor remained less than 0.02 in wide frequency range.

A Carboxyl-Terminated Polybutadiene Liquid Rubber Modified Epoxy Resin with Enhanced Toughness and Excellent Electrical Properties

The modification of epoxy (EP) resin with carboxyl-terminated polybutadiene (CTPB) liquid rubber was carried out in this work. The chemical reaction between the oxirane ring of EP and the carboxyl group of CTPB and kinetic parameters were investigated by Fourier transform infrared and differential scanning calorimetry. The resulting pre-polymers were cured with methyl hexahydrophthalic anhydride. Scanning electron microscopic observations indicate that the micro-sized CTPB particles dispersed uniformly in the EP matrix formed a two-phase morphology, mainly contributing to the improved toughness of the modified network. The best overall mechanical performance was achieved with 20 phr CTPB; above it, a fall in the strength and modulus was observed. The storage modulus and loss declined with the CTPB concentration due to its lower modulus and plasticizing effect from dynamic mechanical analysis measurements. Moreover, due to the weak polarity and excellent electrical insulation of CTPB, the CTPB-modified EP presented higher electrical resistivities and breakdown strength, and low dielectric permittivity and loss compared with neat EP.

Critical Effect of Segmental Dynamics in Polybutadiene/Clay Nanocomposites Characterized by Solid State 1H NMR Spectroscopy

The segmental dynamics of rigid, intermediate, and mobile molecular components in carboxyl terminated polybutadiene (CTPB)/organo–clay (C18–clay) systems was characterized by fully refocused 1H NMR FID. In addition, 1H DQ NMR experiments allowed semiquantitative monitoring of changes in segmental dynamics near the interface. Both methods suggest a critical concentration of 60 wt % CTPB, indicating a saturation effect for the surface-adsorbed polymer. While the critical concentration value of a polymer/clay system can be measured in several ways, this is its first direct evidence at the molecular scale. The polymer–clay interaction is found to profoundly change with the removal of the CTPB end group or the organic modifier on the clay surface thus impacting the polymer segmental dynamics near the clay surface. In C18–clay by itself, with increasing temperature, the dynamic behavior of surface modifier changes from homogeneous to heterogeneous, on the basis of which the nonreversible exfoliation process of CTPB/clay nanocomposites could be explained at the molecular level. Based on the 1H NMR results, a tentative model was proposed to illustrate the evolution of the structure and segmental dynamics in CTPB/organo–clay nanocomposites.

Derivatization of carboxyl-terminated polybutadiene for determining relative functionality distribution

A new and highly efficient method for determining relative carboxyl group distribution in carboxyl-terminated polybutadiene has been developed using practical synthetic and analytical techniques. Using oxalyl chloride, samples of carboxyl-terminated polybutadiene were rapidly transformed to acid chlorides that were then chemically derivatized with benzyl alcohol, 4-nitrobenzyl alcohol, and 3,5-dinitrobenzyl alcohol. This provided quick and quantitative conversion to the corresponding benzyl ester derivatives. Each new derivative was fully characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. The benzyl ester modified polymers were investigated in detail to determine their relative carboxyl group concentrations. To do this, gel permeation chromatography combined with ultra violet/refractive index dual detection was employed. The 4-nitrobenzyl ester, having the highest extinction factor at 270 nm provided the best UV data for analysis. The ultra violet/refractive index data of four separate polymer samples were plotted as a function of molecular weight. The data were compared with a theoretical plot (carboxyl group = two for all molecular weights) to illustrate the relative carboxyl concentration over the entire molecular weight range. Supplemental characterization of the 4-nitrobenzyl modified polymer was carried out using matrix-assisted laser desorption ionization coupled with time of flight mass spectrometry. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

EFFECT OF ORGANOCLAY ON THE RHEOLOGICAL BEHAVIOR OF CARBOXYL-TERMINATED POLYBUTADIENE GELS

The unique rheological behavior of carboxyl-terminated polybutadiene(CTPB)/organoclay nanocomposite gels was studied under steady shear on a HAAKE RheoStress 600 instrument.The microstructure of nanocomposite gels was characterized by X-ray diffraction(XRD) and transmission electron microscopy(TEM).The experimental results show that both irreversible and reversible viscosity transitions were observed in the temperature range from 26℃ to 116℃ in steady shear experiments on as-prepared samples.The irreversible viscosity transition is attributed to the exfoliation of the clay sheets,and the reversible viscosity transition can be understood as a shear-induced orientation-disorientation transition of the clay sheets.Moreover,the in-situ dispersion process of organoclay in CTPB matrix was observed by rheological experiments,and three important factors that significantly affected the rheological behavior of CTPB/organoclay nanocomposite gels in the steady shear measurement were studied:the temperature effect,the shear-induced orientation effect and temperature-sensitive polymer-clay interaction.Finally,a possible mechanism was suggested on the basis of the clay exfoliation and orientation-disorientation transition,and the mechanism was used to explain the effect of organoclay on the rheological behavior of CTPB gels and the relationship between the observed unique rheological behavior and the microstructure of nanocomposite gels.

Improvement in gas permeability of biaxially stretched PET films blended with high barrier polymers: The role of chemistry and processing conditions

Improvement in oxygen gas barrier properties of polyester/polyamide blends used in packaging industry is the main objective of the present study. For this purpose poly(ethylene terephthalate) (PET)/poly(m-xylene adipamide) (nylon-MXD6) (95/5 w/w) and poly(ethylene terephthalate-co-isophthalate) copolymer (PETI)/MXD6 (95/5 w/w) blends have been prepared with a PET copolymer which consists of 5 wt.% sodium sulfonated isophthalate (PET-co-5SIPA) as compatibilizer and a carboxyl-terminated polybutadiene (CTPB) as filler by using a co-rotating intermeshing twin screw extruder. The effects of chemical architecture and morphology on oxygen gas permeability and processability were analyzed by using a range of characterization techniques including differential scanning calorimetry (DSC), scanning electron microscopy (SEM), oxygen gas permeability analyzer, and a special computer controlled uniaxial stretching system that provides real-time measurement of true stress, true strain and birefringence. The morphological analysis revealed that PET-co-5SIPA was an effective compatibilizer for both PET/MXD6 and PETI/MXD6 blends. DSC analysis and spectral-birefringence technique were used to understand the thermal and stress-induced crystallization behavior of the blends. Morphological analysis of the films after biaxial stretching indicated that the spherical nylon phase was converted to 75 nm thick disks during stretching (aspect ratio L/W = 6) that creates a tortuous pathway for oxygen ingress. Stretching enhanced the barrier properties of PET/MXD6 and PETI/MXD6 blends.

Synthesis, Characterization and Application of Coatings Based on Epoxy Novolac and Liquid Rubber Blend

Phenol‐based novolac resins were synthesized with different mole ratios of phenol‐to‐formaldehyde. These novolac resins were epoxidized with molar excess of epichlorohydrin at 120 °C in basic medium. Novolac and epoxy novolac resin were characterized by FTIR, NMR and GPC analysis. Molecular weight was found to be 838. The epoxidized novolac resins were separately blended with different weight ratios of carboxyl‐terminated polybutadiene liquid rubber ranging between 0‐25 wt % with an interval of 5 wt %. All the blends were cured at 150 °C with 40 wt % polyamide. The cured films of blend samples were checked for use them in coating applications.

Room temperature spontaneous exfoliation of organo-clay in liquid polybutadiene: Effect of polymer end-groups and the alkyl tail number of organic modifier

Disorderly exfoliated telechelic liquid polybutadiene/organo-clay nanocomposite gel was, for the first time, successfully prepared at room temperature of 26°C by simply compounding of carboxyl-terminated polybutadiene (CTPB) with organo-clay containing surfactant modifier with two alkyl tails. The dispersion behavior of organo-clay in liquid polybutadiene/organo-clay nanocomposite gels were systematically investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), rheology and compatibility experiments, focusing on the influence of the functional end-groups of the liquid rubber and the alkyl tails number of the organic modifier on the clay exfoliation. A unique liquid-like reversible rheological behavior was observed for CTPB/exfoliated clay nanocomposite gels with organic modifier having two alkyl tails, which is totally different with that of other samples (HTPB/C18-clay, HTPB/D18-clay and CTPB/C18-clay). And it is noteworthy that CTPB exhibits a higher level of dispersion with an organo-clay with two alkyl tailed surfactant than that with one alkyl tail.

Studies on the blends of cardanol-based epoxidized novolac resin and CTPB

Cardanol-based novolac-type phenolic resins were synthesized with different mole ratios of cardanol-to-formaldehyde, viz., 1:0.6, 1:0.7, and 1:0.8. These novolac resins were epoxidized with molar excess of epichlorohydrin at 120 °C in basic medium. The epoxidized novolac resins were, separately, blended with different weight ratios of carboxyl-terminated polybutadiene liquid rubber ranging between 0–25 wt% with an interval of 5 wt%. All the blends were cured at 150 °C with 40 wt% polyamide. The formation of various products during the curing of blend samples has been studied by Fourier-transform infra-red spectroscopic analysis. The tensile strength and elongation-at-break of the cured samples increased up to 15 wt% in the blend and decreased thereafter. This blend sample was also found to be most thermally stable system. The blend morphology, studied by scanning electron microscopy analysis, was finally correlated with the structural and property changes in the blends.

Studies on the blends of modified epoxy resin and carboxyl-terminated polybutadiene (CTPB)—II: thermal and mechanical characteristics

Blend samples were prepared by physical mixing of resole–epoxy blend with carboxyl-terminated polybutadiene (CTPB) liquid rubber ranging between 0 and 25 wt% in the interval of 5 wt%. Resoles were synthesized with phenol and various alkyl phenols. The blends were cured with 40 wt% polyamide. The structural changes during the curing were investigated by infra-red spectroscopic analysis. The presence of CTPB in resole-epoxy blends did not affected the values of cure times and ΔH whereas the gel time decreased up to 15 wt% addition of CTPB in the blends. The blend systems containing p-cresolic resole, epoxy and CTPB showed minimum gel time amongst all other blend samples. A clear-cut two-step mass loss in thermogravimetric (TG) trace of unmodified and CTPB-modified systems was observed. The mechanical properties of the blend samples were found to be affected by the CTPB addition. The plane strain fracture toughness (KIC) values of CTPB-modified matrix resins were greater that that for the unmodified resole/epoxy blends. This was further verified by scanning electron microscopic (SEM) analysis.

Studies on the blends of cardanol-based epoxidized novolac type phenolic resin and carboxyl-terminated polybutadiene (CTPB), I

Six blend samples were prepared by physical mixing of epoxidized cardanol-based novolac type phenolic resin with different weight ratios of carboxyl-terminated polybutadiene (CTPB) liquid rubber ranging between 0 and 25 wt% with an interval of 5 wt%. Blend sample containing 15 wt% CTPB showed least cure time at 150 °C amongst all other blend samples. The formation of various products during the curing of blend samples has been studied by Fourier-transform infra-red (FTIR) spectroscopic analysis. The tensile strength and elongation-at-break of the cured samples increased up to 15 wt% in the blend and decreased thereafter. This blend sample was also found to be the most thermally stable system. The blend morphology, studied by scanning electron microscopy (SEM) analysis, was finally correlated with the structural and property changes in the blends.

Composite materials based on modified epoxy resin and carbon fiber

Epoxy resin networks have been modified with block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)-based on epoxy resin. The epoxy resin modified with carboxyl-terminated polybutadiene presented improved impact resistance and outstanding mechanical performance in terms of flexural and tensile properties because of the presence of rubber particles homogeneously dispersed inside the epoxy matrix. This modified system also resulted in an improvement of mechanical properties of the corresponding carbon fiber based composites. The outstanding properties were attributed to a better interaction fiber-matrix, as indicated by SEM micrographs.

Compatibility study of 1,3,3-trinitroazetidinewith some energetic components and inert materials

Abstract The compatibility of 1,3,3-trinitroazetidine (TNAZ) with some energetic components and inert materials of solid propellants was studied by using the pressure DSC method. Where, cyclotetramethylenetetranitroamine (HMX), cyclotrimethylenetrinitramine (RDX), nitrocellulose (NC), nitroglycerine (NG), 1.25/1-NC/NG mixture, lead 3-nitro-1,2,4-triazol-5-onate (NTO-Pb), aluminum powder (Al powder) and N-nitrodihydroxyethylaminedinitrate (DINA) were used as energetic components and hydroxyl terminated polybutadiene (HTPB), carboxyl terminated polybutadiene (CTPB), polyethylene glycol (PEG), polyoxytetramethylene- co-oxyethylene (PET), addition product of hexamethylene diisocyanate and water (N-100), 2-nitrodianiline (2-NDPA), 1,3-dimethyl-1,3-diphenyl urea (C2), carbon black (C.B.), aluminum oxide (Al2O3), cupric 2,4-dihydroxybenzoate (β-Cu), cupric adipate (AD-Cu) and lead phthalate (ϕ-Pb) were used as inert materials. The results showed that the binary systems of TNAZ with HMX, NC, NG, NC+NG and DINA a...