High performance toughened cyanate ester resin with low injection temperature for RTM process

A high‐performance modified cyanate resin system with low injection temperature for fabricating advanced composites via resin transfer molding (RTM) was developed, which was made of bisphenol A dicyanate ester (BADCy) and diallyl phthalate (DAP). The processing characteristics, mechanical, and thermal properties of the resin were studied, and the effect of the content of DAP on the processing and performance parameters was discussed. The results show that the processing properties of the modified cyanate system are dependent on the content of DAP. All the formulations studied in this paper have good processing characteristics; their injection temperatures are between 30 and 40°C and the pot life is about 20 hr at 50°C. The cured resins exhibited good thermal stability, excellent toughness, and good hot–wet resistance, suggesting that the toughened cyanate resin is a potential high‐performance RTM matrix for advanced composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on curing of novolac epoxy resin

The optimization of proportions of novolac epoxy resin, Dobeckot E4 and polyamide hardener, EH411 has been established by DSC and the data indicates that resin-polyamide, 100∶40 and 100∶50, appear to be optimum where ‘extent of cure’ is maximum. The kinetic parameters for these formulations have been evaluated using isothermal and dynamic modes by employing DSC. The rate constants have been evaluated for curing process of these formulations using isothermal DSC mode in the temperature range of 70°–90°C. These have also been predicted at 20°±1°C (room temperature) by extrapolating the data obtained at elevated temperatures. A comparison of the predicted values with the experimental values shows that there is a good agreement between them.     

Rheological Study on Polypropylene/Cycloolefin Copolymer Blends

Summary: Polypropylene, cycloolefin copolymer and their blends were characterized by means of melt flow analysis and capillary rheometry at temperatures between 190 and 230 °C in order to shed more light on COC fiber formation obtained in injection molding process. Melt viscosity and its activation energy as functions of blend composition show negative deviation from the expected additivity (Negative Deviating Blends). The COC/PP viscosity ratio increases with shear rate, but decreases with temperature. High temperature, low viscosity ratio and high shear rate seem to be favorable for fiber formation. Glass transition (from the reversible heat flow curve of modulated DSC) of dumbbell specimens produced by injection molding at 230 °C with COC minor component was 2–4 °C higher than that of grinded pellets obtained from mixing at 190 °C.     

Ternary upper-critical-solution-temperature behavior in a blend system comprising poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene

 Upper-critical-solution-temperature (UCST) behavior in a ternary blend of poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene is reported. The as-cast ternary blend is immiscible at ambient conditions and comprises two different phases, and, however, turns into a miscible system above the “clarity point” ranging from 160 to 300 °C for different ternary compositions. The maximum clarity point is labeled as the UCST for the ternary system, which is about 295 °C. Above the clarity point, the originally immiscible ternary blend turned into one miscible phase. Owing to the thermodynamic UCST behavior and kinetic hindrance, the immiscible ternary polymer blend can be locked into a pseudo-miscible state if it is heated to a temperature above the clarity point followed by a rapid-cooling processing scheme. The quenched ternary blend can remain in a pseudo-miscible state as long as the service temperature does not exceed the glass-transition temperature of the blend. Received: 17 July 2001 Accepted: 3 October 2001     

The synergetic effect of phenylphosphonic acid zinc and microfibrillated cellulose on the injection molding cycle time of PLA composites

This study evaluates the effects of nucleants phenylphosphonic acid zinc (PPA-Zn) and talc, mold temperature, and microfibrillated cellulose (MFC) reinforcement in the acceleration of injection molding cycle of polylactic acid (PLA). PLA was dissolved in an organic solvent, mixed with nucleant and MFC, and dried compounds were injection molded into molds at temperatures ranging from 40 °C to 95 °C and holding times from 10 s to 120 s. Our results showed that PPA-Zn is more effective nucleating agent compared to talc. The addition of 1 wt% PPA-Zn and the mold temperature of 95 °C exhibited the fastest crystallization rates for the molded PLA, however, at this temperature the parts could not be quickly ejected without distortion. Addition of 10 wt% MFC increased the stiffness of PLA at high temperatures and allowed ejection of parts without distortion at a holding time of just 10 s. At this holding time, the crystallinity of the PLA composite was 15.3% but the storage modulus above T _g was superior to that of fully crystallized neat PLA due to MFC reinforcement, retaining the shape of the molded part during demolding. The mechanical properties of the composite at room temperature were also higher than those of fully crystallized neat PLA.     

Thermal properties of pure and doped (polyvinyl-alcohol) PVA

Films ≈350 μm of poly(vinyl-alcohol) composites, containing copper (Cu), aluminium (Al) and iron (Fe), metallic powder very fine, were prepared by a casting method. Thermal conductivity, phonon velocity, mean free path and specific heat were studied. The pure sample of PVA has a lower values of thermal conductivity than that which are doped with metals. For all samples the thermal conductivityK increases up to a certain temperatureT _gg (120–160°C) and then decreases with temperature. The specific heat increase with temperature up to ≈120°C and above 120°C is nearly independent on temperature. The pure sample of PVA has small values of mean free path (L)≈0.2 Å at room temperature, but for PVA⁺ metalsL≈2.0 Å. The phonon velocity of pure PVA is larger than that of PVA containing metals.     

Dynamic mechanical properties of two copolymers of styrene and n-hexyl methacrylate

The storage (J′) and loss (J″) shear compliances have been measured for two random copolymers of styrene and n-hexyl methacrylate with styrene contents of 18% and 30% (by weight) in the frequency range 45–4400 Hz and the temperature range 31–107°C. The data at different temperatures were combined by the method of reduced variables, and the WLF coefficients were calculated from the temperature shift factors by the method of Pierson and Kovacs. The data were compared with earlier data for the two homopolymers. The thermal expansion coefficient of the fractional free volume, and the free volume at the glass transition temperature, varied monotonically with composition, but the fractional free volume at a reference temperature of 100°C appeared to pass through a maximum as a function of concentration. Comparison of isothermal plots of J′ at 100°C, plots of the relaxation spectrum at 100°C, the monomer friction coefficient and its temperature dependence, and isochronal plots of the storage shear moduls at 100 radians/see all show that the properties of poly(n-hexyl methacrylate) are very slightly affected by incorporation of 18% styrene and only moderately affected by 30% styrene. By contrast, comparison of styrene–butadiene rubber with 1,4-polybutadiene shows a very large effect of incorporation of 23.5% styrene. These differences may be associated with local packing relations of the comonomer residues and suggest that copolymer properties cannot be readily predicted from those of the component homopolymers.     

An investigation of the effect of sample preparation on the thermal behavior and the small-angle x-ray scattering of a polyurethane block copolymer

The effect of varying sample preparation parameters on the thermal behavior and on the small-angle x-ray scattering (SAXS) properties of a polyether polyurethane were investigated. The polyurethane studied was a methylene bis(p-phenyl isocyanate) (MDI)/butanediol/poly(tetramethylene oxide) (PTMO) system synthesized in a 6/5/1 mole ratio by a two-step solution polymerization. The PTMO had a nominal molecular weight of 2000. The samples were compression molded under different conditions for the SAXS experiments. The preparation parameters studied included molding time and temperature, sample thickness, and quenching rate from the molding temperature. The molding temperature has the greatest effect on the SAXS data. In this case the domain size was observed to increase as the molding temperature increased from 130 to 200°C. The thermal properties were also found to be strongly dependent on the molding temperature, as measured by differential scanning calorimetry (DSC). An endotherm related to the annealing that occurs during the molding process appears in each sample near the molding temperature. The other preparation parameters have little or no effect on the SAXS and thermal properties of this sample.     

Structure of Liquids. VIII. An X-Ray Diffraction Study of Liquid Mercury-Gallium Systems

Abstract

X-ray diffraction measurements were made at 0°, 30°, and 50°C on pure mercury and on two mercury-gallium systems of composition 0.9658 and 0.0197 mole fraction of mercury. Peak positions of the radial distribution functions for all samples show no significant change with temperature; the average position of the first and second peaks of the mercury curves are 3.01 Å and 5.80 Å, respectively. Coordination numbers for mercury as determined by the symmetrical curve method are 7.5, 7.3, and 7.0 atoms for 0°, 30°, and 50°C. The scattering function and the features of the structure obtained for the Ga-in-Hg solution are not significantly different from those of pure mercury; for the Hg-in-Ga solution, however, the coordination numbers are smaller than those for pure gallium, and the scattering functions are significantly different.     

Polyimide incorporated cyanate ester/epoxy copolymers for high-temperature molding compounds

The rapid development of high-power devices has driven the requirement for high-temperature stable epoxy molding compounds. In this work, a designed polymer blend system consisting of cyanate ester/epoxy copolymers modified by polyimide (CE/EP-PI) has been studied. Polyimide used in this study has shown excellent dispersity in the cyanate ester and epoxy copolymer network (CE/EP), exhibiting homogeneous phase with a denser polymer network structure. With this polymer blend structure, CE/EP-PI system was proved to have a glass transition temperature as high as ~270 °C, increased modulus, and largely enhanced fracture toughness up to 2.06 MPa m^1/2. CE/EP-PI resins showed outstanding long-term stability at high temperature with low mass loss and increased fracture toughness after aging at 200 °C. This work provides a novel insight into the development of molding compounds based on polymer blends system with excellent high-temperature properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2412–2421     

Novel high performance RTM bismaleimide resin with low cure temperature for advanced composites

A novel performance matrix, coded as LCRTM, with low cure and post‐cure temperature (≤ 200°C) for fabricating advanced polymer composites via resin transfer molding (RTM), was successfully developed, made up of 4,4′‐bismaleimidodiphenylmethane (BDM) and N‐allyl diaminodiphenylether (ADDE). Investigations show that the stoichiometry of BDM and ADDE has great effect on the processing and performance parameters of the resultant resins. In the case of the optimum formulation (the mole ratio of BDM and ADDE is 1:0.55), the injection temperature range is between 70–82°C, and the pot life at 80°C is 300 min, moreover, the cured resin has desirable thermal and mechanical properties after being cured at 200°C for 6 hr, reflecting a great potential as high performance matrices for fabricating advanced composites via the RTM technique. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation and characterization of chemically bonded aramid-titania hybrids using isocyanatopropyltrimethoxysilane

Transparent aramid based titania hybrid films have been prepared by the sol–gel process. A mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride forming aromatic polyamide chains in dimethylacetamide solvent. The titania network was generated insitu in this matrix by the hydrolysis and condensation of the various amounts of tetraethylorthotitanate. Hybrid films with concentrations of titania varying from 2.5 to 12.5 wt% were prepared; the higher percentages of titania in the organic matrix showed a tendency towards phase separation. These films were tested for their thermo-mechanical properties. To achieve a further improvement in properties of the matrix, the aramid chain was functionalized and the inorganic network was chemically bonded using isocyanatopropyltrimethoxysilane. The bonded hybrids showed a narrower distribution of titania particles and these were distributed as a co-continuous phase. The glass transition temperature (Tg) of the hybrid films measured through dynamic mechanical analysis showed a relatively higher increase with inclusion of titania in the covalently bonded hybrids. The maximum value of Tg noted in the chemically bonded composites with 12.5 wt% titania was 361 °C and the storage modulus value was 5.214 GPa at 100 °C, showing an increase of 62 % over the pure polymer. The hybrid films with titania showed an improved UV-stability as compared to the pure polymer.     

Molecular structure and conformation of gaseous vinyldimethylchlorosilane as determined by electron diffraction

The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (r_g) and bond angles (∠_α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data.     

Evaluation of interfacial region of microphase-separated SEBS using modulated differential scanning calorimetry and dynamic mechanical thermal analysis

The continuous structural changes of Poly(styrene-b-ethylene-butylene-b-styrene) [SEBS] due to the effect of temperature are hard to evaluate using conventional differential scanning calorimetry (DSC). This paper presents an accurate and simple way to evaluate microstructural and glass transitions of SEBS using modulated differential scanning calorimetry (MDSC). The weak crystalline nature of –(CH₂-CH₂)–_n in the ethylene-butylene (EB) block melted around 36 °C. The premature molecular moment and Tg of the styrene block were at 62 °C and 96 °C, respectively. The interfacial region at high temperature was explained with respect to order-order transition (OOT) at 144 °C and a prominent Order-Disorder Transition (ODT) at around 202 °C. Dynamic mechanical thermal analysis (DMTA) and dynamic mechanical rheological testing (DMRT) measurements also revealed that the T_g of the PS transition were consistent at around 96 °C.     

Preparation of acrylic resin/modified nano-SiO<Subscript>2</Subscript> via sol-gel method for leather finishing agent

Acrylic resin/nano-SiO₂ (AR/nano-SiO₂) composite was prepared by physical blends of acrylic resin (AR) and nano-SiO₂, which was synthesized via the sol-gel method of tetraethoxysilane (TEOS) catalyzed with alkali. The synthetic conditions, such as surfactant type, the content of nano-SiO₂ sol, stirring speed, mixed temperature and ultrasonic treatment, on nanocomposites’ property were studied in detail. DSC indicated the glass transition temperature of AR/nano-SiO₂ (Tg = −26.7°C) was a little higher than that of the acrylic resin (Tg= −29.6°C). Water uptake confirmed that the water resistance of AR/nano-SiO₂ was improved by 55.94% and the solvent resistance by 54.79% when compared with AR. The improved properties of leather finished by AR/nano-SiO₂ were shown, in contrast to AR treatment; water vapor permeability was increased by 9.15% and the finish adhesion by 10.35%.     

Molecular relaxations in dual-frequency nematic liquid crystals

The preparation of nematic liquid crystals mixtures results in changing of molecular relaxations in comparison to pure substances. Typical example is the creation of dual-frequency nematic liquid crystals using a base mixture and functional admixtures. In this paper, we present how dielectric properties of starting compounds change at mixture preparation. Three dual-frequency nematic mixtures of different composition were prepared and examined by means of dielectric spectroscopy in a wide frequency (100 Hz to 10 MHz) and temperature range (170°C to ?60°C). Parameters of detected modes for pure compounds and final mixtures were calculated and their relationships with crossover frequency are discussed.     

Optimization of tensile properties of injection molded α-nucleated polypropylene using response surface methodology

Tensile properties are among the significant properties of isotactic polypropylene (iPP). The mechanical properties including the tensile properties are fairly dependent on the overall crystallinity and crystallite size and their distribution in molded product, type of crystal structure and testing conditions. In presence of α-nucleating agents, the crystallization rate and onset temperature of isotactic PP increase. In this paper, the role of externally added commercial α-nucleating agent HPN-20E (Milliken Inc.) on tensile properties was investigated with respect to tensile properties of pure iPP. The experimental part includes the use of design of experiment (DoE) - response surface methodology (RSM) with central composite design (CCD) having three factors namely mold temperature, melt temperature and injection rate. Two levels of each factor with six centre points and five numbers of replicates were selected. The nucleating agent, HPN-20E, was added 1.0% by wt. in iPP (mfr 11.0 g/10min) using a lab scale co-rotating twin screw extruder. The compounded pellets were dried at 85 °C in a circulating hot air oven for 24 h. The tensile samples (ASTM-638D, type-I) were molded on a micro-injection molding machine (make BabyPlast, Italy). The samples were tested for tensile properties on a universal testing machine (make Lloyds, USA). The measured responses were tensile strength (MPa), Young's modulus (MPa) and work to break (N.mm). The same experimental procedure was also followed for pure iPP and same responses were measured to set the baseline of experiment. The analysis of variance (ANOVA) tests unearth that mold and melt temperatures are highly interacting in nature. That is why previous attempts based on traditional way of varying one parameter at a time were not so successful to relate tensile properties with injection molding variables. The RSM tests resulted into useful quantitative relationship between the tensile properties and injection molding process variables.     

Thermal properties of some hydrogenated poly(α-methyl styrenes)

The Synthesis of poly(isopropenyl cyclohexane) via the hydrogenation of poly(α-methyl styrene) is described. Depending on the reaction time and catalyst system a homopolymer or a copolymer is obtained. Under the conditions of synthesis both materials are highly syndiotactic. For the pure hydrogenated homopolymer (>99.9%) the glass transition temperature was found to be 185.4°C, about 20°C above T_g of poly(α-ethyl styrene). Contrary to expectations, the glass transitions of the 92/8, 33/67 poly(isopropenyl cyclohexane-co-methyl styrene) and poly(α-methyl styrene) are almost identical, as are the decomposition temperature ranges. Thermal data indicate that the decomposition mechanism of the copolymers and hydrogenated homopolymer is random scission. The thermogravimetric curves also indicate that the copolymers are random. Thus, chain stiffness appears not to increase rapidly with hydrogenation of this highly syndiotactic polymer.     

Transfer molding imide resins based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride

Phenylethynyl containing imide oligomers have been under investigation as part of an effort to develop resins for non-autoclave composite fabrication processes such as resin transfer molding (RTM). These high performance/high temperature composites are potentially useful on advanced aerospace vehicles such as reusable launch vehicles (RLVs). New phenylethynyl terminated imide oligomers (PETI) based upon 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) were prepared and characterized primarily by rheological behavior and cured glass transition temperature (Tg). In comparison to resins from the symmetrical isomer (3,3′,4,4′-biphenyltetracarboxylic dianhydride, s-BPDA), a-BPDA afforded corresponding resins with lower melt viscosities and upon curing, higher Tgs. Several resins exhibited an attractive combination of properties such as low and stable melt viscosities required for RTM composite fabrication, high cured Tgs, and moderate toughness. One resin (P10) was used to fabricate flat, void free laminates by RTM. The laminates exhibited high mechanical properties at temperatures to 288°C. The chemistry and physical properties of these new PETIs and the laminate properties of one composition are discussed.     

Poly(3-octylthiophene) and polystyrene blends thermally treated as coatings for corrosion protection of stainless steel 304

The effect of thermal annealing of poly(3-octylthiophene) (P3OT) and polystyrene (PS) blend coatings on the corrosion inhibition of stainless steel in a 0.5 M NaCl solution was investigated. P3OT was synthesized by direct oxidation of the 3-octylthiophene monomer with ferric chloride (FeCl₃) as oxidant. Stainless steel electrodes with mirror finish were coated with P3OT/PS blend by drop-casting technique. In order to study the temperature effect on the function like physical barrier against the corrosive species of P3OT/PS polymeric blend, the coatings were thermally annealed at three different temperatures (55?°C, 80?°C, and 100?°C). The corrosion behavior of P3OT/PS-coated stainless steel was investigated in 0.5 M NaCl at room temperature, by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy. The LPR values indicated that, at 100?°C, P3OT/PS coatings showed a better protection of the 304 stainless steel in 0.5 M NaCl; the corrosion rate diminished in two orders of magnitude with regard to the bare stainless steel. The superficial morphology of the coatings before and after the corrosive environment was researched by atomic force microscopy, optic microscopy, and scanning electronic microscopy. Morphological study showed that the increased temperature benefited the integration of the two polymeric phases, which improved the barrier properties of the coatings. The coating/metal adhesion and the coating thickness were evaluated. The temperature increases the adhesion degree coating/substrate; thus, the coating annealed at 100?°C showed the best adhesion.