Preparation and characterization of rubber‐toughened poly(trimethylene terephthalate)/organoclay nanocomposite

Rubber‐toughened poly(trimethylene terephthalate) (PTT)–organoclay nanocomposite (RTPTTCN) was prepared by a melt mixing technique. The rubber‐toughened PTT (RTPTT) was made by blending it with ethylene propylene diene terpolymer (EPDM) and with a small amount of maleated EPDM as a compatibilizer. XRD and TEM analysis indicated that the RTPTTCN forms a partially exfoliated nanocomposite. It was observed from SEM analysis that the clay nanoparticles induced a reduction of rubber particle size in the PTT matrix. Tensile and dynamic mechanical analysis indicated that the clay nanoparticles enhance the stiffness of the RTPTT without adversely affecting its toughness. Melt rheological studies revealed that the nanocomposites exhibited strong shear thinning behavior, and a percolated network of the clay particles was formed. It was also observed from DSC that the clay nanoparticles caused an increase in the nonisothermal crystallization temperature of the PTT. POLYM. ENG. SCI., 47:863–870, 2007. © 2007 Society of Plastics Engineers     

Study on Tribological Properties of Polytetrafluoroethylene Drawn Uniaxially at Different Temperature

Summary: Wear behavior correlations with morphology have been established from polytetrafluoroethylene (PTFE) drawn at 200, 327, and 375 °C with draw ratio about 4. The friction coefficient and wear rate for PTFE drawn at 327 °C are lower and the wear rate is lower than that of undrawn PTFE by about 30%. The structures of samples were characterized by scanning electron microscope (SEM), DSC, and wide angle X‐ray diffraction (WAXD). Results indicate that the debris morphologies of samples are different. The differences in the tribological behavior of undrawn and drawn samples were attributed to the improvement of the degree of the crystalline, fibrillation, and orderliness by drawing, especially, for PTFE drawn at 327 °C. The orderliness of molecular arrangement along the drawn direction is also higher for PTFE drawn at 327 °C than those of PTFE drawn at 200 and 375 °C, respectively. Therefore, the intensity of covalent bond along drawn direction is higher. The shear resistance and the deformability of the material are greatly improved and the size of the wear breakage unit decreases, which results in a good tribological property for PTFE drawn at 327 °C.

SEM morphology of fractured surface perpendicular to the draw direction for PTFE drawn at 327 °C.     

Solid‐state polymerization of poly(ethylene terephthalate). I. Experimental study of the reaction kinetics and properties

The solid‐state polymerization (SSP) reaction kinetics of poly(ethylene terephthalate) were investigated in connection with the initial precursor intrinsic viscosity (IV; molecular weight). Evaluations were performed with otherwise equivalent precursors melt‐polymerized to IVs of 0.50, 0.56, and 0.64 dL/g. The changes in the molecular weight and other properties were monitored as functions of the reaction times at solid‐state temperatures of 160–230°C. Precursors with higher initial molecular weights exhibited higher rates of SSP than those with lower initial values, as discussed in connection with the levels of crystallinity and the carboxyl and hydroxyl end‐group composition. Activation energies decreased at temperatures above 200°C, and this indicated a change in the SSP reaction mechanism. At temperatures of 200–230°C, similar activation energies were required for the polymerization of all three precursors. Lower temperature polymerizations, from 160 to 200°C, required higher activation energies for all precursors, with the 0.50‐IV material requirement almost twice as high as that calculated for the higher IV precursors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 197–212, 2003     

Sol-Gel Alumina Coating for Improved Cyclic Oxidation Resistance of Silicon Nitride

A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.     

Blends of chlorinated isotactic polypropylene with poly(ethylene-co-vinyl acetate) II. Phase studies of the miscible blends

By measuring T_g, T_m and T_c (cloud point) phase diagrams for the four miscible blends of chlorinated isotactic polypropylenes (chlorine content 39.2 (CPP-40) and 49.8 wt.-% (CP-50)) with Poly(ethylene-co-vinyl acetate)s (vinyl acetate contents 40 (EVA-40) and 45 wt.-% (EVA-45)) were investigated. The blend of CPP-50 with EVA-40 was the most compatible of the four blend pairs.     

Synthesis and characterization of novel aromatic condensation polymers containing rigid benzoxazole pendent groups

A new aromatic diamine monomer containing benzoxazole substituents was prepared by a multistep synthesis starting from 1,4‐dibromo‐2,5‐difluorobenzene. The diamine was polymerized with commercial aromatic dianhydride or dicarboxylic acid chloride monomers to provide several different poly(amic acid)s and polyamides with their inherent viscosities in the range of 0.24–0.46 dL/g. Thermal properties of these polymers including thermal imidization of poly(amic acid)s into polyimides were investigated by using FTIR, DSC, and TGA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 178–185, 2004     

Microwave Dielectric Properties of CaTiO3-Ca(Al1/2Ta1/2)O3 Ceramics

The microwave dielectric properties of CaTi_1-χ(Al_1/2Ta_1/2)_cHO₃ solid solutions (0.3 ≤χ≤ 0.5) have been investigated. The ceramic samples had perovskite structures similar to CaTiO₃. The partial substitution of Ti₄₊ by a coupled Al₃₊/Ta_s+ permitted improvement of the quality factor Q . The dielectric constant (τ_r) and temperature coefficient of resonant frequency (τ_r) decrease rapidly with an increase of χ. A new high-quality microwave dielectric material was found at χ= 0.46 with σ_r= 46.5, Q f = 27300 GHz, and π_f= 0 ppm/°C. The relationship between microstructures and dielectric properties is presented.     

A novel spin-finishing method for antistatic modification of polyester fiber. Surface reaction onto amine-containing copoly(amide-ethers) blended with polyester fiber

Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 10⁶ to 10⁸ Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity.     

Fatigue failure mechanisms in polymers

Fatigue testing of polymers has revealed significant differences between the fatigue response of polymers and metals. Generally, fatigue failure in metals is a process of crack initiation, propagation, and failure. Also, fatigue damage in metals is cumulative and cycle dependent, but remains essentially independent of test frequency. Unlike that of metals, the fatigue behavior of polymers is influenced by viscoelastic effects. At high frequencies, softening and melting occur, and fatigue failure depends largely on the test frequency. At lower frequencies, fatigue failure becomes less sensitive to test frequency and results from crack initiation and propagation. These polymer characteristics arise from the production of hysteresis energy during fatigue. A portion of this energy is released as heat, some of which is dissipated, but most is absorbed in the sample, raising its temperature. This temperature rise leads to degradation of the material and a short fatigue life. Experiments were conducted to measure hysteresis energy and temperature rise for a talc-filled polypropylene. A mathematical model was developed to calculate the energy and temperature distribution during fatigue. Correlation of the temperature rise predicted by the model with that observed experimentally provided values for the various energy terms that quantitatively defined the thermomechanical fatigue response of this polymer.     

Study of stability of high‐temperature polyimides using TG/MS technique

The oxidative stability of the carbon fiber‐reinforced composite of polyimide was examined, in real time, using the evolved gas analysis techniques. Off‐gas degradation products suggested the onset temperature for chain scissions to be fairly low at about 190–220°C. Based on the off‐gas products present and the trend of their release, the composite degradation mechanism appeared to be similar between 190 and 371°C, thereby marking 371°C to be the highest accelerated aging temperature for its long‐term lifetime prediction. Beyond 371°C, different degradation mechanisms would apply. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1219–1227, 2002