Thermally stimulated creep of polyethylene,polypropylene, copolymers,and blends

The technique of Thermo Stimulated Creep (TSC) has been applied to the study of anelastic properties of polyethylene, polypropylene, their copolymers and blends. In the temperature range ?200 to 100°C, complex TSC peaks were observed in all samples, namely around 0°C, about the same temperature as for the homopolypolymer polypropylene. By applying “fractional stresses”, with a convenient choice or the loading program, these peaks have been experimentally resolved. Two components can be distinguished: 1. The “low temperature” component is characterized by mechanical retardation times following a compensation law. It has been attributed to microbrownian motions of polypropylene sequences liberated at the glass transition of the “true” amorphous regions. 2. The “high temperature” component which is influenced by thermal treatment has been assigned to microbrownian motions of polypropylene sequences liberated at the glass transition of the “constrained” amorphous regions. In block polymers, an additional TSC peak is observed around ?50°C: it has been associated with the glass transition of ethylene-propylene-rubber (EPR) interphase. The coupling of this interphase with polyethylene and polypropylene phases is insured by diffusion of some ethylene and propylene sequences in-EPR. At about ?140°C, a TSC peak associated with the low temperature component of the glass transition of polyethylene can be distinguished in all the materials studied.     

An investigation into the relationship between the impact performance of rotationally molded polyethylene products and their dynamic mechanical properties

In this paper, a study of the relationship between the impact performance of rotationally molded polyethylenes and their dynamic mechanical properties is carried out. A wide range of conventional linear low density polyethylene powders and met‐allocene catalyzed linear low density polyethylene powders were rotationally molded and tested. Instrumented falling weight impact tests were carried out over a temperature range of ?60°C to 20°C. Dynamic Mechanical Thermal Analysis (DMTA) tests were also carried out between ?100°C and 90°C, at a frequency of 100 Hz. Comparisons between the impact performance of metallocene catalyzed LLDPEs and Ziegler‐Natta LLDPEs are made. The transitions evident in the DMTA results are related to changes in impact performance with temperature. The beta transition is found to fall in the transition region between high impact performance at low temperatures and lower impact performance at ambient temperatures.     

Thermal and mechanical properties of linear segmented polyurethanes with butadiene soft segments

A series of segmented polyurethanes based on a hydroxyl terminated polybutadiene soft segment (HTPBD) have been prepared with varying hard segment content between 20 and 60 weight percent. These materials are linear and amorphous and have no potential for hydrogen bonding between the “hard” and “soft” segments. The existence of two-phase morphology was deduced from dynamic mechanical behavior and thermal analysis. Both techniques showed a soft segment glass transition temperature, T_gs, at ?56°C and hard segment transitions between 20 and 100°C, depending on the urethane content. The low value of T_g, only 8° higher than the T_g of free HTPBD and independent of hard segment concentration indicated nearly complete phase segregation. Depending on the nature of the continuous and dispersed phases, the urethanes behaved as elastomers below 40 weight percent hard segment or as glasslike materials at higher hard segment contents. The effect of thermal history on transitions of the HTPBDurethanes was also investigated and the results suggest that the absence of hydrogen bonding to the soft segment must account for the extraordinary insensitivity to thermal history in dynamic mechanical, thermal and stress-strain behavior. Comparisons are made to the more common polyurethanes containing polyether and polyester soft segments.     

Optimization of the thermomechanical behavior of a poly(chromium(III) trisphosphinate)

A two-component reactive system consisting of a poly(chromium(III) bisphosphinate) and dioctylphosphinic acid reacts to form a poly(chromium(III) trisphosphinate). Extensive thermomechanical hysteresis is displayed throughout the temperature range ?180°C to >300°C by specimens containing filaments of glass. Thermal pretreatment to about 400°C (the limit of thermal stability) eliminated these instabilities. These results correlate with the reported brittle and tough character of films of the poly(chromium (III) bisphosphinate) and poly(chromium (III) trisphosphinate), respectively. Regardless of thermal history (between 200°C and 400°C), the polymer system displayed three major transition regions: the glass transition centered at about 0°C, another centered at about 230°C, and a third at about ?200°C.     

Dynamic mechanical and thermal properties of fire-retardant polypropylene

A study of the effect of a series of fire retardants and antimony oxide upon the dynamic mechanical and thermal properties of polypropylene suggests three categories. (1) “Inert Fillers”—These raise the elastis modulus and the heat distortion temperature of polypropylene without shifting its glass transition temperature. The melting point of polypropylene is only depressed by 1–3°C, the heat of fusion and the percentage of crystallinity of polypropylene in these composites is ～10 percent lower at additive concentrations of ～30 percent. Very poor interaction exists between the additive and the thermo-plastic which apparently exist in two separate phases. (2) “Chain Stiffener”—These raise the elastic modulus (～25 percent) and the glass transition (～11°C) for polypropylene; the melting point of polypropylene in the composite is lowered by ～6°C indicative of good interaction between the additive and polypropylene. (3) “Plasticizer”—These lower the room temperature elastic modulus (～20 percent) and the glass transition temperature (～11°C) of polypropylene; the melting point of polypropylene in the composite is depressed by ～10°C indicating good interaction. The efficacy of the “plasticizer” and “chain stiffener” are attributed partially to melting of polypropylene at the processing temperature.     

Effect of fillers on the relaxation behavior of chlorobutyl vulcanizates

The effect of addition of fillers (carbon black (CB), carbon silica dual phase filler (CSDPF), and nanoclays) on the relaxation behavior of chlorobutyl vulcanizates has been studied. The primary relaxation (α‐transition, the glass transition) was studied by dynamic mechanical analysis as a function of temperature (?60 to +100°C) and positron annihilation life time spectroscopy (?70 to +110°C). Irrespective of the filler and its loading, all the composites showed the glass transition temperature in the range of –29 to –33°C, which was explained on the basis of relaxation chain dynamics of polyisobutylene in the vicinity of fillers. The secondary relaxation (α* or β relaxation) was studied using dielectric relaxation spectra in the frequency range of 100–10⁶ Hz. Nanoclays had a profound influence on the secondary relaxation, whereas CSDPF and CB had a marginal effect. The nonlinear strain dependent dynamical parameters were also evaluated at double strain amplitudes of 0.07–5%. The nonlinearity in tan δ and storage modulus has been explained on the concept of filler–polymer interactions and the interaggregate attraction (filler networking). The “percolation limit” of the fillers in the composites has been studied by DC conductivity measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3161–3173, 2006     

Dynamic mechanical analysis and its relationship to impact transitions

Detailed, instrumented impact tests were carried out between about ? 100 and 60°C for flexible poly(vinyl chloride) (PVC), ethylene vinyl acetate (EVA), and polypropylene (PP) films. Secondary impact transitions in addition to the main transitions were detected for all three films, indicating that multiple impact transitions may be far more general in occurrence than commonly expected. Wide frequency (from 0.05 to 100 Hz) dynamic mechanical spectra of the same materials were also generated over similar temperature ranges. A new data treatment method was proposed whereby the material dissipation function was evaluated by summing the responses over broad frequency ranges of the loss modulus and the impulse spectrum. The dissipation function when plotted as a function of temperature was found to accurately (to within 3 to 5°C) predict the location of the main impact transitions for all three polymers. In addition, the existence and location of the secondary impact transitions for both PVC an PP were predicted. Both the functional form and the temperature match between the experiments and predictions strongly support the validity of the proposed method. However, some discrepancy remained in predicting the very low temperature (?65°C) impact transition for EVA.     

Studies on sublimation of disperse dye out of dyed polymers. II. Rate of sublimation and amorphous transition of polypropylene

The diffusion coefficient D of disperse dyes through unmodified polypropylene (dyed at 120° and 137°C) was measured at 50°–160°C in the dry system. The diffusion transition points indicated by the breaks in the log D versus 1/T°K were obtained at about 70°, 90°, and 115°C. The 70° and 115°C transitions are in good accordance with the transition temperature of smectic into monoclinic phase and with the temperature of abrupt change in lattice expansion of monoclinic crystal, respectively. These phenomena were explained on the basis of the intimate correspondence between amorphous and crystalline transitions, as expressed by one of us for poly(ethylene terephthalate). The 115°C transition was confirmed by the same sort of diffusion transition occurring, expectedly, at 83°C in the case of polyethylene, an abrupt increase in lattice expansion of which had been found at about 80°C. The diffusion transitions were also confirmed by dilatometry and shrinkage measurement. The 90°C transition has never been reported and it cannot be explained at present.     

Dynamic mechanical properties of polymers

A technique, employing samples in the form of tuning forks, to measure the mechanical properties of polymers is presented. Results for low density polyethylene, polypropylene, and polycarbonates are shown. A large transition is observed for polypropylene at approximately +10°C and a small transition at ?100°C for the polycarbonates. Polycarbonate data has also been obtained from 20 to 150°C, at approximately 70 cps. Effects of time, temperature, and history are presented.     

Low temperature transitions in a crosslinked urethane

We have investigated the low temperature transitions in a urethane prepolymer crosslinked with various amines and triols by measuring their dynamic mechanical properties over a temperature range of 25°C to approximately ? 190°C. In the formulations studied, a low temperature transition was observed near ? 140°C and the transition was shown to be related to the electronic and steric influences of the curing agent structure at the crosslink site. A quantitative relationship was demonstrated between the low temperature transition peak intensity and the polymer's crosslink density. The above relationships were derived from torsion pendulum and solvent swell experimentation.     

Aging of the Binders GAP-N100 and HTPB-IPDI Investigated by Torsion-DMA

The aging of the binders GAP-N100 and HTPB-IPDI was investigated by DMA in torsion mode to find out the changes in the storage shear modulus G′(ω), loss shear modulus G″(ω) and in the glass transition temperature T_G. The forced sinusodial deformation method was used with measuring frequencies between 0.1 Hz and 56.2 Hz. A measurement temperature range between −100°C and +50°C was applied. The DMA instrument was a Rheometrics Dynamical Spectrometer, type RDS II/7700. Non-aged GAP-N100 shows a well defined steep glass transition between −40°C and −25°C, which is found with aged samples also but shifted to higher temperatures. The glass transition of the binder HTPB-IPDI lies between −70°C and −10°C, but HTPB-IPDI has not a well defined glass transition. With aging it looses its glass transition, which can be seen by a smoothing out of the transition step in the curve G′(ω)=f(T). The behaviour and the differences of these binders are explainable on a molecular basis. The systematic shift of the glass transition temperature of the non-aged and aged GAP-N100 as well as of the non-aged HTPB-IPDI is describable by the Williams-Landel-Ferry equation. This equation was used to extrapolate the values of the glass transition temperatures to shear rates possible during operational use of propellants.     

Bi(Zn2/3Nb1/3)O3–(K0.5Na0.5)NbO3 High‐Temperature Lead‐FreeFerroelectric Ceramics with Low Capacitance Variation in a Broad Temperature Usage Range

The xBi(Zn_2/3Nb_1/3)O₃–(1?x)(K_0.5Na_0.5)NbO₃ (abbreviated as xBZN–(1?x)KNN) ceramics have been synthesized using the conventional solid‐state sintering method. The phase structure, dielectric properties and “relaxorlike” behavior of the ceramics were investigated. The 0.03BZN–0.97KNN ceramics show a broad and stable permittivity maximum near 2000 and lower dielectric loss (≤5%) at a broad temperature usage range (100°C–400°C) and the capacitance variation (ΔC/C_150°C) is maintained smaller than ±15%. The 0.03BZN–0.97KNN ceramics only possess the diffuse phase transition and no frequency dispersion of dielectric permittivity, which indicates that 0.03BZN–0.97KNN ceramics is a high temperature “relaxorlike” ferroelectric ceramics. These results indicate that 0.03BZN–0.97KNN ceramics are excellent promising candidates for preparing high‐temperature multilayer ceramics capacitors.     

Comparison of Effects of Calcium and Magnesium Doping on the Structure and Biological Properties of NaTaO3 Film on Tantalum

Tantalum is widely used in hip joint replacement and knee joint repair, but its clinical application is limited due to its poor biological activity and weak ability to promote new bone formation. Ca and Mg ions are thought to be involved in bone metabolism and play an important physiological role in the angiogenesis, growth, and mineralization of bone tissue. In this work, NaTaO₃ films doped with Ca²⁺ and Mg²⁺ were prepared by hydrothermal synthesis and molten salt method. The doping amounts of Ca²⁺ doped at 450, 550, 650 and 750 °C were 0.59, 3.44, 32.75 and 29.88 at%, and that of Mg²⁺ doped at 300, 350, 400, 450, 500, 550 and 650 °C were 0.62, 1.03, 1.54, 20.12, 21.38, 14.37 and 0.74 at%, respectively. Ca²⁺ and Mg²⁺ are evenly incorporated into NaTaO₃ and cause the change of crystal plane spacing without any significant changes of morphologies below 550 and 400 °C respectively. XPS shows that the cations are the A-site substitution of perovskite structure (ABO₃). According to the morphology and composition analysis of Ca-incorporated samples and Mg-incorporated samples, the optimal preparation temperature of them is 550?°C and 400?°C, respectively. The results show that for “550?°C-Ca” and “400?°C-Mg” the hydrophilicity is 13.9° and 96.1°, the roughness is 114.3 and 54.3?nm, the doping ion concentration of Ca and Mg is 3.44 and 1.54 at%, and the 7-day ICP results is 69.8 and 1.4?ppm, respectively. In addition, cell proliferation experiments and cell morphology related to biological activity and osteogenic properties are discussed, and it is found that the performance of “550?°C-Ca” is better than “400?°C-Mg”. Ca²⁺–NaTaO₃ is a promising implantable material that will be extensive used in bone implants, joint replacements and dental implants.

     

Catalytic-assisted synthesis, characterization and low frequency AC conduction of nanostructured conducting polyaniline

Polymerizations of aniline at the reaction temperatures of 25 and 50 °C have been performed in the presence of iron catalyst. The prepared conducting polyaniline at different reaction periods was investigated for physicochemical and electrical properties, through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR) and frequency-dependent electrical conductivity measurements, respectively. XRD studies established the improved nanostructured crystalline nature for the polymer prepared at 50 °C. Size of the particles ranging from 10 to 20 nm was calculated for the prepared polyaniline. SEM analysis shows the cauliflower-like morphology for optimized reaction temperature. The study further establishes the attainment of uniform distribution of polyaniline at the reaction temperature of 50 °C. The charge transitions between benzenoid (B-band) and quinonoid (Q-band) bands were witnessed by UV–Vis spectrum analysis. The band gap analysis revealed the narrow band gap direct transition semiconducting nature of the conducting polymer. Quinonoid and phenylene rings were identified through vibrational bands between 1570 and 827 cm^?1 via FTIR spectroscopy analysis. The AC conductivity of the sample synthesized at 50 °C showed 1.50 × 10^?1 S cm^?1. Enhancement in conductivity with increasing temperature represented the improved crystalline nature of the polyaniline prepared at 50 °C.     

Plane stress and plane strain fractures in polypropylene

The concepts of Linear Elastic Fracture Mechanics (LEFM) are applied to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, K_Ic. The effect of thickness, notch sharpness, and the mode of loading on K_Ic have been investigated in order to determine the plane strain toughness values, K_cI for the materials. The two types of material are compared in terms of their toughness values over a range of temperatures between +30 and ?160°C. Evidently, the small amounts of ethylene added to the copolymers show plasticizing effects, suppressing the yield stress and the ductile-brittle transition temperature. In addition, the copolymers exhibit a ductile-brittle region between ?100 and ?45°C where notch strengthening is apparent in the tension mode and a slow crack growth region between ?45 and ?30°C where slow growth precedes unstable fracture. The homopolymer, however, shows no clear evidence of such intermediate regions, except for slight amounts of slow growth above 0°C, and becomes ductile around 30°C.     

The Viscoelastic Properties of Chinese Fir During Water-Loss Process Under Hydrothermal Conditions

In this article, the viscoelastic properties of water-swollen Chinese fir during a water-loss process under different hydrothermal conditions (30–90°C, 40–80% RH) were investigated. After the 300 min hydrothermal process at 70 or 90°C, the moisture contents (MCs) of the specimens were well below the MC value at the fiber saturation point. During the hydrothermal process, normalized E′ increased at first, and then leveled off at temperatures above 50°C. The wood specimens were softened due to the hydrothermal effect. The glass transition of hemicellulose appeared at 50°C. Lignin transition was observed at 70 and 90°C. Superposition of transitions of lignin and hemicellulose moved to low storage modulus E′ with increasing temperature and RH level.     

Effects of Monoacylglycerols on the Cold Flow Properties of Biodiesel

Biodiesel is a renewable alternative fuel made from plant oils and animal fats that may be burned in a compression–ignition (diesel) engine. It is composed of mono-alkyl fatty acid esters made from plant oils or animal fats mainly by transesterification with methanol or ethanol. This process leaves behind small concentrations of minor constituents including monoacylglycerols (MAG). Saturated MAG have low solubility in biodiesel and may form solid residues during storage in cold weather. Soybean oil-fatty acid methyl esters (SME) were mixed with up to 1.0 mass% MAG to evaluate the effects on cloud point (CP), freezing point (FP), cold filter plugging point (CFPP), and wax appearance point (WAP). Differential scanning calorimetry (DSC) results showed that MAG with only 27.6 mass% total long chain (C16–C18) saturated fatty acid content had melting transitions between 54 and 59.0 °C. Furthermore, DSC analysis indicated that pure monoolein may be problematic with respect to melting transitions between 25.4 and 33.4 °C. Solubility data for SME–MAG mixtures indicated a broad transition temperature range from solid at low temperature to liquid at temperatures exceeding 60 °C. Increasing the added MAG content from 0.10 to 1.0 mass% increased both CP and FP. Cold filter plugging point demonstrated higher sensitivity than CP or FP at added MAG content below 0.10 mass%, though it was not affected by increasing MAG concentration above 0.50 mass%. Wax appearance point showed no effects until added MAG content exceeded 0.25 mass%. Kinematic viscosity measured at 5 °C similarly showed no effects until added MAG concentration exceeded 0.20 mass%. Specific gravity at 15.6 °C and refractive index at 25 °C were not greatly affected by added MAG except at concentrations greater than 0.10 mass%.     

Spontaneous current emission in metal-ferrocene-doped ethyl cellulose-metal systems

Spontaneous current emission (SCE) has been studied in sandwiched different electrode configurations [metal(1)–undoped/doped ethyl cellulose (EC)–metal (1)/(2)] as a function of heating rate, film thickness and dopant concentration in the temperature range 40–200°C. The magnitude and direction of current depend on the combination of electrode metals. SCE thermograms for the Al undoped/doped EC–AI system exhibit two well resolved transition at 110 and 160°C in opposite directions to each other. The phenomena related to these transitions are explained in terms of creation of field at the interfaces and field produced in the bulk of the material. No negative direction transition was observed for electrode systems like Ag–Ag, Pb–Pb, Sn–Sn and Au–Au except for a shoulder of a peak around 100°C. When dissimilar electrode systems (i.e. Al–undoped/doped EC–Ag/Pb/Sn) are used, the current rises and then saturates beyond around 160°C.     

Mechanical behavior of polytetrafluoroethylene around the room-temperature first-order transition

The effect of the room-temperature first-order transition on the plastic yield behavior of polytetrafluoroethylene (PTFE) has been investigated. Stress-strain curves were measured at different strain rates and temperatures. Tensile creep under constant dead load was also measured as a function of temperature and stress level. The effect of degree of crystallinity was investigated by using both a rapidly quenched and slow-cooled polymer. Observations were extended to large deformations, so that the phenomenon primarily observed was plastic yield rather than linear viscoelastic behavior. The curve of yield stress vs. temperature in the temperature range from –50 to +68°C was found to be almost identical with the curve of elastic modulus vs. temperature; the yield stress shows a marked local decrease at the first-order transition. The yield elongation was almost constant (at about 5%) over this same range, which is in accord with the above result. The more highly crystalline polymer is always more rigid than the less crystalline polymer at small deformations, but above 19°C its stress-strain curve shows a “cross-over” in stress level with the curve of the less crystalline polymer as extension increases. That is, above 19°C the less crystalline polymer shows a more rapid rate of “strain hardening”, even though the strain-hardening effect is pronounced in both polymers. Attempts to apply time-temperature superposition to creep data at different temperatures were partially successful; the lateral shifts required corresponded to an activation energy of approximately 80 kcal. The experimental observations suggest a model of the solid-state structure of PTFE which could be described as an “elastic-plastic network”, in which crystalline domains are connected by elastic amorphous regions, and in which the crystalline domains can flow plastically at sufficiently high stress or temperature.     

A Study on the Change in the Dielectric Properties of CR-39 Polymer Track Detector Due to α-Irradiation in the Frequency Range from 100 Hz to 100 kHz

The dielectric properties in the frequency range from 100 Hz to 100 kHz of polyallyldiglycol carbonate “CR-39” samples before and after irradiations have been investigated. The irradiations were verified with 4.84 MeV α-particles at different irradiation times. The dependence of the dielectric properties of unirradiated and irradiated samples at room temperature (25°C) and constant frequency (10 kHz) on the total number of α-particles have been studied. It was found that the CR-39 can be used as a detector for high α-particles fluxes.