Physical properties of some organophosphazene copolymers. II. Thermoelasticity andin situ reinforcement of the cross-linked networks

Aryloxy phosphazene copolymers with phenoxy andp-ethyl phenoxy substituents were cross-linked into elastomeric networks and studied with regard to their stress-strain and thermoelastic (force-temperature) behavior. The thermoelastic results showed that the energetic contribution to the elastic force was negative, indicating that the unperturbed dimensions of the polymer chains decrease with increases in temperature.In situ precipitation of silica into the elastomers by hydrolysis of an absorbed alkoxysilane was found to give excellent network reinforcement.     

Evaluation of the properties of bitumen modified by SBS copolymers with different styrene–butadiene structure

Four styrene–butadiene–styrene(SBS) modified bitumens had been prepared by a base bitumen, a crosslinking agent and four SBS copolymers which differ in styrene blocks content and molecular configuration (radial or linear) under the same experimental conditions. Conventional properties, morphology, thermal behavior and microstructure were investigated by means of conventional tests, fluorescence microscopy, differential scanning calorimetry (DSC), and Fourier transform infrared (FT‐IR) spectroscopy. In terms of linear SBS polymers, the SBS molecule with the styrene content of 30% has a perfect dispersion and complete stretching in bitumen matrix, and in this case, the conventional properties and thermal stability of bitumen are enhanced substantially. However, the star SBS polymer due to long branched chains forming the preferable steric hindrance to enhance the intensity of base bitumen, plays a more important role in improving the conventional properties of base bitumen than linear SBS polymers. Furthermore, the FT‐IR spectra indicate that, the main bands assignations of four modified bitumens are identical and the significant variation is the peak intensity. And a noncomplete crosslinking reaction happens between the bitumen and each SBS polymer, which can efficiently prevent excessive cross‐linking from affecting the intrinsic bitumen characteristics. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40398.     

Crystallization properties of polycaprolactone composites filled with nanometer calcium carbonate

Polycaprolactone (PCL) composites filled with nanometer calcium carbonate (nano‐CaCO₃) were prepared by means of a twin‐screw extruder in this study. The nano‐CaCO₃ surface treated with stearate. The crystalline properties of the PCL/nano‐CaCO₃ composites were measured with a differential scanning calorimeter to identify the influence of the nanometer filler content on the crystalline properties. The results show that the crystallization onset temperature, crystallization temperature, and crystallization end temperature of the composites were obviously higher than those of the unfilled PCL resin, and the crystallization degree (χ_c) of the composites increased with increasing particle weight fraction (?_f) when ?_f was more than 1%. When ?_f was 1%, χ_c of the composite was less than that of the unfilled PCL resin. Moreover, the dispersion of the inclusions in the matrix was observed by means of scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Solvents for thermoporosimetry analysis of natural rubber networks

Thermoporosimetry is known as an analytical method to investigate network structures in swollen elastomers. Despite this interesting potential capability, only few investigations are published in literature which apply different solvents on differently crosslinked natural rubber samples. The choice of the solvent is critical as it strongly influences the separation of confined and bulk solvent transition signal, the confined solvent signal intensity and the peak width representing the pore size resolution. No critical comparison has been done in these investigations regarding the solvent choice related to peak separation, pore size resolution or signal intensity. Furthermore, no critical assessment is available relating thermoporosimetry results to solvent parameters to identify an optimal solvent regarding the mentioned criteria. This argument motivated the present investigation to identify the most appropriate solvents for the analysis of natural rubber compounds by thermoporosimetry. Different types of solvents (aliphatic, aromatic, non‐polar, and polar) were selected and benchmarked against each other. It was concluded that n‐heptane was identified as the best solvent for these investigations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43998.     

Evolution of the amorphous fraction of PEEK during annealing at atmospheric and high pressure above the glass transition temperature

The constrained fraction of the amorphous phase of semi‐crystalline polymers is in an out‐of‐equilibrium state so that "physical aging"‐like features can be observed (e.g., by calorimetry) even above the glass transition temperature. This was already addressed in the literature in several semi‐crystalline polymers at atmospheric pressure. Despite the well‐known influence of pressure on molecular mobility, the pressure‐sensitivity of these microstructure rearrangements has never been tackled. This study focuses on annealing in highly pressurized Poly‐Ether‐Ether‐Ketone (PEEK), compared with atmospheric pressure. The phenomenon is tracked by ex‐situ Differential Scanning Calorimetry (DSC). A significant influence of pressure is evidenced, without any complete equivalence with temperature. Indeed, pressure seems to confine rearrangements within spatially limited domains. The stability and coexistence of reorganization processes upon successive annealings is also investigated. Finally, relationships between constrained and free amorphous phase rearrangements are discussed via the different glass transition shifts observed after atmospheric or high pressure annealing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1148‐1157, 2013     

Physical properties of some organophosphazene copolymers. II. Thermoelasticity andin situ reinforcement of the cross-linked networks

Aryloxy phosphazene copolymers with phenoxy andp-ethyl phenoxy substituents were cross-linked into elastomeric networks and studied with regard to their stress-strain and thermoelastic (force-temperature) behavior. The thermoelastic results showed that the energetic contribution to the elastic force was negative, indicating that the unperturbed dimensions of the polymer chains decrease with increases in temperature.In situ precipitation of silica into the elastomers by hydrolysis of an absorbed alkoxysilane was found to give excellent network reinforcement.     

Viscoelastic rheology in the melting and crystallization domain: Application to polypropylene copolymers

The purpose of this article was to study the relationship between the rheological properties and the crystallization or melting of two polypropylene‐based copolymers used in the welding of the coating of offshore pipelines. The materials microstructure was studied via X‐ray diffraction, scanning electron microscopy, and optical microscopy. Differential scanning calorimetry was used to determine the crystallization and melting properties at different cooling and heating rates. Dynamic rheological analysis was used to define the rheological properties in the molten and in the transition zone from the molten to solid state and inversely. Both experiments (DSC and rheology) were performed under non‐isothermal conditions to allow complete accessibility to the transition zone. Crystallization and melting are both complex processes in which coexist amorphous and crystalline phases in the sample. A correlation between the rheological properties and crystallization was proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44690.     

Thermally induced microstructural changes and its influence on electrical conductivity of a polymer‐based bakelite RPC detector material: A positron lifetime study

Annealing studies have been carried out to understand the temperature induced microstructural changes in Bakelite (P‐120 NEMA LI‐1989 Grade XXX) Resistive Plate Chamber (RPC) detector material using Positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), and XRD. The variation of positron lifetime parameters viz., ortho‐Positronium lifetime (τ₃) and free volume size (V_f) increases marginally above glass transition temperature T_g as a result of structural changes due to segmental mobility. The drastic increase of free volume parameters above 240°C attributed to the reduction in strength of C—H bond of the aliphatic bridges and cleavage of methylene bridges of the polymer network, which is supported by the FTIR results. The XRD results show the reduction in crystallinity and average crystallite size of Bakelite on annealing correlates well with the free volume and electrical conductivity. The temperature induced electrical conductivity and activation energy is also correlated with the positron lifetime parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 793‐800, 2013     

Glass transition and cold crystallization in carbon dioxide treated poly(ethylene terephthalate)

An amorphous poly(ethylene terephthalate) (aPET) and a semicrystalline poly(ethylene terephthalate) obtained through the annealing of aPET at 110°C for 40 min (aPET‐110‐40) were treated in carbon dioxide (CO₂) at 1500 psi and 35°C for 1 h followed by treatment in a vacuum for various times to make samples containing various amount of CO₂ residues in these two CO₂‐treated samples. Glass transition and cold crystallization as a function of the amount of CO₂ residues in these two CO₂‐treated samples were investigated by temperature‐modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). The CO₂ residues were found to not only depress the glass‐transition temperature (T_g) but also facilitate cold crystallization in both samples. The depressed T_g in both CO₂‐treated poly(ethylene terephthalate) samples was roughly inversely proportional to amount of CO₂ residues and was independent of the crystallinity of the poly(ethylene terephthalate) sample. The nonreversing curves of TMDSC data clearly indicated that both samples exhibited a big overshoot peak around the glass transition. This overshoot peak occurred at lower temperatures and was smaller in magnitude for samples containing more CO₂ residues. The TMDSC nonreversing curves also indicated that aPET exhibited a clear cold‐crystallization exotherm at 120.0°C, but aPET‐110‐40 exhibited two cold‐crystallization exotherms at 109.2 and 127.4°C. The two cold crystallizations in the CO₂‐treated aPET‐110‐40 became one after vacuum treatment. The DMA data exhibited multiple tan δ peaks in both CO₂‐treated poly(ethylene terephthalate) samples. These multiple tan δ peaks, attributed to multiple amorphous phases, tended to shift to higher temperatures for longer vacuum times. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Understanding the effect of chain entanglement on the glass transition of a hydrophilic polymer

In this article, we report an interesting phenomenon of the glass transition temperature (T_g) deviation of a hydrophilic polymer. Polyacrylamide (PAL) samples with different extents of chain entanglement were prepared by spray drying and solution casting. We found that the glass transition temperature increases as the extent of chain entanglement decreases upon the sub‐T_g annealing. The water content in the PAL matrix is found with no direct correlation to T_g. However, the observation of a faster diffusion process of water in the disentangled PAL matrix offers an evidence of a faster relaxation process of disentangled PAL molecules. The T_g increase of the disentangled PAL samples is believed to be associated with the increased molecular interaction during the chain relaxation process upon the sub‐T_g annealing. A macroscopic evidence is the fact that the density of the hot‐laminated samples increases as the extent of chain entanglement decreases. A thermodynamic analysis suggests that enthalpy more than entropy favors an elevated T_g of a disentangled hydrophilic polymer upon the sub‐T_g annealing. We believe that this research provides new understanding of T_g of the hydrophilic polymers, which are being extensively used in bio‐related studies. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of water on drawability,structure, and mechanical properties of poly(vinyl alcohol) melt‐spun fibers

Poly(vinyl alcohol) (PVA) melt‐spun fibers with circular cross‐section and uniform structure, which could support high stretching, were prepared by using water as plasticizer. The effects of water content on drawability, crystallization structure, and mechanical properties of the fibers were studied. The results showed that the maximum draw ratio of PVA fibers decreased with the increase of water content due to the intensive evaporation of excessive water in PVA fibers at high drawing temperature. Hot drying could remove partially the water content in PVA as‐spun fibers, thus reducing the defects caused by the rapid evaporation of water and enhancing the drawability of PVA fibers at high drawing temperature. The decreased water content also improved the orientation and crystallization structure of PVA, thus producing a corresponding enhancement in the mechanical properties of the fibers. When PVA as‐spun fibers with 5 wt % water were drawn at 180 °C, the maximum draw ratio of 11 was obtained and the corresponding tensile strength and modulus reached ～0.9 GPa and 24 GPa, respectively. Further drawing these fibers at 215 °C and thermal treating them at 220 °C for 1.5 min, drawing ratio of 16 times, tensile strength of 1.9 GPa, and modulus of 39.5 GPa were achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45436.     

Poly(l‐lactic acid) with the organic nucleating agent N,N,N′‐tris(1H‐benzotriazole) trimesinic acid acethydrazide: Crystallization and melting behavior

N,N,N′‐Tris(1H‐benzotriazole) trimesinic acid acethydrazide (BD) was synthesized from 1H‐benzotriazole acetohydrazide and trischloride to serve as an organic nucleating agent for the crystallization of poly(l ‐lactic acid) (PLLA). First, the thermogravimetric analysis of BD exhibited a high thermal decomposition temperature; this indicated that BD maybe used as a heterogeneous nucleating agent of PLLA. Then, the effect of BD on the crystallization and melting behavior of PLLA was investigated through differential scanning calorimetry, depolarized light intensity measurements, and wide‐angle X‐ray diffraction. The appearance of a nonisothermal crystallization peak and increases in the glass‐transition temperature and the intensity of the diffraction peak suggested that the presence of BD accelerated the overall PLLA crystallization. Upon cooling at a rate of 1°C/min, the addition of just 0.5 wt % BD to PLLA increased the onset crystallization temperature from 101.4 to 111.3°C, and the nonisothermal crystallization enthalpy increased from 0.1 to 38.6 J/g. The isothermal crystallization behavior showed that the crystallization half‐time of PLLA with 0.5 wt % BD (PLLA/0.5% BD) decreased from 49.9 to 1.1 min at 105°C. However, the equilibrium melting point of PLLA/0.5% BD was lower than that of the pristine PLLA; this resulted from the increasing nucleating density of PLLA. The melting behavior of PLLA/0.5% BD further confirmed that BD improved the crystallization of PLLA, and the double‐melting peaks of PLLA/0.5% BD were assigned to melting–recrystallization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42402.     

Effect of 1,3,5‐trialkyl‐benzenetricarboxylamide on the crystallization of poly(lactic acid)

A series of 1,3,5‐trialkyl‐benzenetricarboxylamides (BTA‐Rs) with different side‐chain lengths of n‐alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt‐crystallization with addition of the synthesized nucleating agents. Among these BTA‐Rs, BTA‐n‐butyl (BTA‐nBu) shows the most excellent nucleation ability for PLA. The influences of BTA‐nBu on the nonisothermal melt‐crystallization and cold‐crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA‐nBu to improve the crystallization of PLA. In the case of isothermal melt‐crystallization from melt, the addition of BTA‐nBu shortens the crystallization half‐time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA‐nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1328‐1336, 2013     

Thermal and viscoelastic properties of some commercial starch products

Three commercial starch products for polyolefins, marketed under the Mater‐Bi, Cornplast, and Bioefect trademarks, were subjected to an accelerated soil burial test. Their thermal and viscoelastic behaviors were studied by differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy. Degradation in soil leads to more significant changes both in the DSC thermogram and the mechanical relaxation spectrum of Mater‐Bi. The relaxation spectra of Cornplast and Bioefect, two products containing polyethylene, basically coincide with that of pure low density polyethylene. The α‐relaxation zone of these starch products is the most affected by the degradation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1242–1251, 2003     

Heterocyclic‐based epoxy‐terminated structural adhesive. II. Curing,adhesive strength,and thermal stability

We studied the curing behavior of heterocyclic‐based epoxy‐terminated resins using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylicdianhydride, and the commercial hardener of Ciba‐Geigy's two‐pack Araldite as curing agents. The adhesive strength of the adhesives was measured by various ASTM methods such as lap‐shear, peel, and cohesive tests on metal–metal, wood–wood, and wood–metal interfaces. All of these results were compared with those of an epoxy resin prepared from bisphenol‐A and epichlorohydrin resin with an epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3520–3526, 2002     

Improvement of the thermal stability of polyhydroxybutyrates by grafting with maleic anhydride by different methods: Differential scanning calorimetry,thermogravimetric analysis,and gel permeation chromatography

The crystallization and thermal degradation behaviors of polyhydroxybutyrate (PHB) grafted with maleic anhydride (MA) by different techniques were analyzed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The results of DSC, TGA, and GPC analyses indicated that the grafting method could affect the crystallization rate, crystallinity, and thermal stability of PHB because of changes in the molecular weight of PHB and the amount of MA grafted during the reaction. The reduction of the molecular weight of PHB that reacted during the processing followed this order of methods: melt grafting > solvent grafting > mechanical grafting. However, the grafting ratio of MA followed this order of methods: melt grafting > mechanical grafting > solvent grafting. All three grafting methods significantly improved the thermal stability, therefore increasing the crystallization rate and melting temperature of the as‐received PHB. A grafting ratio of MA as low as 0.07 wt % could result in a significant improvement in the heat resistance of PHB. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of magnesium sulfate whiskers on the structure and properties of melt‐stretching polypropylene microporous membranes

The influence of magnesium sulfate (MgSO₄) whiskers on the structure and properties of polypropylene cast films and stretched microporous membranes was investigated. We found that for the cast films, MgSO₄ showed some nucleation effects, and the introduction of MgSO₄ led to the decrease of the orientation degree along the machine direction (MD), whereas that along the transverse direction (TD) was improved; this indicated that MgSO₄ whiskers were mainly arranged along the TD. The introduction of MgSO₄ up to 10 wt % did not induce apparent changes in the pore structure and air permeability properties of the stretched microporous membranes but improved the electrolyte absorption ability. The most pronounced change for the stretched microporous membranes was the strength along the TD. It was increased by 110% when the MgSO₄ content was 2 wt %. During the fabrication of microporous membranes, only stretching along the MD was carried out to initiate pore formation; this resulted in a lower strength along the TD. This study gave us a method for improving the mechanical properties of stretched microporous membranes along the TD. The obtained microporous membranes with better electrolyte absorption and higher mechanical strength along the TD could be used in lithium‐ion batteries as separators. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43884.