Long-Term Hydrothermal Aging Behavior and Life-Time Prediction of Polyamide 6

The long-term hydrothermal aging behavior of polyamide 6 (PA6), with and without stabilizers at 100% relative humidity/90ºC was studied. It was found that the first stage of aging was the Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in slight change of reduced viscosity and chemical structure of the sample of PA6. The second stage of aging was the initiation process of hydrolytic degradation of PA6, which resulted in a decrease of reduced viscosity and increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased monotonically, and end groups increased continuously, resulting from the hydrolysis of amido links and molecular degradation of PA6. The presence of four types of stabilizers effectively weakened the oxidation reaction and resulting molecular degradation of PA6 during aging. The lifetime of PA6 in a hydrothermal environment was predicted through a method based on the Arrhenius model by considering both temperature and humidity as environmental factors, and, furthermore, was predicted through the time–temperature superposition method.     

Long-Term Hydrothermal Aging Behavior and Aging Mechanism of Glass Fibre Reinforced Polyamide 6 Composites

Long-term hydrothermal aging of polyamide 6 (PA6)/glass fibre (GF) composites was conducted and the effects of the GF on variations of structure and properties of the composites with aging time were investigated. It was found that the first stage of aging was a Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in a slight change of reduced viscosity and chemical structure of the PA6. The water diffusing process was slowed down slightly by addition of the GF. The second stage of aging was the initiation process of hydrolytic degradation of PA6, resulting in a rapid decrease of reduced viscosity and an increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased and the end groups increased slowly. The degradation rate and carbonyl index of PA6 increased with increasing GF content, and the increasing rate of end groups concentration of the composites was higher than that of pure PA6 during the aging process, indicating addition of GF accelerated the hydrolysis degradation and oxidative aging of PA6. In mechanical property tests, compared with unaged samples of the composites which underwent matrix rupture around the matrix-fiber interfacial layer, for aged samples several smooth fibres without coatings were pulled out and the interfacial debonding was the main failure mode, causing severe deterioration in mechanical properties. The hydrolytic degradation activation energy (E_a) was calculated through a method based on the Arrhenius model by considering both temperature and humidity as environment factors; with increasing GF content, E_a decreased, indicating that the addition of GF made PA6 easier to degrade.     

Thermoplastic Elastomer by Terpolymer Reactive Blending of Polyamide-6, Ethylene-1-Butene Rubber and Ethylene Ionomer

Reactive blending of polyamide-6 (PA6), maleic anhydride grafted ethylene-1-butene copolymer (EB-g-MAH) and ethylene-methacrylic acid ionomer partially neutralized by sodium ions (EMAA-Na) was performed to obtain a heat and oil resistant thermoplastic elastomer (TPE). The strain at break of the PA6/EB-g-MAH (40/60) was clearly higher than that of the PA6/EB (40/60). Addition of 2 wt% of EMAA-Na to the PA6/EB-g-MAH (38/60) blend induced an increase of the tensile modulus. TEM images confirmed that the PA6 was the matrix phase in the PA6/EB-g-MAH (40/60) blend, while the EB rubber phase was the matrix in the PA6/EB (40/60) blend. It was considered that the reaction between amino end groups of PA6 and maleic anhydride in EB-g-MAH induced the significant change of blend morphology. The PA6/EB-g-MAH/EMAA-Na blend showed similar morphology with the PA6/EB-g-MAH blend, and the EMAA-Na was expected to be located within the EB-g-MAH phase. It was found that ionic aggregates were formed in the EB-g-MAH phase by neutralization of the hydrated EB-g-MAH with sodium ions. The change of the mechanical properties by addition of EMAA-Na was due to the ionic aggregate formation which acted as physical crosslinks in the EB-g-MAH phase.     

Phase Morphology and Mechanical Properties of Polyamide-6/Polyolefin Elastomer-g-Maleic Anhydride Blends

The effects of addition of varying amounts of polyolefin elastomers (POE) (with and/or without grafted maleic anhydride) on the morphology and mechanical properties of polyamide-6 (PA6)-based blends were studied. Scanning electron microscopy (SEM) was employed to obtain some detailed quantitative analyses of the morphology of the fracture behavior for the blends containing 80 wt% PA6 and 20 wt% total elastomer. Impact strength, tensile strength, and flexural strength were also measured for these blends. The results showed that POE and PA6 were an incompatible system, but the POE-g-MAH was compatible and had a toughening effect on PA6. PA6-g-POE was formed through the reaction between POE-g-MAH and PA6 during the melt extrusion process, which reduced the size of the dispersed phase and improved the impact and tensile strength of the blends. The impact strength was improved by nine times compared with the pure PA6 or the binary blend PA6/POE when the blend ratio of the ternary blend PA6/POE/POE-g-MAH was 80/16/4.     

Insights into ultrasound-promoted degradation of naphthenic acid compounds in oil sands process affected water. Part I: Accelerated H-abstraction and decarboxylation of aromatic and alicyclic compounds

Propelled by enormous increase in demand for fuel sources, Canadian oil sands are becoming increasingly important as a fuel source due to their abundance and upgrading capability. However, extraction of bitumen, a high acid crude (HAC) oil, requires 2–3 units of water per unit of oil resulting in naphthenic acid (NA)-rich oil sands process affected water (OSPW) collected in effluent ponds. This study illustrates the role of sonochemistry in the accelerated degradation through H-abstraction and subsequent decarboxylation of aromatic and alicyclic naphthenic acid model compounds. Benzoic acid and 3-methylcyclohexane carboxylic acid were selected as model NA compounds to investigate the mechanism of hydroxyl radical (OH^•) initiated carboxylic acid degradation in 378 KHz sonochemical reactor. Established FTIR methods with low resolution LCMS spectroscopy confirmation were applied to determine the extent of carboxylic acid degradation and identify the formation of products. FTIR monitoring showed a non-linear degradation of carboxylic acids with formation of many intermediates highlighting the shift from cyclic carboxylic acids to cyclic alcohols during BA degradation. Subsequent decrease in carboxylic acid groups signifies scission of cyclic structures before complete mineralization. This is confirmed with the LCMS identification of products such as: 3-hydroxybenzoic acid and phenol. This study postulated new breakdown pathways for degradation of benzoic acid with complete mineralization at a sonochemical reaction time (SRT) of 4 h. A radical quenching process was also inferred through the formation of conglomerates during sonochemical degradation of BA. Extension of the study to 3-methylcyclohexane carboxylic acid (3mCHA) shows similar non-linearity with an increase in carboxylic acid groups indicating H-abstraction followed by ring-opened compounds. However, due to the complex nature of 3mCHA’s ring-opened compounds, complete mineralization is not achieved. The putative role of sonochemistry is a promising and sustainable degradation method for mitigating NAs in OSPW, but sonication periods need to be considered carefully to ensure adequate mineralization of their constituents and combinatorial methods with other advanced oxidation methods may be needed to enhance industrial application.In Part II, an in silico screening approach using first principles is reported to identify the breakdown of the organic compounds and determine molecular rates of reaction to confirm the mechanistic origins of the compounds formed.     

Oriented Crystallization of Polyethylene in Compatible Blends with Polyamide 11

The oriented crystallization of polyethylene (PE) in uniaxially oriented films of compatible blends with polyamide 11 (PA11) was studied. The PE sample used was a random copolymer of PE with methacrylic acid (MAA), poly(ethylene-co-methacrylic acid) (PEMAA), with 4wt% MAA units. Oriented films of PA11/PEMAA blends were prepared by uniaxial drawing of the melt-mixed blends. The drawn films with fixed lengths were heat-treated at 120°C for 3min to melt the PE component, followed by cooling the sample to room temperature at a rate of 2°C/min to recrystallize the PE (designated slowly crystallized sample). The PE component crystallized in elongated domains of PEMAA with diameters of 0.5–2 μ m and lengths of 5–10 μ m for the PA11/PEMAA = 80/20 blend, resulting in the oriented crystallization of PE crystals. The crystal b-axis of PE was highly oriented in the direction perpendicular to drawing, while the crystal a-axis was weakly oriented in the drawing direction in the slowly crystallized sample of the PA11/PEMAA = 80/20 blend. The a-axis orientation of PE crystals in the PA11/PEMAA = 80/20 blend contributes to the improvement of mechanical properties in the direction perpendicular to drawing.     

Chemical Modification of Polyamide 6 by Chain Extension with Terephthaloyl-biscaprolactam

The chain extension behaviors of terephthaloyl-biscaprolactam (TBC), 2,2′-bis(2-oxazoline)(BOZ), 2,2′-(1,3-phenylene)bis(2-oxazoline)(MPBO), TBC/BOZ, and TBC/MPBO, were studied to evaluate the coupling effect on polyamide 6 (PA6) in a Haake Rheocord mixer and an extruder. For the chain extension of PA6 with TBC only, the coupling results showed that there was an optimal dosage of chain extender, shortage of which caused incomplete chain extensions and excess of which led to more blocking reactions. When the added amount of TBC chain extender in PA6 was 0.684 wt%, the intrinsic viscosity of the PA6 increased from 1.630 to 1.848 dl/g, and the concentration of the amine end groups in the chain-extended PA6 decreased from the initial 5.12 × 10^?5 to 1.96 × 10^?5 mol/g. However, for the chain extension of PA6 with TBC/BOZ and TBC/MPBO mixtures, the intrinsic viscosity of PA6 increased to 2.189 dl/g and 2.097 dl/g, respectively, while at the same time both the concentration of carboxyl end-groups and amine end-groups of chain-extended PA6 decreased. The effect of temperature on the time needed for the completion of the chain extension reaction was not obvious, and the time needed for the completion of the reaction was about 200 sec. The chain-extended PA6 dissociated at high temperature, and the degradation is suggested to proceed simultaneously from the onset of the chain extension reaction. Furthermore, the effects of chain extenders on the thermal properties of chain-extended PA6 were investigated. The thermal stability of chain-extended PA6 was slightly improved.     

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO₂- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO₂-COOH was used to enhance the compatibility between SiO₂ and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO₂-COOH composites with low content of EBS and SiO₂-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO₂-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO₂-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO₂-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO₂-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO₂-COOH was 0.2 wt%, the SiO₂-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (T_m), degree of crystallinity (X_c), and crystallization temperatures (T_c) of PA 6/EBS/SiO₂-COOH composites were lower than the pure PA 6.     

一种尼龙老化评价的新方法

作为一种广泛使用的工程塑料,尼龙的老化备受关注。当作为电力系统芯片的封装材料时,尼龙在自然环境下的老化有可能会导致封装失效,从而影响芯片使用的可靠性,严重时甚至导致芯片的失效,给电力行业带来巨大损失。常规的自然老化和人工加速老化评价周期非常漫长,不同因素对尼龙老化的影响机理十分复杂,且这种影响难以研究,使得评价尼龙的老化稳定性成为一大难题。采用自主开发的原位老化评价系统,对尼龙6（PA6）和尼龙66（PA66）的老化稳定性及湿度对老化的影响进行了研究。该系统可以实现光照/温度/湿度/氧气等环境因素的加载,通过高灵敏度地测定材料在综合环境因素作用下产生的气相降解产物来评价材料的老化稳定性,评价时间缩短到几小时。实验表明,PA6和PA66的气相降解产物以H₂O和CO₂为主,由于H₂O在气相中的浓度不稳定,因此以CO₂的产生量作为老化评价指标。通过对不同自然老化时间PA6和PA66的原位老化评价,并与其ATR-FTIR红外光谱图进行对照,证明了原位老化评价方法能够较好地反映尼龙的老化程度,自然老化时间越长,PA6和PA66的稳定性越低,CO₂的产生量越大。进一步,采用该方法研究了湿度对PA6和PA66老化反应的影响,证明增大湿度对尼龙老化存在促进作用,而且升高温度会进一步促进湿度对老化的促进作用。研究表明,原位老化评价方法是一种快速评价尼龙老化稳定性及环境因素影响的有力手段。     

Polyamide 6/modified Carbon Black Nanocomposites Prepared via In Situ Polymerization

Polyamide 6/modified carbon black (PA6/MCB) composites were prepared via in-situ ring opening polymerization of caprolactam in the presence of dispersed carboxyl group modified carbon black (MCB). The dispersion of MCB in the PA6 matrix, nonisothermal crystallization and melting behaviors, and volume resistivity of the composites were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and a resistivity meter, respectively. The results indicated that MCB dispersed well in the PA6 matrix. When the MCB content was 5 wt%, the MCB particles were of a nanoscale. The conductivity percolation threshold of the PA6/MCB composites was 8 wt% due to the good dispersion of MCB in the PA6 matrix. The addition of MCB elevated the cold crystallization temperature of PA6, reflecting the effectiveness of MCB as nucleating agents. However, the MCB decreased the crystallization enthalpy of PA6 during both heating and cooling processes.     

Effects of Blend Ratio on Rheology,Morphology, Mechanical and Oil-Resistant Properties in Chlorinated Polyethylene Rubber and Copolyamide Blends

The elastomeric chlorinated polyethylene (CPE) blended with a low melting point copolyamide (PA6/PA66/PA1010, PA) was prepared by a melt mixing technique. The mixing characteristics of the blends were analyzed from the rheographs. The influence of copolyamide (PA) content on the morphology, mechanical properties, crystallization and oil-resistance, and the addition of compatibilizers on the mechanical properties were also systematically investigated. Morphological examinations clearly revealed a two-phase system in which CPE/PA blends exhibit a cocontinuous morphology for 50/50 composition, and the continuous phase of PA turns into a disperse phase for 70/30, 80/20, and 90/10. There is a distinct interface between the two phases. The mechanical properties, crystallization, and oil-resistance have a strong dependence on the amount of PA. The blends with higher proportions of PA have superior mechanical properties; they are explained on the basis of the morphology of the blend and the cystallinity of PA. In addition, compatibilizers, including chlorinated polyethylene-graft-copolyamide (CPE-G-PA), chlorinated polyethylene-graft-maleic anhydride (CPE-G-MAH), ethylene-n-butyl acrylate-monoxide (EnBACO), and ethylene-n-butyl acrylate-monoxide-graft-maleic anhydride (EnBACO-g-MAH) were added into the blends. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on the basis of the total mass of the blend) of 20 wt% while the PA content is 30 wt%.     

Chain Extension of Polyamide 6 Using Bisoxazoline Coupling Agents

The chain extension behaviors of 2,2′-(1,3-phenylene)bis(2-oxazoline) (MPBO) and 2,2′-bis(2-oxazoline) (BOZ) were studied to evaluate the coupling effect on polyamide 6 (PA6) in a Haake Rheocord mixer and an extruder. The coupling results showed that there existed an optimal dosage of chain extender, lack of which caused deficiency of chain extension and excess of which led to more blocking reaction. The effect of chain extension with MPBO was shown to be inferior to BOZ. When the optimum amount of chain extenders was added in PA6, the intrinsic viscosity of the polyamide 6 increased from 1.632dl/g to 1.787dl/g(MPBO) and 2.031dl/g(BOZ), respectively. The reaction time decreased very fast with an increase in the temperature. The chain-extended products dissociated at high temperature; the degradation is suggested to proceed from the onset of the chain extension reaction, as do the coupling and blocking reactions. Furthermore, the effects of MPBO and BOZ on the thermal and mechanical properties of chain-extended PA6 were also investigated.     

铕掺杂纳米二氧化钛透明光触媒乳液的制备及光催化性能研究

本文采用常温络合—控制水解法,以TiCl_4,有机羧酸,氨水,硝酸铕,D-山梨醇等为主要实验药品,制备了Eu掺杂纳米TiO_2光触媒乳液。以酸性红3R染料为待降解物,分别考察了不同条件下制备的TiO_2光触媒乳液在太阳光模拟器生成光照射下的光催化性能。此外,还考察了Eu掺杂纳米二氧化钛透明光触媒乳液对于不同浓度染料的光催化性能。通过酸性红3R染料的降解实验,研究了影响Eu掺杂纳米二氧化钛透明光触媒乳液光催化活性的因素。通过X射线衍射仪(XRD)、纳米激光粒度分析仪、紫外可见分光光度计(UV-Vis)等对样品进行表征。结果表明:样品的平均粒度为4.1 nm左右,晶型为锐钛矿,样品的吸收光谱可拓宽至可见光区。当Eu掺杂量为0.3%,pH值为6,回流时间是15 min时,制备的Eu掺杂纳米二氧化钛光触媒乳液的光催化性能最佳。该光触媒乳液经太阳光照射1 h之后,对浓度为25 mg/L的酸性红3R模型反应物的降解效率最高,达到97%以上。     

Grafting of bifunctional phosphonic and carboxylic acids on Phynox: Impact of induction heating

Phynox, a cobalt-chromium alloy, exhibits interesting mechanical properties making it a valuable material for a number of applications. However, its applications (especially biomedical ones) often require specific surface properties that can be imparted via suitable surface functionalizations. Based on Faraday's law of induction, induction heating is a widely used method to heat metallic substrates directly and contactless. The aim of this work is to compare the influence of induction heating and a conventional heating method on the functionalization of Phynox surfaces with bifunctional (6-phosphonohexanoic and 11-phosphoundecanoic acids) monolayers in order to create a platform for a large variety of post-grafting chemical reactions, e.g. with alcohols and amines, to modify and control the surface properties. In a first part, we assess the influence of the heating method on the interaction between the two terminal moieties of the 6-phosphonohexanoic and 11-phosphoundecanoic acids and the Phynox surface by studying the grafting of n-dodecylphosphonic acid and n-dodecanoic acid separately. The suitability of such bifunctional molecules for post-grafting chemical reactions has then been assessed by studying the post-grafting of a fluorinated alcohol by the Steglich esterification reaction between the carboxylic end of the grafted bifunctional molecules and the alcohol function of the post-grafted molecule. It has been shown that induction heating can lead to a much more selective adsorption of bifunctional molecules on the surface of Phynox, leaving a higher amount of free carboxylic acid functions to react during the second modification step.     

Mechanical Properties and Solid-State Structure of Photodegraded Polyoxymethylene and Effect of UV Stabilizers Modification

Ultraviolet (UV) light exposure can lead to photodegradation of polyoxymethylene (POM), resulting in a change of its physical and chemical properties. Benzophenone UV absorber (UV-9), benzotriazole light stabilizer (UV-327), and hindered amine light stabilizer (LD-622) were used as UV stabilizers to improve the photostabilization of POM. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were employed to characterize POM before and after aging. The change of its solid-state structure during the aging process was investigated. The surface molecular weight and the mechanical properties of modified POM after UV aging were also determined. The results showed that the degradation of amorphous molecules mainly occurred at the surface, while crystalline reorganization occurred in the interior part of the sample as a result of the UV irradiation, both of which led to an increase of the crystallinity. After UV irradiation for 1000 h, the elongation at break and notched Charpy impact strength were only 16.6% and 27.4% of the initial sample, respectively. However, 1%–3% of the additives could reduce the chain scission and restrain the recrystallization of POM after UV irradiation. Furthermore, mechanical properties were maintained to a certain degree by adding the UV stabilizers.     

Highly efficient and photostable solid-state dye lasers doped with PM567 with the addition of Tinuvin770

Solid-state dye samples based on polymethyl methacrylate (PMMA) doped with pyrromethene 567 (PM567) with the addition of Tinuvin770 were prepared. The effects of a light stabilizer and concentration on the laser performances of the solid state dye PM567, including spectra properties, slope efficiency and photostability were investigated. The highest slope efficiency 66.6% was obtained in the sample (PM567:Tinuvin770 = 2.0:0.5). The addition of Tinuvin770 resulted in a dramatic enhancement of photo-stability. Pumping the samples at a rate of 5 Hz with a pulse energy as high as 100 mJ (the pump energy density was 0.26 J/cm²), the output energy dropped to half of its initial value after approximate 149500 shots and the normalized photostability reached 97.2 GJ/mol in the sample (PM567:Tinuvin770 = 2:5). All results have shown that a high efficient and photostable solid-state dye laser with the addition of Tinuvin770 can be obtained.     

Morphology and Mechanical Properties of Polyamide 6/Acrylonitrile-Butadiene-Styrene Blends Containing Carbon Nanotubes

The blends of polyamide 6/acrylonitrile-butadiene-styrene (PA6/ABS), with added styrene-maleic acid copolymer (SMA) compatibilizer, were prepared through melt mixing in an internal mixer. The effects of blend composition and various process conditions, as well as the addition of multi-wall carbon nanotubes (MWCNTs) to the blends, on the morphology and mechanical properties were investigated. The morphology of the blends and blend nanocomposites were observed by scanning electron microscopy (SEM) and analyzed using an image analysis technique. The mechanical behavior of the blends was investigated by tensile and also impact testing. The results showed that the blend composition as well as the processing conditions significantly affected the morphology and mechanical properties of the PA6/ABS blends. Among the various compositions, the blend with 36?wt.% of ABS and 4?wt.% of SMA compatibilizer exhibited the best mechanical properties. Comparing various speeds and times of mixing, it was found that less mixing speed and longer mixing times resulted in the favorable morphology and conditions for achievement of the desired toughness for the polyamide 6. By adding different amounts of MWCNTs to the blends, it was found that the presence of the carbon nanotubes changed the viscosity of the resulting nanocomposite and thus changed the morphology. These nanocomposites also showed an improvement in mechanical properties. The MWCNTs acted as a second compatibilizer, resulting in a synergistic effect on the mechanical properties of the PA6/ABS blend nanocomposites.     

A Kinetic Study of the Thermal Degradation of Nylon-6/Attapulgite Nanocomposites

The thermal degradation behavior of nylon-6 (PA6) and PA6/attapulgite (ATP) nanocomposites was investigated by thermogravimetric analysis under non-isothermal conditions at various heating rates in nitrogen. It is suggested that during thermal degradation, ATP, as a protective barrier, can slow down degradation of polymer, but the catalytic effects of structural water and hydroxyl groups may accelerate the degradation of PA6. The combination of these two effects determined the final thermal stability of nanocomposites. The apparent activation energies of the samples were evaluated by the Kissinger and Flynn–Wall–Ozawa methods. The results showed that the presence of ATP adversely affected the thermal stability of PA6. The degradation activation energies of PA6/ATP nanocomposites decreased monotonically with increase in ATP content; thus, it is suggested that the ATP has a disadvantageous effect on the thermal stability of PA6.     

Simultaneously Enhancing Mechanical Properties and Melt Flow Ability of Polyamide 6 by Blending with a Hyperbranched Polymer

A series of polyamide 6/hyperbranched polymers (PA6/HBP) blends with different HBP contents was prepared by melt processing using a twin-screw extruder. The HBP was synthesized on the basis of pentaerythritol and dimethyl terephthalate according to a one-step method. The melt flow behavior, crystallization behavior, morphology, and mechanical properties of the PA6/HBP blends were investigated. The results showed that the melt flow index of the blends was greatly improved by a small amount of HBP. The yield strength, tensile modulus, Izod impact strength, and flexural strength of samples were simultaneously enhanced from 54.6 MPa, 0.5 GPa, 3.8 kJ/m², 56.9 MPa for pure PA6 to 61.1 MPa, 0.7 GPa, 5.3 kJ/m², 67.1 MPa for PA6 blends with 2.0 wt% HBP, respectively. The PA6/HBP blends showed the higher content of α-form crystal and a higher degree of crystallinity than those of pure PA6.     

Magnetic transition behavior of perovskite manganites Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 polycrystalline

A polycrystalline sample Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction(XRD) patterns, a superconducting quantum interference device(SQUID), and electron spin resonance(ESR). The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 undergoes three magnetic transitions: ferromagnetic transition at TC≈ 210 K, charge-ordering at TCO≈ 175 K, and antiferromagnetic transition at TN= 155 K. In addition, the activation energy Ea ≈ 52.78 me V can be extracted by curve fitting.