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Online Raman spectra, obtained at different points along the spin line during pilot‐scale nonisothermal melt spinning of high density polyethylene (HDPE) fibers, are presented for the first time. The fraction of the crystalline phase corresponding to each spectrum was determined from the normalized integrated intensity of the 1418 cm?1 Raman band. It is well established that this band represents the orthorhombic crystalline phase in polyethylene. The estimates of percent crystallinity obtained from decomposition of the Raman spectrum were compared with the percent crystallinity from differential scanning calorimetry (DSC) measurements. It is concluded that online Raman spectroscopy can be successfully used to monitor the development of crystallinity in HDPE fibers as a function of distance from the spinneret. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 545–549, 2003 相似文献
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Archana Paradkar Vikas Kumar S.V. Kamat A.K. Gogia B.P. Kashyap 《Materials Science and Engineering: A》2008,486(1-2):273-282
The effect of grain size and composition on the fracture toughness of Ti–Al–Nb alloys in β solution-treated condition was investigated. The fracture toughness of the alloys was found to increase with an increase in grain size initially, reach a maximum and subsequently decrease with further increase in grain size. This trend was attributed primarily to the effect of grain size on the enhancement of fracture toughness due to stress-induced martensitic transformation (SIMT) at the crack tip, which in turn can be related to the effect of grain size on trigger stress for SIMT. Alloys containing higher Al and Nb showed a higher toughness for the same grain size, which was also explained in terms of effect of composition on the trigger stress. 相似文献
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A Fourier transformed near-infrared (FT-NIR) method for rapid determination of cholesterol in dairy products was demonstrated. FT-NIR spectrum of pure cholesterol was characterized and the region between 3550 and 3650 cm−1 was found to be the most significant in cholesterol content determination. The FT-NIR method was found to accurately predict the cholesterol content in a variety of dairy products with r 2 value greater than 0.98 and SEP estimates of less than 1.70. The FT-NIR procedure with suitable multivariate statistical model was further validated by recovery studies and compared with a conventional method. Results indicate that FT-NIR has the potential for rapid estimation of cholesterol. 相似文献
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Crosslinked elastic fibers, made from a low density (0.875 g/cc) ethylene‐octene copolymer, were studied after constrained at 300% elongation and annealed at different temperatures (40–80°C) to simulate conditions encountered in yarn and textile processing. It is surprisingly found that the transition from pseudo hexagonal to orthorhombic structure is much faster under simultaneously constraining and annealing than that without strain. Almost a neat orthorhombic structure can be produced when the fiber is annealed at 60°C. Annealing above 60°C leads to mixed orthorhombic and pseudo‐hexagonal structures. The average melting point increases with an increase in the fraction of orthorhombic phase. It is also surprisingly noted that the simultaneously constraining and annealing of the fiber can produce highly oriented crystals, even annealed at 80°C (above the average melting point of 65°C). The unique effect of annealing under large strain can be attributed to the crosslinking of the fiber, which makes it possible for the fiber to have strong chain orientation (even in molten state) under large strain. The strong chain orientation in melt leads to a faster structural transition from pseudo hexagonal to more stable orthorhombic structure. The strong chain orientation is also very likely the reason why highly oriented crystal and amorphous phases are formed, including the case where the fiber is annealed above melting point. These findings could be leveraged for improving thermal and mechanical properties of the fabrics made with such fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3565–3573, 2013 相似文献
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Wenting Bao Shaoyun Guo Anant Paradkar Adrian Kelly Elaine Brown 《Polymer-Plastics Technology and Engineering》2013,52(9):927-934
In this work, effect of ultrasound on molecular structure development of Polylactide (PLA) was studied. It was found that the intrinsic viscosity of PLA decreased with increasing treating time, temperature and ultrasound time. Different from traditional thermal degradation of PLA, the degradation of PLA under ultrasound treatment showed that chain scission and chain combination of PLA competed with each other in the degradation process, which could be divided into two steps. The mechanism of ultrasound degradation of PLA was proposed. Furthermore, Thermal properties were characterized by DSC to show heat and ultrasound effects on molecular structure development of PLA. 相似文献
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Tirtha Chatterjee Rajen Patel John Garnett IV Rajesh Paradkar Shouren Ge Lizhi Liu Kenneth T. Forziati Jr. Nik Shah 《Polymer》2014
In this study, blown films were produced from three different high density polyethylene (HDPE) resins. Further, these blown films were oriented along the machine direction using either traditional machine direction orientation (MDO) or compression roll drawing (CRD MDO) technology. The stretched/oriented films were compared for their water vapor transport and optical properties as a function of the extent of orientation (i.e., draw ratio, DR). In addition to that, these properties were directly compared between the oriented and unoriented (blown) films of the same thickness. The present study revealed that the water vapor transmission rate (WVTR) as a function of draw ratio (DR) went through a maxima. Detailed morphological characterization showed that initially, at low DR, stretching resulted in lamellar organization (along the MD). Consequently, the tortuosity in the diffusion path decreased and the overall WVTR increased. However, beyond a critical DR, lamellar crystals transformed to microfibrillar crystals. During this process the amorphous content of the HDPE chains decreased and geometric redistribution of the amorphous phase occurred along with some orientation. As a combination of all these effects, the WVTR was found to decrease beyond the critical DR. Unlike transport properties, optical properties monotonically improved as a function of DR. Further, for both, the barrier and optical properties, the absolute values were found to be a strong function of the resin physical properties. Finally, compression roll drawing technology (CRD MDO) utilizes a patented process that simultaneously applies a stretching and compressive force to orient polymer chains homogeneously without any tiger striping (uneven deformation). Consequently, CRD MDO stretched samples showed a lower surface roughness compared to their traditional MDO stretched counterpart. Therefore, for the same resin and DR, CRD MDO stretched samples displayed markedly better barrier properties and optics, especially lower total haze and higher gloss. 相似文献
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Stability indicating HPTLC determination of linezolid as bulk drug and in pharmaceutical dosage form
Agrawal H Mahadik KR Paradkar AR Kaul N 《Drug development and industrial pharmacy》2003,29(10):1119-1126
A simple, selective, precise, and stability-indicating high-performance thin layer chromatographic method of analysis of Linezolid both as a bulk drug and in formulations was developed and validated in pharmaceutical dosage form. The method employed TLC aluminium plates precoated with silica gel 60F-254 as the stationary phase. The solvent system consisted of toluene-acetone (5:5, v/v). This system was found to give compact spots for Linezolid (Rf value of 0.29 ± 0.01). Linezolid was subjected to acidic, alkali hydrolysis, oxidation, and photodegradation. The degraded products also were well separated from the pure drug. Densitometric analysis of Linezolid was conducted in the absorbance mode at 254 nm. The linear regression data for the calibration plots showed good linear relationship with r2 = 0.997 ± 0.001 in the concentration range of 300-800 ng/spot. The mean value of correlation coefficient, slope, and intercept were 0.998 ± 0.003, 0.15 ± 0.009, and 19.52 ± 1.66 respectively. The method was validated for precision, accuracy, ruggedness, and recovery. The limits of detection and quantification were 20 ng/spot and 50 ng/spot, respectively. The drug undergoes degradation under acidic and basic conditions, oxidation and photo degradation. All the peaks of degraded product were resolved from the standard drug with significantly different Rf values. This indicates that the drug is susceptible to acid-base hydrolysis, oxidation, and photo degradation. Statistical analysis proves that the method is reproducible and selective for the estimation of the said drug. Because the method could effectively separate the drug from its degradation products, it can be used as a stability indicating one. 相似文献
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Paradkar AR Pawar AP Chordiya JK Patil VB Ketkar AR 《Drug development and industrial pharmacy》2002,28(10):1213-1220
Celecoxib exhibits poor flow properties and compressibility. Spherical crystallization of celecoxib was carried out using the solvent change method. An acetone:dichloromethane (DCM):water system was used where DCM acted as a bridging liquid and acetone and water as good and bad solvent, respectively. Hydroxypropylmethylcellulose (HPMC) was used to impart strength and sphericity to the agglomerates. The effect of amount of bridging liquid and speed of agitation was studied using 32 factorial design. Primary properties of the agglomerates were evaluated by infrared spectroscopy, powder X-ray diffraction, and differential scanning calorimetry. The effect of variables on micromeritic, mechanical, compressional, and dissolution behavior was evaluated by response surface methodology. Particle size, bulk density, mean yield pressure (MYP), and drug release were found to be significantly affected by either of the two variables. Interaction of variables significantly affected the MYP. 相似文献