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Crystallinity Measurements (crystallinity + measurement)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Crystallization and chemi-crystallization of recycled photodegraded polyethylenes

POLYMER ENGINEERING & SCIENCE, Issue 4 2005
I.H. Craig
Test bars (3 mm thick) made from a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were injection-molded from virgin polymer and from blends containing recycled photodegraded polymer of the same kind. The molded bars were then subjected to ultraviolet (UV) exposure. Crystallinity measurements were made at different depths from the exposed surface using differential scanning calorimetry. The effects caused by processing and photodegradation were separated by comparing thermograms obtained in the initial DSC run and in a reheating run, respectively. Chemi-crystallization was produced by UV exposure. The results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission accounts for the observed chemi-crystallization, whereas the molecular defects inhibit crystallization and eventually limit chemi-crystallization. After remelting, crystallization of the photodegraded materials is influenced both by the molecular mass distribution and by the defect content of the material. The changes in crystallization behavior caused by photodegradation are different for the three polyethylenes. The results obtained using blends that included photodegraded recyclate were consistent with this material acting as a pro-degradent. The recyclability of the materials is discussed. POLYM. ENG. SCI., 45:588,595, 2005. © 2005 Society of Plastics Engineers [source]

Evaluation of three methods for the measurement of crystallinity of pet resins, preforms, and bottles

POLYMER ENGINEERING & SCIENCE, Issue 11 2000
Z. Bashir
The control of crystallization is important at all processing stages of the PET bottle industry, from the manufacture of bottle resins to the fabrication of preforms and bottles. In this work, we sought to evaluate critically three methods of crystallinity measurement. We have used density, Differential Scanning Calorimetry (DSC), and Modulated Differential Scanning Calorimetry (MDSC) to study the crystallinity of PET chips, preforms, and bottles. The accuracy, precision, and general validity of each technique and the problems of interpretation are discussed. [source]

Raman spectroscopy for spinline crystallinity measurements.

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008

Abstract The original Doufas,McHugh two-phase microstructural/constitutive model for stress-induced crystallization is expanded to polyolefin systems and validated for its predictive capability of online Raman crystallinity and spinline tension data for two Dow homopolymer polypropylene resins. The material parameters,inputs to the model,are obtained from laboratory-scale material characterization data, that is, oscillatory dynamic shear, rheotens (melt extensional rheology), and differential scanning calorimetry data. The same set of two stress-induced crystallization material/molecular parameters are capable of predicting the crystallinity profiles along the spinline and fiber tension very well overall for a variety of industrial fabrication conditions. The model is capable of predicting the freeze point, which is shown, for the first time, to correlate very well with the measured stick point (i.e., the point in the spinline at which the fiber bundle converts from a solid-like state to a liquid-like state and sticks to a solid object such as a glass rod). The model quantitatively captures the effects of the take-up speed, throughput, and melt flow rate on the crystallization rate of polypropylene due to stress-induced crystallization effects. This validated modeling approach has been used to guide fiber spinning for rapid product development. The original Doufas,McHugh stress-induced crystallization model is shown to be numerically robust for the simulation of steady polypropylene melt spinning over a wide range of processing conditions without issues of discontinuities due to the onset of the two-phase constitutive formulation downstream of the die face, at which crystallization more realistically begins. Because of the capturing of the physics of polypropylene fiber spinning and the very good model predictive power, the approximations of the original Doufas,McHugh model are asserted to be reasonable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Raman spectroscopy for spinline crystallinity measurements.

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008

Abstract Online Raman spectra, obtained at different points along the spinline during the melt spinning of polypropylene homopolymer (hPP) fibers, are presented. The percentage crystallinity corresponding to each spectrum was determined from the normalized intensity of the 809-cm,1 Raman band. A calibration curve for propylene crystallinity was established offline with compression-molded films and fibers spun under different processing conditions. Several hPPs and propylene,ethylene copolymers (with 5,15% ethylene) were used to cover a wide calibration range for propylene crystallinity (9.5,60.9%) with an R2 value of 0.989. This calibration curve was subsequently used to predict the polypropylene crystallinity in the spinline as a function of distance from the spinneret. Under identical conditions of quench and throughput, at a fixed point along the spinline, the overall crystallinity developed in the fiber was found to increase with an increase in the spinning speed. As the spinning speed increased, the point of the onset of crystallization moved closer to the spinneret. The rise in crystallinity was more gradual, at 750 m/min as opposed to 1500 m/min. Increasing the throughput at constant spinning speed was found to decrease the rate of crystallization because of a decrease in the spinline stress. At a fixed distance from the spinneret under identical conditions of quench and spinning speed, fibers spun at a higher throughput showed less overall crystallinity. The onset and rate of crystallization was found to be faster in the lower melt index H502-25RG resin as compared to the 5D49 resin under the spinning conditions explored. The experimental data presented here were used to validate fundamental fiber-spinning models (see part II of this series of articles). The validated models and experimental observations can be used to guide the fiber spinning of isotactic polypropylene for rapid product development. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]