Crystallization Of Amorphous Poly Research Articles

Crystallization of poly(L-lactic acid)/poly(D-lactic acid) blend induced by organic solvents

Crystallization of amorphous poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) blend has been investigated by immersion in various organic solvents, acetone, ethyl acetate, tetrahydrofuran (THF), toluene, o-xylene, o-dichlorobenzene, and benzene. Crystalline structure of the blend samples was studied by wide angle X-ray diffraction pattern and differential scanning calorimetry measurement. Immersion of the amorphous blend sample in the solvents, except o-xylene, induced the crystallization of both the homo- and stereocomplex (SC) crystals of PLA. Among the used solvents, benzene, THF, and acetone were effective to form the SC crystal. Increase in the conducting temperature accelerated the formation of the SC crystal. The crystallization of the amorphous PLLA/PDLA blend has been also investigated by exposing to vapor of some organic solvents, acetone, THF, benzene, and chloroform. The vapor of chloroform induced crystallization of the SC crystal effectively. High compatibility, close solubility parameter, of PLA and the solvent should be essential to induce effective formation of the SC crystal by the vapor of the solvents.

Crystallization of Amorphous Poly(Lactic Acid) Induced by Vapor of Acetone to Form High Crystallinity and Transparency Specimen

Crystallization of amorphous poly(lactic acid) (PLA) was investigated by exposing to vapor of acetone. The vapor of acetone induced crystallization of the amorphous PLA effectively. It took about 24 min to complete the crystallization of a 1 cm × 2 cm × 0.55 mm specimen at 25℃. The crystallization rate increased with increasing of conducting temperature. The crystallization method yielded high crystallinity about 40%, which was almost equal to that attained by annealing or immersion methods conducted as references. The specimens crystallized by the vapor showed higher transparency than those prepared by the reference methods. The crystallization was induced by diffusion of acetone into the amorphous phase of PLA, and polarized optical photomicrographs cleared that the diffusion obeyed Fick type diffusion.

Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film

AbstractThe effects of 60 organic solvent on poly(lactic acid) (PLA) were systematically investigated using the Hansen solubility parameter (HSP). The hydrogen bonding solubility parameter accurately reflects the solubility of PLA films using HSP but it depends on hydrogen bonding, as well as dispersion and polar parameters. The PLA films immersed in organic solvent became cloudy and showed no changes in chemical structure. However, solvent‐induced crystallization of the PLA films was observed. Crystalline structures do not dependent on the organic solvent but on the degree of swelling. The organic solvent‐induced crystallization formed a crystallized mixture of a‐ and β‐forms. The density of the crystalline PLA films was lower than that of amorphous PLA films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Crystallization of amorphous poly(lactic acid) induced by organic solvents

AbstractCrystallization of amorphous poly(lactic acid) (PLA) was investigated in various organic solvents, such as acetone, ethylacetate, diethylether, tetrahydrofurane, methanol, hexane, toluene, xylene, and o‐dichlorobenene. Most of the solvents, except hexane, induced crystallization of amorphous PLA. Acetone was the most effective solvent to accelerate the crystallization among the solvents used. The crystallization was induced by permeation of acetone into the amorphous phase of PLA, and the permeation obeyed Fick type diffusion. The crystallization rate increased with increasing of conducting temperature. Crystallized PLA formed α crystalline structure. The permeated acetone in the crystallized PLA gradually evaporated as time passes, and the elimination of acetone affected thermal and mechanical properties of the crystallized PLA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Evolution of density fluctuation to a lamellar crystal in a poly(trimethylene terephthalate) film revealed by the resonance light scattering technique

The dynamic process of cold crystallization of amorphous poly(trimethylene terephthalate) (PTT) was investigated with resonance light scattering (RLS). By using an enhanced scattering peak at 329 nm, which was in close proximity to the absorption band of PTT film, density fluctuation due to gradual transition from amorphous to crystalline with increasing temperature was monitored. Accordingly, molecular chains movement and structure evolution in PTT during cold crystallization, in particular, the information about each phase of crystallization, including induction, nucleation, nucleus growth and secondary crystallization, were thoroughly revealed. The experimental results indicated that the kinetics parameters measured by the RLS method were in good agreement with those obtained by differential scanning calorimetry (DSC) and fluorescence spectroscopy. In addition, the RLS method can tell more details of the movement and variation in fine structures than DSC and fluorescence techniques as a result of its significantly enhanced scattering signals, like the orientation fluctuations of rigid segments in the course of glass transition and crystallization induction.

Oriented and thermal crystallization of poly(ethylene terephthalate)

The oriented and thermal crystallization of amorphous poly(ethylene terephthalate) (PET) films was investigated in terms of the morphological aspects. When the amorphous PET films were stretched up to the desired draw ratios in a hot water bath at 62, 72, and 80 °C, the birefringence of the specimens increased with increasing draw ratio (λ). This tendency becomes most significant when the specimen was drawn in the bath at 62 °C. The storage modulus of the specimen drawn at 62 °C was higher than those of the specimens drawn at 72 and 80 °C. The exothermic peak in the DSC curves was observed clearly for the specimen drawn up to λ=4 in the hot water bath at 80 °C, while the peak did not appear for the specimen drawn up to λ=4 at 62 °C. Under an Hv polarization condition, light scattering patterns from the specimens drawn in the hot water bath showed four lobes at small azimuthal angles and four sharp streaks at large azimuthal angles. Such a profile was independent of the drawing temperatures from 62 to 80 °C. Based on the observed Hv patterns, a model was proposed by assuming the existence of a row-nucleated sheaf-like structure whose rows were preferentially oriented at a particular angle with respect to the stretching direction. The patterns calculated by using the above model were rather close to the patterns observed. This agreement implies that row-nucleated sheaf-like texture arises with lamellar overgrowth.

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) has been investigated. Heat flow responses were measured after annealing the amorphous samples obtained by quenching the melt into an ice-water bath close to, but below, the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process, which was estimated by a Williams-Watt expression, is similar in magnitude to that obtained for the cold crystallization for the aged samples. The quenched glass is a metastable glass. The conformation of molecular chains rearranges with physical aging which results in the formation of a denser packing in the amorphous phase. The dense amorphous phase may form an initial nucleus for crystallization. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant n is about 2. An Arrhenius expression was used to evaluate the activation energy of relaxation upon physical aging and the activation energy of transportation upon isothermal crystallization. The activation energy of relaxation is similar in magnitude to that of crystallization for aged samples. Results obtained are interpreted as kinetic effects associated with the glass formation process.

Change of distribution of free volume holes during crystallization of poly(ethylene terephthalate) revealed by positron annihilation lifetime spectroscopy

Change of free volume holes during crystallization of amorphous poly(ethylene terephthalate) at 130 °C was investigated by positron annihilation lifetime technique together with the measurements of specific density and wide angle x-ray scattering (WAXS). The o-Ps intensity, I3, decreased by 24.6% with the crystallization. This value agreed with the degree of crystallinity determined by the specific density and WAXS, which indicates that o-Ps annihilation takes place in the amorphous part. The average o-Ps lifetime increased slightly by the crystallization. Detailed analysis of the o-Ps lifetime by a continuous distribution model showed that the small size component of the distribution disappeared due to the crystallization. The result is favorably compared with the recently proposed picture of crystallization which deals with the conformational change of ethylene group.

CO 2-induced crystallization of poly(ethylene terephthalate)

Crystallization of amorphous poly(ethylene terephthalate) (PET) induced by sorbed CO 2 has been investigated at several temperatures and pressures up to 50 atm and compared with thermal crystallization. From the results of X-ray diffraction, infra-red spectroscopy and density measurements, it was shown that, by sorption of CO 2, crystallization takes place even at temperatures well below the T g measured in air, and the crystallization rate at temperatures above T g was greatly increased. This means the sorbed CO 2 acts as an intensive plasticizer for PET. From the effects of the sorbed CO 2 on the crystalliation rate, the plasticizing ability of CO 2 was estimated in terms of temperature, which is equivalent to enhancement of the mobility of the polymer segments. The density of the sample crystallized by sorbed CO 2 was smaller than that of a thermally crystallized sample having the same crystallinity determined by infra-red measurements. It is assumed that the sample crystallized by sorbed CO 2 contains more microvoids than that crystallized by thermal annealing.

Dependence of Molecular Orientation, Crystallinity, and Thermal Dimensional Stability of Poly(ethylene Terephthalate) on Elongation Temperature

Orientation of amorphous chain segments and oriented crystallization of amorphous poly(ethylene terephthalate) (PET) were affected by the elongation temperature. That is, the crystallinity and birefringence of the specimen stretched in 65°C water below the glass transition temperature Tg increased, when the elongation ratio was beyond λ = 2.25, while crystallinity and birefringence in 80°C were constant values equivalent to those in the film prior to stretching. The Young's modulus and thermal dimensional stability were also dependent on the crystallinity of the drawn PET film. The experimental result for the thermal dimensional stability was estimated using the statistical theory of rubber elasticity. The observed result was somewhat in agreement with the calculated result.

The melting behaviour of heat crystallized poly(ethylene terephthalate)

The crystallization of amorphous poly(ethylene terephthalate) has been investigated using differential scanning calorimetry ( dsc) and x-ray techniques. In particular, the occurrence of double melting peaks in the dsc thermograms has been examined. It is shown that the high temperature peak is due to a recrystallization and melting process taking place while the material is being scanned. Hence the dsc peaks are not a direct reflection of the state of the material at room temperature prior to the scan. As a result, some proposals in the literature for the structural changes accompanying the crystallization of poly(ethylene terephthalate) must be re-examined. Some interesting differences between the effect of temperature and time on the crystallization of poly(ethylene terephthalate) are also reported.