Polymer physics
Fatima Mustafayeva; Najaf Kakhramanov; Khayala Allahverdiyeva
Abstract
The article presents the results of studies of the influence of aluminum hydroxide concentration on the crystallization process regularities of nanocomposites based on compatibilized polypropylene random copolymer and aluminum hydroxide (PP-R/PPH-g-MAH/Al(OH)3). The isothermal crystallization kinetics ...
Read More
The article presents the results of studies of the influence of aluminum hydroxide concentration on the crystallization process regularities of nanocomposites based on compatibilized polypropylene random copolymer and aluminum hydroxide (PP-R/PPH-g-MAH/Al(OH)3). The isothermal crystallization kinetics of compatibilized polypropylene random copolymer composites containing 1, 3, 5, 10, 20, 30 and 50 wt. % of aluminum hydroxide was determined by the stepwise dilatometry method using the Kolmogorov-Avrami equation. The crystallization behaviors of composites were investigated on an IIRT-1 device converted into a dilatometer, in the process of stepwise cooling of samples under a load of 5.3 kg. In this study, maleic anhydride functionalized homopolypropylene (PPH-g-MAH) was employed as a compatibilizer to enhance the compatibility between the PP-R and Al(OH)3. Considering the dependence of specific volume and free specific volume on temperature, the first-order phase transition was established and the glass transition temperature values of the composites were determined. The mechanism of formation and development of crystallization centers in the region of the first-order phase transition was investigated. The obtained values of “n” prove that the mechanism or nature of the growth of crystallization centers changes into three-dimensional spherulitic - two-dimensional disc-shaped - one-dimensional rod-shaped with an increase in the amount of aluminum hydroxide in composite. The study of the temperature dependence of the specific volume for the studied samples showed that the first order phase transition occurs at a temperature of 125°C. It was determined that the second order phase transition temperature (the glass transition temperature determined by the dilatometric method) increases with the increase in the amount of filler.
Structure and property relationship
Buncha Suksut; Pathamanat Poonkasem; Sirirat Prasittinawa; Patcharapon Somdee
Abstract
Composites of polypropylene (PP) and calcium lactate (CL) with a constant weight percentage of 60% and 40%, respectively, were compounded with 3, 5 and 7 phr of epoxidized soybean oil (ESO) plasticizer using an internal mixer. The testing samples were prepared using an injection molding technique. The ...
Read More
Composites of polypropylene (PP) and calcium lactate (CL) with a constant weight percentage of 60% and 40%, respectively, were compounded with 3, 5 and 7 phr of epoxidized soybean oil (ESO) plasticizer using an internal mixer. The testing samples were prepared using an injection molding technique. The effects of the mold temperature and annealing treatment on the morphological and mechanical properties of PP-based composites using polarized optical microscopy (POM), differential scanning calorimetry (DSC), universal testing machines (UTM), and impact tester were performed. The results showed a remarkable increase in the elongation-at-break and impact strength, but a noticeable decrease in tensile strength and stiffness with increasing ESO contents. The experimental results also indicated that the higher mold temperature significantly improved the tensile strength and stiffness of samples due to an increase in spherulite size for neat PP, PP/CL composite and PP/CL composite with 3 phr of ESO. Additionally, annealing treatment enhanced the tensile and impact strengths of both neat PP and PP/CL composite, which was attributed to the increase in the crystal perfection and degree of crystallinity. These findings suggested that mechanical improvements using high mold temperature and annealing treatment were confined to the incorporation of an ESO plasticizer. The resulting performance of the plasticized PP composites after thermal treatment was described by two possibilities: the loss in the adhesion between the components and the migration of plasticizer.
Characterization
Ahmed Hamdi
Abstract
Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization ...
Read More
Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization and thus can lead to an unexpected solidification. This study explores how flow fields influence the crystallization behavior of PP. A controlled-stress rheometer was used to investigate the effect of short shear stress steps on crystallization kinetics. The results revealed that applying a stress step significantly increased the rate of crystallization compared to a non-stressed sample. This acceleration is attributed to the stress-induced orientation of macromolecules, which promotes nucleation. Furthermore, longer durations of applied stress led to a faster increase in viscosity, indicating a higher nucleation density with increasing stress exposure. A mastercurve approach validated the consistency of the model describing the stress-crystallization relationship. The calculated parameter relating to nucleation density confirmed a linear increase with stress duration, allowing estimation of the nucleation rate during shear.
Simulation & Modeling
Jieqi Wang; Li Zhao; Minju Song; Fenge Hu; Xuelian He
Abstract
The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior ...
Read More
The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior of the two systems by molecular dynamics simulation. This paper explains the influence of long branches on the isothermal crystallization process and the non-isothermal crystallization process with similar initial interchain contact fraction (ICF) in terms of final ICF, crystal regions, crystallinity, concentration of tie chains and energy. It is found that the crystallization process is classified as two stages: the nucleation stage and the crystal growth stage. The existence of long branches is favorable for the first stage while unfavorable for the second stage. Knots that act as crystalline defects are excluded from the lamella, resulting in decreasing in regularity and crystallinity of molecular chains. From the perspective of potential energy and non-bond energy, LCB-PE has lower energy than linear-PE in the nucleation stage while the energy of linear-PE is lower than that of LCB-PE in the second stage. In short, the long branched chains inhibit the crystallization process.
Characterization
Sepideh Gomari; Ismaeil Ghasemi; Mohammad Karrabi; Hamed Azizi
Abstract
Nanocomposites based on polyamide 6 (PA6) and poly(ethylene-co-1-butene)-graft-maleic anhydride (EB-g- MAH) blends have been prepared via melt mixing. The effect of blend ratio and organoclay concentration on the crystallization and melting behavior of specimens were studied. Three types of commercial ...
Read More
Nanocomposites based on polyamide 6 (PA6) and poly(ethylene-co-1-butene)-graft-maleic anhydride (EB-g- MAH) blends have been prepared via melt mixing. The effect of blend ratio and organoclay concentration on the crystallization and melting behavior of specimens were studied. Three types of commercial organo-modified clay (Cloisite 30B, Cloisite 15A and Cloisite 20A) were employed to assess the importance of the nanoclay polarity and gallery distance. The crystallization behavior was investigated using differential scanning calorimetry (DSC) and wide angle X-ray diffraction spectroscopy (WAXD). The strong interactions between amine end groups of PA6 and maleic anhydride groups of EB-g-MAH led to complete inhibition of EB-g-MAH crystallization according to the DSC results. A transformation from the α form to the γ form crystals of PA6, induced by both organoclays and EB-g-MAH, was monitored by WAXD and DSC. Small angle X-ray scattering (SAXS) was used to evaluate the morphology of nanocomposites. Moreover, transmission electron microscopy (TEM) was conducted to determine the location of organoclays and indicated that the organoclays mainly present in the PA6 matrix and rarely distribute in the EB-g-MAH phase in the case of low polarity organoclays. It was also evidenced that the organoclay with the most affinity to PA6 (Cloisite 30B) had the largest effect on the thermal and crystallization behavior of this phase in the blend.
