Lili I. Minkova

Bio: Lili I. Minkova is an academic researcher from University of Pisa. The author has contributed to research in topics: Isothermal process & Crystallization. The author has an hindex of 1, co-authored 1 publications receiving 43 citations.

Crystallization behavior of polyphenylene sulfide in blends with a liquid crystalline polymer

Abstract: Blends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystal copolyesteramide (Vectra-B950) have been prepared by meltblending. The crystallization behavior of neat and blended PPS has been studied by differential scanning calorimetry (DSC), under both non-isothermal and isothermal conditions. It has been found that blending PPS with Vectra-B leads to an increase of the temperature of non-isothermal crystallization and to a pronounced acceleration of the isothermal crystallization, without any reduction of the degree of crystallinity. All these effects have been found to occur independent of the Vectra-B concentration, within the investigated range (2 to 20%, w/w). The results have been interpreted in terms of an incrased nucleation density of the blends, probably due to heterogeneous substances, initially present in the Vectra-B bulk, which dissolve to saturation in the PPS phase, during melt-blending.

Structure, morphology, mechanical and thermal characteristics of the in situ composites based on liquid crystalline polymers and thermoplastics

Abstract: Thermotropic liquid crystalline polymers (LCPs) with rigid molecular backbones exhibit unique physical, mechanical, rheological and thermal properties. The use of LCPs as the minor phase of polymer blends has attracted considerable attention in the past two decades. This is because LCPs can improve the processability and mechanical properties of thermoplastics. LCPs tend to deform into elongated fine fibrils under appropriate processing conditions. The LCP fibrils reinforce thermoplastic matrix effectively, producing the so-called in situ polymer composites. Reinforcing effect arises from improved compatibility between the matrix and dispersed LCP phase. However, the mechanical properties of LCP/thermoplastic blends are far behind expectations, mainly because of poor compatibility between the dispersed LCP phase and thermoplastic matrix. To increase the compatibility between them, graft polymers or copolymers and ionomers have been introduced in the LCP/thermoplastic blends to promote the interfacial interactions. Transesterification reactions between certain phase components of in situ composites can also enhance the interfacial adhesion. In this review paper, current developments in fabrication, rheology, morphology, mechanical and thermal properties of in situ polymer composites will be addressed. Particular attention is paid to the processing–structure–property relationships of several in situ polymer composites.

Crystallization, Morphology, and Enzymatic Degradation of Polyhydroxybutyrate/Polycaprolactone (PHB/PCL) Blends

Abstract: Two types of mixtures were prepared by solution blending: high molecular weight polyhydroxybutyrate (PHB)/poly(e-caprolactone) (PCL) and PHB/low molecular weight chemically modified PCLs (mPCL). The morphology, crystallization, and enzymatic degradation of the blends were studied by differential scanning calorimetry, polarized light optical microscopy, scanning electron microscopy, 1 H NMR, and weight loss measurements. In addition, enzymatic degradation studies were performed by an exposure to Aspergillus flavus. High molecular weight PHB/PCL blends were found to be immiscible in the entire composition range. Phenomena such as PCL fractionated crystallization and a decrease in PHB nucleation density were detected. When PHB was blended with mPCLs, the blends were partially miscible; two phases were formed, but the PHB-rich phase exhibited clear signs of miscibility through a depression of both the T m and the Tg of the PHB component (which was stronger with lower molecular weight mPCL), and an increase in the growth rate of PHB spherulites in the blends as compared to neat PHB or to the PHB component in the PHB/PCL blends. The biodegradation by a exposure to A. flavus showed that the blends are synergistically attacked in comparison to the homopolymers. Two factors may influence the improved degradation rate of the blends: the dispersion of the components and their crystallinity that was reduced in view of the fractionated crystallization and impurities transfer. In the case of the PHB/mPCL blends, the increased miscibility between the components caused a reduction in the degradation rate.

Highly efficient nucleating additive for isotactic polypropylene studied by differential scanning calorimetry

Abstract: The influence of an organic phosphate derivative in the crystallization of the monoclinic phase of isotactic polypropylene was studied by differential scanning calorimetry. To analyze the nucleation activity of the additive, the self-nucleation process of the pure polymer was also studied by thermal techniques. A large increase in crystallization temperatures was obtained even for the lowest concentration of the additive, and its nucleating efficiency is the highest observed for α-nucleating agents in isotactic polypropylene. The nucleating agent was also observed to increase the stability of the crystals formed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1669–1679, 2002; DOI 10.1002/app.10546