The melt-recrystallization behavior of highly oriented α-iPP fibers embedded in a HIPS matrix.

The melt-recrystallization behavior of α-iPP fibers embedded in an amorphous HIPS matrix has been studied by means of optical microscopy. The amorphous HIPS serving as a supporter of iPP fibers does not become involved in the nucleation and crystallization process of the molten highly oriented iPP fibers. It also does not provide any birefringence under the optical microscope with crossed polarizers. This enables the study of orientation-induced ß-iPP crystallization through a control of the melting status of the fibers. Through melting the fibers at different temperatures above 175 °C and subsequent recrystallization, some ß-iPP crystals were always produced. The content of the ß-iPP crystal depends strongly on the melting temperature and melting time of the iPP fibers. It was confirmed that melting the iPP fibers at relatively lower temperature, e.g. 176 °C, less amount of ß-iPP crystals were observed. The content of ß-iPP crystal enhances first with increasing melting temperature and then decreases with further increase of the fiber melting temperature. The ß-iPP crystallization is found to be most favorable upon melting the fibers at 178 °C for 2 min. This demonstrates the requirement of a certain chain or chain segment orientation for generating ß-iPP crystallization on the one hand, while higher orientation of the iPP chains or chain segments encourages the growth of iPP crystals in the α-form on the other hand. This has been further confirmed by varying the melting time of the fiber at different temperatures, since relaxation of the iPP molecular chains at a fixed temperature is time dependent. Moreover, the complete transformation of α-iPP fibers in some local places into ß-iPP crystals implies that the αß-transition may not be required for the orientation-induced ß-iPP crystallization.

Crystallization Behavior and Mechanical Property of Biodegradable Poly(butylene succinate-co-2-methyl succinate)/Cellulose Nanocrystals Composites.

Biodegradable poly(butylene succinate-co-2-methyl succinate) (PBSMS)/cellulose nanocrystals (CNC) composites were successfully prepared at low CNC loadings with the aims of improving crystallization and mechanical properties and extending the practical application of PBSMS. CNC is finely dispersed in the PBSMS matrix without obvious aggregations. The low content of CNC obviously promoted the crystallization behavior of PBSMS under different conditions. The spherulitic morphology study revealed that CNC, as an effective heterogeneous nucleating agent, provided more nucleation sites during the melt crystallization process. In addition, the nucleation effect of CNC was quantitatively evaluated by the following two parameters, i.e., nucleation activity and nucleation efficiency. The crystal structure and crystallization mechanism of PBSMS remained unchanged in the composites. In addition, as a reinforcing nanofiller, CNC significantly increased Young's modulus and the yield strength of PBSMS. The crystallization behavior and mechanical properties of PBSMS were significantly improved by the low content of CNC, which should be interesting and essential from the perspective of biodegradable polymer composites.

A robust framework for enhancing cardiovascular disease risk prediction using an optimized category boosting model.

Cardiovascular disease (CVD) is a leading cause of mortality worldwide, and it is of utmost importance to accurately assess the risk of cardiovascular disease for prevention and intervention purposes. In recent years, machine learning has shown significant advancements in the field of cardiovascular disease risk prediction. In this context, we propose a novel framework known as CVD-OCSCatBoost, designed for the precise prediction of cardiovascular disease risk and the assessment of various risk factors. The framework utilizes Lasso regression for feature selection and incorporates an optimized category-boosting tree (CatBoost) model. Furthermore, we propose the opposition-based learning cuckoo search (OCS) algorithm. By integrating OCS with the CatBoost model, our objective is to develop OCSCatBoost, an enhanced classifier offering improved accuracy and efficiency in predicting CVD. Extensive comparisons with popular algorithms like the particle swarm optimization (PSO) algorithm, the seagull optimization algorithm (SOA), the cuckoo search algorithm (CS), K-nearest-neighbor classification, decision tree, logistic regression, grid-search support vector machine (SVM), grid-search XGBoost, default CatBoost, and grid-search CatBoost validate the efficacy of the OCSCatBoost algorithm. The experimental results demonstrate that the OCSCatBoost model achieves superior performance compared to other models, with overall accuracy, recall, and AUC values of 73.67%, 72.17%, and 0.8024, respectively. These outcomes highlight the potential of CVD-OCSCatBoost for improving cardiovascular disease risk prediction.

Synthesis, Thermal and Mechanical Properties of Fully Biobased Poly (hexamethylene succinate-co-2,5-furandicarboxylate) Copolyesters.

Poly (hexamethylene succinate) (PHS) is a biobased and biodegradable polyester. In this research, two fully biobased high-molecular-weight poly (hexamethylene succinate-co-2,5-furandicarboxylate) (PHSF) copolyesters with low hexamethylene furandicarboxylate (HF) unit contents (about 5 and 10 mol%) were successfully synthesized through a two-step transesterification/esterification and polycondensation method. The basic thermal behavior, crystal structure, isothermal crystallization kinetics, melting behavior, thermal stability, and tensile mechanical property of PHSF copolyesters were studied in detail and compared with those of PHS. PHSF showed a decrease in the melt crystallization temperature, melting temperature, and equilibrium melting temperature while showing a slight increase in the glass transition temperature and thermal decomposition temperature. PHSF copolyesters displayed the same crystal structure as PHS. Compared with PHS, PHSF copolyesters showed the improved mechanical property. The presence of about 10 mol% of HF unit increased the tensile strength from 12.9 ± 0.9 MPa for PHS to 39.2 ± 0.8 MPa; meanwhile, the elongation at break also increased from 498.5 ± 4.78% to 1757.6 ± 6.1%.

Effect of low multi-walled carbon nanotubes loading on the crystallization behavior of biodegradable poly(butylene adipate).

The effect of low carboxyl-functionalized multi-walled carbon nanotubes (f-MWCNTs) loading on the crystallization behavior of biodegradable poly(butylene adipate) (PBA) was studied with various techniques in this work. For the nonisothermal melt crystallization, f-MWCNTs accelerate the crystallization process of PBA apparently due to the heterogeneous nucleation effect. The Ozawa method fails to describe the nonisothermal crystallization process of neat PBA and its nanocomposite. Isothermal melt crystallization kinetics of neat PBA and its nanocomposite was analyzed by the Avrami equation. The overall isothermal crystallization rate of neat PBA and its nanocomposite increases with increasing crystallization temperature. The addition of f-MWCNTs accelerates the isothermal crystallization of PBA as compared with that of neat PBA at a given crystallization temperature, indicative of the nucleating agent effect of f-MWCNTs; however, the crystallization mechanism does not change. The crystal structure of PBA remains unchanged in the PBA/f-MWCNTs nanocomposite despite the presence of f-MWCNTs.

Crystallization kinetics and thermal property of biodegradable poly(3-hydroxybutyrate)/graphene oxide nanocomposites.

Biodegradable poly(3-hydroxybutyrate)/graphene oxide (PHB/GO) nanocomposites were prepared successfully via a solution mixing method. Transmission electron microscopy and wide angle X-ray diffraction results indicate that the GO sheets were homogeneously dispersed in the PHB matrix. Effect of GO on the thermal stability, nonisothermal melt crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of PHB in the nanocomposites was investigated in detail with various techniques. The observed decomposition temperature of PHB has been improved dramatically in the PHB/GO nanocomposites relative to neat PHB. Both nonisothermal and isothermal melt crystallization of PHB have also been enhanced significantly in the nanocomposites because of the efficient nucleating agent effect of GO. However, the presence of GO does not change the crystallization mechanism and crystal structure of PHB in the PHB/GO nanocomposites.

Significantly Enhanced Crystallization of Poly(ethylene succinate-co-1,2-propylene succinate) by Cellulose Nanocrystals as an Efficient Nucleating Agent.

Poly(ethylene succinate-co-1,2-propylene succinate) (PEPS) is a novel aliphatic biodegradable polyester with good mechanical properties. Due to the presence of methyl as a side group, the crystallization rate of PEPS is remarkably slower than that of the poly(ethylene succinate) homopolymer. To promote the potential application of PEPS, the effect of cellulose nanocrystals (CNC) on the crystallization behavior, crystalline morphology, and crystal structure of PEPS was investigated in this research with the aim of increasing the crystallization rate. CNC enhanced both the melt crystallization behavior of PEPS during the cooling process and the overall crystallization rate during the isothermal crystallization process. The crystallization rate of PEPS became faster with an increase in CNC content. The crystalline morphology study directly confirmed the heterogeneous nucleating agent role of CNC. The crystal structure of PEPS remained unchanged in the composites. On the basis of the interfacial energy, the nucleation mechanism of PEPS in the composites was further discussed by taking into consideration the induction of CNC.

Synthesis, Thermal Behavior, and Mechanical Properties of Fully Biobased Poly(Hexamethylene 2,5-Furandicarboxylate-Co-Sebacate) Copolyesters.

In this research, three fully biobased poly(hexamethylene 2,5-furandicarboxylate-co-sebacate) (PHFSe) copolyesters with low contents of hexamethylene sebacate (HSe) unit (10 mol%, 20 mol%, and 30 mol%) were successfully synthesized through a two-step transesterification/esterification and polycondensation method. The chemical structure and actual composition of PHFSe copolyesters were confirmed by hydrogen nuclear magnetic resonance. The thermal behavior and mechanical property of PHFSe copolyesters were investigated and compared with those of the poly(hexamethylene 2,5-furandicarboxylate) (PHF) homopolymer. Both PHFSe copolyesters and PHF showed the high thermal stability. The basic thermal parameters, including glass transition temperature, melting temperature, and equilibrium melting temperature, gradually decreased with increasing the HSe unit content. PHFSe copolyesters crystallized more slowly than PHF under both the nonisothermal and isothermal melt crystallization conditions; however, they crystallized through the same crystallization mechanism and crystal structure. In addition, the mechanical property, especially the elongation at break of PHFSe copolyesters, was obviously improved when the HSe unit content was greater than 10 mol%. In brief, the thermal and mechanical properties of PHF may be easily tuned by changing the HSe unit content to meet various practical end-use requirements.

Crystallization, mechanical properties, and controlled enzymatic degradation of biodegradable poly(epsilon-caprolactone)/multi-walled carbon nanotubes nanocomposites.

Biodegradable poly(epsilon-caprolactone) (PCL)/multi-walled carbon nanotubes containing carboxylic groups (f-MWNTs) nanocomposites were prepared via simple melt compounding at low f-MWNTs loading in this work. Scanning and transmission electron microscopy observations indicate a homogeneous and fine distribution of f-MWNTs throughout the PCL matrix. The effect of low f-MWNTs loading on the crystallization, mechanical properties, and controlled enzymatic degradation of PCL in the nanocomposites were studied in detail with various techniques. The experimental results indicate that the incorporation of f-MWNTs enhances both the nonisothermal crystallization peak temperature and the overall isothermal crystallization rate of PCL in the PCL/f-MWNTs nanocomposites relative to neat PCL; moreover, the incorporation of a small quantity of f-MWNTs has improved apparently the mechanical properties of the PCL/MWNTs nanocomposites compared to neat PCL. The enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites at low f-MWNTs loading was studied in detail. The variation of weight loss with enzymatic degradation time, the surface morphology change, the reduced film thickness, the appearance of f-MWNTs on the surface of the films, and the almost unchanged molecular weight after enzymatic degradation suggest that the enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites may proceed via surface erosion mechanism. The presence of f-MWNTs reduces the enzymatic degradation rate of the PCL matrix in the nanocomposites compared with that of the pure PCL film.

Fully Biodegradable Poly(hexamethylene succinate)/Cellulose Nanocrystals Composites with Enhanced Crystallization Rate and Mechanical Property.

Through a common solution and casting method, low contents of cellulose nanocrystals (CNC) reinforced biodegradable poly(hexamethylene succinate) based composites were successfully prepared for the first time. CNC homogeneously dispersed in PHS matrix at low loadings, showing no obvious aggregation. PHS/CNC composites showed high thermal stability as PHS. As a heterogeneous nucleating agent, CNC promoted the crystallization of PHS under both nonisothermal and isothermal crystallization conditions. In addition, the higher the CNC content, the faster the crystallization of PHS/CNC composites. The heterogeneous nucleating agent role of CNC was directly confirmed by the crystalline morphology study; moreover, the crystal structure of PHS remained unmodified despite the presence of CNC. As a reinforcing nanofiller, CNC also improved the mechanical property of PHS, especially the Young's modulus and yield strength. In brief, low contents of CNC may improve both the crystallization and mechanical property of PHS, providing an easy method to tune the physical property and promote the wider application of biodegradable polymers.

Biodegradable poly(butylene succinate)/multi-walled carbon nanotubes nanocomposite at low carbon nanotubes loading: morphology, crystallization and mechanical property.

Biodegradable nanocomposite based on poly(butylene succinate) (PBSU) and multi-walled carbon nanotubes (MWNTs) was prepared by solution blending method at 1 wt% MWNTs loading. Scanning electron microscopic observation illustrates a homogeneous distribution of MWNTs in the PBSU matrix. Differential scanning calorimetry, optical microscopy, and wide angle X-ray diffraction were used to study the nonisothermal crystallization, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite. The presence of MWNTs enhances the crystallization of PBSU in the nanocomposite due to the heterogeneous nucleation effect while the crystallization mechanism and crystal structure of PBSU do not change. Moreover, the incorporation of a small quantity of MWNTs has improved significantly the mechanical property of PBSU in the nanocomposite compared with that of neat PBSU.

Effect of comonomer content on the crystallization kinetics and morphology of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

Crystallization kinetics and morphology of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) containing 7, 10 and 18 mol% 3-hydroxyhexanoate (HHx) comonomer were investigated by differential scanning calorimetry, polarized optical microscopy and wide angle X-ray diffraction in detail in this work. The experimental results indicate that overall isothermal crystallization rates of PHBHHx copolymers are reduced with increasing crystallization temperature and HHx content; however, the crystallization mechanism remains unchanged. Moreover, the equilibrium melting point temperatures of PHBHHx copolymers decrease with increasing the HHx content. Banded spherulites morphology and spherulitic growth rates of PHBHHx have been studied in a wide crystallization temperature range. Both band spacing and spherulite growth rate decrease with increasing the HHx comonomer content. All the investigated PHBHHx copolymers exhibit a crystallization regime II to III transition, and the crystallization regime transition temperature shifts to low temperature range with increasing the HHx content. In addition, increasing the HHx content does not modify the crystal structure or crystal cell parameters but decreases the crystallinity of PHBHHx.

Crystallization kinetics and morphology studies of biodegradable poly(butylene succinate-co-butylene adipate)/multi-walled carbon nanotubes nanocomposites.

Biodegradable poly(butylene succinate-co-butylene adipate) (PBSA)/carboxyl-functionalized multi-walled carbon nanotubes (f-MWNTs) nanocomposites were prepared through solution casting method with different f-MWNTs contents ranging from 0.5 to 2 wt%. Scanning electron microscopic observations reveal a fine dispersion of f-MWNTs throughout the PBSA matrix. Effect of f-MWNTs on the crystallization behavior of PBSA was investigated in detail via various techniques and different crystallization conditions including nonisothermal crystallization at different cooling rates and isothermal crystallization at different crystallization temperatures in this work. For both nonisothermal and isothermal melt crystallization, the addition of f-MWNTs enhances the crystallization of PBSA apparently due to their heterogeneous nucleation effect. However, the crystal structure of PBSA does not change in the nanocomposites. Moreover, an attempt was made to study the effect of the presence of f-MWNTs and their contents on the nucleation activity and crystallizability of PBSA in the nanocomposites quantitatively.

Effect of low loadings of cellulose nanocrystals on the significantly enhanced crystallization of biodegradable poly(butylene succinate-co-butylene adipate).

Biodegradable poly(butylene succinate-co-butylene adipate) (PBSA)/cellulose nanocrystals (CNC) nanocomposites were successfully prepared via a solution and casting method at low CNC loadings. The nonisothermal and isothermal melt crystallization behaviors of PBSA/CNC nanocomposites were significantly enhanced by low loading of CNC. The nonisothermal melt crystallization peak temperature obviously increased from 56 °C for neat PBSA to 63.6 °C for PBSA/CNC1 (the nanocomposite containing 1 wt% CNC) at 10 °C/min. Crystallization half-time at 80 °C significantly decreased from 31 min for neat PBSA to 8.4 min for PBSA/CNC1. CNC apparently increased the crystallization rate of PBSA; however, the crystallization mechanism remained unchanged. The crystalline morphology study verified the enhanced nucleation density of PBSA spherulites, indicating the role of CNC as an efficient nucleating agent. In addition, low loadings of CNC did not modify the crystal structure of PBSA.

Effect of functionalization of multiwalled nanotubes on the crystallization and hydrolytic degradation of biodegradable poly(L-lactide).

Biodegradable poly(L-lactide) (PLLA)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared via solution blending using two kinds of MWNTs, i.e., pristine multiwalled carbon nanotubes (p-MWNTs) and carboxyl-functionalized multiwalled carbon nanotubes (f-MWNTs). Various techniques were used to investigate the functionalization of MWNTs on the morphology, crystallization, and hydrolytic degradation of PLLA in the nanocomposites. Both MWNTs show fine dispersion in the PLLA matrix; however, the dispersion of f-MWNTs is better than that of p-MWNTs. The incorporation of MWNTs accelerates the crystallization of PLLA in the nanocomposites due to the heterogeneous nucleation effect; furthermore, the crystallization rate of PLLA is faster in the PLLA/f-MWNTs nanocomposite than in the PLLA/p-MWNTs nanocomposite. The exciting aspect of this research is that the hydrolytic degradation of PLLA is enhanced after nanocomposites preparation.

Various crystalline morphology of poly(butylene succinate-co-butylene adipate) in its miscible blends with poly(vinylidene fluoride).

Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-butylene adipate) (PBSA) are crystalline/crystalline polymer blends with PVDF being the high-T(m) component and PBSA being the low-T(m) component, respectively. PVDF/PBSA blends are miscible as shown by the decrease of crystallization peak temperature and melting point temperature of each component with increasing the other component content and the homogeneous melt. The low-T(m) component PBSA presents various confined crystalline morphologies due to the presence of the high-T(m) component PVDF crystals by changing blend composition and crystallization conditions in the blends. There are mainly three different types of crystalline morphologies for PBSA in its miscible blends with PVDF. First, crystallization of PBSA commenced in the interspherulitic regions of the PVDF spherulites and continued to develop inside them in the case of PVDF-rich blends under two-step crystallization conditions. Second, PBSA spherulites appeared first in the left space after the complete crystallization of PVDF, contacted and penetrated the PVDF spherulites by forming interpenetrated spherulites in the case of PVDF-poor blends under two-step crystallization condition. Third, PBSA spherulites nucleated and continued to grow inside the PVDF spherulites that had already filled the whole space during the quenching process in the case of PBSA-rich blends under one-step crystallization condition. The conditions of forming the various crystalline morphologies were discussed.

Preparation and properties of biodegradable poly(L-lactide)/octamethyl-polyhedral oligomeric silsesquioxanes nanocomposites with enhanced crystallization rate via simple melt compounding.

Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.

Study on the oriented recrystallization of carbon-coated polyethylene oriented ultrathin films.

It is confirmed that a layer of vacuum-evaporated carbon on the surface of a preoriented ultrathin polymer film can lead to an oriented recrystallization of the polymer film. This has been attributed to a strong fixing effect of vacuum-evaporated carbon layer on the film surface of the polymer. To study the origin of the strong fixing effect of vacuum-evaporated carbon layer on the polymer films, the melting and recrystallization behaviors of the preoriented ultrathin PE film with a vacuum-evaporated carbon layer were studied by using atomic force microscopy, electron diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. We found that there exists some extent of chain orientation of carbon-coated polyethylene (PE) preoriented ultrathin film above its melting temperature. These oriented PE chain sequences act as nucleation sites and induce the oriented recrystallization of preoriented PE film from melt. Raman spectroscopy results suggest that new carbon-carbon bonds between the carbon layer and the oriented PE film are created during the process of vacuum carbon evaporation. As a result, some of the PE chain stems are fixed to the coated carbon substrate via covalent bond. Such a bonding has retarded the relaxation of the PE chains at the spot and, therefore, preserves the original orientation of the PE stems at high temperature, which in turn derives the recrystallization of the PE chains in an oriented structure.