Large Spherulites Research Articles

Adsorption and Structuration of PEG Thin Films: Influence of the Substrate Chemistry.

This study investigates polyethylene glycol (PEG) homopolymer thin film adsorption on gold surfaces of controlled surface chemistry. The conformational states of physisorbed PEG are analyzed through polarization modulation infrared reflection-absorption spectrometry (PM-IRRAS). The PM-IRRAS principle is based on specific optical selection rules allowing the detection of surface-specific FTIR response of thin polymer films on the basis of differential reflectivity at the polymer/substrate interface for p- and s-polarized light. The intensification of the electric field generated at the PEG/substrate interface for p-polarized IR light in comparison with s-polarized light permits the analysis of PEG chain anisotropy and conformational changes induced by the adsorption. Results showed that PEG adsorbs on model substrates having a rather hydrophilic character in a way that the PEG chains spread parallel to the surface. In the case of a very hydrophilic substrate, the adsorbed PEG chains are in a stable thermodynamic state which allows them to arrange and crystallize as stacked crystalline lamellae after adsorption. The surface topography and morphology of the PEG thin films were also investigated by atomic force microscopy (AFM). While in the bulk state, PEG crystallizes in the form of large spherulites; on substrates whose adsorption is favored by surface chemistry, PEG crystallizes in the form of stacked lamellae with a thickness equal to 20 nm. Conversely, on a hydrophobic substrate, the PEG chains do not crystallize and adsorption occurs in the statistical coil state.

Enhancement of flexural properties of carbon fiber-reinforced polyamide 6 via oriented crystallization of polyamide 6 among carbon fibers

The effect of the crystalline structure of polyamide 6 (PA6) among carbon fiber (CF) on the mechanical properties of PA6/CF composites was explored using two types of PA6 with different spherulite sizes. Infrared (IR) spectroscopy showed that intra/intermolecular interactions were nearly equivalent for the two types of PA6. The viscoelasticities in the molten state were almost identical; that is, the molecular weights of the PA6s were comparable. The mechanical properties of the PA6 matrix with smaller spherulites (PA6a) in PA6/CF were superior to those of the PA6 matrix with larger spherulites (PA6b). Polarized light microscopy, wide-angle X-ray scattering, and polarized Raman spectroscopy revealed oriented crystals of PA6a in the PA6a/CF composite and random crystals of PA6b in the PA6b/CF composite. Therefore, the superior mechanical properties of PA6/CF are due to the oriented crystal chains of PA6, which support the overall stress transfer in composites.

Thermoplastic elastomers based on lactide and caprolactone: The influence of chain microstructure on surface topography and subsequent interaction with cells

Surface biophysical properties of biomaterials, including surface topography and roughness, determine the interaction of a biomaterial with the surrounding cells, tissues and organs once implanted in the human body. Herein, the surface topography of thermoplastic copolymers based on lactide and caprolactone showing elastomeric behaviour was modulated by precisely controlling the chain microstructure (i.e., distribution and length of the repetitive units within the polymeric chain). The synthesized copolymers were subjected to different thermal treatments from the melt, leading to polymeric films with various surface textures and roughness values. Copolymers synthesized with triphenyl bismuth as a catalyst, with a more random distribution of the repetitive units, showed limited crystallization capability. Accordingly, only the copolymer with higher amount of l-lactide (i.e., 80 wt%) subjected to an isothermal treatment from the melt at 70 °C was able to crystallize, and spherulites of around 7 μm were discernible by atomic force microscopy. In contrast, the copolymers synthesized with stannous octoate, which had a more blocky nature, showed axialitic crystalline domains at the submicron-to nanoscale when subjected to an isothermal treatment from the melt at 50 °C, whereas well-defined spherulites of sizes up to 14 μm were obtained at 70 °C. Human fibroblast showed a more elongated morphology when seeded on those samples having higher roughness values and larger spherulites, whereas they had a more spread morphology when seeded on the amorphous, smooth surfaces. As concluded from the present study, by precisely controlling the chain microstructure of the synthesized copolymers, a wide variety of surface topographies can be obtained, which has a clear impact on the way the biomaterial interacts with cells. This opens the possibility to study the influence of surface biophysical properties on more complex cell processes in the future, including inflammatory or foreign body response processes.

Polymerization-Induced Crystallization of Dopant Molecules: An Efficient Strategy for Room-Temperature Phosphorescence of Hydrogels

Conventional hydrogels such as polyacrylamide and polyacrylic acid ones seldom exhibit phosphorescences at ambient conditions, which limit their applications as optical materials. We propose and demonstrate here a facile strategy to afford these hydrogels with room-temperature phosphorescence by polymerization-induced crystallization of dopant molecules that results in segregation and confinement of the gel matrix with carbonyl groups and thus clusterization-induced phosphorescence. As a model system, crown ethers (CEs) are dissolved in an aqueous solution of concentrated acrylamide that greatly increases the solubility of CEs. During the polymerization process, CEs crystallize to form large spherulites in the polyacrylamide hydrogel. The crystallization arises from the drastically reduced solubility of CEs after the conversion of monomers to polymers during the gel synthesis. The resultant composite hydrogel with a water content of 67 wt % exhibits extraordinary phosphorescence behavior yet maintains good stretchability and resilience. We found that the partial gel matrix is squeezed and confined by in situ-formed crystals, leading to carbonyl clusters and thus phosphorescence emission. The composite gel shows green phosphorescence with an emission peak at 512 nm and a lifetime of 342 ms. The afterglow emission is detectable by the naked eye for several seconds. This strategy has good universality, as validated in other hydrogels with different polymeric matrices and dopant molecules. The development of hydrogels with good mechanical and phosphorescent properties should merit the design of multifunctional soft machines with applications in biomedical and engineering fields.

Structured lipids produced from palm-olein oil by interesterification: A controllable lipase-catalyzed approach in a solvent-free system

Palm olein (POL) was modified by enzymatic interesterification with different degrees of acyl migration in a solvent-free packed bed reactor. The fatty acid and acylglycerol composition, isomer content, thermodynamic behavior, and relationship between crystal polymorphism, solid fat content (SFC), crystal microstructure, and texture before and after modification were studied. We found that the increase in sn-2 saturation interesterification was not only due to the generated tripalmitin (PPP) but also caused by acyl migration, and the SFC profiles were changed accordingly. The emergence of high melting point acylglycerols was an important factor accelerating the crystallization rate, further shortening the crystallization induction time, leading to the formation of large crystal spherulites, thereby reducing the hardness. The transformation from the β' to the β form occurred during post-hardening during storage. The isomer content also affected the physicochemical properties of the modified POL.

The synergistic effect of heterogeneous nucleation and stress-induced crystallization on supramolecular structure and performances of poly(lactic acid) melt-spun fibers

As a kind of bio-based polymer, poly (lactic acid) has potential application in fibers fields. Due to the weak nucleation ability, PLA crystallizes slowly and forms large spherulites during the forming process, which deteriorates the properties of PLA fibers. In this work, melt-spun method is employed for the fabrication of PLA/T composite fibers using succinate diphenyl dihydrazide (TMC-306) as the nucleating agent, and then the hot-drawing and heat setting is performed to the as-spun fibers. Compared with pure PLA fibers, PLA/T fibers show faster crystallization rate and improved performance due to the synergistic effect of heterogeneous nucleation and stress-induced crystallization. The characterization of non-isothermal crystallization behavior indicates that the peak crystallization temperature as well as crystallinity of PLA composites is increased to 121.5 °C and 36.78 % respectively by blending 0.3 wt% TMC-306. Meanwhile, the obtained PLA/0.3T composite fibers are highly crystallized and oriented at hot-drawing ratio of 2.4 folds and heat setting temperature of 100 °C, and the conformational stability is noticeably enhanced. Further, the tensile strength and storage modulus of PLA/0.3T composite fiber are 3.46 cN/dtex and 46,953 MPa respectively, which are increased by 42 % and 41 % compared with neat PLA fibers.

Study on the mechanism of enlarged spherulite diameter for aliphatic polyester ionomers

Aliphatic polyesters with repeated chemical cycle performance are the promising candidate to eliminate environment pollution evoked by the petroleum-based plastics. The incorporation of ionic group can improve the strength, thermal resistance and melt viscosity of polyesters and promote them to utilize at high performance film or foam. Interestingly, these semi-crystalline ionomers achieve significant enlarged spherulite diameter (Du) when the content of ionic group is 0.58 mol%. To explore the unexpected phenomenon, poly(ethylene succinate) and poly(decamethylene succinate) phosphorus-containing ionomers (PESIs-K and PDSIs-K) with 0.58–1.91 mol% ionic group containing phosphorus (PCIG) were prepared by condensation polymerization of ethylene glycol (or 1, 10-decamethylene glycol), succinic acid and phosphorous ion monomers (DHPPO-K), respectively. The effects of PCIG content and types of diols on the chemical structures, thermal behavior, crystallization, and rheological behavior of samples were characterized by FTIR, NMR, DSC, POM, XRD, SAXS, DMA and rotational rheometer, respectively. Strikingly, the t1/2 of PESI1-K decreased from 7.0 to 2.9 min, while its Du increased from 103 to 171 μm. The reasons were that PESI1-K with moderate heterogeneous nucleation sites and melt viscosity guaranteed it to achieve high crystal growth rate, and enough growth time and space for each grain. Moreover, the incorporation of electrostatic interactions by ionic clusters facilitated the crystalline grains to cumulate in large spherulites without collapse. However, due to the improved flexibility, the relaxation time of PDS and its ionomers were much lower than those of PES and PESIs-K, while their self-nucleation capacity increased, which decreased the Du. Summarily, the effects of PCIG on crystallization behaviors were elaborated in detail and the improved Du mechanism of ionomers was proposed.

Correlative light and electron microscopy of poly(ʟ-lactic acid) spherulites for fast morphological measurements using a convolutional neural network.

Polarized optical microscopy (POM) and transmission electron microscopy (TEM) are widely used for imaging polymer spherulite structures. TEM provides nanometer resolution to image small spherulites of sub-micrometer in diameter, while POM is more suitable for observing large spherulites. However, high-resolution images with a large field of view are challenging to achieve due to the deformations of ultrathin sectioned samples used for TEM observations. In this study, we demonstrated that correlative light and electron microscopy (CLEM) combining POM and TEM could effectively characterize the spherulite structures in a wide range from nanometer to several hundred micrometers that neither TEM nor POM alone could cover. Furthermore, the deformations of the TEM ultrathin sections were corrected by referencing to the POM images at the same position of the sample, and large-area TEM images without deformations were successfully produced. The spherulite structures of poly(ʟ-lactic acid) were successfully analyzed using CLEM and TEM in a wide range of spatial scales at the same field of view. The large-area TEM image (250 µm × 250 µm), consisting of 702 TEM images stitched together, was subjected to machine learning to extract the essential structural information of spherulites. Analysis using the convolutional neural network, a well-known algorithm You Only Look Once (YOLO), demonstrated that it was practical to accurately obtain the diameter distribution and the space-filling factor (relative crystallinity) of the spherulites. This study presents a new approach for acquiring high-resolution images with a large field of view and processing the images at a fast speed.

Dependence of Crystallization Behavior of Interacting Telechelic Poly(butylene succinate) Oligomer on Molecular Weight

A large spherulite structure deteriorates the mechanical properties of crystalline polymers, and therefore various methods have been explored to increase primary nucleation density. Recently, chain-end modification has been proposed as an effective approach for regulating polymer crystal nucleation. However, the relevant nucleation mechanism still requires investigation. Therefore, in this work, 2-ureido-4[1H]-pyrimidinone (UPy) units, which can form stacks via quadruple hydrogen bonds with each other, are introduced as end groups for the preparation of interacting telechelic poly(butylene succinate) (PBS-UPy) oligomers with different molecular weights (Mns). The crystallization, especially the nucleation behavior of PBS-UPy, is studied in detail by comparing with the corresponding pre-polymer, the hydroxyl-terminal PBS (PBS-OH). The thermal properties of PBS-UPy exhibit similar Mn-dependent tendency to those of PBS-OH, but with weaker total crystallization rate. The spherulite growth rate is significantly reduced, whereas the primary nucleation density is highly promoted, after introducing UPy groups. Further investigation reveals that the mechanism of UPy stacks’ influence on nucleation ability changes from inhibition to promotion with respect to Mn. Even under an inhibition of nucleation ability, the final nucleation density is obviously increased because of a significant decline of the growth rate. In addition, the change in the impact of UPy stacks on nucleation ability is speculated to originate from the memory expression feasibility of ordered conformation in the melt during crystallization.

Thin polyethylene (LDPE) films with controlled crystalline morphology for studying plastic weathering and microplastic generation

Plastic pollution has become one of the most visible environmental issue. Studying the aging and the fragmentation mechanism of polymers therefore raises environmental and health issues. Since it is particularly difficult to monitor all these processes in the real environment, laboratory studies are still necessary to obtain more accurate data and to identify the pathways leading to the outcome of plastic debris in the environment. In this paper we present a new method to prepare micrometer thick LDPE films with different thicknesses and controlled crystalline morphologies (i.e. spherulite size) using dip-coating process. LDPE films presenting different spherulite dimensions were submitted to an accelerated weathering test which indicates that spherulite size has only a weak influence on the rate of photo-oxidation. However, films presenting large spherulites morphologies seem to be more sensitive to surface erosion and crack initiation. We believe that the method developed in this paper can be used to study with more control and more rapidly (i.e. thin film and accelerated weathering) the influence of crystalline morphology on a wide range of semi-crystalline polymers in different aging conditions and thus help to better understand the fragment production of plastics in the environment.

Non-isothermal cold crystallization, melting, and moisture barrier properties of silver-loaded kaolinite filled poly(lactic acid) films

Silver-loaded kaolinite (AgKaol), an antibacterial agent along with a barrier enhancer, was incorporated into poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and tetrabutyltitanate (TBT) blend resulting in the formation of polymer composite. The introduction of AgKaol could improve the barrier and the crystallization properties of PLA/PBAT/TBT blend. The barrier property of composite polymer was investigated by water vapor permeability (WVP) to study the influence of AgKaol content (0.0, 1.0, 2.0, 3.0 and 4.0 phr) in polymer matrix. The values of WVP decreased with increasing AgKaol content and amount of crystallite in PLA composite. The cold crystallization property of this PLA/PBAT/TBT composited with 0.0, 2.0 and 4.0 phr of AgKaol was completely investigated by the non-isothermal differential scanning calorimetry (DSC) technique. From the non-isothermal DSC analysis, the crystallization rates (dX(T)/dt) of PLA composite increased with increasing of the heating rate and AgKaol content. The Avrami, Ozawa and Liu models were applied to describe the non-isothermal crystallization kinetics and determine crystallization parameters for PLA/PBAT/TBT/AgKaol composite. The crystallization mechanism of PLA/PBAT/TBT/AgKaol composite was proposed thorough the nucleation and three dimension growths. The activation energies of crystallization (Ea) were determined by the Kissinger-Akahira-Sunose (KAS) isoconversional method. The determined Ea for the crystallizations of PLA/PBAT/TBT with 4.0 phr of AgKaol were lower than 2.0 and 0.0 phr, respectively. Polarized optical microscopy (POM) showed more and larger spherulites with a nanocrystal structure of PLA/PBAT/TBT/AgKaol composite than neat PLA. The nucleating effect of AgKaol on PLA/PBAT/TBT blend might be useful for preparation of PLA composite as a gas barrier protection material in the future. Corresponding to the melt flow index (MFI) results, PLA composites could produce as a film with promising antibacterial packaging due to silver nanoparticles in AgKaol.

Mechanical performance and supermolecular morphology of void free polypropylene manufactured by fused filament fabrication

AbstractIt is known from the literature that freedom from macroscopic defects (voids) is an essential prerequisite for good mechanical properties of 3D‐printed components manufactured using fused filament fabrication. The present study further shows that the morphology and mechanical properties of void free components are significantly influenced by the choice of process parameters. Components that were printed at low temperatures and high speeds show fair and inhomogeneous supermolecular morphology, clearly visible weld seams and a special flow‐induced staggered structure of the individual strands laid‐up. At higher magnification in the optical microscope, transcrystalline structures are visible starting from the contact area between the strands, that is, crystallization has started at the interface between the strands and is moving forward towards the center of the strands. In contrast, the samples printed at high temperatures and low speeds show a homogeneous supermolecular morphology with overall larger spherulites and a higher degree of crystallinity and compared to the specimens printed with the low temperature/high speed‐set much better mechanical properties. A numerical simulation of the temperature at the contact point of the strand emerging from the hot nozzle and the cooled strand neighbor agrees well with the measured behavior. The thermal simulation thus enables the temperature to be calculated at any point in time in the welding contact and thus access to the local thermal conditions during joining, cooling and the formation of the morphology.

Influence of Different Solvents and High-Electric-Field Cycling on Morphology and Ferroelectric Behavior of Poly(Vinylidene Fluoride-Hexafluoropropylene) Films.

P(VdF-HFP) films are fabricated via a solution casting doctor blade method using high (HVS) and low (LVS) volatile solvents, respectively. The structural properties and the ferroelectric behavior are investigated. The surface structure and crystal phase composition are found to be strongly dependent on the type of solvent. LVS leads to a rougher copolymer surface structure with large spherulites and a lower crystallinity in contrast with HVS. The crystalline phase of copolymer films fabricated with HVS consists almost exclusively of α-phase domains, whereas films from LVS solution show a large proportion of γ-phase domains, as concluded from Raman and X-ray diffraction spectra. Virgin films show no ferroelectric (FE) switching polarization at electric field amplitudes below 180 MV/m, independent of the solvent type, observed in bipolar dielectric displacement—electric field measurements. After applying electric fields of above 180 MV/m, a FE behavior emerges, which is significantly stronger for LVS films. In a repeated measurement, FE polarization switching already occurs at lower fields. A shielding effect may be related to this observation. Additionally, Raman bands of polar γ-phase increase by high-electric-field cycling for the LVS sample. The solvent used and the resulting crystal phase composition of the virgin sample is crucial for the copolymer behavior during bipolar electrical cycling.

Facile strategy to improve thermal conductivity of anisotropic poly(butylene succinate) phosphorus‐containing ionomer films via compression molding

One of the defect for polymers based film is the low thermal conductivity which restricts their application. In this study, an effective strategy in improving the thermal conductivity of poly(butylene succinate) phosphorus‐containing ionomer [phosphorus‐containing ionic group (PCIG) content was 1wt%, denoted as PBSI1‐K] by compression molding was proposed. PBSI1‐K films with anisotropic thermal transport were fabricated by thermal compression molding with different compression molding pressure (2000, 2500, 3000, and 3500 psi). The relationships between the compression molding pressure and properties, including thermal conductivity, crystallization behavior and chain orientation degree of PBSI1‐K films were investigated. Strikingly, PBSI1‐K film fabricated at 2500 psi pressure, denoted as PBSI1‐K‐2500, achieved 5‐fold increase in in‐plane thermal conductivity when PBS was used as the contrast. The impressive improved thermal conductivity (542 mW m−1 K−1) in horizontal direction are ascribed to the fact that PBSI1‐K‐2500 obtained the large spherulite diameter (517 um) and high chain orientation degree (1.90). Furthermore, we introduced graphene into PBSI1‐K and the thermal conductivity of GNS/PBSI1‐K composites have also been discussed. We hence showcase compression molding here as a facile strategy to prepare ionomer film with improved thermal conductivity. The prepared PBSI1‐K‐2500 can serve as biodegradable films to replace petroleum‐based plastic materials and remedy the pollution of “microplastics.”

Detailed thermal analysis of crystallization kinetics and band morphology for future blending of absorbable poly(p‐dioxanone) monofilament surgical suture with poly(ε‐caprolactone)

AbstractThe thermal effects on crystallization kinetics and the band morphology of absorbable poly(p‐dioxanone) (PDS) were studied in detail with TGA, AFM, DSC and polarized optical microscopy techniques. The polymer film was crystallized with isothermal and non‐isothermal conditions over a wide temperature range, cooling from the melt at 140 °C (beyond the equilibrium melting temperature but below the degradation temperature). With the isothermal crystallization process, a well‐defined spherulitic morphology of the PDS polymer, linearly growing in all directions with time, was observed. A microstructure analysis by polarized optical microscopy and AFM revealed that the crystallized PDS shows large spherulites with band morphology, the nucleation density decreases and the spacing between the band increases with crystallization temperature. The periodic band morphology of the spherulites is related to edge‐on and flat‐on lamella orientation. The crystallization temperature dependent spherulite growth rate displayed a bell‐shaped curve, showing a highest spherulite growth rate at 60 °C, explained by classical nucleation theory. These results allowed a good understanding of the thermal and morphological properties of the PDS polymer over a wide temperatures range in both isothermal and non‐isothermal conditions. Additionally, the crystallization and melting behaviors of the PDS polymer were studied and compared for the future application of blending with other compatible polymers, e.g. poly(ε‐caprolactone). © 2020 Society of Industrial Chemistry

Preparation and properties of biodegradable multi-block copolymer/graphite oxide composite phase change materials

A novel biodegradable solid–solid phase change heat storage composite materials (GO-PBSEG) were synthesized by in situ polymerization reaction of high molecular weight poly(ethylene glycol) (PEG4000) with succinic acid, 1,4-butanediol (BD) and graphite oxide (GO). PEG was used as a working substance in GO-PBSEG composite materials. To characterize the resulting product, Fourier transform infrared spectroscopy, NMR spectrometer, differential scanning calorimetry, thermal constant analyzer, polarization optical microscopy measurements and scanning electron microscopy were employed to investigate the structure, thermal properties, crystalline behavior and enzymatic degradation of phase change materials. The experimental results indicated that the GO-PBSEG composite materials showed typical solid–solid phase transition properties, and the exothermic phase change enthalpy of PEG unit reached 64.8 J g−1. With the increase in GO content, the thermal conductivity properties of composite materials were improved, and the enzymatic degradation rate gradually increased. POM observations indicated that the 1.0 mass% GO-PBSEG sample had the largest spherulites and the lowest nucleation ability.

Determination of the Growth Time Period of Loose Zinc Deposit Using Interval Analysis Methods

A characteristic of obtaining metal powders by direct current electrolysis is changes in the morphology of particles over the loose deposit layer thickness up to the formation of large spherulites. Deposits should be periodically removed from the cathode in order to obtain a powder with homogeneous composition. This paper justifies the choice of the parameter describing the change in loose deposit properties and proposes a method for determining the periodicity of its removal from the cathode. Loose zinc deposits were obtained at 25°C from zincate electrolyte containing 0.3 mol L–1 of ZnO and 4 mol L–1 of NaOH at a current setpoint exceeding six times the limiting diffusion current calculated using the smooth electrode. Electrode potential, deposit thickness and evolved hydrogen volume were measured directly in the process of electrolysis. Current redistribution between the metal reduction and hydrogen evolution leads to a change in the structure of loose deposit particles. It is shown that the differential current efficiency of zinc is the parameter describing the change in the loose zinc deposit density. Its value should not exceed 0.96, in order to ensure deposition of loose deposit with homogeneous properties. A further increase in current efficiency will lead to the formation of aggregates at the deposit growth front. It is proposed to determine the periodicity of loose deposit removal from the cathode using the empirical equation for the time dependency of differential current efficiency of zinc. The mathematical and statistical analysis of the data obtained in six replicates was carried out. The interval approach made it possible to significantly narrow the range of permissible differential current efficiency values and, as a consequence, to determine empirical equation coefficients with acceptable accuracy and calculate the growth time period of a deposit with homogeneous structure. The obtained approach can be used to estimate the time period of loose metal deposition accompanied by hydrogen evolution.

Texture Induced by Molecular Weight Dispersity: Polymorphism within Poly(L-lactic acid) Spherulites

Poly(L-lactic acid) (PLLA) has drawn much attention due to its excellent medical and pharmaceutical applications for decades. As a semi-crystalline polymer, morphology and crystal structure of PLLA greatly determine its properties. Here, we demonstrate, for PLLA films, a non-conventional texture featuring two types of spherulites emerging in pairs to form a distinct nested structure where a small spherulite (~10 µm) is embedded in a large one (100 µm to 300 µm). In addition to the size, the molecular weight and polymorph are different in the large and small spherulites. Crystallographic α-form and relatively low molecular weight are identified in the large spherulites, while meta-stable α′-form and relatively high molecular weight in the small ones. These differences suggest that the polydisperse PLLA polymers fractionate during film formation and the high-molecular-weight fraction crystallizes into the small spherulites with meta-stable structure because of its complicated polymer entanglement and high viscosity. In contrast, the rest of polymers crystallize into the large spherulites with the thermodynamically stable polymorph. Furthermore, this texture exhibits accelerated PLLA degradation initiated from the small spherulites, which is distinct from the typical PLLA spherulites. Insights provided by this work may lead to new texture-properties relationship associated with polydispersity of molecular weight.

Nucleation and crystallization of Ba2Si3O8 spherulites in a barium aluminum silicate glass, and mechanical properties of the obtained glass-ceramics

The effect of spherulitic crystallization on the elastic moduli and fracture toughness of a barium aluminum silicate glass was investigated. The crystallization process results in Ba2Si3O8 phase and is initiated from Ba rich nuclei. Nucleation is optimal in the 690-720 °C interval. Young’s modulus is increased by 12.5% when the glass-ceramic conversion is nearly complete. Nevertheless, as the size and the volume fraction of crystals are increased, some microcracking shows up upon cooling from the crystallization temperature. An optimal improvement of the fracture toughness (SEPB method) by 27 % is observed for a 49 % volume fraction of 5 to 10 μm large spherulites.

Preparation, crystallization and degradation properties of poly(butylene succinate-co-neopentyl glycol succinate) copolymer/graphite oxide composites

In this study, graphene oxide (GO) was prepared by the modified Hummers’ method and poly(butylene succinate-co-neopentylglycol succinate)/graphene oxide (GO–PBNPGS) nanocomposites were synthesized via in situ polymerization with a series of GO contents (from 0.01 to 0.10 mass%). The GO was characterized by Fourier transform infrared spectrum, atomic force microscopy and wide-angle X-ray diffractometry. The non-isothermal crystallization kinetics and crystalline morphology of the neat PBNPGS and its nanocomposites were analyzed by differential scanning calorimetry and polarized optical microscopy (POM), respectively. The results showed that GO was prepared successfully and dispersed in PBNPGS uniformly during the experimental process. The non-isothermal crystallization kinetics was characterized using Avrami equation modified by Jeziorny. The experimental results indicated that the non-isothermal crystallization behavior of the GO–PBNPGS was influenced by the GO content and cooling rate, the crystallization rate first increased and then decreased with an increase in GO content. Therefore, it was expected that the GO could accelerate the crystallization process. POM observations indicated that GO served as an effective nucleating agent for the crystallization of GO–PBNPGS when 0.10 mass% GO was added, and 0.05 mass% GO in PBNPGS had the largest spherulites and the lowest nucleation ability. In addition, the experimental data also showed that the biodegradation rate increased with the increasing of GO content, with a significant rate of degradation occurring in the composite sample with 0.10 mass% GO content.