Increase In Degree Of Crystallinity Research Articles

Retardation effect of nanohydroxyapatite on the hydrolytic degradation of poly (lactic acid)

AbstractPoly (lactic acid) (PLA) and PLA/nanohydroxyapatite (nHA) composites, containing 2 wt% and 5 wt% of nHA were subjected to in vitro hydrolytic degradation tests in saline phosphate solution at different temperatures (37°C, 48°C, 60°C, and 72°C) to accelerate degradation. Samples were characterized by water uptake, weight loss tests, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and visual analyses. Arrhenius equation was used to describe the behavior of weight loss as a function of time. The PLA activation energy of weight loss showed to be lower than that of the PLA/nHA composites, indicating that the incorporation of nHA retarded the hydrolytic degradation. The rate and percentage of weight loss increased with increasing temperature. All samples presented a decrease in Tg and an increase in degree of crystallinity as a function of time. Incorporation of nHA retarded this behavior that showed to be more expressive in PLA containing 5 wt% nHA.

Thermal properties and non-isothermal crystallization kinetics of biocomposites based on poly(lactic acid), rice husks and cellulose fibres

Bioplastics reinforced by agricultural waste fibres show promise to provide degradation back into the environment when they are no longer needed. These biocomposites have the potential to replace synthetic polymers from non-renewable resources in some applications and may turn out to be one of the material revolutions of this century. Unlike synthetic composites, biocomposites are renewable, carbon neutral, biodegradable and non-petroleum based and have low environmental, human health and safety risks. In this paper, poly(lactic acid) (PLA)-based biocomposites filled with technical cellulose fibres (CeF) and rice husks (RHs) at 10–30 mass% loading were prepared by twin-screw extrusion and injection moulding to enhance stiffness of resulting biocomposites. Particular attention was given to the enhancement of adhesion between the polymer matrix and natural filler through the physical modification by ozone (O3) and dielectric barrier discharge (DBD) plasma (p) surface treatments. Further than, compatibilizing agent based on PLA-g-MAH was produced and introduced into the PLA systems. The non-isothermal crystallization behaviour and thermal properties were investigated through differential scanning calorimetry (DSC) under various cooling rates (5, 10, 20 and 40 °C min−1). The addition of both fillers increased overall crystallization kinetics of resulted biocomposites, especially at high cooling rates. An increase in crystallinity degree from 2.4 (neat PLA) up to 51% has been observed for PLA/30CeFO3 samples at 40 °C min−1 cooling rate. An increase in crystallinity degree based on mass percentage of filler was noticed especially for PLA/RH. Mass percentage increase in CeF did not notice significant increase in PLA crystallinity. The influence of RH and CeF on transformation behaviours of PLA αʹ-/α-polymorphs was observed. The elimination of imperfect αʹ-crystals was observed with increasing amount of RH and CeF.

Isolation of Cellulose Nanofibers from Oryza sativa Residues via TEMPO Mediated Oxidation

ABSTRACT Cellulose nanocrystals (CNCs) or cellulose nanofibers (CNFs) with different morphologies, chemical, mechanical and physical properties can be obtained when microcrystalline cellulose is subjected to enzymatic, chemical or mechanical treatment. With the aim of utilizing cellulose nanofibrils (CNFs) from Oryza sativa, we isolated microcrystalline cellulose using the Kraft process, followed by successive fiber fibrillation using mechanical grinding, then (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) mediated oxidation. Analysis of pulp fibers obtained after each treatment step revealed that fiber properties such as length, crystallinity and crystal size changed when the pulp was subjected to mechanical grinding, ultrasonication and TEMPO mediated oxidation. The degree of crystallinity of the fibers increased while crystal size and fiber length decreased after each treatment. TEMPO mediated oxidation led to a decrease in fiber length and an increase in degree of crystallinity of the fibers as compared to mechanical treatment and ultrasonication. It further introduced carboxyl functional groups (COOH) on the surface of the fibrils, which implies that the nanofibers obtained in this study could be further functionalized. Hence, TEMPO mediated oxidation offers the possibility of further chemical functionalization of cellulose nanofibers isolated from agricultural residues.

Effect of silver ion implantation on surface physicochemical properties of composite materials based on polylactic acid and hydroxyapatite

The investigation of surface physicochemical and biological properties of polylactic acid and hydroxyapatite and composite materials based on them modified by Ag 1 × 1015 ion/cm2 and 1 × 1016 ion/cm2 40 keV ion implantation is presented. X-ray analysis reveals that ion implantation of the above mentioned materials leads to crystallite size and degree of crystallinity increase. The intensity of -С = О line is found by IR-spectroscopy to be decreased that is associated with surface layer carbonization processes of PLA during ion implantation. Silver ion introducing is established to enhance hydrophobic properties of the materials; this process is accompanied by free surface energy decreasing. It is shown that cell viability of non-implanted PLA is comparable with a control sample and ion implantation negatively affects to cell viability. The investigated materials can be promising for biomedical application.

Modified Densified Waste of Expanded Polystyrene and Its Blends With Polyamide 6

The regularities of expanded polystyrene (EPS) waste modified by polyvinylpyrrolidone (PVP) with the simultaneous gas release in various solvents were revealed. The upper sorption limit depends on the nature of the solvent, the concentration and molecular mass of the PVP, the temperature of the process, and the apparent density of the EPS. It was established that the sorption limit of PVP increases with increasing of its concentration in the system and decreases with molecular mass increasing. Based on XRD and FTIR analyses, it was determined that materials based on polyamide 6 and EPS modified by PVP have an increased crystallinity degree by 10–15%, a smaller average crystallite size and higher technological compatibility. The addition of PVP‐modified EPS contributes to the increase of the yield strength of polyamide 6 by about 5%–10%. The increase of the Vicat softening point by 5–8 K and the surface hardness by 25–30 MPa of materials based on polyamide 6 and modified polystyrene was investigated. It is caused by the redistribution of intermolecular bonds between the components of the blend under by the effect of a uniformly distributed PVP in the EPS resulting in increased compatibility between the components and the compacted structure. POLYM. ENG. SCI., 60:935–943, 2020. © 2020 Society of Plastics Engineers

Structure-property correlation of poly(ethylene glycol) based form stable phase change materials with different crosslinking structure

Chemical crosslinking is an important strategy for preparation of form stable phase change materials (FSPCMs). However, the influence of different crosslinking structure on the properties of FSPCMs is not very clear currently. In this work, PEG-based FSPCMs are synthesized by free-radical polymerization. They possess different crosslinking densities, and the location of PEG moieties include two different sites (backbone or side chain). The chemical structure, phase change property, crystal structure, mechanical performance, and thermal reliability of the FSPCMs are studied and compared with respect to their different crosslinking structure. It is found that the phase change enthalpy and degree of crystallinity increase with decreasing crosslinking density, and PEG moieties locating in side chain is preferable. With decreasing crosslinking density, the spherulites of the FSPCMs become larger, but always smaller than that of pristine PEG. The results can be explained by the restriction on movement/assembly of PEG moieties by the crosslinking network. The mechanical performance of FSPCMs with PEG moieties located in backbone is preferable than that in side chain. Tensile strength is maximized with poly(ethylene glycol) acrylate (Mn = 12000) as monomer, and elongation at break increases monotonically with decreasing crosslinking density. The findings of this work will contribute to the future design of FSPCMs with optimized overall thermal energy storage and mechanical properties.

Preparation and characterization of polypropylene composites reinforced by functional ZnO/lignin hybrid materials

Abstract The aim of this study was to obtain polypropylene composites filled with a ZnO/lignin hybrid filler and to examine their chemical and mechanical properties. Inorganic-organic hybrid materials were obtained using an environmentally-friendly, low-cost mechanical method. The use of an inorganic component mainly influenced the improvement of thermal properties, in turn, the use of lignin was mainly supported by its low price as well as unique properties. The effectiveness of ZnO/lignin materials production was confirmed using Fourier transform infrared spectroscopy and, indirectly, by colorimetric analysis. In addition, the thermal stability and porous structure analyses were also carried out. Polymer composites containing 3 wt% of each filler were subjected to wide angle X-ray diffraction tests and differential scanning calorimetry studies to define their supermolecular structure as well as thermal properties. Polarized light microscopy was performed to assess the influence of fillers on the crystallization of polypropylene. Tensile tests provided information regarding the mechanical properties of produced materials. The presence of hybrid fillers influences the nucleation activity and it was responsible for an increased crystallinity degree of composite samples. It was also established that introduction of ZnO and hybrid fillers with high amount of ZnO into the polypropylene matrix resulted in a significant increase of density of the formed nuclei.

Morphological, barrier and mechanical properties of films from poly (butylene succinate) reinforced with nanocrystalline cellulose and chitin whiskers using melt extrusion

Nanocomposites from biodegradable poly (butylene succinate) (PBS), blended with nanofillers chitin whiskers (CHW, 1–5%) and nanocrystalline cellulose (NCC, 1–5%), were synthesized using melt extrusion. Morphological studies using transmission electron microscopy showed the dispersion of nanofillers in the polymer matrix. The nanofillers restricted the mobility of polymer chains, and promoted nucleation and recrystallization of polymer as reflected by increase in degree of crystallinity (Xc) from 65.9 to 75.6%. Addition of NCC and CHW increased the tensile strength of PBS based films from 23.2 MPa to 32.9 MPa and 43.6 MPa, respectively. Decrease in oxygen transmission rate of PBS films from 737.7 to 280 cc/m2/day was observed by adding 3% NCC, which further reduced to 23.8 cc/m2/day by adding compatibilizer methylene diphenyl diisocyanate (MDI, 4%). Water vapor transmission rate of PBS films reduced from 83.8 to 49.4 g/m2/day with 3% NCC addition and addition of 4% MDI further reduced it to 30.8 g/m2/day. This research suggested potential of NCC and CHW as nanofillers for enhancement of mechanical and barrier properties of PBS based films used in biodegradable food packaging applications.

Structure of Zinc Nanotubes

The formation of Zn-based nanotubes by electrochemical synthesis in pores of template polymer matrices is considered. It is established that the number of defects in the synthesized nanotubes decreases with a decrease in the mean crystallite size, while the degree of crystallinity increases. The number of defects directly affects the structural properties of Zn nanotubes. However, an uncontrolled growth of nanotubes is observed at a potential difference of 2.0 V, as a result of which amorphous inclusions are formed in the crystal structure of nanotubes, thus leading to their partial destruction.

Ion Gel Dynamic Templates for Large Modulation of Morphology and Charge Transport Properties of Solution-Coated Conjugated Polymer Thin Films.

Dynamic surfaces play a critical role in templating highly ordered complex structures in living systems but are rarely employed for directing assembly of synthetic functional materials. We design ion gel templates with widely tunable dynamics ( Tg) to template solution-coated conjugated polymers. We hypothesize that the ion gel expedites polymer nucleation by reconfiguring its surface to facilitate cooperative multivalent interactions with the conjugated polymer, validated using both experimental and computational approaches. Varying ion gel dynamics enables large modulation of alignment, molecular orientation, and crystallinity in templated polymer thin films. At the optimal conditions, ion-gel-templated films exhibit 55 times higher dichroic ratio (grazing incidence X-ray diffraction) and 49% increase in the relative degree of crystallinity compared to those templated by the neat polymer matrix. As a result, the maximum hole mobilities increase by factors of 4 and 11 along the π-π stacking and the backbone directions. Intriguingly, we observe a synergistic effect between the gel matrix and the ionic liquid that produces markedly enhanced templating effect than either component alone. Molecular dynamics simulations suggest that complementary multivalent interactions facilitated by template reconfigurability underlie the observed synergy. We further demonstrate field-effect transistors both templated and gated by ion gels with average mobility exceeding 7 cm2 V-1 s-1.

Supercritical Fluid Media in Challenges of Substance and Material Dispersion

The paper deals with the problem of material dispersion using supercritical fluid media. At the same time, emphasis is made on modifications (SAS, GAS, SEDS and ASES) of the supercritical fluid anti-solvent method of dispersion. The results of SAS method implementation for dispersion of pure polycarbonate and polycarbonate doped with “CdSe/CdS - core/shell” quantum dots (carried out in the pressure range of 8.0-25.0 MPa at temperatures of 313.15 K and 358.15 K) are submitted. The range of the operating parameters has been established through the example of pure polycarbonate dispersion, which provides the production of nanoparticles with the size range of 10 100 nm. Encapsulation of CdSe/CdS quantum dots into polycarbonate using the SAS method has no effect on optical properties of the encapsulated quantum dots. The results of paracetamol dispersion using the SEDS method are presented. The effect of operating conditions of the paracetamol dispersion process on morphology of the obtained product is described. Co-dispersion of ethylene–vinyl acetate copolymers and low-density polyethylene mixtures by SEDS method has been carried out under pressures of 8.0-25.0 MPa at temperatures of 313 K, 323 K, and 333 K. The comparison of melting and crystallization between the resulting copolymer mixtures and mixtures with the same composition obtained by mixing in the liquid melt, has shown that implementation of SEDS results in an increase of crystallinity degree of the polymer mixtures.

COMPARATIVE STUDIES OF PHYSIC-CHEMICAL PROPERTIES AND STRUCTURE OF COTTON CELLULOSE AND ITS MODIFIED FORMS

Comparative studies of the physicochemical properties and structures of cotton cellulose, microcrystalline cellulose, and nanocellulose were carried out using IR, NMR spectroscopy, X-ray diffraction, thermal analysis in order to identify the dependence "particle size - structure - properties". It was revealed that in the series “cotton cellulose – microcrystalline cellulose – nanocellulose” the degree of polymerization decreases (1200, 230, 110 respectively), the degree of crystallinity increases (66%, 72%, 83% respectively). The IR spectra of microcrystalline cellulose and nanocellulose are characterized by sharp peaks (in the range 1000–1500 cm–1) compared with cotton cellulose. The amount of bound water in gels of microcrystalline cellulose and nanocellulose increases with decreasing particle size, the degree of stability of colloidal systems increases with the transition from microcrystalline cellulose to nanocellulose. Nanocellulose and microcrystalline cellulose have relatively smaller mass loss and relatively large temperature ranges of intensive decomposition and their thermal stability is higher than cotton cellulose. It was found that the periodate oxidation rate of nanocellulose is higher than that of microcrystalline cellulose and cotton cellulose. It was established that microcrystalline cellulose is quantitatively susceptible to periodate oxidation in 7–8 hours, and nanocellulose in 0.5–1 hour.

Thermolysis of sprayed suspensions for obtaining highly spinel ferrite nanoparticles

Thermal treatment of ferrite magnetic nanoparticles in NaCl matrix gives an opportunity to increase their specific magnetization with preservation of nanoscale size. Composite materials based on mixed ferrites Co0.65Zn0.35Fe2O4 and Mg 0.5Zn0.5Fe2O4 were synthesized by spray-drying of aqueous suspensions in presence of NaCl and annealed at 300 –900 °C. The microstructure and phase composition of nanoparticles before and after annealing were studied by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction analysis and IR spectroscopy. The magnetic properties of nanoparticles were estimated using a ponderomotive method of measuring the specific magneti zation at room temperature in a magnetic field with an induction of 0.86 T. The increase of the annealing temperature up to 900 °C was established to lead to the increase in the specific magnetization of ferrites – from 32.79 to 91.3 emu/g (Co0.65Zn0.35Fe2O4) and from 2.76 to 22.31 emu/g (Mg 0.5 Zn 0.5Fe2O4) due to recrystallization processes and increase of crystallinity degree of the ferrites. Due to the NaCl insulating layer, the particle size increases just slightly (from ~ 10 nm before annealing to ~ 60 nm after annealing at 900 °C). This method is effective for substantial increase in specific magnetization of ferrite nanoparticles with preservation of their nanoscale size.

OBTAINING TECHNOLOGY FOR NANOCOMPOSITES BASED ON POLYAMIDE-6 AND ORGANOMODIFIED MONTMORILLONITE

The obtaining technology of nanocomposites based on polyamide-6 and organomodified montmorillonite is developed. The technological parameters of extrusion and injection molding, and their influence on the formation of nanoscale inorganic phase of the polyamide are investigated. Morphology and thermal behavior of polyamide-6, composites based on polyamide-6 and modified montmorillonite are studied by WAXS, XRD, DTA and DSC data. Morphology and thermal behavior of polyamide-6 and composites based on polyamide-6 and modified montmorillonite are shown to be in a strong juxtaposition. New γ-phase formation is revealed in composite polyamide-6 – 1–2 % of modified montmorillonite in contrast with polyamide-6 and mechanical mixtures of polyamide-6 and montmorillonite. Optimal concentrations of modified montmorillonite in the composites stated as 1 – 2 % are shown to correspond with composites improved properties as compared to initial polyamide-6. It is explained by increasing crystallinity degree, which resulted from acting of modified montmorillonite particles as nucleation heterogenetic agents.

Influence of Cd0.99Eu0.01SiO3 nanoparticles concentration on Cd0.99Eu0.01SiO3/PVDF nanocomposite films

Nanocomposites of piezoelectric PVDF doped with Cd0.99Eu0.01SiO3 of varying concentration was prepared by spin coating technique. The prepared nanocomposites were investigated by X-ray diffraction technique and it showed an α to β transformation compared to pristine PVDF. This phase exhibits piezoelectric property employed in the design of Sensors and Actuators. SEM micrographs indicated a modification in surface morphology of the nanocomposites. Results of EDX indicate the incorporation of the elements of the nanodopant in PVDF. Differential Scanning Calorimetry showed an increase in degree of crystallinity. Optical bandgap energy of the nanocomposites increased with increase in concentration of nanodopant. Dielectric studies showed an enhancement in Dielectric permittivity and AC conductivity of the nanocomposites which can be employed in the design of energy storage devices

Phase-dependent mechanical properties of two-dimensional silica films: A molecular dynamics study

The recently discovered two-dimensional (2D) silica films can be grown in both crystalline phase and vitreous phase. Using molecular dynamics simulations, we show that these two phases of 2D silica possess vastly different mechanical properties. It is shown that the Young’s modulus of crystalline 2D silica is 54% greater than that of its vitreous counterpart. The vitreous 2D silica fails via the ductile fracture with serrated stress-strain curves, while its crystalline counterpart exhibits the abrupt brittle rupture. Both the fracture strength and fracture strain of crystalline 2D silica are significantly larger than those of its vitreous counterpart. Fracture mechanics theory is utilized to give some explanations to the different fracture properties of these two phases. Moreover, 2D silica mixed by crystalline phase and vitreous phase is also studied. Owing to the different mechanical properties of crystalline and vitreous phases, the elastic and fracture properties of this mixed-phase 2D silica are strongly dependent on its crystallinity. Specifically, we find that the Young’s modulus of the mixed-phase 2D silica, ranging between the values of its crystalline and vitreous counterparts, increases as the degree of crystallinity increases. Meanwhile, with the increase of the degree of crystallinity the fracture strain of the mixed-phase 2D silica is found to decrease, making its value smaller than that of the purely crystalline and vitreous 2D silica.

Influence of the mold temperature on the material properties and the vibration welding process of crosslinked polyamide 66

Radiation crosslinking of polyamide 66 with electron beams alters the material characteristics. This leads to a varied relationship between the process, the structure, and properties for vibration welding crosslinked polyamide 66. A three‐dimensional network of covalent bonds in the amorphous areas results in an impeded melt flow and altered welding characteristics. A possible way to influence this three‐dimensional network is to change the mold temperature during the injection molding process. At higher mold temperatures, the degree of crystallinity increases and leads to a decrease in the resulting covalent bonds in the amorphous area. The altered degree of covalent bonds influences the vibration welding process. Higher temperatures during the process can be achieved. The scope of this article is to show how the mold temperature influences the material characteristics and, by extension, the resulting processing and welding characteristics of radiation crosslinked polyamide 66. Optical, thermal, mechanical and chemical investigations serve to highlight the influence of the mold temperature on the material and the welding process of radiation crosslinked polyamide 66. POLYM. ENG. SCI., 58:E207–E214, 2018. © 2017 Society of Plastics Engineers

Ethylene/POSS copolymerization behavior of postmetallocene catalysts and copolymer characteristics

ABSTRACTCopolymerization of ethylene with iso‐butyl substituted monoalkenyl(siloxy)‐ or monoalkenylsilsesquioxane (POSS) comonomers over bis(phenoxy‐imine) and salen‐type titanium and zirconium catalysts was studied. It was found that the polyreaction performance was significantly depended by the kind of the catalyst and by the structure and concentration of POSS in the feed. The POSS comonomer was efficiently incorporated into the polymer chain at up to 0.2 mol %. The differences in the copolymer compositions as the functions of the catalyst kind and the POSS comonomer were observed, including the varied number‐average sequence length of ethylene and unsaturated end groups, as determined by 1H NMR and FT‐IR. The presence of POSS comonomers affected also the melting and crystallization behavior of the copolymers, as evidenced by DSC, because of influence on the polymer chain arrangement. The POSS units could act as the nucleating agents. Moreover, the crystal and structural parameters of ethylene/POSS copolymers were evaluated on the basis of X‐ray results, and the limited self‐aggregation of POSS incorporated into the polymer chain, the small number and size of POSS aggregates, and the increased crystallinity degree of copolymers were demonstrated. The ethylene/POSS copolymers produced by postmetallocenes offered also high thermal stability and interesting morphological properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3918–3934

Influencia de la temperatura en la compactación hidrotérmica en caliente de polvos de magnesio hidroxiapatita

Preparation of hydrothermal hot-pressed (HHP) compacts of the stoichiometric hydroxyapatite and solid-solution of magnesium hydroxyapatite powders (HAp and Mg-HAp) was carry out at different temperatures 150, 175 and 200°C, using uniaxial pressure load of 60MPa for 6h, with the addition of 10% wt. of deionized water as a solvent. The starting powders were obtained by hydrothermal synthesis at 150°C for 10h. The HHP compacts were chemical, physical and mechanically characterized. According to the results, it has been determined that an increase of the HHP temperature stimulate the reaction between the added water and the particles of HAp or Mg-HAp, which results on an increase of crystallinity degree without the formation of any addition products or alteration of the HAp structure. This result is particularly relevant, due to during HHP process, the production of effective packing of the particles which is activate by the dissolution-recrystallization mechanism in presence of added water which allow a densification near of 70%. For the HHP compacts of the HAp and Mg-HAp prepared at 200°C, with porosity near to 30-36% of open pores, achieve the maximum apparent density value of 3.085±0.138g/cm3 and 2.792±0.021g/cm3, respectively, with the maximum tensile strength of 7.10±0.20 and 5.89±0.06MPa. From these results, the obtained HHP compacts might be useful for orthopedics and/or dentist applications.

Microencapsulation of sacha inchi oil using emulsion-based delivery systems

In this study, sacha inchi oil (SIO) was microencapsulated by emulsion-based systems using ovalbumin (Ova), pectin (Pec), and xanthan gum (XG), followed by freeze-drying. The microencapsulation was confirmed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The stability of omega-3 in SIO alone as well as in microencapsulated SIO was assessed by nuclear magnetic resonance (1H NMR) spectroscopy after human gastric simulation (HGS). The SEM results revealed distinct structures for the two types of microcapsules. The thermograms showed that the thermal resistance was increased in the microencapsulated SIO, indicating that the emulsion-based system may be a way to protect the omega-3 in the SIO. In addition, the microencapsulation conferred an increased crystallinity degree, indicating a higher structural organization. Moreover, this method did not affect the stability of SIO, as confirmed by 1H NMR. The release of omega-3 acyl units from the SIO was correlated with the decrease of the methynic proton (sn, 2 position) of triacylglycerol (TAG). In contrast, the increase of 1,3-diglycerides was negatively correlated with the decrease of glyceryl groups (sn, 1,3 positions). The HGS conditions did not significantly alter the stability of the omega-3 of SIO over 180min. The SIO-Ova microcapsules had a similar behavior to the SIO, and the presence of Ova was not enough to prevent the decrease of omega-3 content over 180min. The SIO-Ova-Pec and SIO-Ova-XG microcapsules were shown to protect the omega-3 content effectively. In conclusion, the microcapsules developed in this study can be used to transport nutraceutical compounds because they are resistant to the human gastric conditions tested in vitro.