Increase In Degree Of Crystallinity Research Articles

Cellulose nanocrystal dispersion-ability in polylactides with various molecular weights prepared in dichloromethane/dimethyl sulfoxide solvents for electrospinning applications

In this study, effects of polylactide molecular weight, i.e., high (HPLA), medium (MPLA), low (LPLA), and dichloromethane (DCM)/dimethyl sulfoxide (DMSO) blend ratio on cellulose nanocrystal (CNC) dispersion quality in solution casted PLA/CNC nanocomposites were investigated via small amplitude oscillatory shear rheological analysis, while crystallization behavior, thermal degradation, morphological structure of the nanocomposites were also reported. Due to its low dielectric constant, none of the nanocomposites with 100DCM indicated a change in their complex viscosity as a result of poor CNC dispersion. This is while the increase in DMSO content (50%vv−1) improved CNC dispersion. The superior CNC dispersion-ability in PLAs with lower molecular weight was confirmed. The poorer CNC dispersion in HPLA attributes to hindering effect of higher molecular weight on solvent and nanoparticle diffusion. The better dispersed CNCs influenced crystal nucleation behavior of PLAs and increased crystallinity degree. In addition, the impact of well-dispersed CNCs on fiber formation quality of nanocomposites was reported. Introducing finely dispersed CNCs (1 wt%) in LPLA refined fiber diameters around 1200 nm with more homogenous structure. Besides, the use of 100DCM and the use of DMSO at high contents (50%vv−1) deteriorated fiber formation, respectively, due to low conductivity of DCM and high boiling temperature of DMSO.

Pyro-dextrinization, acid hydrolysis, and cross-linking impacts on functional, pasting and structural properties of elephant foot yam starch

Underutilized plants represent valuable reservoirs of starch, urging the need for prominent exploration of these botanical resources. The effects of pyrodextrinization, acid hydrolysis and cross linking modification on the physico-chemical, functional, structural and pasting properties of elephant foot yam (Amorphophallus paeoniifolius) starches were studied. Yam starch was cross-linked using boric acid, which is for the preparation of cross-linked yam starch. The results suggested that cross linking modification significantly decreased moisture content (10.46–1.91 %), swelling power (3.71–1.69 %) and solubility (3.58–1.51 %) of yam starch. At the same time it significantly (P < 0.05) improved amylose content (13.89–18.04 %) of starch. Increase in degree of crystallinity of all modified starches was depicted from X-ray diffractogram. Decrease in viscosity profile of modified starches was observed using Rapid Visco Analyzer. The morphology of the starch granules presented surface fissures in case of acid, whereas smooth surface of native, pyrodextrinized and cross-linked starches were observed. This research has demonstrated that chemical alterations induce notable transformations in the inherently flexible starch polymer, thereby influencing its functional characteristics and structural features. The treatment which resulted in the most thermostable starch obtained in this study was cross-linked yam starch. The ultimate goal is to offer yam starch suitable for a wide range of applications across various industries, including both food and non-food sectors positively revealing its utmost applicability for food packaging industry to be utilized as a film or coating material (cross-linked starch), fat replacers/mimickers in low-fat starch based healthy foods (acid-hydrolyzed starch).

Valorization of guinea grass seed (Megathyrsus maximus): Synthesis and utilization of cellulose microfiber to reinforce esterified and cross-linked guinea starch films

The present study extracts starch from guinea grass seed and fiber from the starch extraction residue. The fibrous residue was chemically converted into cellulose microfiber (CMF) and used to reinforce the native, esterified and crosslinked guinea starch films. The films were developed with 5 % starch, 40 % glycerol and 0, 2.5, 5, and 10 % CMF based on the dry matter of starch. SEM images of all film samples showed good compatibility of CMF with starch molecules, and no fractures or pores were observed. Adding filler materials to modified starch films slightly increased the film thickness (0.24 to 0.30 mm) due to the high dimensions of CMF, which comprise a significant amount of the composite's volume. A synergetic effect of starch modification and CMF in films decreased the moisture content (21.98 to 9.21 %), water solubility (25.65 to 15.47 %), water vapor permeability (6.96×10−7 to 1.65×10−7g∙mm2∙day∙Pa), and elongation at the break (33.51 to 16.79 %) while increasing the tensile strength (1.84 to 3.85 MPa) and Young's modulus (5.49 to 22.93 MPa). The L* and a* values of the films decreased, and the b* and opacity values of the films increased with the addition of CMF. The XRD graph showed that all films have semicrystalline structures with peaks at 18°, 20°, and 22°, and the degree of crystallinity increases (32.3 to 55.1 %) with CMF. All film samples showed good thermal stability up to 315 °C. In conclusion, esterified starch-based films exhibited superior barrier properties and flexibility. On the contrary, cross-linked starch films demonstrated higher tensile strength and lower water solubility.

Comparative effects of different coastal weathering on the thermal, physical, and mechanical properties of rubberwood–latex sludge flour reinforced with polypropylene hybrid composites

The influence of coastal weathering in tropical countries is a concern in terms of applications of wood-plastic composites (WPCs). Therefore, developing the WPCs into hybrid composites for increasing the resistance to the coastal climate needs further investigation. The current work studies the effects of different coastal climates (Gulf of Thailand and Andaman Sea), exposure times, and latex sludge contents on the properties of rubberwood-latex sludge flour reinforced with polypropylene hybrid composites. The hybrid composites were manufactured with a twin-screw extruder for mixing and a compression molding machine for forming. The results revealed that the hybrid composites weathered for 12 months significantly (α = 0.05) decreased the modulus of rupture, modulus of elasticity, screw withdrawal strength, and hardness with a maximum reduction of 218.6%, 207.4%, 84.2%, and 11.4%, respectively. However, adding the latex sludge flour of about 25 wt% increased crystallinity degree and thermal stability as compared with the WPCs filling 50 wt% rubberwood flour. The hybrid composites weathered under the Andaman Sea exhibited less loss of all the mechanical properties than that weathered under the Gulf of Thailand. It is therefore suggested that the hybrid composites added to the latex sludge waste have the potential to be used to produce the engineering products that were applied under the coastal climates.

Non-Arrhenian hydrolysis of polyethylene terephthalate – A 5-year long aging study above and below the glass transition temperature

The hydrolysis of PET was studied over a wide range of temperatures from 25 to 105 °C for duration up to 5 years in water. It was demonstrated that independent of the aging temperature, a decrease in the molar mass was witnessed due to chain scissions that occur during hydrolysis of the ester group. Above Tg, it was shown that chain scissions induced an increase in degree of crystallinity and amorphous layer thickness. However, this phenomenon, chemi-crystallization, was not observed at low temperatures, i.e. below Tg. This change reflects a different behavior when the polymer is exposed to water in the glassy or rubbery state. This was highlighted by the quite different activation energies below and above Tg, respectively equal to 31 ± 12 and 134 ± 4 kJ/mol.

Magnetron deposition of copper oxide coatings in a metallic mode enhanced by RF-ICP source: A role of substrate biasing

The article describes deposition of copper oxide coatings using magnetron sputtering in a metallic mode enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source. The role of substrate biasing (floating potential, −70 and −140 V) on structural properties and elemental composition of copper oxide coatings is determined using SEM with EDS, XRD and TEM. This study shows the change of coating microstructure from columnar to dense/compact and the increase in crystallinity degree of coatings, when the substrate is biased. EDS analysis reveals the presence of Ar and the increase in O content in the coating due to intensive ion bombardment. Deposition conditions are changed using substrate biasing, which suggests the contribution of ion bombardment to the coating deposition in the case of magnetron sputtering of copper oxide in the metallic mode.

Synergistic effect of endogenous gluten and oleic acid on wheat starch digestion by forming ordered starch-fatty acid-protein complexes during thermal processing

The aim of this study was to understand the potential of endogenous gluten inhibiting the digestibility in vitro of wheat starch (WS) in starch-fatty acid-protein system. Therefore, the influences of gluten and whey protein isolate (WPI) on the properties, multi-scale structure and in vitro digestibility of WS in WS-oleic acid (OA)-protein system were compared. The results of digestibility in vitro indicated that the ternary system of starch-fatty acid-protein showed higher resistant starch (RS) content as well as lower rapidly digestible starch (RDS) content than the binary system of WS-OA, demonstrating protein decreased WS digestion of WS-OA system. The results of pasting properties showed that gluten and WPI both increased the viscosities of WS-OA system during the cooling period due to the formation of WS-OA-protein ternary complex. The results of swelling power and solubility analysis showed that gluten and WPI both decreased the swelling power and solubility of WS-OA binary system. Laser Confocal Raman and X-ray diffraction (XRD) studies indicated that gluten and WPI both increased the ordered degree of WS-OA binary system by decreasing the full width at half maximum (FWHM) of the peak at 480 cm−1 and increasing crystallinity degree. Strikingly, compared with WPI, gluten had greater effects on the digestibility in vitro, pasting properties and ordered degree of WS in WS-OA-protein system. Therefore, gluten as an endogenous protein has the potential application in reduction the enzymatic digestibility of WS by regulating the reassembly of starch and fatty acid during thermal processing.

Thermal and Structural Properties of Poly(Lactic Acid)/Silica/Alumina Composite Materials

In the present study, Polylactic acid/ silicon dioxide (SiO2)/ alumina (Al2O3) composite films were produced by a casting method. Thermal, morphological, optical and structural properties of obtaining samples investigated. The addition of aluminum monoxide and silicon dioxide fillers in PLA matrix increases the glass transition temperature significantly, and the Al2O3 and SiO2 particles behave as good nucleating agents with PLA matrix. A homogeneous distribution of SiO2 and Al2O3 particles was observed in the composite films. XRD results revealed that the addition of SiO2 particles improved the crystallinity of PLA, knowing that the degree of crystallinity increase from 2.75% to 31.63% by adding the nucleating agents. The DSC results showed that the glass transition temperature increases by 12 °C in the composites than the pure PLA.

A New Multistep Chemical Treatment Method for High Performance Natural Fibers Extraction

ABSTRACT A new chemical treatment method to extract rich cellulosic fibers from date palm agro-residues is developed. The method yielded high-performance natural date palm fibers based on multistep process, which is efficient, sustainable, and unique. The proposed method consists of three steps: dewaxing, acetylation, and mercerization, which are unique in terms of time control and their sequence resulting in optimal properties of extracted fiber. Each step is strictly time-controlled and designed to achieve specific objectives in preparation for the next step. Optimization techniques including design of experiment are used to adjust input parameters so as to obtain optimized output from the treatment method. Two approaches are used for supplying heat during the fiber extraction procedure i.e. conventional heat source and microwave heat source. Experimental characterization of extracted fibers is carried out to determine its mechanical and physical properties. Results showed 32% increase in crystallinity degree of the treated fiber over the untreated one. The new method achieved around five-fold increase in ultimate tensile strength and three-fold increase in elastic modulus. The significant enhancement in properties of treated fibers over untreated counterparts confirms the effectiveness of the new process.

Mechanical, thermal, rheological assessment of polyamide-6 reinforced composites by addition of lamellar zirconium phosphate

The improvement of properties has been pursued through the addition of an immense variety of fillers in polymers. In this work we studied the effect of lamellar zirconium phosphate (ZrP) on the physico-mechanical properties of polyamide-6 (PA-6). The ZrP was synthesized and incorporated into PA-6 matrix at 1, 2 and 3 wt.%. Structural, thermal, relaxometric, tensile, melt flow and rheologic characteristics were assessed. Thermogravimetry indicated a low influence of the filler on thermal stability. The deconvolution of the melting peaks indicated transformation of the PA-6 α to γ phase and increase in crystallinity degree. Sample with 1 wt.% of ZrP showed an additional peak at higher relaxation time indicating restriction of polymer molecular mobility. By infrared, amine and carbonyl indices evaluation suggested ZrP interfered on the PA-6 hydrogen bonds. The elastic modulus increased slightly for all composition. Melt flow rate decreased with the amount of ZrP. The composite with 1 wt.% of ZrP exhibited the highest storage modulus and shear thinning effect noticed in the complex viscosity.

Biopolyethylene/macaíba shell (Acrocomia intumescens) composites compatibilized with PE‐g‐MA and PE‐g‐AA: Influence of macaíba oil on processing

AbstractThe present investigation aimed to produce ecological composites of biopolyethylene (BioPE) with macaíba shell (MS), using polyethylene‐graft‐maleic anhydride (PE‐g‐MA) and polyethylene‐graft‐acrylic acid (PE‐g‐AA) as compatibilizers, as well as macaíba almond oil as a plasticizing agent. The composites were processed in a co‐rotational twin‐screw extruder and injection molded. The addition of 30% by weight of MS in the BioPE matrix caused a reduction in impact strength and elongation at break, but improved stiffness and heat deflection temperature. The PE‐g‐MA and PE‐g‐AA compatibilizers improved the impact strength of the composites, suggesting increased interactions between the phases. There was an increase in the composites degree of crystallinity, indicating that the MS acted as a nucleating agent. The macaíba oil addition to the composites increased the impact strength, indicating a plasticizing effect. However, the elastic modulus, tensile strength, and degree of crystallinity tended to decrease. In general, the use of PE‐g‐MA compatibilizer was more effective to improve the composites mechanical properties. The reuse of MS is feasible for the production of sustainable composites.

Influence of early thermal-oxidative ageing on the structure and properties of polyoxymethylene copolymer.

Thermal-oxidative ageing of polyoxymethylene (POM) copolymer in the oven at 100°C for 1, 2, 3, 5, 7, 10, 14 and 21 days and the influence of early thermal-oxidative ageing on POM structure and properties were studied by means of wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and tensile test. Based on the results, we found that the early thermal-oxidative ageing of POM copolymer can be divided into three regions. The region I is the initial 3 days. In this region, some molecular chains rearranged, resulting in internal stress relaxation, increase of crystallinity degree and grain size due to the perfection of crystal structure; both extended chain crystal (ECC) and folded chain crystal (FCC) increased and ECC grew faster than FCC. The region II is from 3 days to 10 days, and in this region, chain scission took place in amorphous region and led to chemi-crystallization. The region III is after 10 days. In this region, the structure and performance of POM copolymer reached a stable situation at this stage. In this work, the difference between skin and core were also analysed.

Crystallization Behavior and Mechanical Properties of Poly(ε-caprolactone) Reinforced with Barium Sulfate Submicron Particles.

Poly(ε-caprolactone) (PCL) was mixed with submicron particles of barium sulfate to obtain biodegradable radiopaque composites. X-ray images comparing with aluminum samples show that 15 wt.% barium sulfate (BaSO4) is sufficient to present radiopacity. Thermal studies by differential scanning calorimetry (DSC) show a statistically significant increase in PCL degree of crystallinity from 46% to 52% for 25 wt.% BaSO4. Non-isothermal crystallization tests were performed at different cooling rates to evaluate crystallization kinetics. The nucleation effect of BaSO4 was found to change the morphology and quantity of the primary crystals of PCL, which was also corroborated by the use of a polarized light optical microscope (PLOM). These results fit well with Avrami–Ozawa–Jeziorny model and show a secondary crystallization that contributes to an increase in crystal fraction with internal structure reorganization. The addition of barium sulfate particles in composite formulations with PCL improves stiffness but not strength for all compositions due to possible cavitation effects induced by debonding of reinforcement interphase.

Nano-carbonated hydroxyapatite precipitation from abalone shell (Haliotis asinina) waste as the bioceramics candidate for bone tissue engineering

In this study, nano-carbonated hydroxyapatite (n-CHAp) was successfully synthesized with abalone shells ( Halioitis asinina) as the calcium source using precipitation methods with aging time variations, namely, 0 (without the aging process), 24, and 48 h. Based on an analysis of X-ray diffraction characterization, the spectrum of the n-CHAp is shown for all sample variations in aging time. The results of the calculation of lattice parameter values confirm that the phase formed is the B-type CHAp phase with the increasing crystallinity degree, crystallite size, particle size, and polydispersity which is confirmed by the presence of the CO32- functional group at 1438 cm−1 and 878 cm−1, that is, the B-type carbonate substitution characteristic. The presence of the carbonate ions identified as smaller during the extension of aging time causes the decreasing value of the Ca/P mole ratio but still has a value greater than the HAp Ca/P value (1.67), which is 1.80–1.72. Based on the transmission electron microscopy analysis, the nanometer-size of B-type CHAp particles was successfully obtained. According to the criteria for nanostructures, crystallographic properties, carbonate content, and chemical processes, B-type CHAp samples based on abalone shells ( Halioitis asinina) are one of the candidates in bioceramics for bone tissue engineering applications.

Biodegradation evaluation of poly (lactic acid) for stent application: Role of mechanical tension and temperature

AbstractIn this study, an experimental investigation is conducted on mechanical characteristics of poly(lactic acid) (PLA), before, and during degradation for stent application. A bioreactor is designed and fabricated to mimic in‐vivo environment of the body for studying degradation behavior of PLA fibers manufactured by melt spinning method. Beside PLA fibers, the degradation of PLA braided stents is investigated as control samples. To measure stress–strain and stress relaxation properties of PLA fibers, tensile, and relaxation tests are conducted. The decreasing trend of Young's modulus, variations in residual stress value after relaxation and pattern of stress relaxation are found during degradation. The influence of effective parameters, that is, temperature and stress, on PLA degradation is also studied. Moreover, the PLA degradation is analyzed by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and microscopic images. GPC results indicate the molecular weight decreases from 196,000 to 80,000 due to degradation while DSC analysis confirmed that the degradation promote an increase in PLA degree of crystallinity (from 43.3% to 59.8%). In addition, TGA results show that the PLA thermal stability decreases during degradation. This study provides useful information on PLA properties during degradation to assess the material in context of degradable stents.

Influence of Polymer-Silicate Nucleator on the Structure and Properties of Polyamide 6

Physico-chemical properties of developed nickel-containing modified silicate materials as the nucleators for composites based on polyamide 6 are presented. As it was established, additive of the nucleator modified by polyvinylpyrrolidone promotes the increase of crystallinity degree of polyamide 6 and the decrease of crystallite size. It was found that changes in the structure of the material cause the increase of its tensile strength, surface hardness and Vicat softening point.

Fabrication of zirconia ceramics by sintering in a magnetic field

An external magnetic field was applied for activating the process of sintering the ZrO2-based ceramic materials in order to lower high sintering temperatures and improve the quality of the ceramics. The regularities of the formation of the structure of crystalline phases and the strength properties of zirconium ceramics during sintering of compacts from ultradispersed powders in the presence of a constant magnetic field (H = 4.01·1010–7.87·1010 A/m) with the symmetry Fp = C3 have been investigated. Sintering was carried out in the volume of a resistance furnace. The magnetic field inside the furnace volume was created by a toroidal coil with a special symmetrized winding. It has been established that the crystal structure, morphology and shape of grains in ZrO2 ceramics sintered in the constant magnetic field at 1400 °C are characterized by more perfect crystallographic forms when compared with sintering without an applied magnetic field, and the degree of isometricity increases. In this case, the degree of crystallinity increases, on average, by 2.4 times its initial value. The observed formation and stabilization of high-temperature phases (high-temperature modifications of the о* and с phases) of zirconium dioxide when sintering in the presence of the magnetic field are associated with directional changes in the structural characteristics (a decrease in crystalline microdistortions, an increase in the degree of uniformity). The oxide ceramics sintered in the presence of a constant magnetic field (B = 0.02–1 T) with a given symmetry С3 possess improved physical and mechanical characteristics (the strength and density increase by 54% and 15% from their initial values, respectively) and more perfect crystalline forms of microstructures, as compared with sintering without the imposition of an external magnetic field.

Carboxymethyl modification of Cassia obtusifolia galactomannan and its evaluation as sustained release carrier

Carboxymethylation of Cassia obtusifolia galactomannan was carried out by Williamsons synthesis. Modification of galactomannan was confirmed by Fourier-transform infrared and 1H-Nuclear magnetic resonance spectroscopy. The degree of carboxymethyl substitution was found to be 1.69. Carboxymethylation was observed to increase the powder flow, solubility and swelling, while decrease the viscosity and alter the compression characteristics from elastic to plastic. The results of X-ray diffraction and scanning electron microscopy studies indicated increase in degree of crystallinity. The modified gum was used for preparing diclofenac sodium-loaded, Ca2+-gelled beads which were coated with gastroresistant Eudragit-L100. The formulation of beads was optimized using central composite experimental design. The optimal formulation of beads contained carboxymethylated Cassia galactomannan-2.85%,w/v and calcium chloride −15%,w/v, which showed yield −185.4%, entrapment-95.41% and release of 93.32% of diclofenac over 24 h. The release of diclofenac followed first-order kinetics by Super case-II transport. Thus, carboxymethyl Cassia galactomannan appears suitable for sustained drug delivery.

The Crystallization Process of Vaterite Microdisc Mesocrystals via Proto-Vaterite Amorphous Calcium Carbonate Characterized by Cryo-X-ray Absorption Spectroscopy

Investigation on the formation mechanism of crystals via amorphous precursors has attracted a lot of interests in the last years. The formation mechanism of thermodynamically meta-stable vaterite in pure alcohols in the absence of any additive is less known. Herein, the crystallization process of vaterite microdisc mesocrystals via proto-vaterite amorphous calcium carbonate (ACC) in isopropanol was tracked by using Ca K-edge X-ray absorption spectroscopy (XAS) characterization under cryo-condition. Ca K-edge X-ray absorption near edge structure (XANES) spectra show that the absorption edges of the Ca ions of the vaterite samples with different crystallization times shift to lower photoelectron energy while increasing the crystallization times from 0.5 to 20 d, indicating the increase of crystallinity degree of calcium carbonate. Ca K-edge extended X-ray absorption fine structure (EXAFS) spectra exhibit that the coordination number of the nearest neighbor atom O around Ca increases slowly with the increase of crystallization time and tends to be stable as 4.3 (±1.4). Crystallization time dependent XANES and EXAFS analyses indicate that short-range ordered structure in proto-vaterite ACC gradually transform to long-range ordered structure in vaterite microdisc mesocrystals via a non-classical crystallization mechanism.

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.