Increase In Degree Of Crystallinity Research Articles

Polyethylene/sepiolite fibers. Influence of drawing and nanofiller content on the crystal morphology and mechanical properties

The influence of sepiolite content (1, 2, and 3 wt%) and successive drawing steps on the final properties of polyethylene/sepiolite nanocomposite fibers are reported. Particularly the effects of these variables on crystallinity, fiber macroscopic morphology, and tensile mechanical properties are analyzed applying different experimental techniques: differential scanning calorimetry, wide angle x‐ray diffraction, scanning electronic microscopy, and tensile mechanical characterization. The study evidenced the important role of both sepiolite content and stretching on the crystalline morphology and mechanical properties of the nanocomposites fiber. Both variables favor the appearance of the monoclinic phase during polyethylene crystallization, and produce an increase of crystallinity degree (35 % with drawing steps and 10 % by the sepiolite incorporation in non drawing fiber). This change of crystal morphology influences mechanical properties enhancing with both sepiolite content and drawing steps. Thus, Young Modulus increases 17 times with drawing in pure PE fibers and 1.5 times because sepiolite presence. The strength shows similar behavior, but the elongation at break decreases 14 timed with draw steps and to a half by the sepiolite influence. The final properties of drawing nanocomposite fibers are so acceptable for textile applications and they content particles that enhance their moisture and odors absorptive capacities. POLYM. ENG. SCI., 55:1096–1103, 2015. © 2014 Society of Plastics Engineers

Biodegradable composites: Morphological, chemical, thermal, and mechanical properties of composites of poly(hydroxybutyrate‐co‐hydroxyvalerate) with curaua fibers after exposure to simulated soil

ABSTRACTComposites produced from biodegradable polymeric matrixes reinforced with vegetable fibers have attractive mechanical properties and are environmentally friendly. This work is directed to the biodegradation of a composite made of a poly(hydroxybutyrate‐co‐hydroxyvalerate) matrix reinforced with curaua fibers (with and without alkaline treatment) in simulated soil. The composites were developed by extrusion and injection and were later buried in simulated soil according to the ASTM G160‐03 method. Scanning electron microscopy showed evidence of microbial attack on the samples surfaces. Infrared spectra showed that the composites biodegradation was mainly caused by erosion of the surface layer resulting from microorganisms activity. Thermogravimetric analysis pointed out reduced thermal stability of the samples, and results of differential scanning calorimetry showed that the degree of crystallinity increases and then decreases progressively throughout the degradation period, indicating that enzymatic degradation primarily occurs in the amorphous phase material and thereafter in the crystalline phase. For curaua composite fibers, reductions in tensile strength and elastic modulus are more significant, indicating that the presence of fibers promotes biodegradation of the curaua fiber. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40712.

Post-irradiation effects on gamma-irradiated nylon 6,12 fibers

Abstract Post-irradiation effects on nylon 6,12 crystalline fibers gamma-irradiated 6 years previously (6YI) were studied, including thermal stability and morphology; their relationship with storage time was also studied. The results of these studies were compared with those obtained for non-irradiated (NI) and namely freshly irradiated (FI) crystalline fibers. The results include analyses like thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and optical images for (6YI and FI) both kinds of nylon 6,12 fibers. The results showed that the most prominent effect is related to the reaction progress. The chain scission and/or crosslinking mechanisms, as well as the free radicals, allow proceeding with the reaction, and consequently, changes on the properties of the FI samples. The melting point, degree of crystallinity, degradation temperature and morphology prove that additional chemical reactions and surface modifications keep occurring in the fibers long after the irradiation process has ended. With storage time, the surface becomes rougher, the color turns yellowish, the melting point diminishes and the degree of crystallinity increases.

Structure and Morphology of Microbial Degraded Poly(ε-caprolactone)/Graphite Oxide Composite

Biodegradation of poly(e-caprolactone) composite with graphite oxide (GO) by the action of Bacillus subtilis (BS) was studied in this work. Nanocomposite produced in a form of thin film was exposed to nutrient cultivation medium with BS as well as to abiotic nutrient medium (control run) at 30 °C. The matrix itself was exposed to the same conditions for comparison. Biodegradation was demonstrated by the weight loss and the decrease of molecular weight during 21 days of the experiment as well as by changes in the surface morphology and structure. Both degraded and control materials were characterized by confocal laser scanning microscopy, differential scanning calorimetry, thermogravimetry, and Fourier transform infrared spectroscopy with attenuated total reflectance. The bacterial growth expressed as the measure of the optical density/turbidity in McFarland units and pH of medium were measured in situ during the experiment. Lipolytic activity of BS was determined by spectrophotometric assay. Degradation process was accompanied by the increase of matrix crystallinity degree. GO served as nucleating agent and facilitated absorption of cultivation media into the composite which led to the increase of the crystallinity degree also for control nanocomposite specimens. It was not evaluated to be promoter of biodegradation. The surface cracks formation was initiated by BS action. Large surface cracks were formed on BS-degraded composite surfaces while surface erosion was more significant on BS-degraded matrix.

Effect of Tension on Mechanical Properties and Structure of Aramid Fibers during Heat Treatment

The heat treatment was carried out to modify the aramid fibers, and the effect of tension on the mechanical properties and structure was investigated through Fiber Strength Equipment, viscosity, XRD and SEM . The results show that fibers，strength slightly decrease, but modulus increase significantly according to the increasing of tension at 480°C and 10s, and reach a maximum when the tension value is 300 g. After heat treatment, molecular weight decrease and the degree of crystallinity increase. SEM show that there is little effect on the surface topography of the fibers during treatment.

Structural and magnetic behavior of ferrogels obtained by freezing thawing of polyvinyl alcohol/poly(acrylic acid) (PAA)-coated iron oxide nanoparticles

Superparamagnetic ferrogels with high swelling ability and potential applications as solvent absorbers and stimuli-responsive drug delivery devices were obtained by a non-toxic and environmentally friendly route based on dispersion of poly(acrylic acid)-coated iron oxide nanoparticles (PAA-coated NPs) in poly(vinyl alcohol) (PVA) solutions followed by freezing–thawing. Presence of carboxylate groups arising from the PAA coating allowed hydrogen bonding formation between NPs and PVA and enabled the synthesis of optically homogenous, superparamagnetic materials formed by a homogenous distribution of NPs diffuse clusters in the PVA matrix. The addition of PAA-coated NPs produced a remarkable increase in crystallinity degree, thermal degradation and swelling percentage respect to the neat matrix, which demonstrates that ferrogels with improved properties can be obtained by this procedure. Thereafter, combination of a cryogenic technique with the use of non-toxic components and magnetic NPs coated by a pH sensitive polymer makes these ferrogels very promising for applications in the biomedical field.

Ordered mesoporous tungsten oxide and titanium oxide composites and their photocatalytic degradation behavior

Highly ordered mesoporous WO3/TiO2 (MWTs) composite materials with tunable chemical compositions were obtained by a surfactant template-assisted evaporation-induced self-assembly (EISA) processes. The structure properties of the MWT materials were characterized by small angle XRD, TEM and N2 sorption. The resultant materials showed large amount of ordered mesopores and high chemical homogeneity. With increasing crystallinity degree, the order degrees of mesostructure turned worse gradually. The MWT hybrids exhibited excellent visible light response due to the addition of WO3 with narrow band gap. Photocatalytic performances of the MWT samples were determined by measuring the photo-degradation of rhodamine B dye and phenol under simulated solar light irradiation. The effect of material parameters such as surface area, crystallinity and chemical compositions in the binary heterostructured system on photocatalytic performance were discussed in details.

Simple preparation of multi-branched poly(l-lactic acid) and its role as nucleating agent for poly(lactic acid)

The present work proposes a simple preparation of multi-branched poly(l-lactic acid)s (m-PLLAs) and their performance as nucleating agents for PLA. By a simple polycondensation of l-lactic acid (l-LA) on the multi-functional core molecules of succinic acid (SA), malic acid (MA) and citric acid (CA) using stannous octanoate (SnOct2) as a catalyst, the m-PLLAs as two, three, and four branched PLLA can be obtained easily. Averagely, about 80% of the l-LA feed contents are successfully polymerized on core molecules. Non-isothermal crystallization studies of the PLA blend which contains 1 wt% m-PLLAs indicate that m-PLLAs induce the crystallization of PLA as evidenced from the decreases in glass transition temperature (Tg) and crystallization temperature (Tc), and the increase in degree of crystallinity (χc) under the α-form of perfect crystalline in PLA. Isothermal crystallization studies related to Avrami exponent (n), kinetic constant (k) and crystallization half-time (t1/2) indicate that the blend maintains its three-dimensional growth for the film thickness 0.05 mm, whereas the crystallization growth rate increases more than 4 times as observed from polarized optical microscope (POM). Among m-PLLA, the highest number of multi-branches with the shortest chain PLLA, i.e. CA-PLLA1, initiates the blends to increase its tensile strength and elongation at break for as high as 1.5 times and 1.2 times, respectively.

The Morphology and Tensile Strength of High Density Polyethylene/Nano-Calcium Carbonate Composites Prepared by Dynamic Packing Injection Molding

In this article, dynamic packing injection molding (DPIM) was used to prepare pure high density polyethylene (HDPE) and its composite with nano-CaCO3 samples, whose mechanical properties were improved significantly. Compared with conventional injection molding (CIM), the enhancement of tensile strength of dynamic HDPE/ nano-CaCO3 samples are 122%. According to the SEM, WAXD, and DSC measurement, it was found that a much better dispersion of nano-CaCO3 was achieved by the technology of DPIM. More importantly, DPIM also caused an obvious increase in orientation of HDPE matrix. The crystallinity degree of HDPE in dynamic sample increased by 5.52% compared with a conventional one. The improvement in mechanical properties for dynamic HDPE/ nano-CaCO3 is attributed to the even distribution of nano-CaCO3 particles, the orientation of HDPE crystals, as well as increase of crystallinity degree under the influence of DPIM.

Characterizing the effects of ambient aging on the mechanical and physical properties of two commercially available bacterial thermoplastics

Physical aging of commercial poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate)-co-poly(3-hydroxyvalerate) (PHBV) films has been investigated in this work. Aging-related changes in mechanical properties and crystalline matrix morphology were characterized using mechanical tensile tests, gas chromatography, differential scanning calorimetry, and gel permeation chromatography. Both PHB and PHBV samples, which were verified to contain a heterogeneous mixture of processing additives, experienced significant embrittlement upon aging in a desiccated isothermal (15°C) environment set moderately above their glass transition temperatures. Significant increases in the tensile modulus of elasticity were accompanied by decreases in ultimate strain; however, the aged samples exhibited no sizable variation in ultimate tensile strength after 168 days. Melt extrusion and ambient aging did not lead to any significant reduction in polymer molecular weights. Calorimetry results suggested that aged samples exhibited only a slight increase in overall degree of crystallinity, and multiple melting peaks were observed, indicating the presence of crystals of multiple thermal stabilities. Upon aging, the major melting peaks shifted to lower melting temperatures in both PHB and PHBV. The results demonstrate that physical aging of the two industrial biopolyesters can induce substantial changes in physical and mechanical properties in PHB and PHBV when stored just above their respective glass transition temperatures, and that the governing mechanism for embrittlement in both biopolymers is restricted to the non-crystalline phase.

Impact of crystallinity of poly(lactide) on helium and oxygen barrier properties

The helium and oxygen gas barrier properties of poly(lactide) were investigated as a function of stereochemistry and crystallinity degree. Poly(l-lactide) and poly(d,l-lactide) films were obtained by extrusion and thermally cold crystallized in either α′- or α-crystalline form with increasing crystallinity degree. Annealing of the films at low temperatures yielded to α′-crystals as well as the creation of a rigid amorphous fraction in the amorphous phase. Unexpectedly, the quantity of the rigid amorphous fraction was highest in poly(l-lactide) crystallized under α′-form. Unexpectedly, the gas permeability increased with increasing quantity of α′-crystals in poly(l-lactide) and remained constant with increasing quantity of α′-crystals in poly(d,l-lactide). A gain in gas barrier properties was obtained upon crystallization at higher temperatures yielding α-crystals. The analysis of the oxygen transport parameters, in particular the diffusion and the solubility coefficient showed that the diffusion was accelerated upon crystallization, while the solubility coefficient decreased in an expected manner which led to conclude that it remained constant in the amorphous phase. The acceleration of the diffusion seems to be correlated to the occurrence of the rigid amorphous fraction, which holds larger free volume. To conclude, for optimization of poly(lactide) gas barrier properties by focussing on the decrease of the diffusion coefficient it can be suggested to work with poly(d,l-lactide) and to aim a crystallization in α-form avoiding the formation of a rigid amorphous fraction.

Conductivity, structure, and thermal properties of chitosan‐based polymer electrolytes with nanofillers

AbstractThis paper focus on the effect of nanosize (<50 nm BET) inorganic alumina (Al2O3) filler on the structural, conductivity, and thermal properties of chitosan‐based polymer electrolytes. Films of chitosan and its complexes were prepared using solution‐casting technique. Different amounts of Al2O3 viz., 3, 4.5, 6, 7.5, 9, 12, and 15 wt% were added to the highest room temperature conducting sample in the chitosan–salt system, i.e. sample containing 60 wt% chitosan–40 wt% NH4SCN. The conductivity value of the sample is 1.29 × 10−4 S cm−1. On addition of 6 wt% Al2O3 filler the ionic conductivity increased to 5.86 × 10−4 S cm−1. The amide and amino peaks in the spectrum of chitosan at 1636 and 1551 cm−1, respectively, shift to lower wavenumbers on addition of salt. The glass transition temperature Tg for the highest conducting composite is 190°C. The increase in Tg with increase in more than 6 wt% filler content is attributed to the increase in degree of crystallinity as proven from X‐ray diffraction studies. Copyright © 2009 John Wiley & Sons, Ltd.

Vacuum-infused anionic polyamide-6 composites: The effect of postprocessing

Research on postprocessing of glass fiber–reinforced anionic polyamide-6 (APA-6) composites was performed in order to optimize the processing time. The two main points of investigation were the cure time and the annealing cycle. It was shown that the optimal mechanical properties (short-beam strength) coincided with the maximum degree of crystallinity for a cure time of 90 min at a cure temperature of 180°C. Annealing close to the crystallization temperature of APA-6 showed the largest increase in degree of crystallinity. For enhanced mechanical properties, however, the processing history is of importance. It was seen that for short cure times, sufficient annealing time at elevated temperatures is beneficial for the polymer chains to branch, cross-link, or adhere to the fibers, hence, significantly improving the mechanical properties.

Improving degradation rate and apatite formation ability of nanostructure forsterite

Although micron size forsterite is biocompatible, the degradation rate of this ceramic is extremely low, and the apatite formation ability is poor as well. In this study, the influence of nanostructure and the degree of crystallinity on the apatite formation ability and degradation rate were investigated. Forsterite was synthesized by 5 h of milling of talc and magnesium carbonate and subsequent annealing at 1000 °C in the presence of chloride ion. To investigate the in vitro bioactivity and degradability, the prepared forsterite powder was pressed in the form of tablets and then immersed in simulated body fluid (SBF) and Ringer's solution, respectively. The results showed that nanostructure forsterite powder with crystallite size of about 20 nm was bioactive and released magnesium ions in the SBF solution. With increasing crystallinity degree of nanostructure forsterite, the apatite formation ability and degradation rate decreased.

Linear low density polyethylene/cycloolefin copolymer blends

Linear low density polyethylene (LLDPE) was melt compounded with various amounts of a cycloolefin copoly- mer (COC). Scanning and transmission electron microscopy evidenced, at qualitative level, some interfacial adhesion between LLDPE and COC. Another indication of interactions between the components was the increase of crystallinity degree with rising COC content and the enhancement of COC glass transition temperature with the LLDPE fraction. In order to explain this behaviour, the incorporation of ethylene segments of COC into the LLDPE crystalline phase, leading to an increased number of norbornene units in the remaining COC component undergoing the glass transition, was hypoth- esized. The thermo-oxidative degradation stability of LLDPE was substantially enhanced by COC introduction for filler contents higher than 20 wt%, especially when an oxidative atmosphere was considered. An increasing fraction of COC in the blends was responsible for an enhancement of the elastic modulus and of a decrease in the strain at break, while tensile strength passed through a minimum, in agreement with the model predictions based on the equivalent box model and equa- tions provided by the percolation theory. The introduction of a rising COC amount in the blends increased the maximum load sustained by the samples in impact tests, but decreased the blend ductility. Concurrently, a significant reduction of the creep compliance of LLDPE was observed for COC fractions higher than 20 wt%.

X-ray diffraction study of temperature dependence of Nairit polychloroprene permolecular structure

With use of the X-ray technique the permolecular structure of Nairit polychloroprene has been investigated. It is shown that the relative degree of crystallinity decreases with the increase in the polymerization temperature. At relatively low temperatures (18–30°C), in Nairits intensive formation of nuclei occurs and simultaneously existing crystallites collapse. Although mean sizes of crystallites decrease, the degree of crystallinity increases. At higher temperatures (above 30°C) melting of existing crystallites and decrease in the number of nuclei lead to decrease in crystallinity and mean sizes of crystallites.

Multi-electrochromism behavior and electrochromic mechanism of electrodeposited molybdenum doped vanadium pentoxide films

Molybdenum doped vanadium pentoxide (Mo doped V 2O 5) films are prepared by cathodic electrodeposition on indium tin oxide substrate from Mo doped V 2O 5 sol. As an anodic and cathodic coloration electrochromic material, the electrodeposited Mo doped V 2O 5 film presents a better cycling stability, reversibility and multi-electrochromic behavior (orange–yellow–green–blue) with an optical modulation of 60–90% in the spectral region 550–900 nm, which can be expected as a result of enhanced electron intervalence transfer between Mo 6+ and V 5+, V 4+ states, in addition to V 5+ and V 4+ transition. The electrochromic mechanism of Mo doped V 2O 5 films is investigated with atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The surface roughness of the film increase at the different coloration states due to the increasing crystallinity degree. The change of the interlayer spacing for the host V 2O 5 and the change of the C and Li element states verify the insertion of organic solvent into the interlayer of the host V 2O 5 and some of the Li + ions into the sites in the V–O layers. The electrochromic kinetics process indicates that the electrochromism of Mo doped V 2O 5 films can be considered as a reversible reduction/oxidation process accompanying the insertion/extraction of Li + ions and electrons.

Effect of melt vibration on structure and mechanical properties of HDPE/nano-CaCO3 blend

Melt vibration technology was used to prepare injection sample of HDPE/nano-CaCO3 blend, whose mechanical properties were improved significantly. Compared with conventional injection molding, the enhancements of the tensile strength and impact strength of the sample molded by vibration injection molding were 41.2 and 43.2%, respectively. According to the SEM, WAXD, and DSC measurement, it was found that a much better dispersion of nano-CaCO3 in sample was achieved by vibration injection molding. Moreover, crystal orientation degree of matrix HDPE increased under the effect of melt vibration. The crystallinity degree of HDPE in vibration sample increased by 5.5% compared with conventional one. The improvement of mechanical properties of HDPE/nano-CaCO3 blend prepared by low-frequency vibration injection molding attributes to the even distribution of nano-CaCO3 particles and the orientation of HDPE crystals and increase of crystallinity degree under the influence of melt vibration.

Effects of organosolv pretreatment and enzymatic hydrolysis on cellulose structure and crystallinity in Loblolly pine

Ethanol organosolv pretreatment was performed on Loblolly pine to enhance the efficiency of enzymatic hydrolysis of cellulose to glucose. Solid-state 13C NMR spectroscopy coupled with line shape analysis was used to determine the structure and crystallinity of cellulose isolated from pretreated and enzyme-hydrolyzed Loblolly pine. The results indicate reduced crystallinity of the cellulose following the organosolv pretreatment, which renders the substrate easily hydrolyzable by cellulase. The degree of crystallinity increases and the relative proportion of para-crystalline and amorphous cellulose decreases after enzymatic hydrolysis, indicating preferential hydrolysis of these regions by cellulase. The structural and compositional changes in this material resulting from the organosolv pretreatment and cellulase enzyme hydrolysis of the pretreated wood were studied with solid-state CP/MAS 13C NMR spectroscopy. NMR spectra of the solid material before and after the treatments show that hemicelluloses and lignin are degraded during the organosolv pretreatment.

Investigations on the electrical and structural properties of PVA doped with (NH4)2SO4

AbstractSolid polymer electrolytes based on poly(vinyl alcohol) (PVA) complexed with ammonium sulfate (NH4)2SO4 at different weight percent ratios were prepared using solution cast technique. The structural properties of these electrolyte films were examined by X‐ray diffraction (XRD) studies. The XRD data revealed that the amorphous domains of PVA polymer matrix increased with the increase of ammonium sulfate added up to 5 wt %, after which the degree of crystallinity increases. The complexation of the salt with the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy. Electrical conductivity was measured in the temperature range of 303–373 K. The conductivity was found to obey Arrhenius formula. The dielectric permittivity ε′ was studied as function of temperature and frequency, respectively.The data showed increasing in ε′ values with the increase in temperature while decreased with increase in frequency for polymer electrolyte system up to 10% of ammonium sulfate added. For values of addition greater than 10%, ε′ is independent of both temperature and frequency. The ac conductivity is found to obey the power relation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010