Wide-angle X-ray Diffraction Measurements Research Articles

Structural evolution from shish-kebab to fibrillar crystals during hot-stretching process of gel spinning ultra-high molecular weight polyethylene fibers obtained from low concentration solution

The pre-stretched gel-spinning ultra-high molecular weight polyethylene fibers with low concentration solution obtained from industrial production line were used to study the structural transition from shish-kebab to fibrillar crystals during hot-stretching process via in-situ small-angle X-ray scattering, wide-angle X-ray diffraction measurements, and scanning electron microscopy. With the increase of hot-stretching strain, the kebab crystals (lamellae) undergo stress-induced fragmentation and recrystallization at 90, 100, and 110 °C and melting and recrystallization at 120 °C to transform to fibrillar crystals. Furthermore, the shish length of pre-stretched fibers at all stretching temperatures first increase and then gradually decrease with the strain, but the number of shish continuously increase and the shish diameter increase firstly and finally keep almost constant. The degree of crystal orientation for all stretching temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish-kebab crystals of ultra-high molecular weight polyethylene fibers prepared from low concentration solution can smoothly transform to fibrillar crystals through the hot stretching process.

The influence of the preparation conditions and filler content on thermal properties of poly-l -lactide and hydroxyapatite/poly-l -lactide nanocomposite

Poly-l-lactide (PLLA) and hydroxyapatite/poly-l-lactide (HAp/PLLA) are two widely used biomaterials for three-dimensional scaffolds, drug release matrices and implantable medical devices for reparation of bone tissue; diversity in the initial preparation and filler content has a significant influence on different properties such as morphology and crystallinity, thus playing a considerable role in most of these applications. For this reason, PLLA and HAp/PLLA samples with a large difference in crystallinity (from below 20% to over 70%) and filler content (up to 86 wt% of HAp nanoparticles with an average diameter of 80 nm) were prepared and consequent dissimilarities in morphology, crystallinity and thermal properties were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) measurements and Fourier transform infrared (FTIR) spectroscopy. Special attention was devoted to analyzing data obtained from thermal measurements. A three-phase model was employed in order to describe the heat capacity step decline in the nanocomposite; the evolution in different polymer fractions, the crystalline fraction and the mobile and rigid amorphous fractions, with filler content was determined. © 2017 Society of Chemical Industry

Construction of a Cordyceps sinensis exopolysaccharide-conjugated selenium nanoparticles and enhancement of their antioxidant activities

A Cordyceps sinensis exopolysaccharide (EPS)-conjugated selenium nanoparticles (SeNPs) were successfully constructed through the reduction of SeO32−. The EPS-SeNPs were characterized in terms of formation, morphology, size, Se distribution and phase by UV–vis, FT-IR, transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray (EDX) and wide angle X-ray diffraction (WAXD) measurements. Results revealed that the SeNPs conjugated to EPS were amorphous and could be well dispersed at a size range of 80–125nm. The interactions between the OH groups of EPS and SeNPs substituted for intermolecular interaction in native EPS to form new CO⋯Se bonds, resulting in good dispersion of SeNPs in the EPS matrix. Besides, the EPS-SeNPs at different Se/P ratios exhibited significant scavenging ability on superoxide anion radical (O2−) and ABTS radical cation (ABTS+) when compared to pure EPS, indicating that the conjugated SeNPs reinforced antioxidant effect of EPS. This work not only provides a simple and efficient way to construct well-dispersed SeNPs in aqueous system, and demonstrates the vital role of the EPS as a biopolymer template for dispersion, stabilization and size control of SeNPs, but also finds the EPS-SeNPs can potentially serve as a good antioxidant towards O2− and ABTS+.

A new approach to improve the local compressive properties of PPDO self-expandable stent

The radial performance of bioabsorbable polymeric intravascular stents is extremely important in assessing the efficiency of these devices in expanding narrow lumen, reducing stent recoil, and recovering to their original states after suffering from pulsating pressure. However, these stents remain inferior to metallic stents. Several thermal treatment conditions (60°C, 80°C, and 100°C for 1h) were investigated to improve the characteristics of poly(p-dioxanone) (PPDO) self-expandable stents. The local compressive force, stiffness, and viscoelasticity of these stents were also evaluated. Wide-angle X-ray diffraction and different scanning calorimetry measurements were performed to evaluate the recrystalline and thermodynamic changes of molecular chains. The declining conformer entropy of PPDO monofilaments was examined via energy analysis. The untreated stents had compressive modules of 514.80±70.59mN/mm, which was much higher than those of 80°C and 100°C treated stents (332.35±66.08mN/mm and 394.31±64.71mN/mm, respectively). Nevertheless, 100°C annealing stents had less stress relaxation and prior elastic recovery rate of 82.32±3.43mN and 92.55±1.61%, respectively, showing a much better shape stability than untreated stents (139.51±16.67mN and 86.18±3.57%, respectively). These findings present important clinical implications in the stent manufacturing process and warrant further study to develop new bioabsorbable stents with outstanding clinical efficacy.

Interplay between structure and property of graphene nanoplatelet networks formed by an electric field in a poly(lactic acid) matrix

For melt-compounded poly(lactic acid) composites containing graphene nanoplatelets (GNPs) at low volume fractions, ϕGNP ≤ 0.34 vol. %, this study focused on correlation between the composite properties and a large-scale structure of GNPs formed by a strong alternating current electric field (with the frequency and intensity of 60 Hz and 1.75 kV/mm, respectively). The electric field was applied to the composite in a rheometer through the parallel plate fixture, so that the parallel plates served as the rheological measurement fixture as well as the electrodes. Optical microscopy, transmission electron microscopy, and two-dimensional wide-angle X-ray diffraction measurements revealed that almost randomly oriented, thin stacks of GNPs in the as-fabricated composites were aligned by the electric field in the field direction and further organized into an extended chain (or column) of stacks. This chained-stack structure bridged two parallel plate electrodes when ϕGNP was above a threshold value, ϕGNP* ≅ 0.17 v...

Observations of Enamel Microstructure in Incipient Lesions Remineralized by NaF Dentifrices

Synchrotron Radiation (SR) Wide-angle X-ray Diffraction (WAXD) and Small-angle X-ray Scattering (SAXS) techniques were used to assess microstructure of bovine enamel white-spot lesions (WSL) evaluated in a 10-day pH cycling model comprising three different dentifrice groups: (A) 0.21% NaF plus TCP (Clinpro Tooth Crème), (B) 1.1% NaF plus TCP (Clinpro 5000), or (C) 0% NaF (Tom’s of Maine) dentifrice. Each day consisted of four 2-minute treatments, one 4-hour acid challenge (pH=5.0), and immersion in artificial saliva (pH=7.0) between these events. These specimens were also examined with cross-sectional microhardness, digital light microscopy and FE-SEM (field emission scanning electron microscope), and demonstrated the remineralization model effected changes in subsurface microstructure. X-ray diffraction data from WAXD and SAXS were collected on enamel slab cross-sections extending from 0 μm to 150 μm, in 6 μm microbeam increments. A primary outcome of this observational study was that simultaneous WAXD and SAXS measurements were able to resolve significant differences (ANOVA, Student’s t-test, p<0.05) between the effects of the two fluoridecontaining dentifrices on subsurface lesion microstructure. In particular, enamel lesions treated with 1.1% NaF dentifrice group manifested an abundance of nanometer-sized crystallites, while treatment with the 0.21% NaF dentifrice produced larger apatite-like crystals. While the presence of fluoride in both cases promoted regularity in crystal size and orientation, this was not observed for lesions treated without fluoride. Altogether, our observations demonstrate the pathological processes for remineralization are markedly influenced by the presence and concentration of fluoride, the microstructural characteristics of which can be distinguished using the simultaneous WAXD and SAXS technique.

Crystal structures and phase transition behavior of Poly(nonamethylene terephthalamide) and its model compounds

The crystal structure and phase transition behavior of poly(nonamethylene terephthalamide) (PA9T, -[CO-C6H4-CONH-(CH2)9-NH]n-) and its related model compounds (ATm,C6H5-CONH-(CH2)m-NHCO-C6H5 (m = 7–12)) have been investigated by carrying out the temperature dependent measurements of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and infrared spectra along with the DSC measurement. The crystal structure of PA9T at room temperature was determined by analyzing the X-ray diffraction diagram measured for the uniaxially-oriented sample. The nonamethylene segmental part takes the zigzag conformation, which was supported by the quantitative analysis of the methylene progression bands observed in the infrared spectra. The temperature dependence of WAXD, SAXS and infrared spectra of PA9T revealed the existence of the 2-staged order-to-disorder phase transitions: at room temperature this polymer exists as phase I, the crystal structure of which was analyzed as mentioned above. In the relatively low and wide temperature region (190–270 °C for the unoriented sample), phase I transforms to phase II, in which the methylene conformation is disordered, the aromatic amide part is slightly rotated and the intermolecular hydrogen bonds become weaker but the hydrogen bonds are still kept alive. In the temperature region immediately below the melting point (270–310 °C for the unoriented sample), the phase II is melted once and recrystallizes into phase III, where the intermolecular hydrogen bonds are mostly broken in addition to the further disordering of the methylene segments and aromatic amide groups. The thus-occurring violent thermal motions cause a remarkable increase of the long period in this transition region. The molecular chains are still highly oriented and so the phase III may be assumed to be in a kind of liquid crystalline state. The crystal structural changes detected in these phase transitions of PA9T were confirmed by the analysis of the X-ray diffraction and IR spectral data collected for the low molecular-weight model compounds.

Preparation of novel xGNPs/SBS composites with enhanced dielectric constant and thermal conductivity

AbstractPolystyrene‐block‐polybutadiene‐block‐polystyrene triblock copolymer (SBS) has the potential to be used as a dielectric elastomer for actuator, sensor, energy harvesting, and so on, but its low dielectric constant and thermal conductivity seriously limit this application. In this study, novel exfoliated graphite nanoplates (xGNPs)/SBS composites were prepared by a solution‐blending method using N,N‐dimethylformamide and tetrahydrofuran as co‐solvents. Wide‐angle X‐ray diffraction measurement confirms that xGNPs have been incorporated into SBS. Furthermore, the result of scanning electron microscopy shows that xGNPs disperse well in the SBS matrix. The effects of xGNPs on the dielectric constant and thermal conductivity of the resultant xGNPs/SBS composites were investigated. The dielectric constant at 1,000 Hz significantly increased from 2.72 for pure SBS to 15.96 and 40.94 for xGNPs/SBS composite containing 1.19 and 1.27 vol.% of xGNPs, respectively. Moreover, the thermal conductivity of the xGNPs/SBS composite containing 1.27 vol.% of xGNPs has been improved from 0.18 to 0.41 W/m·K in comparison with that of pure SBS.

Synthesis and properties of poly(L-lactide-co-glycolide)-b-Poly(ɛ-caprolactone) multiblock copolymers formed by self-polycondensation of diblock macromonomers

Poly(L-lactide-co-glycolide)-b-poly(ɛ-caprolactone) multiblock copolymers (PLGA-PCL MBCs) were synthesized via the self-polycondensation of PLGA-PCL diblock copolymers (PLGA-PCL DBCs) in the presence of condensation agents. PLGA-PCL DBCs were synthesized via the ring-opening copolymerization of lactide and glycolide initiated by benzyl-protected PCL in the presence of tin 2-ethylhexanoate (Sn(Oct)2) or organic catalysts (N-cyclohexyl-N’-[3,5-(trifluoromethyl)phenyl]thiourea (TU) and Tris[2-(dimethylamino)ethyl]amine (Me6TREN)). The introduction of glycolide segments hampered the formation of poly(L-lactide) (PLLA) crystals in PLGA-PCL MBCs, which was confirmed by wide-angle X-ray diffraction (WAXD) measurements. Despite the loss of crystallinity, PLGA-PCL MBCs showed better tensile strength and modulus than the PLLA-PCL random copolymer. The phase-segregated PLGA domains observed by small-angle X-ray scattering (SAXS) measurements acted as hard domains improving the tensile properties. The hydrolytic degradation of PLGA-PCL MBC in phosphate-buffered saline (PBS: pH=7.4) proceeded much faster than that of PLLA-PCL MBC. Both the loss of PLLA crystallinity and the presence of glycolide–glycolide and glycolide–lactide bonds contributed to the enhanced hydrolysis behavior of PLGA-PCL MBCs. The good tensile properties and degradation behavior in PBS expand the applicability of PLGA-PCL MBCs in biomedical applications, particularly for elastic implanting materials. Poly(L-lactide-co-glycolide)-b-poly(ɛ-caprolactone) multiblock copolymers (PLGA-PCL MBCs) were synthesized by the self-polycondensation of PLGA-PCL diblock copolymers (PLGA-PCL DBCs) in the presence of condensation agents. The phase-segregated PLGA domains acted as hard domains, improving the tensile properties. The hydrolytic degradation of PLGA-PCL MBC films in phosphate-buffered saline (PBS: pH=7.4) proceeded much faster than that of poly(L-lactide) (PLLA)-PCL MBC.

Chemical Synthesis of Multiblock Copolypeptides Inspired by Spider Dragline Silk Proteins.

Novel multiblock polypeptides with a structure similar to the unique sequence observed in spider silk proteins (spidroins) were synthesized via a two-step chemical synthesis method, that is, chemoenzymatic polymerization, using papain followed by postpolycondensation. Two types of polypeptide fragments were prepared by chemoenzymatic polymerization: polyalanine as a hard block, which forms β-sheets in the spider silk fibers, and poly(glycine-random-leucine) as a soft block. These two fragments were ligated by postpolycondensation using polyphosphoric acid as a condensing agent. Wide-angle X-ray diffraction (WAXD) and IR measurements revealed that the resulting multiblock polypeptides formed an antiparallel β-sheet structure with a degree of crystallinity similar to that of spider silk, which resulted in a fibrous morphology. This work provides the first example of a synthetic multiblock polypeptide mimicking the secondary structures of spider silk.

Crystallization behavior of crystalline/crystalline polymer blends under confinement in electrospun nanofibers of polystyrene/poly(ethylene oxide)/poly(ε-caprolactone) ternary mixtures.

We have studied the crystallization behavior of crystalline/crystalline blends of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) in electrospun nanofibers fabricated from ternary blends of polystyrene (PS), PEO, and PCL, where PS was present as the majority component. It was demonstrated previously that PEO in PS/PEO binary blend nanofibers with a low PEO weight fraction (≦0.2) crystallized predominantly through homogenous nucleation due to the small PEO domain size which excluded the presence of heterogeneities (Soft Matter, 2016, 12, 5110). Here, it was found that PCL in PS/PCL binary blend nanofibers exhibited similar behavior, but at a much lower weight fraction of PCL (≦0.1) due to the presence of an inherently higher concentration of heterogeneities in the PCL homopolymer. In the PS/PEO/PCL ternary blend nanofibers, where the combined weight fraction of PEO and PCL was kept at 0.2 or less, the crystallization of the two components took place separately through both heterogeneous and homogenous nucleation mechanisms. The phase segregated crystallization behavior was further confirmed by the melting behavior of the blend nanofibers and wide angle X-ray diffraction (WAXD) measurements. Most significantly, the homogenous nucleation of both PEO and PCL was suppressed whereas the heterogeneous nucleation was enhanced in the ternary blend nanofibers even at very low weight fraction of PEO or PCL. This was plausibly attributed to the coupling between the crystallization and the liquid-liquid phase separation (LLPS) of the PEO/PCL mixture dispersed in the PS matrix during non-isothermal cooling of the blend nanofibers. Furthermore, it was observed that thermal treatment of the PS/PEO/PCL blend nanofibers above the glass transition temperature of PS further promoted the heterogeneous nucleation-initiated crystallization of PEO because of a complex interplay between Plateau-Rayleigh instability-induced domain breakup and its further coalescence and demixing within the PEO/PCL domains embedded in the PS matrix.

Multiple Melting Behavior of High-Speed Melt Spun Polylactide Fibers

ABSTRACTHigh-speed melt spinning of polylactide (PLA) was conducted and the structure and multiple melting behavior of the as-spun fibers were investigated. In the analysis of temperature modulated differential scanning calorimetry (TMDSC) thermograms for the as-spun PLA fibers taken-up at 1 and 6 km/min, the peaks around the melting temperature region in the reversing heat flow (RHF) and nonreversing heat flow (NRHF) curves were mainly separated into (1) a pair of an endothermic peak (Peak L) in RHF and an exothermic peak (Peak R) in NRHF in a low temperature region, (2) an endothermic peak (Peak M) both in RHF and NRHF (only in RHF for PLA fiber spun at the low-speed) in an intermediate temperature region, and (3) an endothermic peak (Peak H) both in RHF and NRHF in a higher temperature region. Wide-angle X-ray diffraction (WAXD) measurements were conducted during the heating process of the as-spun fibers cut into powders. In the case of fibers obtained at 1 km/min, disordered crystals, i.e. α′-form crystals, were formed through cold crystallization followed by a disorder-to-order phase transition, i.e. α′ to α crystalline modification, with partial melting of the α′ crystals around 148.5°C in the temperature range of Peaks R and L. Finally, the α form crystals melted above 169.4°C, in the temperature range of Peak H. On the other hand, the PLA crystals generated by the orientation-induced crystallization during the spinning process at a spinning velocity of 6 km/min did not show a WAXD profile of perfect α form crystals but showed an intermediate structure having lattice spacings between the α′ and α forms. Such intermediate crystals did not transformed into α form crystals during the heating process.

The effects of two-step reactive processing on the properties of recycled poly(ethylene terephthalate)

A simple approach for preparing recycled poly(ethylene terephthalate) (r-PET) with excellent processability and melt strength has been developed in this research. To increase the intrinsic viscosity of r-PET, a two-step chain extension process using a combination of SAG-008 and tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) was investigated. To evaluate the chain extension degree of the modified r-PET, its intrinsic viscosity (IV) and rheological properties were characterized, and found to be correlated to the long-chain branches and molecular weight. The results indicated that the combination of SAG-008 and TGDDM at the optimized conditions provided the highest IV of 1.18 dl/g while controlling the gel formation to a low value. The increases in storage modulus, loss modulus and complex viscosity revealed the enhancement of melt strength and viscoelasticity of r-PET. The differential scanning calorimetry results showed that the crystallinity was reduced with the addition of chain extenders. On the other hand, stepwise annealing method from room temperature to crystal melting temperature promoted the crystallization, which was confirmed by wide-angle X-ray diffraction measurement.

Synthesis and characterization of new aromatic polyesters with a (4-phenoxyphenyl)phenylmethene linkage

A series of new aromatic polyesters containing a (4-phenoxyphenyl)phenylmethene linkage were prepared by phase transfer-catalyzed interfacial polycondensation of 1,1-bis(4-hydroxyphenyl)-1-(4-phenoxyphenyl)-1-phenylmethane with terephthaloyl chloride, isophthaloyl chloride, and so on. The inherent viscosities of the polyesters ranged from 0.62 to 0.90 dL/g, while number-average molecular weights were in the range of 30,500–35,500 g/mol. All the polyarylates were readily soluble in organic solvents such as dichloromethane, chloroform (CDCl3), tetrahydrofuran, meta-cresol, pyridine, N, N-dimethylformamide, N, N-dimethylacetamide, and 1-methyl-2-pyrrolidinone at room temperature, and could be cast into tough, transparent, and flexible films from their CDCl3 solutions. Wide-angle X-ray diffraction measurements revealed the amorphous nature of the polyarylates. These polymers showed glass transition temperatures ( Tgs) between 178°C and 240°C and decomposition temperatures at 10% weight loss ranging from 446°C to 483°C, while the initial degradation temperatures in the range of 410–435°C under nitrogen atmosphere. These new polyarylates exhibited higher Tgs and better solubility than bisphenol A-based analogues.

Subnanoscopic inhomogeneities in model end-linked PDMS networks probed by positron annihilation lifetime spectroscopy and their effects on thermomechanical properties

The subnanoscopic free volume hole properties of model poly(dimethylsiloxane) (PDMS) networks with unimodal and bimodal distribution of chain lengths between the cross-links were determined using positron annihilation life time spectroscopy (PALS). Wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) studies were carried out to further understand the structural inhomogeneities of the networks at different length scales. The networks were prepared by end-linking combinations of sufficiently longer (Mn = 18,952) and shorter (Mn = 4323) precursor PDMS chains relative to entanglement spacing (Me). The macroscopic properties of the networks were studied by tensile testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), as well as equilibrium swelling measurements. Through PALS studies it was possible to delineate the subtle variations in the elementary mesh sizes, a measure of the segmental spacing, of the unimodal short and long chain networks influenced by cross-links or entanglements. The intersegmental spacing of the unimodal PDMS networks at a length scale of few angstroms obtained from WAXD measurements were found to be almost in quantitative agreement with the free volume hole sizes obtained from PALS. SAXS measurements on solvent swollen PDMS networks from short and long chain precursors were used to obtain correlation length of the networks at a higher length scale of a few nanometers. Further, the studies revealed that the enhanced mechanical properties seen in certain bimodal elastomer networks are connected with topological features of the networks. A noteworthy finding from PALS studies was that the bimodal composition with 20 wt% short chain, which showed the best combination of mechanical properties with a feature of stress-upturn in tensile testing, exhibited the least free volume size and relatively lower dispersion in its size distribution among the networks. These fundamental studies are expected to provide new insights into the network structure of model elastomers at a molecular scale and its possible connection with macroscopic properties.

Formation of poly(9,9-dioctylfluorene) β-phase by incorporating aromatic moiety in side chain

Two novel polyfluorene-based blue-light emitting copolymers consisting of aromatic carbazole or dibenzothiophene-S,S-dioxide (SO) moiety in side chain are designed and synthesized based on a palladium-catalyzed Suzuki polymerization. The UV–vis absorption, photoluminescence characteristics and wide-angle X-ray diffraction measurements of the resulting copolymers demonstrate that the incorporation of such aromatic units can induce the formation of the β-phase. The resulting copolymers consisting of aromatic units exhibit improved electroluminescence properties relative to the pristine PFO film. A maximum luminous efficiency of 2.25 cd A−1 with Commission Internationale de l’Eclairage coordinates of (0.17, 0.09) is obtained from the light-emitting device based on the copolymer consisting of SO unit (PFO-SO). Device based on copolymer PFO-SO also exhibits stable electroluminescent spectra and relatively low roll-off of luminous efficiency at high current densities. These observations indicate that the incorporation of aromatic moiety in side chain is a promising strategy to obtain stable blue-light-emitting polyfluorenes with enhanced efficiency.

Synthesis and characterization of novel triptycene dianhydrides and polyimides of intrinsic microporosity based on 3,3ʹ-dimethylnaphthidine

Abstract Two intrinsically microporous polyimides were obtained by high-temperature, one-pot polycondensation reaction of novel triptycene-based dianhydrides containing dimethyl- or diisopropyl-bridgehead groups with a commercially available highly sterically hindered 3,3ʹ-dimethylnaphthidine (DMN) diamine monomer. The dimethyl bridgehead groups in the triptycene building block provided the DMN-based polyimide (TDA1-DMN) with larger surface area (760 m 2 g -1 ) than the diisopropyl-based polyimide (TDA i 3-DMN) (680 m 2 g -1 ), greater fraction of ultramicroporosity, as observed from N 2 and CO 2 NLDFT adsorption analysis, and higher gas permeability and selectivity. Wide-angle X-ray diffraction (WAXD) measurements demonstrated that TDA1-DMN and TDA i 3-DMN exhibited a bimodal pore size distribution, where TDA1-DMN showed smaller d-spacing values and broader intensity peaks. Both TDA-DMN-based polyimides showed very high gas permeabilities with moderate selectivities. For example, fresh TDA1-DMN exhibited an O 2 permeability of 783 Barrer coupled with an O 2 /N 2 selectivity of 4.3 and H 2 permeability of 3050 Barrer with H 2 /N 2 selectivity of 16.7, values that surpassed the 2008 Robeson permeability/selectivity upper bounds. Physical aging of the TDA-DMN polyimide films over a period of 250 days showed relatively small changes in permeability (∼20%) and selectivity (∼5%).

Effect of non-rubber components on the mechanical properties of natural rubber

Effect of the nanomatrix structure on mechanical properties of natural rubber was investigated in relation to the strain-induced crystallization. Structure of natural rubber was analyzed through Fourier transform infrared spectroscopy, wide-angle X-ray diffraction measurement and transmission electron microscopy. The nanomatrix of the non-rubber components was found to be inevitably formed in natural rubber, in which natural rubber particles linking to fatty acids were dispersed in the nanomatrix of the proteins and phospholipids. The nanomatrix disappeared after deproteinization of natural rubber with urea. Tensile strength and modulus of natural rubber were reduced by removal of the fatty acids and the proteins, which resulted in disappearance of the nanomatrix structure. The effect of fatty acids on the crystallization of natural rubber in small particles as a dispersoid was proved by tensile test of blend of natural rubber and styrene butadiene rubber. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of epoxidized soybean oil grafted poly(12-hydroxy stearate) on mechanical and thermal properties of microcrystalline cellulose fibers/polypropylene composites

A new green compatibilizer named epoxidized soybean oil grafted poly(12-hydroxy stearate) (ESO-g-PHS) was successfully synthesized using 12-hydroxy stearic acid and epoxidized soybean oil (ESO). The chemical structure of ESO-g-PHS was investigated through Fourier transformed infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. ESO-g-PHS was used as a compatibilizer to enhance the interfacial compatibility between polypropylene (PP) and microcrystalline cellulose fibers (MCF). The results showed that the impact strength and tensile strength were 33.55 and 27.57 MPa when the content loading of MCF reached 10 wt% and ESO-g-PHS was 4 wt%, which enhanced by 75.4 and 30.04 %, respectively, compared to that of composites without ESO-g-PHS. In addition, the SEM images of the fracture surfaces display that PP was highly bonded to MCF with ESO-g-PHS treated. In addition, the wide angle X-ray diffraction measurement revealed that the addition of ESO-g-PHS did not change the crystal structure of PP. Moreover, there was a slight improvement in thermal properties for PP composites with the addition of ESO-g-PHS.

Structural development of gel-spinning UHMWPE fibers through industrial hot-drawing process analyzed by small/wide-angle X-ray scattering

The ultrahigh molecular weight polyethylene (UHMWPE) fibers were obtained directly from the industrial production line. Two-step industrial hot-drawing-to-specific-drawing ratios were carried out at the temperature of 120 and 130 °C, respectively. Small-angle X-ray scattering (SAXS) measurements using synchrotron radiation were applied to study the evolution of kebab structure and the formation of shish structure. The slight increase of long period and the rapid decrease of lateral sizes indicated the destruction of original lamellae which was accomplished by chain slip resulted in the orientation of lamellae to form shish structure. The decrease of average shish length was explained that the formed new shish structure had shorter shish length than the original shish at the early stage with the high concentration of spinning solution. Wide-angle X-ray diffraction (WAXD) measurements were performed to explore the changes of the degree of orientation of the crystals. It was found that the elevated drawing temperature was benefited to the evolution of the orientational order. The DSC result confirmed the evolution of shish–kebab structure through the melting behavior.