The mechanical property and phase structures of wheat proteins/polyvinyl alcohol blends studied by high-resolution solid-state NMR

The phase structures of thermally processed wheat proteins (WP) and polyvinyl alcohol (PVOH) blends were studied by solid-state high-resolution NMR spectroscopy. The intermolecular interactions among the multi-component systems and the behavior of each component in the blends on scales of nanometers were examined. The mechanical properties of the blends were also measured and related to the phase structure studies. The results indicated that the polymer chains of WP could be homogeneously mobilized when thermally processed with glycerol and water as plasticisers, but the glycerol predominately associated with WP rather than PVOH in the blends. The intermolecular hydrogen bonding interactions between WP and PVOH caused some extent of miscibility in the system on scales of nanometers especially when the PVOH content was low. The tensile strength and modulus of the blends were improved as compared to WP. However, the intermolecular interactions were relatively weak and could not be further enhanced by increasing PVOH component in the blends. The particle miscible WP/PVOH blends contained plasticised WP and PVOH phases in conjunction with the miscible WP/PVOH phase. Increasing the PVOH content in the blends did not result in an increase of the percentage of the miscible phase and the blends tented to be immiscible while the elongation of the blends was reduced when increasing the PVOH content in the blends.     

Solid state NMR study of segmented polymer networks: fine-tuning of phase morphology via their molecular design

Segmented polymer networks (SPNs) based on thermo-sensitive poly(N-isopropyl acryl amide) (PNIPAA) and poly(tetrahydrofuran) (PTHF) have been synthesized by free radical copolymerization of PTHF bis-macromonomers with N-isopropyl acrylamide. The nature of the polymerizable end group on the bis-macromonomer has been varied, respectively from acrylate to acrylamide end groups. The multiphase behaviour of the corresponding SPNs has been examined as a function of the nature of the end group by making use of solid-state ¹³C CP/MAS NMR relaxometry, ¹H wideline NMR relaxometry and dynamic mechanical analysis (DMA). When PTHF with acrylate end groups was used during the SPN formation, analysis of proton spin-lattice relaxation times (T_1H) and proton spin-lattice relaxation times in the rotating frame (T_1ρH) revealed phase separation with domain sizes larger than 5 nm when the PTHF fraction exceeds 10 wt%. Only for lower PTHF-amounts, the SPNs were homogeneous on the nanometer scale. On the other hand, when PTHF with acrylamide end groups was used as macromolecular cross-linker, the NMR results showed the absence of any domain formation for SPNs with PTHF fractions up to 50 wt%. The major impact of the molecular design on the ultimate phase morphology of bicomponent polymer networks has been confirmed in all cases by DMA-analysis.     

Crystallization of magnesium substituted aluminophosphate of type-36 as studied by solid-state NMR spectroscopy

The crystallization process of aluminophosphate molecular sieve MgAPO-36 is characterized by the evolution of intermediate gels. Multinuclear solid-state NMR techniques in combination with powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) reveal in detail the nature of the intermediate gels and their evolution into crystalline structure. The long-range ordering of the aged as well as heated intermediate gels are probed by PXRD, showing that the crystallization of the framework begins after heating the gels at 423 K for 1.5 h. ³¹P NMR indicated that the structural Al–O–P and Mg–O–P units from the ATS framework are formed at the same time. More information about the local ordering of the gels is obtained from two-dimensional ²⁷Al → ³¹P HETCOR and ¹H → ³¹P CP/MAS experiments. Two types of microstructure regions could be differentiated by partially and fully condensed P species, in which five types of P(nAl) (n = 2–4) units are identified by ³¹P/²⁷Al double-resonance experiments. A possible evolution mechanism consisting of three stages is proposed for the crystallization process.     

Ageing of EPDM elastomers exposed to γ-radiation studied by H broadband and C high-resolution solid-state NMR

Ageing of EPDM synthetic elastomers exposed to γ-irradiation has been investigated using solid-state NMR Spectroscopy. Both ¹³C high-resolution and ¹H wideline measurements were carried out to evaluate chemical degradation including oxidation products formation, chain scission and crosslinking phenomena. Highly specific structures were tentatively proposed as a result of careful examination of ¹³C chemical shifts. The importance of diene monomer, the stabilising effect of curing process and the addition of antioxidants were evaluated on the basis of several polymer compositions.     

Counterion motions and thermal ordering effects in perfluorosulfonate ionomers probed by solid-state NMR

Perfluorosulfonate ionomers (PFSIs) neutralized by tetraalkylammonium ions have been investigated using variable temperature ¹H and ¹³C solid-state NMR (ssNMR) spectroscopy to probe the thermally induced properties of tetraalkylammonium ions at temperatures near the α-relaxations. Tetramethylammonium (TMA⁺), tetraethylammonium (TEA⁺), tetrapropylammonium (TPA⁺) and tetrabutylammonium (TBA⁺) ions have been incorporated in our study for the systematic control of ionic interactions within PFSIs according to the chain-length of ammonium ions. ¹³C static ssNMR results show that bulkier TPA⁺ and TBA⁺ ions undergo molecular tumbling motions near or above the α-relaxation temperature of the corresponding PFSI ionomers, with jumping rates of κ ≈ 1 kHz. Moreover, the results of ¹H spin-lattice (T₁) relaxation time measurements suggest that smaller TMA⁺ ions in the PFSI exhibit a thermally induced ordering effect as the sample temperature approaches the α-relaxation temperature of TMA⁺-PFSI. This ordering phenomenon is also supported by the results from small-angle X-ray scattering.     

Structure and dynamics of a vinylidene fluoride oligomer and its cyclodextrin inclusion compounds as studied by solid-state F MAS and H → F CP/MAS NMR spectroscopy

The molecular structure and dynamics of a vinylidene fluoride oligomer telomerized by carbon tetrachloride (Cl-OVDF) and its inclusion compound (IC) with β-cyclodextrin (β-CD) have been investigated using solid-state ¹⁹F magic angle spinning (MAS) and ¹H → ¹⁹F cross-polarization (CP)/MAS NMR spectroscopy. The preferential IC formation of the lower-molecular-weight components with β-CD was used to refine as-received Cl-OVDF. The refined Cl-OVDF with larger molecular weight readily takes γ-form (tttg⁺tttg⁻) conformation, and it also forms ICs with β-CD (Cl-OVDF/β-CD IC) under a certain condition. ¹⁹F MAS NMR indicates that Cl-OVDF chains virtually isolated in the β-CD cavities take no specific conformations even at −40 °C. The temperature dependence of the magnetic relaxation times (T₁^F, T_1ρ^F) indicates that the Cl-OVDF chains in ICs undergo molecular motions similar to the amorphous phase in the bulk, although the intramolecular spin diffusion among ¹⁹F nuclei is more significant in the former because of the one-dimensional confinement.     

Evolution of interphase in styrene-butadiene block copolymers as revealed by H solid-state NMR: Effect of temperature and molecular architecture

¹H spin-diffusion solid-state NMR, in combination with other techniques, was utilized to investigate the effect of molecular architecture and temperature on the interphase thickness and domain size in poly(styrene)-block-poly(butadiene) and poly(styrene)-block-poly(butadiene)-block-poly(styrene) copolymers (SB and SBS) over the temperature range from 25 to 80 °C. These two block copolymers contain equal PS weight fraction of 32 wt%, and especially, polystyrene (PS) and polybutadiene (PB) blocks are in glass and melt state, respectively, within the experimental temperature range. It was found that the domain sizes of the dispersed phase and interphase thicknesses in these two block copolymers increased with increasing temperature. Surprisingly we found that the interphase thicknesses in these two block copolymers were obviously different, which was inconsistent with the theoretical predictions about the evolution of interphase in block copolymer melts by self-consistent mean-field theory (SCFT). This implies that the interphase thickness not only depends strongly on the binary thermodynamic interaction (χ) between the PS and PB blocks, but also is influenced by their molecular architectures in the experimental temperature range.     

Aggregation and degradation of plasticized wheat gluten during thermo-mechanical treatments, as monitored by rheological and biochemical changes

Different thermo-mechanical treatments were carried out on plasticized gluten samples using the rubber process analyser (RPA 2000) which allows to record changes in viscoelastic properties during sample treatment. Temperatures ranging from 90 to 150 °C were tested at two oscillatory strains (7%: linear domain; 70%: high deformation domain). Biochemical changes of gluten proteins during treatments were followed by SE-HPLC. Rheological and biochemical changes were found to be in good accordance and allow us to characterize two major phenomena: aggregation and degradation of wheat gluten proteins upon heating. A kinetic approach of both phenomena was carried out in order to determine the temperature dependency of both reactions with respect to applied strain. Strain was found to decrease the temperature dependency of modulus values, to moderately accelerate the gluten protein aggregation reaction, and to greatly accelerate the gluten thermal degradation.     

Strain-induced crystallization of natural rubber as studied by high-resolution solid-state C NMR spectroscopy

A series of high-resolution solid-state ¹³C NMR experiments were performed on both unstretched and in situ stretched natural rubber samples. From the ¹³C CP/MAS spectra, it was found that natural rubber does form small crystals at room temperature though the degree of crystallinity is very small. Furthermore, from the ¹³C DD/MAS spectra, the crystalline signals were found to increase with the increase of draw ratio. ¹³C spin-lattice relaxation time (T₁) and ¹H spin-spin relaxation time (T₂) of in situ stretched natural rubber were measured for the first time, which provided further evidences for the conclusion that there exist crystals in both stretched and unstretched natural rubber samples. Quantitative ¹³C NMR measurements indicated that strain-induced crystallization occurs when the draw ratio reaches about 2.0 and the maximum crystallinity of our natural rubber samples can be as high as 19.3% upon stretching.     

Heterogeneous structure of poly(glycolic acid) fiber studied with differential scanning calorimeter, X-ray diffraction, solid-state NMR and molecular dynamic simulation

The heterogeneous structures of poly(glycolic acid) (PGA) fibers which have been used as bio-degradable suture were studied by differential scanning calorimeter (DSC),X-ray diffraction and ¹³C solid state NMR. The ¹³C cross polarization NMR spectra without magic angle spinning of the stretched fibers observed by changing the angle between the fiber axis and the magnetic field clearly showed the heterogeneous structures which consist of three components; well-oriented, poorly-oriented and isotropic amorphous components. The local structure, distribution of the fiber axis and fraction of each component were determined quantitatively. Change in the heterogeneous structure by changing the stretching method in the sample preparation and by changing the stretching ratio was also monitored. The X-ray diffraction data of the fibers are in good agreement with the ¹³C CP NMR data. Change in the heterogeneous structures correlate with change in the thermal properties observed by DSC method. The molecular dynamic simulation showed the generation of trans conformation of PGA chain and also change in the fraction of other conformations by stretching, which supports the experimental results obtained above and gives additional structural information.     

An investigation of the adsorption of aromatic hydrocarbons in zeolite Na–Y by solid-state NMR spectroscopy

The adsorption of toluene inside zeolite Na–Y was investigated by solid-state NMR spectroscopy. The environment of Na⁺ ions at different sites in Na–Y before and after adsorption was characterized by ²³Na magic-angle spinning (MAS) NMR. The information on the dynamic behavior of guest molecules inside the supercage of Na–Y was obtained by analyzing wideline ²H NMR spectra. The effect of loading level and temperature on molecular dynamics was also examined. The cation–sorbate interactions were directly probed by ²³Na{¹H} rotational-echo double-resonance (REDOR) experiments at different temperatures. Molecular Monte Carlo simulations were also performed to assist in the interpretation of the NMR data. ²³Na MAS and ²³Na{¹H} REDOR results show that each toluene molecule is facially coordinated to a Na⁺ ion at the SII site in the supercage, forming a π-complex. The adsorption also causes the Na⁺ ions initially located at the SI′ site to slightly shift to a new position within the sodalite cage, but has little effect on the Na⁺ at the SI site. The ²H NMR results indicate that the toluene molecules undergo a 2-site flip around the molecular long axis in addition to the methyl group rotation about its C₃ axis. ²³Na MAS spectra suggest that the adsorptive behavior of benzene and p-xylene in Na–Y is similar to that of toluene/Na–Y. ²³Na{¹H} REDOR results further indicate that inside the supercage, the degree of molecular motion follows the order of benzene > toluene > p-xylene.     

Structural analysis of cellulose triacetate polymorphs by two-dimensional solid-state C-C and H-C correlation NMR spectroscopies

For the elucidation of the crystal structures of the two crystalline allomorphs of cellulose triacetate (CTA), namely CTA I and CTA II, two-dimensional (2D) solid-state through-bond ¹³C-¹³C and ¹H-¹³C correlations NMR techniques applied to the two crystalline allomorphs of CTA. As a result, the ¹³C and ¹H chemical shifts of the glucopyranose ring of CTA I and CTA II were completely assigned by the 2D NMR spectra of these allomorphs. On the 2D ¹³C-¹³C correlation spectrum of CTA II, two sets of the ¹³C-¹³C correlations from C1 to C6 were observed. This indicated that the CP/MAS ¹³C NMR spectrum of CTA II can be characterized by its overlapping of the ¹³C subspectra of two kinds of 2,3,6-triacetyl-anhydroglucopyranose units and that there are two magnetically non-equivalent sites in the unit cell of CTA II. In the case of CTA I, the numbers of respective ¹³C and ¹H shifts of CTA I agreed with the those of the glucopyranose residue in the allomorph, strongly suggesting that the asymmetric unit of CTA I is only one glucose residue. In addition, conformational differences in the exocyclic C5-C6 bonds between CTA I and CTA II were strongly suggested by the notable differences in the ¹H and ¹³C chemical shifts at the C6 sites of these allomorphs.     

Structural characterization of FCC feeds from Indian refineries by NMR spectroscopy

Fluid catalytic cracking (FCC) feeds from four Indian refineries are structurally characterized by ¹H, gated-decoupled ¹³C, distortionless enhancement by polarization transfer (DEPT) and 2D ¹H–¹³C HETeronuclear CORrelation (HETCOR) and other 2D nuclear magnetic resonance (NMR) methods. Detailed structural analyses are completely supported by a range of NMR information including chemical shifts of ¹H and ¹³C, CH_n type distributions and ¹H –¹³C connectivities. The average structural parameters like branching sites, average number of branching per molecule, average length of side chains, percentage of saturates, aromatics and naphthenes are obtained from these NMR data. A novel approach based on “multipoint spline base line correction” is employed for estimation of naphthenes and n-paraffins that gives better quantitative estimation than the conventional methods. In this paper, importance is given to the study of those structural parameters that plays a key role in cracking chemistry as well as coke forming tendency of the feedstock. To the best of our knowledge, this is the first attempt to characterize and quantitatively estimate compositions of the high boiling fractions of petroleum feed by NMR methods and especially the complex structure of vacuum gas oil (VGO) fractions used in Indian refineries. The importance of this paper is to help in optimizing the product slate of Indian refineries through proper feedstock blending using few hundreds of million metric tons (MMT) of crude oil consisting of blends of light crudes with different heavy crudes and bottom of the barrel due to escalating cost of crudes.     

Structure and dynamics in the amorphous region of natural rubber observed under uniaxial deformation monitored with solid-state C NMR

Solid-state ¹³C NMR experiments were performed under uniaxial deformation of natural rubber to investigate the changes in the structural and dynamical behavior of the amorphous region induced by elongation. The structural change was detected as the change in the ¹³C cross-polarization (CP) chemical shifts and line shapes. In addition, change in the CP ¹³C peak intensity as a function of time was also observed and was used to monitor the change of the dynamical behavior with time in high resolution. The relationship between ¹³C CP intensity and molecular dynamics under uniaxial deformation of natural rubber was examined by the ¹H magnetization decay behavior in the rotating frame and ¹H-¹³C CP build-up curves. Although the strain-induced crystallization occurred at around 200% strain, the ¹³C lineshapes showed no significant change in the orientation of the amorphous chains. On the other hand, the molecular dynamics of the amorphous chains was greatly affected even under lower extension, that is, the enhanced mobility of the chains was observed at 30% strain. This enhanced mobility induced by deformation decreased after the deformation was stopped.     

Water balance and pore structure development in cementitious materials in internal curing with modified superabsorbent polymer studied by NMR

In this contribution, the water balance between modified superabsorbent polymer particles of various grain sizes and a hydrating cement matrix is studied both for ordinary and white Portland cements by means of NMR relaxometry. Different approaches for the evaluation of the experimental data are compared: inverse Laplace transforms and several multicomponent fitting models. Both evaluations provide well-comparable results with respect to the overall water quantities absorbed and re-released by the superabsorber. The experimental data indicate fast water uptake within less than 5 min after watering the superabsorber/cement mixture. The re-release of the water begins along with the onset of the hydration reaction and is finished after 1 day for superabsorber powders with a dry grain size below 125 μm and takes about 2 days for larger dry grain size. The water uptake of the superabsorber inside the cement matrix is quantified to about 2250% of its dry weight.     

Evaluation of the phase composition of amylose by FTIR and isothermal immersion heats

Amylose, a linear component of starch, has been shown to be directly responsible for many of starch's physical properties. In this study isothermal DSC assisted by FTIR spectroscopy was used to determine the phase composition of amylose under various pH conditions and while shear was used to disrupt chain-chain interactions. The analysis was based on a three-phase model consisting of crystalline (type B and single helices), amorphous, and network (physical entanglements and hydrogen bonds related) environments. Varying the pH of the water present in the samples enables the detection of the presence of the networks. Such networks, preferentially located in the amorphous phase, were found to be more reactive to chemical and probably thermal modifications. However, when chain entanglements or hydrogen bond networks are found near or in the helix of the crystalline phase, the polymer becomes more resistant to chemical and physical modification. Furthermore, it was observed that pH and shear could be used to control the morphology, orientation and phase content of amylose, which had a significant impact on the biodegradability of the treated samples.     

Structural investigations of polyurethane and silk-polyurethane composite fiber studied by 13C solid-state NMR spectroscopy

Bombyx mori silk fibroin (SF) fibers possess excellent mechanical properties together with biocompatibility and have attracted great attention in applications including biomaterials. The SF-polyurethane (PU) composite materials are expected to improve the mechanical properties and expand the application of SF. In this article, PU consisting of isophorone diisocyanate (IPDI) and poly (butylene adipate) is synthesized and characterized using ¹³C solid-state NMR spectroscopy. Then, the regenerated SF-PU (95: 5 wt%) fiber is prepared, which results in a 11.7% increase in tensile strength and 81% increase in elongation-at-break compared with those of SF fiber. The reason for the increase is due to the increase of random coil conformation in SF observed by ¹³C solid-state NMR and the presence of IPDI in the PU. Thus, it can be emphasized that this PU is very effective in changing the conformation of SF fiber by increasing random coil fraction and improve the mechanical properties.     

单质Si对含TiO2刚玉制品烧结性能和相组成的影响

以电熔白刚玉、α-Al2O3、锐钛矿和单质Si为原料,固定配料中电熔白刚玉和α-Al2O3的质量分数分别为80%和20%,锐钛矿的外加量为6%,分别外加0、 2%、4%和6%的单质Si,经混练、成型、干燥后在空气气氛中于1550 ℃保温3 h烧成,检测烧后试样的显气孔率、体积密度、耐压强度、抗折强度和线变化率,并采用XRD分析烧后试样的相组成.结果表明在刚玉材料中同时加入锐钛矿和单质Si能降低材料的显气孔率,提高材料的抗折强度和耐压强度,并有钛酸铝和莫来石生成;另外,单质Si对材料中的钛酸铝具有较好的稳定作用,但随着单质Si含量由2%增加至6%,材料中的钛酸铝含量减少,莫来石含量增加.     

Influence of water and degree of sulfonation on the structure and dynamics of SPEEK studied by solid-state C and H NMR

The molecular motions of sulfonated poly(ether-ether ketone) (SPEEK), synthesized by conventional method with a range of degree of sulfonation (DS) between 42 and 70%, as a function of DS and hydration were studied by ¹H-¹³C dipolar recoupling by rotor-encoded longitudinal magnetization (RELM) and ¹³C spin-lattice relaxations. The proton conductivity increased linearly with increasing DS from 52% and was comparable to that of Nafion 115 measured in the same condition for DS higher than 65%. The RELM dipolar patterns analyzed by the SIMPSON simulation program indicated that the population of phenyl rings in large amplitude motions such as 180°-flips was reduced with increasing DS. On the other hand, T_1ρ (¹³C) and T₁ (¹³C) results suggested that the dynamic chains in both 66 kHz and 100 MHz regimes were more populated with increasing DS, possibly in small-amplitude oscillations.     

Determination of MG and TG phase composition by time-domain NMR

The feasibility of time-domain NMR curve-fitting methodology for the quantitative determination of TG blend phase compositions was investigated. By studying a range of TG in their different crystal forms, it was shown that the transverse NMR relaxation characteristics of TG differ for the respective crystal polymorphs {α,β,β′}. This enables the TG polymorphism in fat blends to be quantitatively determined by curve fitting. If a liquid phase is present in the blend, curve fitting is able to determine the solid fat content, and the results compare well with those of the accepted NMR methods. The curve-fit method is less hindered by some of the disadvantages of these accepted methods, such as the use of a calibration factor.