Broad-line Nuclear Magnetic Resonance Research Articles

Effects of glycerol content on structure and molecular motion in thermoplastic starch-based nanocomposites during long storage

Thermoplastic starch-based nanocomposites with varying glycerol content and montmorillonite as a nanofiller were studied using dynamic-mechanical analysis (DMA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) during one-year storage. DMA results showed that starch-rich and glycerol-rich domains were present in the samples and during storage for up to one year the content of the amorphous phase decreased and molecular mobility changed. 13C NMR and XRD measurements confirmed that ordered structures were formed during storage and its content was larger for samples with higher glycerol content and increased with the storage time. The data obtained from deconvolutions of 1H broad line NMR spectra indicate increased overall molecular mobility in the samples up to four months of storage, while after nine months the trends were opposite. Lower free water content compared to the total water content in the samples determined according to deconvoluted 1H MAS (magic-angle spinning) NMR spectra indicated that a part of water molecules was immobilized in the ordered structures.

Temperature variations of NMR second moments for drawn tapes based on polypropylene and polyethylene

Isotropic and drawn tapes prepared from isotactic polypropylene (PP), low density polyethylene (LDPE) and their blend PP/LDPE (70/30) have been studied by broad-line nuclear magnetic resonance (NMR) in the temperature range from 120 up to 320 K. The glass-transition temperatures, Tg, for studied samples have been determined from the temperature dependencies of the NMR second moments. It was found that the NMR spectra and their second moments are additive for isotropic blend in the whole temperature range, while a significant differences from addition rule appear for drawn PP/LDPE blend, when weighted average second moment is calculated by means of second moments of equally drawn homopolymers. It was found out that the LDPE component in the blend is drawn to a greater extent than PP component.

Study ofβ relaxation in polypropylene fibres modified by several techniques

Polypropylene fibres prepared from polypropylene (PP) blended with 8 wt % of an ethylene aminoalkylacrylate copolymer were studied by means of 1 H nuclear magnetic resonance (NMR) and dynamic mechanical techniques. Measurements were carried out on the fibres spun at the spinning speeds 400 and 1200 m.min -1 and then drawn to the draw ratio λ = 3.5. Spin - lattice relaxation time T 1 and storage E' and loss E components of a dynamic mechanical modulus were measured in the temperature region of the glass transition. Broad line NMR spectra were detected at 313 K. The experimental results show that drawing of the fibres prepared at both spinning speeds results in a restriction of the molecular motion. Simultaneously with the restriction, a chain mobility enhancement was observed in noncrystalline regions of the fibres. Similar effects were induced also by rising the spinning speed. Reasons for this behavior are discussed in the paper.

Macromolecular orientation in drawn polypropylene, polyethylene and their blend, studied by NMR

Drawn tapes made of polypropylene (PP), low density polyethylene (LDPE) and of their PP/LDPE blend (70/30 w/w) were studied by means of broad-line NMR (Nuclear Magnetic Resonance). The parameters characterizing the anisotropy of the NMR second moments were used for estimation of macromolecular orientation in drawn tapes. A model for this particular blend was proposed on the basis of NMR experiments. According to this model the LDPE component of the drawn blend is oriented in a such extent as similarly drawn homopolymer unlike the PP component which is oriented to a much lower degree after drawing of the blend.

Molecular mobility and strengthening of oriented liquid-crystal polymers

Broad-line proton magnetic resonance has been used to study cooperative mesophase molecular motion in the example of a fully-aromatic oriented liquid-crystal polymer Vectra A950. The molecular mobility is found to decrease as a result of heat treatment, which is considered to be the reason for a higher tensile (rupture) strength owing to an increase in the activation energy for the fracture process.

Molecular mobility in liquid-crystalline phase of oriented wholly aromatic copolyester as revealed by proton magnetic resonance

Broad line proton magnetic resonance (PMR) has been used for the study of molecular motion in wholly aromatic thermotropic liquid-crystalline (LC) copolyester at high temperatures up to 340°C. Specimens were thin highly oriented fibers produced from a copolymer of hydroxybenzoic acid and hydroxynaphthoic acid (HBA/HNA). In the vicinity of the thermotropic transition temperature a fine structure of PMR spectra was revealed for as-spun fibers. Annealing leads to smoothing of this structure. Theoretical spectra were calculated and compared with the experimental ones. This made it possible to obtain information on large-scale segmental motion of macromolecules in the LC phase. Heat treatment leads to retardation of the chain cooperative mobility. Dynamic inhomogeneity of the fibers at high temperatures is discussed.

A broad-line nuclear magnetic resonance study of water absorption and transport in fibrous cement roofing tiles

The 1H nuclear magnetic resonance spin–spin relaxation time of water in a fibrous cement roofing tile has been measured as a function of hydration using the Carr–Purcell–Meiboom–Gill pulse sequence with a pulse gap sufficiently short to negate most of the attenuation effects of water diffusion in the pore space magnetic susceptibility gradients of the tile. The data reveal pores with three characteristic sizes, consistent with earlier mercury intrusion porosimetry results and details of the manufacturing process. The relaxation times are constant as a function of hydration, suggesting that, at intermediate hydrations, some pores fill completely while others remain empty. There is also evidence that the smallest pores fill first. Complementary imaging studies reveal a three-layered heterogeneous structure which is consistent with the manufacturing process. The images show the establishment of a dynamic equilibrium water concentration gradient across the slate when one side is exposed to water. The mutual diffusion coefficient of water in the tile is estimated as 4×10-7 cm2 s-1. Finally the effects of a water-resistant coating on water transport are shown. © 1998 Chapman & Hall

The hot compaction of SPECTRA gel-spun polyethylene fibre

The compaction of gel-spun high molecular weight polyethylene (PE) fibre, SPECTRA 1000, has been investigated for a range of compaction temperatures between 142 °–155 °C. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and broad-line nuclear magnetic resonance (NMR) techniques have been used to examine the structure of the compacted materials and to determine the compaction mechanisms. With increasing compaction temperature, the flexural properties of the compacted materials did not show any significant change up to 154 °C, but large changes were observed if the temperature was increased from 154 to 155 °C. DSC and SEM studies revealed that no evident surface melting and recrystallization occurred during hot compaction in the temperature range 144–154 °C, although the rigid crystalline fraction measured by NMR for all compacted materials is significantly lower than that for the original fibre. Significant transverse strength is also developed at the lower compaction temperatures, and this also only markedly increases on going from 154 to 155 °C. Structural investigations show how the fibres deform so as to interlock, and localized welding occurs, so as to bond each fibre to its neighbour. This is distinct from the melting and recrystallization at the surface of the fibres previously observed in melt spun fibres.

1H solid-state nuclear magnetic resonance study of the mobility of the tetrapropylammonium template in a purely siliceous MFI-type zeolite

Dynamics of tetrapropylammonium (TPA) cation occluded during the synthesis in a siliceous MFI zeolite is investigated by 1H broad-line nuclear magnetic resonance (NMR) methods. Second moments M 2, spin-lattice relaxation times T 1 and T 1 ϱ are measured in a large temperature domain. To allow comparison, similar measurements are also reported in bulk tetrapropylammonium bromide (TPABr). Whereas methyl reorientation at low temperature and tumbling of the cation in the plastic phase are observed in crystalline TPABr in accordance with published studies, a new slower motion which could not be identified is observed below the phase transition. Such a motion is much more clearly shown by the existence of a minimum of T 1 ϱ in a quenched sample. Our measurements in the zeolite demonstrate that the TPA template exhibits a larger and more complex mobility below 378 K. Beyond the fast methyl reorientation, the results disclose a motion which probably involves the entire propyl arms inside the channels. So the zeolite framework seems to make such a kind of motion easier. On the contrary, even at 450 K, the highest temperature investigated, the tumbling which would necessitate exchange of the propyl arms between the channels is not observed. A slow motion, responsible for a decrease of T 1 ϱ above 350 K, could not be identified. While a simple correlation time is sufficient to describe the relaxation time dependences in TPABr, a distribution (such as Williams-Watts) is required to account for those in the zeolite.

A study of the diffusion of decane into lightly cross-linked natural rubber by broad-line MRI

The diffusion coefficient of decane in a lightly cross-linked peroxide vulcanizate of natural rubber (polyisoprene) has been measured by broad-line proton magnetic resonance imaging (MRI). The value of the diffusion coefficient deduced from the MRI results is higher than that obtained from conventional mass-uptake measurements. The discrepancy can be removed by assuming that the diffusion coefficient of decane increases exponentially with concentration. Proton MRI has been used for the parallel study of both the diffusing solvent and the mobility of the polymer matrix. This was achieved by exploiting the wide differences in the proton NMR relaxation times of the two components. Broad-line imaging techniques using resonant oscillating field gradients were used to overcome the short T 2 (∽ 1 ms) of the rubber. The results show a good correlation between the ingress of the solvent and the softening of the rubber matrix.

A broad-line nuclear magnetic resonance study of a vinylidene fluoride/trifluoroethylene copolymer

Broad-line nuclear magnetic resonance measurements have been performed for the proton resonance in an oriented 70:30 copolymer of vinylidene fluoride and trifluoroethylene. The spectra show two components with distinctly different linewidths. The broad component is identified with the crystalline regions and the narrow component with the amorphous. An appreciable reversible change in crystallinity with temperature was observed, which could significantly contribute to the pyroelectric response of this material. In addition, measurements through the Curie transition show the increasing libration of the chains prior to the transition, which could also contribute to the pyroelectric response.

A broad-line nuclear magnetic resonance study of stress-induced crystallinity changes in poly(vinylidene fluoride)

Many mechanisms have been proposed to explain the piezoelectric response of poly(vinylidene fluoride) (PVDF), but none of these are adequate to explain why d 32 is so much less than d 31. Although it has been suggested that this difference could relate to the anisotropy of Poisson's ratios, direct measurement of the latter show that this explanation is not correct. The other viable explanation is that there are changes in crystallinity under stress. This possibility is tested in the present investigation using broad-line nuclear magnetic resonance measurements to estimate the change in crystallinity when drawn oriented samples are subjected to a tensile stress applied parallel or perpendicular to the draw direction. The results show that the crystallinity increases for a stress applied parallel to the draw direction and decreases for a stress applied perpendicular to the draw direction. The crystallinity changes give a positive contribution to d 31 and a negative contributon to d 32, which can explain the relatively low figure for d 32 compared with d 31.

Nuclear magnetic resonance and wide-angle X-ray scattering in poly(acrylonitrile- co-methyl acrylate): 2. The influence of comonomer on swelling behaviour

The changes of conformation and supermolecular structure of poly(acrylonitrile- co-methyl acrylate) on swelling have been revealed by combining 1H broad-line nuclear magnetic resonance and wide-angle X-ray scattering techniques. The similarities and differences in swelling behaviour and the resulting structure between polyacrylonitrile and the copolymer have been presented and interpreted.

Nuclear magnetic resonance and wide angle X-ray scattering in poly(acrylonitrile-co-methyl acrylate): 1. The influence of comonomer on structural characteristics and annealing behaviour

The morphology, dynamics and annealing behaviour of acrylonitrile/methyl acrylate copolymer P(AN-co-MA) have been examined by means of broad-line nuclear magnetic resonance ( 1H BL-n.m.r.) and WAXS methods. The difference in conformation between ‘pure’ acrylonitrile sequences and ‘foreign’ unit-centred triads has been revealed and a conformational model of the copolymer has been proposed. Three distinct steps in behaviour of P(AN-co-MA) on annealing have been distinguished and interpreted. The role of the comonomer units in molecular mobility as well as in structural and chemical changes on heat treatment has been emphasized. Both differences and similarities between polyacrylonitrile (PAN) and P(AN-co-MA) have been shown and an attempt has been made to explain the effect of the comonomer units on paracrystalline and amorphous regions.

Molecular mobility and phase structure of isotactic poly(epichlorohydrin) as revealed by broad-line nuclear magnetic resonance

Isotactic partially crystalline poly(epichlorohydrin) (PECH) was studied by broad-line nuclear magnetic resonance in the temperature range from − 170 to + 40°C. The temperature dependence of the linewidth and the second moment, and the fractions of individual lines in the spectrum, obtained through decomposition of the total spectrum, were analysed. The derived data yield conclusions about the changes in molecular mobility in this polymer. The theoretical value of the second moment for the crystal lattice of isotactic PECH was calculated based upon known unit-cell parameters. Comparison of these data with the results of wide-line X-ray diffraction studies allowed conclusions to be drawn about the phase structure of isotactic PECH, and especially about morphological inhomogeneity in the rigid phase.

Structure and dynamics of alpha-tocopherol in model membranes and in solution: a broad-line and high-resolution NMR study.

Nuclear magnetic resonance has been applied to study the conformational dynamics of alpha-tocopherol (vitamin E) in solution and in model membranes. In nonviscous solution, 1H nuclear magnetic resonance (NMR) showed that alpha-tocopherol is in rapid equilibrium between two or more puckered conformers of its heterocyclic ring. The most likely conformers to be so involved are the two half-chair forms. Deuterium NMR spectra of specifically deuteriated alpha-tocopherol in multilamellar dispersions of egg phosphatidylcholine, measured in the liquid-crystalline state, were characteristic of axially symmetric motional averaging. The orientation of the rotational axis within the molecular framework was determined. Studies on oriented multilamellar membranes revealed that this axis is perpendicular to the surface of the membrane. The profile of quadrupolar splittings along the hydrophobic tail does not have a plateau, in contrast to that of the fatty acyl chains of the membrane lipids. Longitudinal relaxation times (T1) were short. The presence of a minimum in their temperature dependence shows that molecular motion with an effective correlation time tau eff approximately equal to 3 X 10(-9)s is responsible for relaxation. However, the temperatures and absolute values of the minima depend on the position of the deuterium in the molecule, demonstrating that tau eff represents a complex blend of motions.

Molecular Motions and Related Mechanical Relaxations in Linear Polyethylene Treated with Fuming Nitric Acid

Molecular motions and related relaxations in solid linear polyethylene degraded by fuming nitric acid were investigated from -170 to 100°C by means of broad-line nuclear magnetic resonance absorption (BL-NMR) and dynamic mechanical measurements. A second-moment vs. temperature curve shows three motional processes around 80, 0 and -140°C, which were named α, β' and γ3 in the order of descending temperature. The molecular origins of these processes are discussed on the basis of a BL-NMR study of a sample swollen with C2Cl4. The α-process is attributed to the motion of the chains in the lamellar core which is not affected by the acid treatment while the β'- and γ3-processes are attributed to the motion of the cilia on lamellar surfaces produced by the acid treatment. Mechanical relaxations corresponding to the β'- and γ3-processes were also observed.

A broad line n.m.r. study of oriented poly(vinylidene fluoride)

Broadline nuclear magnetic resonance measurements have been carried out for the proton resonance in oriented poly(vinylidene fluoride). The spectra in general show two component lines with distinctly different line widths. The broad component shows a high degree of molecular orientation and can be satisfactorily assigned to the crystalline regions of the polymer. The narrow component corresponds to an oriented non crystalline phase which is sufficiently constrained to allow motion about the chain axis only. An appreciable decrease in the value of the rigid mass fraction was observed in both of the samples over the temperature range examined. Our calculations indicate that this could play an important role in the temperature dependence of the pyroelectric response of this material.

A study of conformation, configuration and phase structure of polyacrylonitrile and their mutual dependence by means of WAXS and 1H BL-n.m.r.

Polyacrylonitrile (PAN) samples have been investigated using wide-angle X-ray scattering (WAXS) and broad-line nuclear magnetic resonance ( 1H BL-n.m.r.). The samples differed as far as their tacticity and amorphous and paracrystalline regions amounts are concerned. Structural changes that occur in the analysed PAN samples when they are annealed are discussed, and both structural similarities and differences are presented. An explanation is given to explain the improvement of order within paracrystalline regions in the polymer with an increased amount of isotactic sequences. An attempt is made at determining the dependence between configuration, conformation and phase structure of PAN.

Nuclear Magnetic and Mechanical Relaxations in the γ-Loss Band of Linear Polyethylene Irradiation with γ-Rays

Molecular motion and relaxation processes in the solution-crystallized linear polyethylene irradiated with γ-rays to 100, 200 and 400 Mrad in air are investigated in the temperature range from ca. –170 to –10°C (γ-region) by means of broad-line nuclear magnetic resonance absorption and dynamic mechanical measurements. Of the three relaxations γ1, γ2 and γ3 appearing in this region the γ3-relaxation, attributed to the motion of ciliary chains on the lamellar surface, becomes predominant as the amount of irradiation increases. It is suggested that carboxylic end groups are introduced into the ciliary chains produced by oxidative chain scission, because the values of the NMR second moment in the γ-region agree with those of the HNO3-treated sample.