Structural FTIR analysis and thermal characterisation of lyocell and viscose-type fibres

The microstructure and thermal properties of lyocell and other regenerated cellulose fibres (viscose and modal) were analysed using DSC, TG and FTIR. The FTIR spectral analysis showed that lyocell is the most crystalline fibre and is composed principally of crystalline cellulose II and amorphous cellulose. Likewise, the thermal analysis showed that lyocell has a higher thermal stability than viscose and modal fibres, as the difference between the onset temperature for its decomposition process was as high as 20 °C.     

The hydrolysis and recrystallisation of lyocell and comparative cellulosic fibres in solutions of mineral acid

Regenerated cellulosic fibres undergo a process described as scission-reordering during hydrolysis in solutions of mineral acid. This occurs within disordered polymer regions at lateral crystal interfaces, which are accessible to aqueous agents through the pore spaces and polymer free volume. This process is distinct from that of oligomer-solubilsation, which occurs within disordered polymer regions in series between crystal domains, where no effective template exists for recrystallisation. The degradation of series disorder will have the greatest influence on fibre tensile properties, which fall dramatically even at low levels of hydrolysis. The mechanics of fibrillation are most sensitive to the degradation of lateral disorder, which occurs at a higher rate constant. Soft-touch fabric processing may therefore be possible under conditions where there is a reduced influence on tensile performance. A kinetic model has been proposed to describe the hydrolysis and recrystallisation pathways, which shows that lyocell has longer but thinner crystal domains than viscose or modal fibres, and also a tighter distribution of lateral crystal sizes. Lyocell also has a lower proportion of series disorder and also thinner regions of lateral disorder. This is consistent with the overall greater crystallinity of the original lyocell fibre and the also of the final microscrystalline product.     

Properties and structure of solvent-spun and viscose-type fibres in the swollen state

The conditioned and wet tensile strength resp. modulus of solvent-spun and viscose-type cellulose fibres was correlated with their crystallite and amorphous orientation factor. It was found that the extrapolation of these tensile properties to the maximum degree of orientation results in identical values of the tensile strength resp. modulus in the conditioned and water swollen state. Proportional to a decreasing orientation factor the loss of strength and modulus by swelling increases. Additionally, a positive correlation was found between the wet tensile strength resp. modulus and the intensity of the interference of the equatorial small-angle x-ray scattering measured in the swollen state. This interference is caused by the elementary fibrils. The intensity of this interference is a measure for the fibrillar character of the swollen fibre structure. The fibrillability of the fibres suspended in water correlates positively with the crystallite orientation factor.Extracts presented at the Conference Cellulose '91 December 2–6, 1991 New Orleans, USA     

On the determination of crystallinity and cellulose content in plant fibres

A comparative study of cellulose crystallinity based on the sample crystallinity and the cellulose content in plant fibres was performed for samples of different origin. Strong acid hydrolysis was found superior to agricultural fibre analysis and comprehensive plant fibre analysis for a consistent determination of the cellulose content. Crystallinity determinations were based on X-ray powder diffraction methods using side-loaded samples in reflection (Bragg-Brentano) mode. Rietveld refinements based on the recently published crystal structure of cellulose Iβ followed by integration of the crystalline and amorphous (background) parts were performed. This was shown to be straightforward to use and in many ways advantageous to traditional crystallinity determinations using the Segal or the Ruland–Vonk methods. The determined cellulose crystallinities were 90–100 g/100 g cellulose in plant-based fibres and 60–70 g/100 g cellulose in wood based fibres. These findings are significant in relation to strong fibre composites and bio-ethanol production.     

Binding of Co(II) and Cu(II) cations to chemically modified wool fibres: an IR investigation

Wool fibres were modified by treatment with tannic acid (TA) solution or by acylation with ethylenediaminetetraacetic (EDTA) dianhydride. The unmodified and modified fibres were subsequently treated with Cu²⁺ and Co²⁺ solutions, at alkaline pH, and analysed by Attenuated Total Reflectance, ATR/IR spectroscopy to evaluate the changes induced in the structure of the fibre by metal binding. The spectral changes were correlated to metal adsorption results obtained by Inductive Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

The IR results were discussed in relation to our previous findings on the metal binding mode of Bombyx mori and Tussah silk fibres; the changes observed in the spectra were explained by considering the different affinity of the fibres for the modifying reagent and the amount of the metal absorbed. More relevant spectral changes were observed upon Cu²⁺ complexation rather than Co²⁺ complexation, according to the metal absorption results. The most relevant changes were observed for the EDTA-modified wool sample treated with Cu²⁺, according to the higher affinity of wool for EDTA. The IR spectra were quantitatively evaluated by the intensity ratio between the Amide I and Amide II bands (I_AmideI/I_AmideII) and its trend as a function of metal absorption was reported.

The present investigation demonstrated that the interaction between fibre and metal and the subsequent fibre modification depend on the chemical nature of the fibre, the metal cation and the modifying reagent.     

Composition effects on ethylene/propylene copolymers studied by GPC-MALS and GPC-IR

Copolymer composition and comonomer distribution along the polymer chains are important to determine the properties and the final usefulness of the polymer. There are several ways to study directly or not directly such comonomer distribution because it has a big effect on different kind of properties. GPC-MALS (multi-angle light scattering coupled to size exclusion chromatography), GPC-IR (size exclusion chromatography with an IR detector), CRYSTAF-TREF (crystallization analysis fractionation-temperature rising elution fractionation) or NMR are very common used techniques to obtain such kind of knowledge.In this work several ethylene/propylene copolymers in the whole composition range are characterized using NMR, GPC-IR and GPC-MALS. Average copolymer composition was obtained by ¹³C-NMR and by IR, and a linear correspondence between both results was found. GPC-IR allows to study the percentage of ethylene for each M_w and to check that incorporation of ethylene is done uniformly over the entire range of molecular weights, while the incorporation of propylene presents heterogeneity in the incorporation. GPC-MALS characterization allows the q shape parameter determination and quantification of the effect that the second monomer introduces as impediment to adopt the random coil distribution.     

Layered double hydroxide/polyethylene terephthalate nanocomposites. Influence of the intercalated LDH anion and the type of polymerization heating method

Conventional and microwave heating routes have been used to prepare PET–LDH (polyethylene terephthalate–layered double hydroxide) composites with 1–10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate had been previously intercalated in the LDH. PXRD and TEM were used to detect the degree of dispersion of the filler and the type of the polymeric composites obtained, and FTIR spectroscopy confirmed that the polymerization process had taken place. The thermal stability of these composites, as studied by thermogravimetric analysis, was enhanced when the microwave heating method was applied. Dodecyl sulphate was more effective than terephthalate to exfoliate the samples, which only occurred for the terephthalate ones under microwave irradiation.     

Thermostimulated molecular alteration in sol–gel derived TiO2:MoO3 composite materials

Thermostimulated molecular alteration in TiO₂:MoO₃ composite materials, obtained by sol–gel method, were investigated by IR-spectroscopy, Raman spectroscopy, and ESR spectroscopy. Change of the coordination environment of molybdenum atom from tetrahedral to octahedral in 200–450 °C temperature range was revealed. Two groups of molybdenum paramagnetic centers with different saturation character, responsible for oxygen redistribution in the material were detected.     

Surface characterization of cellulose fibres by XPS and inverse gas chromatography

Inverse gas chromatography (IGC) was used to determine the dispersive component of the free energy as well as the acid-base properties of cellulose fibre surfaces, before and after modification by corona treatment. It was found that the corona treatment increases both the dispersive contribution to surface energy and its acidic character, whereas only a slight increase in its basicity was observed. It was also found that some chemical degradation of the surface occurs at high corona currents. The extent of modification of the surface properties, as revealed by IGC, was correlated to the surface chemical composition deduced from XPS analysis as well as with the electrical conductance and the pH of the water suspensions of the cellulose fibres.     

Characterization of ethylene/propylene copolymers by means of a GPC-4D technique

Copolymer composition and comonomer distribution are important magnitudes in polymer material that have a big effect on different kind of properties and consequently there are several ways to study.In this work several ethylene/propylene copolymers synthesized with two different metallocene catalysts and a Ziegler–Natta catalyst and covering a wide composition range were studied. Characterization was carried out by nuclear magnetic resonance (¹³C NMR) and by gel permeation chromatography with 4 detectors (GPC-4D): refractive index, viscosity, multi-angle light scattering and infrared detectors.Different behaviour in the comonomer distribution along the molecular weight was obtained for metallocene and for ZN copolymers as expected due to the differences between these catalytic systems. Nevertheless, Ziegler–Natta copolymers present more homogeneous comonomer distribution due to the synthesis method. Study of conformation of chains in solution was improved by defining the scaling law of R_g against the number of repeat units because it avoids the effect of the repetitive unit size. Both metallocene copolymer sets show similar dependence of q value with the copolymer composition, however Ziegler–Natta copolymers show different behaviour with q values independent on copolymer composition. This different behaviour has been related with the effects of the heterogeneity of the ethylene distribution and of the molecular weight of the samples.     

生物可降解共聚物聚丁二酸/对苯二甲酸丁二醇酯(PBST)的序列结构及结晶性研究

制备了高分子量的聚丁二酸丁二醇酯,并通过与对苯二甲酸二甲酯的无规共聚调节其生物可降解性及力学性能,得到了具有优良机械性能和不同生物降解速度的一系列共聚物,并对共聚物序列结构、热力学性能、结晶性进行了研究.结果表明,该共聚物为无规共聚物,PBS和PBT分别结晶.共聚物的结晶熔点符合无规共聚物的Flory方程.     

Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage. The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6–15 × 10⁻¹² m²/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K_cell/K_w) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10⁻¹⁴ m²/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 × 10¹⁴, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.     

Heteropolyacid/saponite-like clay complexes and their blends in amphiphilic SEBS

A synthetic saponite-like clay, Sumecton SA (SSA), was self-assembled with 12-phosphotungstic acid (PTA) heteropolyacid for the preparation of new hybrid nanocomposites for proton exchange membranes. Thermogravimetric analysis (TGA) and Fourier transformed diffuse reflectance spectroscopy (DRIFT) measurements indicate the formation of robust PTA-SSA complexes. The Keggin structure of PTA is preserved within the complexes and is thermally stable up to 450 °C. The amount of PTA incorporated into the clay depends on the PTA-SSA weight ratio used for the complex preparation. PTA incorporation achieved is approximately 2-3 times the PTA content of most reported literature. However, higher PTA incorporation is accompanied by a significant loss of structural clay integrity. Low PTA-SSA weight ratios tend to preserve clay structure, but do not preclude its general amorphization generated by the PTA acidic treatment. PTA-SSA complexes present a low degree of order. Inorganic complexes were blended by melt extrusion with chemically-modified styrene/ethylene-co-butylene/styrene block copolymer (SEBS). Poly(oxyethylene/oxypropylene)-grafted-SEBS is more efficient than maleic anhydride-grafted-SEBS at dispersing PTA-SSA complexes. For both nanocomposite systems, nanoparticles’ size varies between 30 and 300 nm.     

Hydrogen-bond structures in poly(2-hydroxyethyl methacrylate): Infrared spectroscopy and quantum chemical calculations with model compounds

Hydrogen-bond structures in poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated by infrared (IR) spectroscopy and quantum chemical calculations (QCC). A monomer of 2-hydroxyethyl methacrylate (HEMA) and model compounds of methyl acetate (MA) and methanol (MeOH) were also used. Evidences for OHOC and OHOH types of hydrogen-bonds were observed in an IR spectrum of a PHEMA solid. It was estimated from the present study that 47.3% of OH groups on the PHEMA side chain terminal are engaged in the OHOC type of hydrogen-bond, while the rest contributes to the OHOH type of hydrogen-bond.     

Cationic complexes of Eu(III) and Sr(II) with diphosphine dioxides in organic extracts

IR spectroscopy was used to study the structure and composition of Eu(III) and Sr(II) complexes formed by cation-exchange extraction of these metals from their aqueous nitrate solutions with dichlorethane solutions of mixtures of chlorinated cobalt(III) dicarbollide (CCD) as a superacid with diphenyldiphosphine dioxides containing a methyl (Me-DPDO), ethyl (Et-DPDO), or polyoxyethylene bridge between two phosphorus atoms of phosphine oxide groups. At molar ratios DPDO/CCD ≤ 1, [Eu(H₂O)_nL₄]³⁺ complexes are formed in organic phases, whereas with an excess of DPDO relative to CCD, Eu(NO₃)L ₄ ²⁺ complexes are formed, where L = Me-or Et-DPDO. Polyoxyethylenediphosphine dioxide forms anhydrous complexes of composition Eu:L = 1:1 and 1:2 with Eu(III) and outer-spheric complexes of composition Sr:L = 1:1 and 1:2 with Sr(II), where the organic ligand molecules envelop the hydrated Sr(H₂O) _n ²⁺ cation. The peculiarities of extraction of the complexes are explained based on data about their composition and structure.     

Detection of adulteration in acetonitrile

To address the increasing concern that acetonitrile may be intentionally adulterated to meet the shortfall in global supplies resulting from a downturn in its manufacturing, three analytical techniques were examined in this study. Gas Chromatography with Thermal Conductivity Detection (GC-TCD), Near Infrared (NIR) spectroscopy and Fourier Transform Infrared (FT-IR) spectroscopy were assessed for their ability to detect and quantify potential adulterants including water, alternative organic solvents, and by-products associated with the production of acetonitrile. The results of the assessment of the three techniques for acetonitrile adulteration testing are discussed.     

Non-invasive detection of superimposed latent fingerprints and inter-ridge trace evidence by infrared spectroscopic imaging

Current latent print and trace evidence collecting technologies are usually invasive and can be destructive to the original deposits. We describe a non-invasive vibrational spectroscopic approach that yields latent fingerprints that are overlaid on top of one another or that may contain trace evidence that needs to be distinguished from the print. Because of the variation in the chemical composition distribution within the fingerprint, we demonstrate that linear unmixing applied to the spectral content of the data can be used to provide images that reveal superimposed fingerprints. In addition, we demonstrate that the chemical composition of the trace evidence located in the region of the print can potentially be identified by its infrared spectrum. Thus, trace evidence found at a crime scene that previously could not be directly related to an individual, now has the potential to be directly related by its presence in the individual-identifying fingerprints. A portion of this work was presented at the 16th Meeting of the International Association of Forensic Sciences, Montpellier, France September 2–7, 2002.     

Temperature and humidity aging of poly(p-phenylene-2,6-benzobisoxazole) fibers: Chemical and physical characterization

In recent years, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. The objectives of this study were to expose woven PBO body armor panels to elevated temperature and moisture, and to analyze the chemical, morphological and mechanical changes in PBO yarns extracted from the panels. A 30% decrease in yarn tensile strength, which was correlated to changes in the infrared peak absorbance of key functional groups in the PBO structure, was observed during the 26 week elevated temperature/elevated moisture aging period. Substantial changes in chemical structure were observed via infrared spectroscopy, as well as changes in polymer morphology using microscopy and neutron scattering. When the panels were removed to an ultra-dry environment for storage for 47 weeks, no further decreases in tensile strength degradation were observed. In a follow-on study, fibers were sealed in argon-filled glass tubes and exposed to elevated temperature; less than a 4% decrease in tensile strength was observed after 30 weeks, demonstrating that moisture is a key factor in the degradation of these fibers.