Chemical modification of hemp,sisal, jute,and kapok fibers by alkalization

Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X‐ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002     

Rheological properties of hyperbranched polymer/poly(ethylene terephthalate) reactive blends

The rheological properties in solution, in shear and in uniaxial elongation of poly(ethylene terephthalate) (PET) reacted together with hyperbranched polymers (HBPs) were investigated. Two different PET grades, of low and high molecular weights, were compounded with sub‐ to over‐stoichiometric concentrations of HBPs of second and fourth pseudo‐generation, and subsequently subjected to a solid‐state polycondensation (SSP). The formation of microgels, which occurs at high HBP concentration, gave rise to a large increase in melt elasticity and a related decrease in melt strength. At low HBP concentrations, the complex viscosity of the unreacted HBP/PET was considerably reduced, thus demonstrating a lubrication effect of the HBP molecules. During SSP, the intrinsic and shear viscosities exhibited a gradual increase, which was similar for both PET and HBP/PET blends, and was correlated to an increase in molecular weight, through linear‐chain extension and branching reactions. The elongational viscosity of the reactive blends was also increased as a function of reaction time, and this increase was much larger in the case of the HBP/PET blends. A 400% increase in melt strength of the PET was obtained by combining SSP and trace amounts of an HBP of second generation, without any decrease in drawability.     

The nutritive value of refined rapeseed oils: A review

Recent findings on the nutritive value of rapeseed oil (RSO) with high erucic acid content have been compared to those of canbra oil (CO), an oil extracted from newly bred Canadian rapeseed with no erucic acid. Erucic acid in diets retards animal growth even if food consumption is not altered. Growth performances of CO are as good as olive or peanut oil. The unbalanced ratio of palmitic acid to monoethylenic acids of CO does not affect rat growth rate. Because of its glyceride structure and high content of erucic acid, RSO has a lower digestibility (81%) than CO (96%) in the rat. Unabsorbed erucic acid is not preferentially excreted as calcium soaps. Interesterification of RSO which converts 31.7% of the erucic chains to the 2 position improves digestibility of erucic acid. 2-Monoerucin is more efficiently absorbed than the free acid. In vivo metabolic conversion of erucic to oleic acid has been proved in the rat. β-oxidation of injected 14-¹⁴C labeled erucic acid proceeded at the same rate as oleic acid but the over-all yield of the reaction was lower. Fatty acid composition of tissues in animals fed RSO or CO is influenced on one hand by erucic and gadoleic (C_20∶1) acids of RSO, and on the other hand by the unbalanced ratio of palmitic-monoethylenic acids and the linolenic acid content of both oils. Nonnegligible amounts of erucic acid are deposited in the body fats of rats, chickens, turkeys, lambs and found in the milk of female rats fed RSO. Almost no erucic acid is incorporated in liver and testicles in the rat and it is not recovered in chicken egg yolk. The effect of RSO on rat reproduction has been re-examined. Dietary lipid and vitamin levels are of great importance in the results obtained. RSO induces myocarditis in several animal species. Similar lesions, although less frequent and severe, have been observed also with CO in the rat. Some authors have reported that erucic acid of RSO was responsible for the effect on heart muscle. Common fatty acid patterns to both RSO and CO have to be further investigated to explain the persisting effect of CO. One of 9 papers presented at the Symposium, “Cruciferous Oil-seeds,” ISF-AOCS World Congress, Chicago, September 1970.     

Structure and dynamics of a pentablock copolymer of polystyrene-polybutadiene in a butadiene-selective solvent

We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains.     

EVALUATION OF A METHOD FOR MEASURING MIXING TIME USING NUMERICAL SIMULATION AND EXPERIMENTAL DATA

A method for measuring mixing performance in large-scale vessels is investigated. The method is evaluated experimentally in a pilotscale reactor and by using a model based on the three-dimensional calculation of the flow field. The method is based on injection of a tracer and measuring the concentration with several detectors at different locations. The mixing performance is measured as the decay rate of the difference between the concentration at the detectors and the final concentration.

The model predicts a strong dependence on injection point. The assumption of a first-order decay rate of the concentration deviation is more appropriate for some injection points.     

Flow distribution and pressure drop in plate heat exchangers—II Z-type arrangement

To investigate the flow distribution and the pressure drop in the Z-type arrangement plate heat exchangers, a theoretical analysis has been made including mass and momentum balances for a flow element in both the intake and exhaust conduits. Calculations based on one-dimensional flow equations have been carried out.It is found that the flow distribution and the pressure drop can be determined by a general characteristic parameter (m). Nearly uniform flow distribution may be obtained when m is equal to zero. In the case when m² is positive, the channel flow rates will increase in the direction of the intake stream. If m² is negative the channel flow rates will also increase in the intake stream direction. The analysis also shows that the total pressure drop in plate heat exchangers is practically the same for both U - and Z-type arrangements. The results are applicable to a wide variety of combinations of heat exchanger dimensions, channel goemetries and fluid velocity. They are summarized by charts that permit a designer quickly to estimate the flow patterns.     

Reaction pathway of benzonitrile formation during toluene ammoxidation on vanadium phosphate catalysts

The reaction pathway of the ammoxidation of toluene on (VO)₂P₂O₇ used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH₃ is chemisorbed on the catalyst surface, forming three different species, i.e., NH ₄ ⁺ ions located on BrØnsted sites, coordinatively bound NH₃ on Lewis sites and NH ₂ ^– groups, presumably P-NH₂. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of V^IV=O groups generates a V...O=CH-C₆H₅ surface structure. This benzaldehyde-like surface species reacts with adsorbed NH₃ according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH ₄ ⁺ ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.     

Tensile strength of polyurethane exposed to nitrogen dioxide

Polyurethane prepared from tetramethylene glycol and diisocyanate was exposed in the form of films to small pressures of NO₂ and to NO₂ plus air. Tensile strength was measured as a function of exposure time and temperature with an apparatus especially constructed for the purpose of measuring mechanical properties in different environmental “atmospheres.”     

Étude expérimentale du mélange réactif au sein d'un réacteur torique ondulé (RTO)

Reactive mixing in a wavy torus reactor (WTR) has been examined experimentally. Its performances are compared to these of two other reactors: a plane torus reactor (PTR) and a baffled stirred tank reactor (BSTR). hydrodynamics of mixing has been studied using a plug flow model with axial dispersion for the WTR and PTR. The effect of axial dispersion on the kinetic of a chemical reaction was then analysed for the WTR, PTR and BSTR. Mixing times were slightly longer for the WTR due to a weaker axial dispersion. We also noticed an improvement of the convertion rate for low dissipated power.     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.