Reduction In Intrinsic Viscosity Research Articles

Ultrasound-based treatment approaches for intrinsic viscosity reduction of polyvinyl pyrrolidone (PVP)

The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO2 at optimized depth of horn and 27°C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions.

Effects of L-Cysteine on some characteristics of wheat starch

In this study the effects of L-Cysteine as a food additive on wheat starch characteristics before and after gelatinization were studied. L-Cysteine (63 mg/kg, starch basis) was added to slurry of wheat starch in water (30%, w/w). One set of samples was prepared by mixing it at 40 °C for 45 min. Another set was gelatinized at 100 °C for 45 min. The scanning electro-micrographs of the samples prepared at 40 °C in the presence of L-Cysteine showed some spots on the granules. However, thermal properties, X-ray patterns and the degree of crystallinity of the samples did not obviously change ( P > 0.05); while a reduction in intrinsic viscosity, peak and final viscosities of the samples was observed. After gelatinization, intrinsic, peak and final viscosities of the samples were reduced. Some of these changes may indicate degradation of starch molecules in the presence of L-Cysteine, particularly after gelatinization.

Effect of melt-processing and ultrasonic treatment on physical properties of high-amylose maize starch

High-amylose maize starch (Hylon VII) was submitted to melt-processing in an internal mixer at 100 °C and 40 rpm for 8 min. Glycerol was used as a plasticiser at different polymer/glycerol ratios. Torque and temperature curves were obtained. After glycerol extraction with ethyl alcohol, the samples were dispersed at 5 g/L, and treated by ultrasound radiation at the same conditions for 30 min. Samples were characterised by 1H NMR spectrometry, viscosity measurements, and X-ray diffractometry. The results revealed that both glycerol and water had an important role on the crystallinity properties of the resulting products. Melt-processed and sonicated samples showed similar 1H NMR spectra. Ultrasound treatment caused a significant reduction in intrinsic viscosity for the sample previously processed with the highest glycerol content, probably because of its higher solubility in water.

Partial characterization of extracellular polysaccharides from cyanobacteria

Four cyanobacterial strains, Cyanothece sp., Oscillatoria sp., Nostoc sp. and Nostoc carneum were studied for physico-chemical characterization of extracellular polysaccharide (EPS) secreted during the controlled growth condition. Hydrolyzed EPSs showed the compositional involvement of four sugar moieties viz. mannose, glucose, xylose and ribose in varying combinations. Infrared spectra of EPSs showed a specific absorbance of O–H stretching at 3448–3400 cm −1, asymmetrical–symmetrical C–H stretching at 2924 and 2854 cm −1 and a bending vibration of C–H at 1400–1380 cm −1. Absorbance at 1259 and 1140 cm −1 with Cyanothece sp. EPS, indicated the presence of sulfur containing functional group. Thermal gravimetric analysis and differential scanning calorimetric analysis confirmed the polysaccharides thermal stability as high as around 250 °C. In the presence of 0.1 M NaCl aqueous solution, the intrinsic viscosity of polysaccharides from Oscillatoria sp. and Nostoc sp. decreased 1.6 fold, whereas, 3–5 fold reduction in intrinsic viscosity was observed with commercially available guar and xanthan gum.

Synthesis and comparative biodegradability studies of three poly(alkylene succinate)s

Poly(alkylene succinates) were synthesized from succinic acid and aliphatic diols with 2 to 4 methylene groups by melt polycondensation. DSC, 1H NMR, WAXD and molecular weight measurements were used to characterise the polymers. Biodegradability studies of polyesters with the same average molecular weight, included enzymatic hydrolysis for several days using Rhizopus delemar lipase at pH 7.2 and 30 °C. DSC traces of biodegraded polyesters revealed that hydrolysis affected mainly the amorphous material. For all polyesters an increase in glass transition, melting point and heat of fusion was recorded. In the first days of enzymatic hydrolysis, fast rates of mass loss were observed accompanied by a rapid reduction of intrinsic viscosity and molecular weight, thus indicating a mixed endo- and exo-type hydrolysis mechanism. Afterwards, it turned to an exo-type mechanism, taking place in the crystalline phase, since after 15–25 days of enzymatic hydrolysis molecular weight was stabilized, while mass loss kept on decreasing though in a slower rate. End-group analysis revealed that carboxyl and hydroxyl groups increased due to ester bonds' scission. The biodegradation rates of the polymers decreased following the order PPSu > PESu ≥ PBSu and it was attributed to the lower crystallinity of PPSu compared to other polyesters, rather than to differences in chemical structure. Finally, a simple theoretical kinetic model was developed and Michaelis–Menten parameters were estimated.

Enzymatic modification of pectin to increase its calcium sensitivity while preserving its molecular weight.

A commercial high-methoxy citrus pectin was treated with a purified salt-independent pectin methylesterase (PME) isozyme isolated from Valencia orange peel to prepare a series of deesterified pectins. A series of alkali-deesterified pectins was also prepared at pH 10 under conditions permitting beta-elimination. Analysis of these pectins using high-performance size exclusion chromatography (HPSEC) with on-line multiangle laser light-scattering, differential viscometer, and refractive index (RI) detectors revealed no reduction in weight-average molecular weight (M(w); 150000) in the PME-treated pectin series, whereas a 16% reduction in intrinsic viscosity (IV) occurred below a degree of esterification (DE) of 47%. In contrast, alkali deesterification rapidly reduced both M(w) and IV to less than half of that observed for untreated pectin. PME treatment of a non-calcium-sensitive citrus pectin introduced calcium sensitivity with only a 6% reduction in the DE. Triad blocks of unesterified galacturonic acid were observed in (1)H nuclear magnetic resonance spectra of this calcium-sensitive pectin (CSP). These results demonstrate that the orange salt-independent PME isozyme utilizes a blockwise mode of action. This is the first report of the preparation of a CSP by PME treatment without significant loss of the pectin's M(w) due to depolymerization.

Effect of Amylose Content on Expansion of Extruded Rice Pellet

ABSTRACTRice pellets were prepared by single‐screw extrusion cooking with an in‐barrel water content of 50 wt%. Three different types of rice, indica glutinous, japonica, and indica, were used as raw materials. Reconstituted rice flour was made to study the effect of amylose content on pellet expansion. The glass transition (Tg) and expansion (Te) temperatures of extruded pellet were determined by differential scanning calorimetry (DSC) and noncontact infrared thermometer, respectively. The amylose content was not significantly affected by extrusion cooking. The reduction in intrinsic viscosity indicated that amylopectin experienced some degradation. The Tg and Te were not functions of amylose content, which affected the expansion ratio of the pellets. The Gordon‐Taylor equation was applied to estimate the Tg of the rice pellets.

In vitro protein release and degradation of poly-dl-lactide-poly(ethylene glycol) microspheres with entrapped human serum albumin: quantitative evaluation of the factors involved in protein release phases.

To quantitatively evaluate the correlations between the amount of initial burst release and the surface-associated protein, and between the onset time for the second burst release and the matrix polymer degradation. Human serum albumin (HSA) was microencapsulated in polylactide (PLA) and poly-dl-lactide-poly(ethylene glycol) (PELA) with PEG contents of 5, 10, 20, and 30%, respectively, using the solvent extraction procedure based on formation of double emulsion w/o/w. Microspheres with similar particle size (1.7-2.0 microm), similar protein entrapment (2.1-2.8%) but different surface-associated proteins (9.3-53.6%) were used to evaluate the in vitro matrix degradation and protein release profiles. Degradation was characterized by studying the intrinsic viscosity decrease, medium pH change, and weight loss of the microspheres. The matrix degradation and protein release profiles were highly dependent on the polymer composition of the microspheres. Faster decreases in the intrinsic viscosity of recovered matrix polymer, the microspheres weight, and the pH of degradation medium, and earlier onsets for the break in intrinsic viscosity reduction and the mass loss were detected for PELA microspheres with higher PEG content. The hydration and swelling of microspheres matrix contributed greatly to the degradation of matrix polymer. The HSA release showed triphasic profile and involved two mechanisms for all the microsphere samples. Smaller amount of initial burst release, larger gradual release rate, and earlier onset for the second burst release were observed for HSA from matrix polymer with higher PEG content. The extent of the initial burst release was quantitatively related with the surface-associated protein. The second burst release of HSA was observed to occur within 1 week after the onset for mass loss, which was also the break in the intrinsic viscosity reduction rate. Protein release profiles could be rationalized by optimizing the matrix polymer degradation and microsphere characteristics.

Study of thermal and mechanical properties of virgin and recycled poly(ethylene terephthalate) before and after injection molding

In this study, we compared the thermal properties (glass transition, melting point and crystallinity) and mechanical properties (Young’s modulus, elongation at break and impact strength) of post-consumer poly(ethylene terephthalate) (PET) bottles with those of the virgin resin. We studied two types of scraps of recycled PET: one arising from homogeneous deposits of bottles and the other of heterogeneous deposits soiled by contaminants such as PVC and adhesives. The presence of contaminants and residual moisture coming in the shape of scraps facilitate the crystallization of recycled PET compared to virgin PET and induces cleavages of chains during the melt processing. This leads to a reduction in intrinsic viscosity and consequently in molecular weight, and these decreases are more significant when the recycled resin is soiled. Virgin PET exhibited a ductile behavior (>200% of elongation at break),whereas post-consumer PET bottles exhibited a brittle one (<10% of elongation at break). This is a consequence of the difference in crystallinity, the presence of impurities in the recycled PET and the different thermal and mechanical history of the virgin and recycled materials.

Preparation and biodegradability of polystyrene having pyridinium group in the main chain

Poly(styrene-co-4-vinylpyridine) (PS-co-VP) was synthesized by bulk copolymerization, and then polystyrene containing a small amount of N-benzyl-4-vinylpyridinium chloride (PS-co-VPC) was prepared by quaternization of PS-co-VP with benzyl chloride. The structures of PS-co-VP and its quaternized product PS-co-VPC were characterized by FTIR. An attempt has been made to give biodegradability to PS-co-VPC which showed significant degradation when placed in an aeration tank of a sewage works. Control polymers possessing no pyridinium group did not show significant degradation under these conditions, and the reduced extent of intrinsic viscosity and weight-average molecular weight during the treatment increased with the content of the pyridinium group. The intrinsic viscosity reduction and elementary analysis exhibited an upper limit after 36 days of treatment. Incorporation of the pyridinium group into polystyrene appeared to have improved the biodegradability. Gel permeation chromatographic analysis showed that the low molecular weight fraction was more easily degraded than the high molecular weight fraction, and molecular weight reduction was more conspicuous when the content of the pyridinium group was higher.

Chain-Scission and Bleaching in Heterophasic Ethylene-Propylene Copolymers

The variations in the viscosity and gloss (yellowness and whiteness index) in isotactic polypropylene, heterophasic E-P copolymers and polyethylene were measured during photo-oxidation. The samples underwent extensive reduction in intrinsic viscosity [[UNKNOWN]] upon U.V. irradiation. The kinetics of oxidative degradation have also been studied using polychromatic light at 60°C in air. These parameters appear to be a sensitive criteria to characterize the photo-oxidative transformation of polymers. The course of degradation is random and the yellowing process brought by the short wavelength U.V. light is accompanied by a photobleaching reaction which is caused by the light of longer wavelengths.

Chain‐scission and yellowing in high impact polystyrene

AbstractDifferent grades of impact‐modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain‐scission during photo‐oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.

Interaction of acridine orange and sodium poly-α, L-glutamate

The interaction of acridine orange and sodium poly-α, L-glutamate in the pH range of 3.8–6.8 was studied by a spectral method and viscosity measurement. From the binding data, the molar change in entropy, enthalpy and the number of binding sites on polymer were calculated. The values of ΔS° were positive. ΔS° for binding decreasing extensively in pH range of 5.0. These results are explained by the transition of helix ⇋ coil of the polymer. The intrinsic viscosity reduction in the presence of the dye, in pH 3.8 is due to the formation of dye bridges between the polymer helix.

On‐line viscometry combined with gel permeation chromatography. II. Application to branched polymers

AbstractGel permeation chromatography (GPC) combined with on‐line flow time measurements have been applied to the analysis of branching in polymers. Three sets of branched polymers were examined: polybutadienes lightly crosslinked by high energy radiation, a styrene‐divinyl benzene copolymer and several of its fractions, and polyvinyl acetates branched by polymer transfer reactions during polymerization. The reduction in intrinsic viscosity due to branching was determined for each GPC fraction of the polybutadiene samples. The branching frequency in these fractions was known from other information, so the results were used to establish a relationship between viscosity ratio G and the theoretical size ratio g. This relationship was then used to calculate the distribution of branching and Mw in the styrene copolymers and the polyvinyl acetates. The results were compared with independent information on these polymers. The agreement was generally good.

Degradation of Ovalbumin by L-Ascorbic Acid in the Presence of Cupric Ion

in the presence of aci-reductone undergo depolymerization during autoxidation. In most cases, the extent of depolymerization was measured by the reduction of intrinsic viscosity, but the depolymerization mechanism still remains obscure. There have been few works concerning the change of peptide chain by the treatment with L-ascorbic acid. 6 ) In general, reductone is formed as an inter­ mediate product of the browning reaction which is caused by the reducing sugars and amino compounds. Their oxidized form fur­ ther reacts with amino compounds resulting in the formation of melanoidin. The brown­ ing reaction in foods generally proceeds in the presence of amino acid, peptide, and protein. It has been recognized that carbonyl compounds react with c-amino groups of lysine and N-terminal groups of protein,7) but the degradation of polypeptide is still unknown. This paper presents evidence for the release of peptide and amino acid from ovalbumin coupled with autoxidation of L-ascorbic acid

Interaction of dye and synthetic sucrose polymer Ficoll

The interaction of Ficoll and Benzopurpurine 4B was studied by spectral method and viscosity measurement. From the binding data the molar changes in entropy and enthalpy, and the number of binding sites on polymer were calculated. Both values of ΔH0 and ΔS0 were positive. The valuen increases with increasing temperature. These results may be explained by the change of the configuration of polymer chain. The intrinsic viscosity reduction in the presence of the dye is due to the formation of dye bridges.

Intrinsic vescosity of a once-broken rod.

The intrinsic viscosity theory of Kirkwood, Riseman, and Auer is applied to a molecular model of two long rods of equal length connected by a flexible joint. In the nondraining limit, the intrinsic viscosity of a solution of such molecules is predicted to be 15% lower than that for rigid rods of the same molecular weight, in good agreement with experimental results of Teramoto, Yamashita, and Fujita. This reduction in intrinsic viscosity is smaller than would be expected from the radius of gyration.

Physicochemical studies of fractionated bovine heparin: I. Some dilute solution properties

Commercially prepared bovine heparin was fractionated by sequential elution from an ECTEOLA column into four discrete fractions and by solvent elution with an ethanol-water mixture into 12 fractions. Equilibrium centrifugation of the fractions in 0.5 m NaCl at pH 2.5 and interference optics revealed wide distribution of molecular weights. The fractions varied in biological activity and intrinsic viscosity. Chemical differences between fractions were minimal while the biological activity for the low molecular weight fractions were uniformly low. Inactivation with HCl, under mild conditions where biological activity was reduced fivefold, was not accompanied by reduction in intrinsic viscosity or molecular weight. A linear intrinsic viscosity-molecular weight relationship for the fractions prepared by alcohol elution can be described by the functions [ η] = 1.75 × 10 −5 M w 0.98 in 0.1 m NaCl, pH 6.5, and [ η] = 7.85 × 10 −5 M w 0.80 in 0.5 m NaCl, pH 2.5. An analogous relation for the sedimentation constant determined in 0.5 m NaCl at pH 2.5 was linear and described by s 0 = 1.2 × 10 −1 M w 0.44. The data suggest that heparin in solution under the conditions studied exhibits substantial flexibility.

Physical characterization of cellulose xanthate in solution

AbstractThe intrinsic viscosity of cellulose xanthate solutions was studied as a function of the electrolyte content of the solvent, and found to decrease sharply with increase in electrolyte concentration. All electrolytes tested except sodium and lithium hydroxides produced essentially the same reduction in intrinsic viscosity for solutions of equivalent ionic strenghts, indicating that the effect was largely one of interaction between the solvent ions and the charged xanthate groups. Hydroxides induced a greater viscosity reduction. The reason for this was not fully resolved; however, indications were obtained that the hydroxides, in addition to behaving as electrolytes toward the charged xanthate groups, also interact with the hydroxyl groups on the parent cellulose chain.Light scattering measurements, as well as data on the variation of the intrinsic viscosity with molecular weight in various solvents, showed that the change in intrinsic viscosity with electrolyte concentration could be accounted for by a change in configuration, or degree of coiling of the molecule. Calculations indicated that in pure water cellulose xanthate should approach a rigid rod configuration whereas in 6% caustic coiling occurs and the molecule resembles more a random configuration.