Effect of thermal treatment on potato starch evidenced by EPR,XRD and molecular weight distribution

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X‐ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright © 2015 John Wiley & Sons, Ltd.     

Dispersion polymerization of styrene in polar solvents: Effect of reaction parameters on microsphere surface composition and surface properties,size and size distribution,and molecular weight

Polystyrene microspheres were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Surface characterization of the formed particles was performed by x-ray photoelectron spectroscopy and critical surface tension measurements. The influence of different reaction parameters, i.e., monomer concentration, stabilizer type (polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinylacetate and polyvinylace tate), stabilizer concentration and molecular weight, and initiator type and concentration, on the molecular weight and on the size and size distribution of the formed polystyrene microspheres was investigated. The correlation between the surface composition and wett ability properties of the particles surface and their size and size distribution was also demonstrated. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1857–1871, 1996     

Effect of low molecular weight additives on immobilization strength, activity, and conformation of protein immobilized on PVC and UHMWPE

Horseradish peroxidase (HRP) was immobilized onto both plasticized and unplasticized polyvinylchloride (PVC) and ultrahigh molecular weight polyethylene (UHMWPE). Plasma immersion ion implantation (PIII) in a nitrogen plasma with 20 kV bias was used to facilitate covalent immobilization and to improve the wettability of the surfaces. The surfaces and immobilized protein were studied using attenuated total reflection infrared (ATR-IR) spectroscopy and water contact angle measurements. Protein elution on exposure to repeated sodium dodecyl sulfate (SDS) washing was used to assess the strength of HRP immobilization. The presence of low molecular weight components (plasticizer, additives in solvent, unreacted monomers, adsorbed molecules on surface) was found to have a major influence on the strength of immobilization and the conformation of the protein on the samples not exposed to the PIII treatment. A phenomenological model considering interactions between the low molecular weight components, the protein molecule, and the surface is developed to explain these observations.     

Solid-State coextrusion of high-density polyethylene. II. Effect of molecular weight and molecular weight distribution

The recently developed technique of solid-state coextrusion for ultradrawing semicrystalline thermoplastics has been applied in the preparation of self-reinforced high-density polyethylene extrudates. The extrudates consist of definite core and sheath phases composed of different molecular weights (M_w) in the range of 60,000–250,000 and different molecular weight distributions (M_w/M_n = 3.0–20). Concentric billets of two different phases were prepared for extrusion by in serting a polyethylene rod within a tubular billet of a different high-density polyethylene followed by melting the two phases to obtain bonding between them. The billet was then split longitudinally to increase extrusion speed and extruded at 120°C, 0.23 GPa through a conical die of extrusion draw ratio 25. Extrudates of high tensile modulus (38 GPa) and strength (0.50 GPa) could be produced in a steady state process at a rate near 0.25 cm/min. The tensile properties of the extrudates from either the single or concentric billets increased with average molecular weight and were insensitive to the molecular weight distribution of the constituent phases. Thermal analysis indicated a high deformation efficiency for the sheath and core phases of the extrudates by the coextrusion technique.     

Effect of method of solution on observed molecular weight distribution of barley starch and starch derivatives in size exclusion chromatography

Summary Samples of native barley starch and six starch derivatives were suspended (0.1% sample concentration) in four different solvents: the eluent (pH 11 buffer), dimethylsulfoxide, 0.1 M NaOH or 0.5 M NaOH and kept in a boilling water bath for 5 to 60 minutes or shaken for 60 minutes. The average molecular weight values , and the polydispersity value were determined with a TSK PW-type column using narrow standard calibration. Only a small part of the samples dissolved in the eluent. The dissolution of sample in dimethylsulfoxide was dependent on sample type. Of the NaOH solutions, 0.5 M NaOH was the only one that dissolved all the samples. Therefore, 0.5 M NaOH appears to be the solvent of choice for starch molecules.     

Effect of polycondensation methods on molecular weight distribution of nylon 610

Polycondensation methods greatly influence the molecular weight distribution of poly(hexamethylene sebacamide) (nylon 610) as determined by gel permeation chromatography (GPC). The ratio of weight average molecular weight to number average molecular weight (M_w/M_n) was used as a measure for estimating the molecular weight distribution. The M_w/M_n ratios of nylon 610 obtained from melt, solid phase, and high temperature polycondensation methods were 2 to 3.5, which were expected values for the most probable distribution. However, those for polymers obtained from the direct polycondensation in the presence of triphenylphosphine, interfacial polycondensation and low temperature polycondensation using an acid chloride varied over a wide range from 3.5 to 8.5. The effect of the kind of organic solvents in the interfacial method on the M_w/M_n ratios was especially large, and the molecular weight distribution could be controlled to some extent by selecting an appropriate solvent.     

Poly(styrene-b-isoprene) micelles. Effect of molecular weight on micelle size

Micelles composed of poly(styrene-b-isoprene) formed in heptane were studied using small-angle X-ray scattering (SAXS). Block copolymers of various molecular weights were synthesized via anionic polymerization employing the sequential monomer addition technique. The radii of gyration of these block copolymers were measured from SAXS data using the method of Guinier; it was found that the radius of gyration varies as the 0.5 power of the molecular weight. The form of the SAXS curve was calculated and reasons for using only the lowest angle region for determination of radii of gyration are discussed.     

Effect of molecular weight and its distribution on the spinodal for polydisperse polymer solutions

The Flory–Huggins interaction parameter χ(r_i) is considered as dependent on the chain length of a polymer. Therefore, a modified free energy expression of Flory–Huggins theory is obtained for the polydisperse polymer solutions. Based on this modified free energy expression and the thermodynamics of Gibbs, the expression of spinodal for polydisperse polymer solutions is obtained. For a given χ(r_i) according to de Gennes, the spinodals are calculated for polydisperse polymer solutions at different molecular weights and their distributions. It is found that all the interested variables r_n, r_w, r_z and molecular weight distribution have an effect on the spinodal for polydisperse polymer solutions, where the effect of changing r_w is much greater than that of changing r_n, r_z and molecular weight distribution.     

Effect of the molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes

This article discusses the characterization of arborescent (hyperbranched) polyisobutylenes (arb‐PIBs) by size exclusion chromatography and differential scanning calorimetry, in comparison with linear PIB standards. The radius of gyration (〈r〉^1/2 = R_z), measured from the angle dependence of light scattering of high‐molecular‐weight arb‐PIBs, was significantly larger than the hydrodynamic radius (R_h) from size exclusion chromatography/viscometry, and the R_h values were significantly smaller than R_h of linear PIBs. The glass‐transition temperature of arb‐PIBs having a branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total number‐average molecular weight and BR up to BR ～ 15. A modified Fox–Flory equation is proposed to describe the effect of architecture on the thermal transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1770–1776, 2006     

Effect of inititiator on the molecular weight distribution in dispersion polymerization of styrene

Dispersion polymerization of styrene in the particle size range of 10 μ with lauroyl peroxide as initiator results in a double-peak molecular weight (MW) distribution. The high-MW fraction was due to emulsion polymerization. The same phenomenon also exists in AIBN and benzoyl peroxide initiation, although it is less obvious. The kinetics of the reaction for dispersion polymerization was dependent on the concentration of the dispersing agent and the nature of the initiator.     

Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part II. Molecular weight distribution

A method has been developed for determining the molecular weight distribution of a polymer sample from the sedimentation–diffusion equilibrium data for a solution under pseudo-ideal conditions. From some theoretical examples it appears that the method works well and that the molecular weight distribution can be determined with a reasonable degree of resolution. From three polymer samples (polyethylene, polystyrene, and polycaprolactam) the molecular weight distribution was determined in this way. The average molecular weights, M?_n, M?_w, M?_z, and M _z+1, calculated from these distribution functions agree well with those calculated directly from the equilibrium data.     

Postpolymerization effect on molecular weight distribution generated by pulsed laser radical polymerization

The postpolymerization effect on molecular weight distribution (MWDs) and on the Pulsed Laser Polymerization (PLP) technique for evaluation of kinetic constants is investigated. General expressions for moments are derived for a polymerization scheme that contains the reactions of chain initiation, propagation, and termination by recombination or disproportionation, under polymerization initiation by an arbitrary sequence of radiation pulses. The results of calculation of MWDs and of the weight-average degree of polymerization (P _w) for methyl methacrylate are presented. It is shown that the P _w value strongly depends on postpolymerization. A new method for determining the rate constants of chain propagation and chain termination from a single experiment by polymerization with packets of laser pulses is presented.     

Molecular weight distribution and molecular structure of polyethylene produced by radiation-induced polymerization

The molecular weight distribution of polyethylene produced by radiation was calculated according to a kinetic scheme. The calculated molecular weight distribution was compared with the results deduced from gel-permeation chromatography. The observed distribution curve from GPC was broader and showed a lower degree of polymerization than the calculated one. Discrepancies between observed and calculated curves can be explained if the polymer contains nonsteady-state products and if the reaction mechanism includes chain transfer to dead polymer. By this reaction long-chain branching would occur. Several long-chain branches per polymer molecule were indeed found, as inferred from solution properties.