Decrease In Degree Of Polymerization Research Articles

High temperature oxidation behavior of liquid phases sintered SiC ceramics with ZrB2 addition

The oxidation property of liquid-phase sintered silicon carbide (LPS-SiC) ceramics with ZrB2 addition was studied after oxidation test in air at 1400 °C. The results indicate that the addition of ZrB2 decreased the degree of polymerization (DOP) of the silicate networks in the oxide layer, suppressing the additional oxidation caused by residual bubbles in the oxide layer of LPS-SiC, which bypassed the layer and directly corroded the material internally. After 100 h of oxidation, the additional oxidation depth was found to be 125 μm in the sample without ZrB2 and 0 μm in those containing 10 wt% ZrB2. Simultaneously, the decrease in DOP facilitates the migration of crystalline phases. The generated ZrSiO4 can migrate and aggregate at the interface between the surface oxide layer and the SiC/ZrB2 matrix, forming a continuous ZrSiO4 barrier. This impedes the diffusion of the oxidant and enhances the oxidation resistance. However, an insufficient ZrB2 content leads to a discontinuous ZrSiO4 layer, thereby weakening its protective effect. Simultaneously, a decrease in DOP increases the rate of oxygen diffusion, resulting in an increase in the oxidation layer thickness. This study contributes to a better understanding of the failure mechanisms of LPS-SiC in oxidizing environments and provide a reference for the design of oxidation-resistant LPS-SiC materials.

Intensification of pre-treatment and fractionation of agricultural residues

Lignocellulose biomass is a unique renewable and sustainable source that can be used in energy generation, production of transport fuels and in chemical industries to replace petroleum-based resources. However, due to its recalcitrance to chemical and enzyme breakdown, it needs to be pre-treated prior to processing. In this study, ultrasound assisted ozone was used to pre-treat the agricultural processing residues corn cob and spelt husk. Following organosolv fractionation, about 90 % and 94 % of lignin with high purity (95 %) were recovered for corn cob and spelt husk with guaiacyl-syringyl lignin the major fraction from corn cob and guaiacyl lignin from spelt husk respectively. In addition, cellulose pulp of 83.6 % and 85.2 % with 78 % purity were recovered for corn cob and spelt husk respectively with a 19 % decrease in cellulose crystallinity and 17 % decrease in degree of polymerization (DP). Thus, the improved quality separation of biomass components will enhance downstream conversion to value added products thereby improving the sustainability and cost effectiveness of the process.

COMPARATIVE STUDIES OF PHYSIC-CHEMICAL PROPERTIES AND STRUCTURE OF COTTON CELLULOSE AND ITS MODIFIED FORMS

Comparative studies of the physicochemical properties and structures of cotton cellulose, microcrystalline cellulose, and nanocellulose were carried out using IR, NMR spectroscopy, X-ray diffraction, thermal analysis in order to identify the dependence "particle size - structure - properties". It was revealed that in the series “cotton cellulose – microcrystalline cellulose – nanocellulose” the degree of polymerization decreases (1200, 230, 110 respectively), the degree of crystallinity increases (66%, 72%, 83% respectively). The IR spectra of microcrystalline cellulose and nanocellulose are characterized by sharp peaks (in the range 1000–1500 cm–1) compared with cotton cellulose. The amount of bound water in gels of microcrystalline cellulose and nanocellulose increases with decreasing particle size, the degree of stability of colloidal systems increases with the transition from microcrystalline cellulose to nanocellulose. Nanocellulose and microcrystalline cellulose have relatively smaller mass loss and relatively large temperature ranges of intensive decomposition and their thermal stability is higher than cotton cellulose. It was found that the periodate oxidation rate of nanocellulose is higher than that of microcrystalline cellulose and cotton cellulose. It was established that microcrystalline cellulose is quantitatively susceptible to periodate oxidation in 7–8 hours, and nanocellulose in 0.5–1 hour.

Lamellae—Parking Garage Structure—Lamellae Transition in Densely Grafted Layers of Amphiphilic Homopolymers: Impact of Polymerization Degree

By means of computer modeling, the self-organization of densely grafted macromolecules with amphiphilic monomer units as a function of macromolecular polymerization degree and solvent quality was studied and a diagram of state was constructed. The diagram contains fields of disordered distribution of monomer units and of prolonged aggregates, regions of lamellae with small and big domain spacing, and transition region. Within the transition region, the lamellae with different spacing coexist: the lamellae with big domain spacing are on the top of the grafting layer and the lamellae with small domain spacing are close to the grafting surface. The lamellae are connected with each other and form bicontinuous parking garage structure joining all side groups into a single cluster. The domain spacing of lamellae does not depend on the macromolecular length, but the width of the transition region decreases with the decrease of polymerization degree until total vanishing at relatively short macromolecules. The sharp switch between lamellae and bicontinuous structure opens the perspective for practical applications of densely grafted layers with amphiphilic monomer units.

Optical activity of films based on chitosan of various molecular masses and modifications

The effect of chemical (polysalt → polybase reaction) and physicochemical (heat and vapor processing) modifications of the films of chitosan of various molecular masses and prehistories on the optical activity of the polysaccharide is studied. For both of the chitosan chemical modifications, the following dependence that is nontrivial for high-molecular compounds is established: [α] = f(log $${\bar M_\eta }$$ ); as the degree of polymerization decreases, the modulus of [α] of the films increases. The X-ray diffraction study shows that the differences in the optical activity of the samples with different $${\bar M_\eta }$$ are caused by a restriction in the mobility of the macromolecular sections upon formation of the films of high-molecular chitosan and incompleteness of the relaxation processes of the film systems to the state with energetically favorable conformations. The comparison of humidity and optical and biological activities of the initial and dehydrated chitosan films is performed. The chitosan films in the salt modification feature moderate bactericidal activity, which decreases with an increase in $${\bar M_\eta }$$ of the polymer. The thermal processing of the salt modification reduces the antibacterial action; a conversion to the base form is accompanied by the loss of bactericidal activity.

Novel Self-Assembling Amino Acid-Derived Block Copolymer with Changeable Polymer Backbone Structure.

Block copolymers have attracted much attention as potentially interesting building blocks for the development of novel nanostructured materials in recent years. Herein, we report a new type of self-assembling block copolymer with changeable polymer backbone structure, poly(Fmoc-Ser)ester-b-PSt, which was synthesized by combining the polycondensation of 9-fluorenylmethoxycarbonyl-serine (Fmoc-Ser) with the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St). This block copolymer showed the direct conversion of the backbone structure from polyester to polypeptide through a multi O,N-acyl migration triggered by base-induced deprotection of Fmoc groups in organic solvent. Such polymer-to-polymer conversion was found to occur quantitatively without decrease in degree of polymerization and to cause a drastic change in self-assembling property of the block copolymer. On the basis of several morphological analyses using FTIR spectroscopy, atomic force, and transmission and scanning electron microscopies, the resulting peptide block copolymer was found to self-assemble into a vesicle-like hollow nanosphere with relatively uniform diameter of ca. 300 nm in toluene. In this case, the peptide block generated from polyester formed β-sheet structure, indicating the self-assembly via peptide-guided route. We believe the findings presented in this study offer a new concept for the development of self-assembling block copolymer system.

Effect of bacterial β-amylase and fungal α-amylase on the digestibility and structural characteristics of potato and arrowroot starches

Retrograded and debranched starch, known as resistant starch type 3 (RS3), is resistant to digestive enzymes and exhibits a behavior similar to that of dietary fibers. In this study, the effect of β- and α-amylase on the digestibility and structural characteristics of potato and arrowroot starches was evaluated and compared. Starch samples were gelatinized, hydrolyzed by β- or fungal α-amylase, debranched, cooled (4 °C/16 h), precipitated with ethanol, and dried. Debranched and gelatinized starch samples were used as control. The degrees of hydrolysis for the two starches were similar (∼25%), regardless of enzyme used. In both starches, β-amylase resulted in a significant decreases in average degree of polymerization (DPn) of short chains (from 16.5 to 12) and in proportion of these chains, while fungal α-amylase caused a significant decrease in DPn of long chains (from 38.9 to 26.8 and from 35.1 to 28.2 for potato and arrowroot starches, respectively) plus a significant increase in proportion of short chains. Gelatinization enthalpy and relative crystallinity of modified starches increased with amylolysis, particularly when α-amylase was used. RS3 content was 20.2% in the debranched potato starch and increased to 36.5% with amylolysis, regardless of the enzyme used before debranching. However, slowly digestible starch content increased from 8.5% to 27.8% when α-amylase was used in this starch. Meanwhile, arrowroot starch had 47.5% and 53.4% RS3 contents when β- and α-amylase were used, respectively. Structural characteristics, particularly the amylopectin branch chain length distribution, are important factors responsible for RS3 formation when amylolysis precedes debranching.

Bio-catalytic action of twin-screw extruder enzymatic hydrolysis on the deconstruction of annual plant material: Case of sweet corn co-products

A continuous process combining an alkaline thermo-mechano-chemical pretreatment neutralization step, followed by injection of enzymes into the twin-screw extruder, was developed using sweet corn co-products as a biomass model. The implementation of the continuous process is described. Particular attention is paid to the influence of the bio-catalytic action of enzymatic hydrolysis on the deconstruction of annual plant material in the twin-screw extruder (a process called “bioextrusion”). The use of a twin-screw extruder allows working with high consistency (20%), in a high shear environment, for a short time (∼2min). In the present work, the nature of the ligno(hemi)cellulosic material transformations, covering solubilization and extraction of saccharides and modification of cellulosic fibers, were investigated. 41% of hemicelluloses and 14% of lignin are extracted by the alkaline pretreatment. Hydrolytic enzymes are not deactivated during bioextrusion, which has a destructing effect on the fiber. It leads to a change of rheological properties and induces an increase of sugars released in the form of mono and polysaccharides (up to 13%/DM of total sugars) with longer chains than in the case of a batch reactor. At the same time, the degree of polymerization decreases and a shortening of the cellulose chains occurs.

Hemicellulose Hydrolysis in the Presence of Heterogeneous Catalysts

A prominent autocatalytic effect in the hydrolysis of hemicelluloses was observed in the presence of heterogeneous cation-exchange catalysts, Amberlyst 15 and Smopex 101. The kinetic models proposed were based on the reactivities of the non-hydrolysed sugar monomer units and the increase of the rate constant as the reaction progresses and the degree of polymerization decreases. General kinetic models were derived and the kinetic parameters, describing the autocatalytic effect, were determined by non-linear regression analysis. The kinetic model explained very well the overall kinetics, as well as the product distribution in the hydrolysis of hemicelluloses.

Effects of NO2 and acetic acid on the stability of historic paper

This research investigates degradation of historic paper in polluted environments during long-term dark storage. In an innovative experiment, degradation rates at realistic pollution levels are compared with degradation rates in the absence of pollution, using a set of real historic papers. The most abundant pollutants in repositories in post-industrial environments are taken into account: acetic acid and nitrogen dioxide. Their action was assessed in terms of reduction of ‘handling’ (as defined by decrease in degree of polymerisation) and ‘display’ (as defined by discolouration) lifetimes. Extrapolations to room conditions enabled lifetime predictions in conditions that are comparable to a real archival or library repository environments while prediction uncertainties were analytically evaluated to assess the significance of conclusions. While 10 ppb of NO2 does reduce the handling lifetime of almost all types of paper, their predicted lifetimes were still assessed to be several millennia, with the exception of acidic paper. Acetic acid at concentrations that are typical for archival and library repositories (<100 ppb) has significantly less effect than NO2 while it does not affect display lifetimes. From a conservation management perspective, it needs to be addressed whether the predicted reductions in otherwise significant handling lifetimes are of real concern and whether air filtration in archival and library repositories is justified.

Characteristics of destarched corn fiber extrudates for ethanol production

The effect of extrusion on characteristics of destarched corn fiber was investigated. Extrusion was conducted at a screw speed of 300 rpm, feed rate of 100 g/min, feed moisture content of 30%, melt temperature of 140 °C and die diameter of 3 mm. After extrusion, characteristics of raw and extruded destarched corn fiber were compared. Raw and extruded destarched corn fibers were enzymatically saccharified and fermented using Saccharomyces cerevisiae (ATCC 24858). Extrusion pretreatment resulted in low crystallinity index, significant decrease in degree of polymerization and microstructure disruption of destarched corn fiber for enzymatic saccharification. This provides a significant increase in xylose yield for fermentation. Significant increase in protein digestibility and free amino nitrogen were additional benefits of extrusion for yeast nutrient in fermentation. Therefore, extruded destarched corn fiber significantly increased (p < 0.05) ethanol yield (29.08 g/L) and higher conversion (88.79%) by improving the physiochemical and functional properties for saccharification and fermentation.

Kinetic modeling of hemicellulose hydrolysis in the presence of homogeneous and heterogeneous catalysts

Kinetic models were developed for the hydrolysis of O‐acetyl‐galactoglucomannan (GGM), a hemicellulose appearing in coniferous trees. Homogeneous and heterogeneous acid catalysts hydrolyze GGM at about 90°C to the monomeric sugars galactose, glucose, and mannose. In the presence of homogeneous catalysts, such as HCl, H2SO4, oxalic acid, and trifluoroacetic acid, the hydrolysis process shows a regular kinetic behavior, while a prominent autocatalytic effect was observed in the presence of heterogeneous cation‐exchange catalysts, Amberlyst 15 and Smopex 101. The kinetic models proposed were based on the reactivities of the nonhydrolyzed sugar units and the increase of the rate constant (for heterogeneous catalysts) as the reaction progresses and the degree of polymerization decreases. General kinetic models were derived and special cases of them were considered in detail, by deriving analytical solutions for product distributions. The kinetic parameters, describing the autocatalytic effect were determined by nonlinear regression analysis. The kinetic model described very well the overall kinetics, as well as the product distribution in the hydrolysis of water soluble GGM by homogeneous and heterogeneous catalysts. The modelling principles developed in the work can be in principle applied to hydrolysis of similar hemicelluloses as well as starch and cellulose. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1066–1077, 2014

Properties of nanofibrillated cellulose from different raw materials and its reinforcement potential

Five commercial wood and wheat straw fiber sources with different morphologies were mechanically disintegrated into nanofibrillated cellulose (NFC). The processing times for disintegration varied, depending on the sizes and the moisture content of the starting materials. A decrease in polymerization degree (DP) for the fibrillated materials between 15% and 63% could be observed. Nevertheless, all isolated NFC materials showed homogenous network structures. They were used for the production of composite films with hydroxypropyl cellulose (HPC) as matrix and different proportions of NFC and two commercial fibrillar-fibrous celluloses as reinforcing components. Films with the commercial, more inhomogeneous fibrillated celluloses showed up to 2.5 times lower strength and up to four times lower stiffness. It appeared that homogeneity of the NFC material is more important for its reinforcement potential than the DP. A proper pre-treatment and choice of starting cellulose materials can reduce energy consumption, a key issue for industrial up-scaling.

Effect of alkali-activation on aluminosilicate-based cementitious materials

High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning (MAS) NMR of 27Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmetrical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of 29Si with different treatments suggest that Q 0 disappears, the quantity of Q 2 increases, and the quantity of Q 4 decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.

Analysis of the effects of catalytic bleaching on cotton

Hydrogen peroxide can be catalyzed to bleach cotton fibers at temperatures as low as 30°C by incorporating dinuclear tri-μ-oxo bridged manganese(IV) complex of the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (MnTACN) as the catalyst in the bleaching solution. The catalytic system was found to be more selective under the conditions applied than the non-catalytic H2O2 system, showing better bleaching performance while causing slightly lower decrease in degree of polymerization (DP) of cellulose. In order to gain fundamental knowledge of the bleach effect on cotton fibers and cellulose as its main component, especially after catalytic bleaching, X-ray Photoelectron Spectroscopy (XPS) was used to study surface chemical effects. The Washburn method was applied to investigate wetting properties, and liquid porosity was used to obtain pore volume distribution (PVD) plots. Parallel analyzes performed on model cotton fabric, i.e. “clean” cotton fabric stained with morin - a pigment regularly found in native cotton fiber, helped to differentiate between pigment oxidation and other bleaching effects produced on the (regular) industrially scoured cotton fabric. Bleaching was not limited to the chemical action but also affected cotton fiber capillary parameters most likely due to the removal of non-cellulosic materials as well as chain-shortened cellulose.

Desorption of cellulases from cotton powder

Cotton fabrics were treated with three different Trichoderma reesei cellulase preparations (total crude – TC, endoglucanase enriched – EG-rich, cellobiohydrolase enriched – CBH-rich) using mechanical agitation to produce cotton powder. Desorption of cellulase enzymes from the cotton powder was then performed by washing with buffer. After 3 washings most of the protein was desorbed from the cotton powder and the amount of sugars released in the latter washings was negligible. TC and CBH-rich preparations produced a finer cellulose powder than EGs. The desorption process caused a decrease in degree of polymerisation (DP) specially for the cotton treated with EGs and a marked increase in polydispersity (P d) for all preparations.

Mechanism of brown-rot decay: Paradigm or paradox

Interest in understanding how brown-rot fungi degrade wood has received increasing attention in recent years because of a need to identify novel targets that can be inhibited for the next generation of antifungal wood preservatives. Brown-rot fungi are unique in that they can degrade holocellulose (cellulose and hemicellulose) in wood without first removing the lignin. Furthermore, they degrade holocellulose in an unusual manner, causing a rapid decrease in degree of polymerization at low weight loss. Despite increased research effort, the mechanism of brown-rot decay remains unclear. Furthermore, this research has not pointed to biochemical targets for inhibition and development of new wood preservatives. In reviewing the brown-rot literature, it became apparent that many beliefs about brown-rot decomposition of wood are based more on tradition or conjecture than on facts. In some cases, these misconceptions have become near dogma. They cloud our understanding of brown-rot decay and as a result may contribute to a misdirection of research efforts. The purpose of this paper is to attempt to identify and clarify some of these misconceptions.

Capillary flow properties of PVC melts (abstract)

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ̇wc’ at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ̇wc’ increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ̇wc’. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is smooth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ̇wc’, becomes fairly smooth again beyond γ̇wc’, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of polymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ̇wc’, where a shark skin appears on the extrudate. Differing from usual thermoplastic resin melts, PVC melts show a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.

Synthesis and characterization of topologically interesting vinyl polymers

AbstractA series of macrocyclic poly(2‐vinylpyridine)&amp;s were synthesized by high dilution (∼10−5 M) coupling of the two‐ended living precursor dianions with 1, 2‐ and 1, 4‐bis‐(bromomethyl)benzene (1, 2‐ or 1, 4‐DBX). SEC measurements indicate that the macrocycles contain less than 5% linear precursor and that the hydrodynamic size of the macrocycles is substantially (∼30%) less than that of the linear precursor. At very low MW, the sizes of macrocyclic and linear polymers differ less, particularly for the case of the 1, 2‐DBX product. Viscometry measurements in THF of linear and macrocyclic polymers also indicated substantial size differences of linear and macrocyclic P2VP.The values of the glass transition temperature (Tg) for both the 1, 2‐ and 1, 4‐DBX macrocycles were found to increase with decreasing MW as qualitatively predicted by entropy calculations. Thus, as the degree of polymerization decreases, the macrocyclic chains become conformationally stiffer and this is reflected by higher Tg values. The differences in Tg between linear and macrocyclic P2VP are quite large (∼40K) around a DP of 40 and decrease to values of a few degrees at a DP of around 200. These differences are diagnostically useful in estimating the linear content of the macrocycles below a DP of 100.

Capillary Flow Properties of PVC Melts

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ′wc at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ′wc increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ′wc. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is soomth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ′wc, becomes fairly smooth again beyond γ′wc, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of ploymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ′wc, where a shark skin appears on the extrudate. Differing from usual thermpolastic resin melts, PVC melts shows a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.