Chain Rupture Research Articles

Scaling relations for brittle fracture of entangled polystyrene melts and solutions in elongational flow

The criterion for brittle fracture of entangled polymer liquids [Wagner et al., J. Rheol. 62, 221–223 (2018)] is extended by including the effects of finite chain extensibility and polymer concentration. Crack initiation follows from rupture of primary C–C bonds, when the strain energy of entanglement segments reaches the energy of the covalent bond. Thermal fluctuations will concentrate the strain energy on one C–C bond of entanglement segments, leading to bond scission and rupture of polymer chains followed by crack initiation and fast crack growth. In start-up flows, entanglement segments characterized by long relaxation times, i.e., predominantly those in the middle of the polymer chain, will be the first to reach the critical strain energy and will fracture. Recent experimental data of Huang [Phys. Fluids 31, 083105 (2019)] of fracture of a monodisperse polystyrene melt and of several solutions of monodisperse polystyrenes dissolved in oligomeric styrene are in agreement with the scaling relations for critical Weissenberg number as well as Hencky strain and stress at fracture derived from this fracture criterion and the extended interchain pressure model [Narimissa, Huang, and Wagner, J. Rheol. 64, 95–110 (2020)].

DEVELOPMENT OF NATIONAL ECONOMIES IN THE CONDITIONS OF PANDEMICS

Among many global problems of mankind, a special place is occupied by the phenomenon of pandemics. A pandemic has been one of the constant companions of human existence since ancient times. This is evidenced by both the texts of religious and mythological orientation, and recorded events in historical life. Pandemic is always an emergency that threatens the very existence of humanity. Various circumstances are heard as the causes of pandemics: sacred (violation of divine laws), domestic (unsanitary conditions of existence), civilizational (technocratic human intervention in the environment), political, economic, etc. The purpose of this article is to study the effects of pandemics that have occurred in different historical periods and their impact on the development of society and the economy. Based on this goal, the objectives of the article are to study the world economy in a pandemic COVID-19; to analyse the trends and forecasts of its further development, including Ukrainian economy; to offer an assessment of the main opportunities and risks of the functioning of Ukraine’s economy in quarantine. This article reveals the theoretical and practical principles of the pandemics impact on global economic development. The result of the article is the statistical analysis of pandemic impact on the world economy, which leads to the rupture of economic chains and slowing down the economic and social development for several months or even up to one year. As a conclusion it may be noted, that since periodic pandemics have become an integral part of human life, no country in the world is safe from their direct or indirect impact and, as a result, countries must be economically ready to provide strict measures according to the formula “combating the epidemic – minimizing the negative effects in the short, medium- and long-term periods”. Practical implications. The main theoretical propositions, the authors’ conclusions presented in the article, are supposed to form a methodological basis in substantiating the priorities of the state support of business in conditions of pandemic and quarantine restrictions. Value/originality. The proposed results can be used for modeling and forecasting the impact of quarantine restrictions on the economic development of countries.

Negotiation during A Crisis: Possible Problems and Three Suggestions for SME Leaders

Negotiation skills are essential for everyone especially business leaders to agree on how to share a limited resource, create mutual benefit and avoid conflicts in crisis. In this recent coronavirus outbreak, the Chinese government is encouraging people to stay at home as much as possible, prohibiting any gathering activities, and forcing some businesses to close. Therefore, this paper will use data analysis, case study and investigation for a small garment processor enterprise to indicate the problem about capital chain rupture and loss of profit from macro to micro perspectives. From the second half of this paper, there are three suggestions including preparation, adjustment of emotions and some common tactics for SMEs to use in negotiation in crisis.

On calculation and assessment of machine reliability

Problems of durability and reliability of machines are of interest not only to scientific constructors and mechanical engineers but also to consumers who operate machines, organize their maintenance and repair. Durability is associated with machine downtime caused by need to determine its performance. Since at the same ones, relatively simple tuning and adjustment operations were performed, and in another, complex installation work is required with replacement of road, parts, and assemblies. Qualitatively, reliability is defined as a property of a mechanical system (machine) to execute, without fail for a specified time, amount of established work, subject to rules of operation. Machines failures are divided into two groups: apparent - accompanying breakdowns of parts, rupture of kinematic chains, destruction of joints; implicit - manifested in deviation of dimensions or parameters that determine quality of work of parts from established or permissible values. The article describes research methodology, which is carried out by quantitative characteristics of reliability of elements. Quantitatively, reliability is determined by probability of completing a task in a timely manner with appropriate quality of work. Then failure rate is determined which shows what proportion of parts from their total number fails during the period under review. Analysis ofequipment failures during periodic tests showed that significant number of them are caused by imperfection and imbalance of established design rules and standards. Thus, it can be noted that reliability is an important indicator, but not sufficient for a full characteristic. The machine must be evaluated for maintainability and durability.

Research on the Marketing Strategy of Online Education -- Taking New Oriental as an Example

In recent years, with the development of society and the progress of science and technology, online learning has penetrated into people's daily life, and people's demand for high-quality curriculum products is more and more strong. From a macro perspective, the continuous growth of national financial investment in education, the continuous upgrading of China's consumption structure, the development of 5G technology and the popularization of AI intelligence make online teaching less limited. The online education industry is showing an explosive growth trend. More and more online education institutions are listed for financing, and the market value is soaring. However, in 2019, except for GSX, the latest online learning platforms such as New Oriental, Speak English Fluently and Sunlands, have been in a state of loss. Most of these agencies seize the market by increasing advertising investment, but at the same time, they also bring huge marketing costs, which affect the financial performance of the company. With the enhancement of Matthew effect, large-scale educational institutions occupy a large market through free classes and low-price classes, while small and medium-sized institutions with weak capital strength are often unable to afford high sales costs, facing the risk of capital chain rupture. Taking new Oriental online as an example, this paper analyzes the problems existing in the marketing strategies of online education institutions. It also puts forward suggestions on four aspects, which are target market, differentiated value, marketing mix and marketing mode, so as to make sure that online education institutions can control marketing expenses and achieve profits by improving course quality, expanding marketing channels and implementing precise positioning.

SYNTHESIS OF AZIDOCELLULOSE NITRATES

A synthesis method of azidocellulose nitrate by chemical interaction between cellulose nitrates or chlorocellulose nitrates with various degree of chlorination with sodium azide in a medium of dimethylsulfoxide and with heating in the temperature range 40–70 °C is proposed. The chemical composition, structure and properties of the obtained compounds are determined on the basis of combination of physico-chemical methods of analysis: IR, 1H NMR and 13C NMR spectroscopy; elemental analysis; gel permeation chromatography; viscometry; thermogravimetric analysis; differential scanning calorimetry; thermal polarization microscopy. The main directions of the chemical interaction between polymers and sodium azide were predicted by quantum-chemical methods using the Gaussian 09 software. The reaction mechanism was confirmed by a mathematical model of kinetics. The scheme of the preferred simultaneously going reaction directions has been composed, which includes substitution of nitrate groups by the azide fragment; rupture of polymer chains by β-glycosidic bond leading to depolymerization; opening of the glucopyranose cycle with addition of the azidogroup to the formed free bonds. Use of the chlorocellulose nitrate for the azidation allows to get products with a higher degree of substitution by azidogroups, and the rate of azidation of chlorocellulose nitrate depends on halogen content directly.

Synthetic Particles for Cancer Vaccines: Connecting the Inherent Supply Chain.

Cancer vaccines have opened a new paradigm for safe and effective antitumor therapy, but they still suffer from shortcomings such as insufficient immunogenicity and immune tolerance, which seldom makes them the first choice in clinic. In fact, similar to providing a high-end product, a robust antitumor effect depends on the inherent supply chain, which attains, processes, and presents tumor-associated antigens via antigen presenting cells to T cells, which then leads to lysis of the cancer cells to release more antigens to complete the supply chain. Under these circumstances, the failure of cancer vaccines can be treated as a blockade or chain rupture. Thus, for effective tumor treatment, the key is to rationally design logistic systems to restore the supply chain.Under these circumstances, this Account summarizes our recent attempts to exploit the immunogenic trait of synthetic particles to enhance the distribution, presentation, and immune activations of the whole priming process in cancer vaccines: (1) Raw material (tumor antigen/signals) procurement: We illustrated the efforts to deliver antigens to antigen presenting cells (APCs) and draining lymph nodes for potent internalizations, and put more emphasis on the structural effect of sizes, charges, shapes, and assembly strategies for the antigen depot, lymph node transfer, and APC endocytosis. (2) Manufacture of cytotoxic T lymphocytes (CTLs) via APC recognition and presentation: We centered on exploiting the softness of two-dimensional graphene and Pickering emulsions to dynamically potentiate the immune recognition, and demonstrating the recent advances in lysosome escape strategies for enhanced antigen cross-presentations. (3) Marketing the accumulations of CTLs and the reversal of an immunosuppressive microenvironment within the tumor: We demonstrated the previous attempts to inherently cultivate the tumor tropism of the T cells via the multiantigenic repertoire and discussed the advances and challenges of combinatory cancer vaccines with an immune checkpoint blockade to reinforce the antitumor efficacy. Collectively, this Account aims to illustrate the potential of the particulate cancer vaccines to recapitalize the inherent host immune responses for the maximum antitumor effect. And by integrating the antitumor supply chain, optimized synthetic particles may shed light on the development of safe and effective particulate cancer vaccines.

Effects of alternating electric field on the imaging of DNA double-helix structure by atomic force microscope

The effects of alternating electric field on the imaging of DNA double-helix structure were explored by atomic force microscope (AFM). First, the DNA sample was located under an alternating electric field in a fixed direction and dried. Then, AFM was used to obtain the DNA images under different alternating electric fields with the voltage range from 0.5 to 6.0 V and the frequency of 50 kHz. Thus, the DNA double-helix structures with different extensions were observed when the DNA molecules were gradually stretched under different field intensities. The distributions of DNA molecules in solution were random if there were no external forces, and the curved DNA molecules were observed in the AFM image. With the increase in alternating electric voltage (0.5–4.0 V), the DNA structure was shifted from random to oriented conformation and the DNA grooves were further unfolded. While the higher voltage (5.0–6.0 V) resulted in the rupture of DNA chains due to the excessive stretching force. It showed that the optimal voltage was 1.0 V, and the double-helix structure was observed. This method provides an efficient way for monitoring and measuring bio-macromolecules. It may also enable the exploration of the DNA–protein binding and DNA molecular self-assembly processes.

Rate-dependent fracture of transient networks

Soft viscoelastic polymers and gels are commonly used a wide range of applications owing to their softness and the ability to accommodate large deformations. Their applicability is however often limited by their tendency to fracture in ways that are cannot be predicted by conventional elastic fracture mechanics. Our understanding of fracture in this class of solid has particularly been hindered by the incapacity of determining the competition viscous flow and fracture under finite strains. To tackle this problem, this paper presents a framework that quantitatively captures the interplay between energy dissipation and crack propagation in soft solids made of a single transient network. Using a combined analytical and numerical study, we investigate the dynamics of crack propagation at various loading rates and for networks that display different sensitivities to force. Our results point out to four different crack characteristic behaviors, for which we unveiled the respective mechanisms, all involving a strong interplay between chain deformation, bond dynamics and rupture.

The transformation and degradation of Nafion® solutions under ultrasonic treatment. The effect on transport and mechanical properties of the resultant membranes

This work addresses the study of the effect of ultrasonic (US) treatment on the properties of alcohol solutions of perfluorinated sulfonic acid polymer Nafion® and cast membranes. The effect of the duration of US treatment on the physico-chemical properties (water uptake, transport and mechanical properties) of the resulted membranes is described for the first time. Upon the US treatment, viscosity of the polymer solutions irreversibly decreases due to deagglomeration and rupture of macromolecular chains. As a result of the US treatment, mechanical properties of the Nafion® membranes are deteriorated. The dependences of water uptake and conductivity of the Nafion® membranes in the proton form on sonication time pass the maximum (at 30–45 min). Due to the sonication of polymer solutions, proton conductivity of the membranes increases by 40–45%. Upon extended sonication, the content of sulfonic acid groups decreases, and carboxyl groups are formed at the ends of macromolecules. Thus, water uptake of the membranes prepared from the polymer solutions after the US treatment for 60 min decreases, and conductivity of the obtained membranes in the H+-form is reduced. However, for the Nafion® membranes in the Na+-form, as the duration of the US treatment is extended, their conductivity and diffusion permeability tend to increase due to the enhanced connectivity of pores and channels as well as due to the participation of carboxyl groups in the ionic transport. Upon extended sonication, selectivity of the cation transfer through the membranes is reduced. The results of this work highlight the importance of the proper selection of favorable conditions of the US treatment of the solutions of perfluorinated sulfonic acid polymers for the preparation of hybrid membranes and for the development of catalytic layers of membrane-electrode assemblies for fuel cells.

Shaving and breaking bacterial chains with a viscous flow.

Some food and ferment manufacturing steps such as spray-drying result in the application of viscous stresses to bacteria. This study explores how a viscous flow impacts both bacterial adhesion functionality and bacterial cell organization using a combined experimental and modeling approach. As a model organism we study Lactobacillus rhamnosus GG (LGG) "wild type" (WT), known to feature strong adhesive affinities towards beta-lactoglobulin thanks to pili produced by the bacteria on cell surfaces, along with three cell-surface mutant strains. Applying repeated flows with high shear-rates reduces bacterial adhesive abilities up to 20% for LGG WT. Bacterial chains are also broken by this process, into 2-cell chains at low industrial shear rates, and into single cells at very high shear rates. To rationalize the experimental observations we study numerically and analytically the Stokes equations describing viscous fluid flow around a chain of elastically connected spheroidal cell bodies. In this model setting we examine qualitatively the relationship between surface traction (force per unit area), a proxy for pili removal rate, and bacterial chain length (number of cells). Longer chains result in higher maximal surface tractions, particularly at the chain extremities, while inner cells enjoy a small protection from surface tractions due to hydrodynamic interactions with their neighbors. Chain rupture therefore may act as a mechanism to preserve surface adhesive functionality in bacteria.

Prevalence of opisthorchiasis in the Pavlodar region of the Republic of Kazakhstan

The territory of the Pavlodar region is a natural focus with a high intensity of the spread of opisthorchiasis invasion among people. One of the important preventive measures in the foci of opisthorchiasis is the elimination of helminths in the body of the main owners, which leads not only to the rupture of the biological chains of helminth development, but also to the protection of the environment from invasive pollution. Opisthorchiasis is widespread in the Pavlodar region, the extensiveness of invasion among carnivores is 5.7%. Cases of the incidence of cats were detected in five out of 10 districts (Aksu, Aktogay, Pavlodar, Shcherbaktinsky, Maysky), dogs -in two districts (Terenkol, Irtysh). Opisthorchiasis was not revealed in the study of the pig population. Cats and dogs, especially in coastal rural settlements of the region, support the existence of opisthorchiasis foci and contribute to their stabilization. The main source of the release of opisthorchis eggs into the external environment are cats, their infection rate is 2 times higher than that of dogs. In the Pavlodar region, opisthorchiasis of animals is caused by the O. felineus pathogen or cat fluke.

Biodegradability Study by FTIR and DSC of Polymers Films Based on Polypropylene and Cassava Starch

The polypropylene resistance to biological attacks is related to the lack of functional groups recognizable by microbial enzymatic systems. The incorporation of compatibilizing agents in polypropylene (PP)/starch (S) blends favors the interactions of their components and can potentially induce the material degradation. In order to study the degradation of PP/S blends, films were prepared with a compatibilizing agent (AC), constituted by polypropylene grafted with acrylamide (PP-g-AAm). The films were placed in an Erlenmeyer flask containing 100 ml of a basal mineral medium with microorganisms inoculated in a cellulose filter, taken from an effluent. The FTIR analyzes of the films with the AC agent showed significant differences in the absorption bands, with respect to the control film. The asymmetric stretch signal of the grafted acrylamide that appeared at 3292 cm -1 increased in intensity only in the inoculated blends. In addition, hydrolysis was evidenced by the stretching signal of the OH bond. Abrupt changes were observed in the carbonyl region (1700-1600 cm -1 ) with the appearance of new bands, which shows the rupture of polymer chains. In the blends DSC analysis, a slight nucleation effect is observed in addition to a considerable increase in the degree of crystallinity, so it is suggested that the degradation could be occurring in the amorphous regions. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1360

Improvements in physicochemical and emulsifying properties of insoluble soybean fiber by physical-chemical treatments

Initial structural, physicochemical and emulsifying properties of insoluble soybean fiber (ISF) obtained by alkaline treatment (AT), ultrasonic alkaline treatment (UAT), steam-cooking alkaline treatment (SAT), ultrasonic-assisted steam-cooking alkaline treatment (USAT) were investigated. The loose structure, porous and wrinkled surface was observed in ISF by scanning electron microscopy (SEM). USAT exerted a greatest influence on ISF micromorphology due to a strong combination of ultrasonic, steam-cooking and alkaline treatment. The rupture of polymer chains in ISF, which indicated release of free hydroxyl groups, was showed by Fourier transform infrared spectroscopy (FTIR) analysis. Water holding capacity (WHC), swelling capacity (SWC) and oil holding capacity (OHC) of USAT-ISF were increased to 3.84, 9.04 and 4.19 folds of NT-ISF, respectively. It was because loose and porous structure of ISF enhanced its ability to capture water or oil, and free hydroxyl groups acted as water holding sites as well. SAT-ISF and USAT-ISF suspensions showed more pronounced shear thinning behavior and higher apparent viscosity, which was related to WHC, SWC and cluster structure. Good dispersion of oil droplets was observed in fresh AT-ISF and UAT-ISF emulsions with little flocculation. AT-ISF emulsion presented a relatively high storage stability over 35 days as a function of broken sheet structure, moderate apparent viscosity and high WHC, OHC. It could be seen from dynamic viscoelastic measurements that SAT-ISF and USAT-ISF emulsions presented weak gel behavior. Results demonstrated that physicochemical and emulsifying properties of ISF were effectively improved by physical-chemical treatments, thus showing promising prospect of ISF as an emulsifier in food industry.

Performance verification of elastomer materials in corrosive gas and liquid conditions

Elastomer seals are essential for zonal isolation in vertical and deviated wells. They are often used either as O-rings (static seals) or as energized seals (packers). For elastomers to perform their functions effectively over an extended period, it is essential that the elastomer withstand the deleterious effects of pressure, prolonged loading effects, severe temperature, corrosive fluids, and acidic gases. As such it is imperative to understand the various elastomer degradation mechanisms and develop methods to reduce the degradation. The objectives of this study are: to investigate if elastomers are “fit for service” for well construction applications and to evaluate elastomer performances under downhole corrosive conditions. To achieve this goal, some dynamic wellbore conditions which close-to-real field conditions are were simulated in a controlled laboratory setup. The following properties were investigated: elastomer hardness, elastomer compression, and elastomer volumetric swelling. In the experimental setup, four frequently used elastomers in the oil and gas industry were studied: Nitrile butadiene rubber (NBR), Ethylene propylene diene monomer (EPDM), Fluoroelastomer (FKM) commonly known as Viton, and Polytetrafluoroethylene (PTFE). The results indicate that NBR exhibited the most significant deterioration. Viton showed the least amount of deterioration but has poor decompression resistance. The aging condition that proved to be the most damaging is CO2. Analysis of Variance (ANOVA) was also performed on the data from the samples as a statistical analysis indicator. Some other observations and conclusions are that the degree of chain growth and chain rupture depends on the temperature and the degree of chemical exposure.

Distribution and chemical structure characteristic of the fast thermal-cracking products of Buton oil sand bitumen by Py–GC/TOF–MS and a fluidized bed reactor

In order to obtain a deep insight into the upgrade of oil sand bitumen (OSB), the composition, distribution and chemical structure of products obtained from the fast thermal cracking of the OSB were investigated via Py-GC/TOF-MS and a laboratory-scale fluidized bed reactor. A detail composition information of fast thermal-cracking products of the OSB was determined by Py-GC/TOF-MS, which mainly contained alkenes (1-alkenes, iso-alkenes and cycloalkenes), alkanes (n-alkanes, iso-alkanes and cycloalkanes), diolefins, aromatics and sulfur-containing compounds. The distribution of fast thermal-cracking products varied under different temperature. Alkenes were the uppermost style in volatile products at the temperature ranging from 500 °C to 700 °C, whereas with the temperature further rising to 800 °C, aromatics products became predominant and were mainly generated from the deep cleavage of alkyl substituent groups and the secondary reactions to form aromatics. Moreover, the relative content and carbon number distribution of volatile products along with various temperature were summarized. The thermal cracking experiments of the OSB over silica sand in a laboratory-scale fluidized bed reactor showed that the gas products had a remarkable increase in yield as the temperature increase, which was connected with the increase in methane and ethylene of dry gas as well as propylene and butenes of LPG. The coke yield also exhibited an increase tendency with the enhancement of temperature, while this variation was slighter in comparison to that of gases. Conversely, the yield of liquid products gradually decreased with the temperature, which was closely related to the significant decrease of VGO and heavy oil fractions due to the coke formation of polyaromatics and the intensive rupture of alkyl side chains. Nevertheless, the light oil fraction (diesel and gasoline) displayed the different variation along with the temperature, which increased firstly and then decreased as a result of the decomposition of heavy fractions and secondary cracking of light oil itself. Compared to the native OSB, there was a slight difference in functional group distribution for liquid products which was concerned with the formation of olefins, whereas the average structural parameters of the liquid products changed dramatically after the fast thermal cracking of the OSB. Furthermore, the effects of the reaction temperature on the chemical structures were significant due to the decomposition, condensation and secondary reactions proceeded during the fast thermal cracking process.

Optimal Financing and Dividend Strategies with Time Inconsistency in a Regime Switching Economy

This paper incorporates a manager’s time‐inconsistent preferences into the unified dynamic q‐theoretic framework to investigate their impact on the optimal external financing and dividend payout strategies in a regime switching economy. We find that with a higher degree of time inconsistency, either in a favorable market condition or in a financial crisis, dividends are paid out earlier and the equity issues are smaller in size in each occurrence; in a favorable market condition equity financing occurs particularly early. Hence, time inconsistency would result in a decreasing of a firm’s precautionary savings, which may directly cause capital chain rupture and make liquidation more likely. It also implies that corporate external financing and dividend payout are highly dependent on the degree of the manager’s time‐inconsistent preferences in a regime switching economy.

Direct Observation of Large Deformation and Fracture Behavior at the Crack Tip of Slide-Ring Gel

Slide-ring gel is a highly deformable polymer gel prepared by cross-linking rings on polyrotaxanes, in which ring molecules are threaded onto a linear polymer chain. The remarkable extensibility of SR gels is due to the stress equalization effect caused by the sliding of cross-links on polymer chains. We directly observed the stress equalization effect by magnifying the instinctive micron-scale defect to artificial millimeter-scale crack and then mapping the crack tip stress field based on photoelasticity. By reducing coverage of rings on polymer chains in SR gels, obvious crack blunting and delayed crack growth are observed. Highly elongated non-linear “cohesive zone” with length of 0.6 mm and width less than 0.1 mm occurs ahead of crack tip before crack propagation. Our results show that SR gels with low ring coverage have large cohesive strength to survive large deformation before elastic chains rupture, which is essentially derived from the sliding of the cross-links that adjusts strand length automatically to equalize stress in the network.

Initiation, development, and achievements of burn rehabilitation therapy in China

Burn rehabilitation in China started from compression therapy in the mid-1970s, which showed the dual effects of prevention and treatment of hypertrophic scars. It not only promoted functional rehabilitation but also strengthened the confidence of patients in rehabilitation treatment. Thereafter, more therapies were brought into practice, such as intra-scar injection of triamcinolone acetonide, application of plastic splints, hydrotherapy, exercises with equipment, skin care, local therapeutic massage, active and passive exercises, as well as external use of drugs for inhibiting scars and pigments. Since the beginning of the 21st century, rehabilitation therapies have been gradually increasing. Psychological rehabilitation, occupational therapy, external use of silicone gel, wax therapy and sound, light, electricity, and radiation therapy have been carried out. Many hospitals have established foundations and held summer camps for children. As far as the whole country is concerned, compared with the huge demand, we still face a number of problems such as shortage of working staff, limited working space, capital chain rupture, lack of multi-disciplinary cooperation, untimely treatment, and incomplete rehabilitation. Nowadays, with increasing knowledge of burn rehabilitation and number of practitioners, improvement of equipment and economic situation, the pace of rehabilitation has accelerated, and the overall implementation of burn rehabilitation therapy has shown great vitality. Patients with burn injury involving over 80% total burn surface area (TBSA) of total burn area or full-thickness burn over 60% TBSA were cured and recovered in different levels of hospitals nationwide, which not only reflects the superb level of burn treatment in China but also reflects the overall improvement of rehabilitation level of the country.

Ultrasonic degradation of Persian gum and gum tragacanth: Effect on chain conformation and molecular properties

The present study introduces the ultrasonic modification of two Iranian native gum exudates, Persian gum (PG) and gum tragacanth (GT) for the first time. They were sonicated at a constant frequency of 20 kHz and temperature of 60 °C for various times (0, 2, 5, 10, 20, 30 and 40 min) and the changes in their molecular properties were investigated using oven drying, gel permeation chromatography-multiangle laser-light scattering (GPC-MALLS), rheometery and FTIR analysis. Results indicated that the soluble dry mass of both hydrocolloids was extensively enhanced (from less than 10% at time zero to more than 90% at the end of treatment time) by sonication. Moreover, the molecular weight and viscosity of gums dispersions were decreased with the increase of the treatment time. Fracture in polysaccharide chains was confirmed by analysis of the molecular weight parameters. Calculation of chain breaks and polydispersity index (PDI) revealed that scissions occurred at the backbone as well as the side branches. PG, owing to its higher molecular weight, displayed more extensive and faster degradation than GT. However, the chain rupture of GT was twice more than that of PG at the end of sonication time. The specific volume for gyration (SVg) and molecular density (ρ) showed that intact PG contains compactly packed molecules with greater number of cross-linked bonds compared to GT. Furthermore, the conformational changes into semi-flexible chains and worm-like coils were determined for both gums after 40 min sonication. Variation of the molecular density along with the results of FTIR analysis demonstrated that ultrasonication broke C–O–C bonds in both PG and GT leading to more flexible chains.