Rheological properties of dispersed-filled polymer composite materials based on polyethylene containing glass microbeads

This article presents the results of a study of the effect of the filler content on the rheological properties of polymer composite materials based on high density polyethylene containing glass microbeads. The flow curves of the compositions were obtained by the method of capillary viscosimetry. Simple mathematical models have been constructed that allow estimating the viscosity of the compositions’ melts based on a given filler content.

Scale-Up of Biosynthesis Process of Bacterial Nanocellulose

Bacterial nanocellulose (BNC) is a unique product of microbiological synthesis, having a lot of applications among which the most important is biomedicine. Objective complexities in scaling up the biosynthesis of BNC are associated with the nature of microbial producers for which BNC is not the target metabolite, therefore biosynthesis lasts long, with the BNC yield being small. Thus, the BNC scale-up problem has not yet been overcome. Here we performed biosynthesis of three scaled sheets of BNC (each having a surface area of 29,400 cm2, a container volume of 441 L, and a nutrient medium volume of 260 L and characterized them. The static biosynthesis of BNC in a semisynthetic nutrient medium was scaled up using the Medusomyces gisevii Sa-12 symbiotic culture. The experiment was run in duplicate. The BNC pellicle was removed once from the nutrient medium in the first experiment and twice in the second experiment, in which case the inoculum and glucose were not additionally added to the medium. The resultant BNC sheets were characterized by scanning electron microscopy, capillary viscosimetry, infrared spectroscopy, thermomechanical and thermogravimetric analyses. When the nutrient medium was scaled up from 0.1 to 260 L, the elastic modulus of BNC samples increased tenfold and the degree of polymerization 2.5-fold. Besides, we demonstrated that scaled BNC sheets could be removed at least twice from one volume of the nutrient medium, with the yield and quality of BNC remaining the same. Consequently, the world’s largest BNC sheets 210 cm long and 140 cm wide, having a surface area of 29,400 cm2 each (weighing 16.24 to 17.04 kg), have been obtained in which an adult with burns or vast wounds can easily be wrapped. The resultant sheets exhibit a typical architecture of cellulosic fibers that form a spatial 3D structure which refers to individual and extremely important characteristics of BNC. Here we thus demonstrated the scale-up of biosynthesis of BNC with improved properties, and this result was achieved by using the symbiotic culture.

PROCESSING ADDITIVES AND RHEOLOGICAL PROPERTIES OF MOLDED PHENOLIC PLASTICS

By the method of capillary viscosimetry, the melt flow curves of the molded phenolic resin and its compositions with lubricant, plasticizer and their mixture were obtained. It was shown that the size (diameter) of the capillary channel influences the dependence of the effective shear rate on the shear stress (flow curves) of the studied compositions. Such rheological behavior of the compositions during flow is associated with the effect of sliding along the surface of the capillary wall. According to the Mooney method, the dependences of the effective shear rate at given values of shear stress on the reciprocal of the capillary radius are plotted. The function of the slip velocity on the shear stress on the capillary wall is characterized in terms of the slip coefficient, which relates the shear stress on the capillary wall to the velocity of the composition along it. For the studied compositions, the total flow through the capillary was divided into volume fractions, one of which is associated with a shear flow; the other is determined by the slip effect. It has been shown that the introduction of both a lubricant and a plasticizer into the composition leads to an increase in the fluidity of the compositions. At the same time, adding of lubricant increases the volume fraction of the slip flow. The greatest effect of increasing the fluidity of the composition gives the use of complex modifying additives containing both lubricant and plasticizer.

Enzymatic Depolimerization of Chitosan for the Preparation of Functional Membranes

This work reports the study of chitosan depolymerization through the synergy of the Celuzyme® XB enzyme complex; it is composed of cellulase, xylanase, andβ-glucanase. The optimal conditions of temperature, pH, and concentration were determined to verify the depolymerization reaction. The specificity of the enzymes at theβ(1-4) glycosidic link site was checked. Low molecular weight chitosan (64 × 103 g·mol−1) with degree of acetylation 15% was obtained. The depolymerized chitosan products were characterized by infrared spectroscopy, the degree of acetylation was obtained by UV-Vis spectroscopy, and the determination of the molecular weight was obtained by capillary viscosimetry. With the depolymerized chitosan, membranes were formed and their antioxidant and antimicrobial functionality was determined; results show that these properties are dependent on the molecular weight and on the acetylation degree of chitosan.

ACRYLAMIDE (CO)POLYMERS DISSOLUTION IN WATER-SALINE SOLUTIONS

Dissolution of acrylamide anionic (co)polymers in saline solutions (potassium and sodium chlorides) with concentration of 3.4 mol/l was studied by atomic absorption spectroscopy, optical microscopy, gel-test and capillary viscosimetry. It has been established that with increasing in the content of ionogenic groups and the transition from sodium chloride to potassium chloride solutions the dissolution rate of (co)polymer increases. The concentration of cations of low molecular weight electrolytes is higher in the swollen polymer phase than in the solution in the swelling stage of polymers, the difference in the counter ion content decreases with increasing dissolution time. Comparative analysis of the Huggins constant and the hydrodynamic radii of acrylamide (co)polymers has showed that increase in the interaction in polymer-solvent system is accompanied by the increase in size of macromolecular coils. The Kuhn segment of polymer macromolecules is higher in sodium chloride solutions than in potassium chloride solutions and increases with the decrease in ionogenic group content.

One-pot synthesis of semicrystalline polyamide imide based on 4,4’-diaminobenzanilide and 2,2-propylidene-bis(1,4-phenyleneoxy)diphthalic anhydride in molten benzoic acid

High-temperature thermoplastic semicrystalline polyamide imide (PAI) with Tg = 250°C, and Tm = 370°C was synthesized from 4,4’-diaminobenzanilide, and 2,2-propylidene-bis (1,4-phenyleneoxy) diphthalic anhydride using three different methods: one-pot high-temperature catalytic polycondensation in molten benzoic acid (BA), low-temperature polycondensation (LTP) in dimethylacetamide (DMAA) followed by chemical imidization, and LTP followed by imidization. The influence of the synthetic route on the crystallinity of PAI was studied by wide-angle X-ray scattering. The PAI synthesized in molten BA comprised a reactive oligomer, which on heating up to 360°C easily transformed into high-molecular-weight PAI. The thermal and rheological properties of the high-molecular-weight PAI thus prepared were studied using differential scanning calorimetry, trimellitic acid, thermogravimetric analysis, and capillary viscosimetry. The rheological characteristics indicate that the obtained PAI can be melt processed by extrusion and hot pressing at 370–380°C.

Per-operative antibiotic/steroid prophylaxis of tympanostomy tube otorrhoea: chemical or mechanical effect?

The per-operative instillation of ototopical antibiotic/steroid drops reduces the incidence of early otorrhoea after tympanostomy tube insertion. Whether this is due to the chemical properties of the antibiotic/steroid or simply the mechanical instillation of fluid is unclear. In this paired matched study of 161 subjects Gentisone HC was shown to significantly reduce the otorrhoea rate compared to normal saline (1.24 per cent compared with 9.32 per cent, p<0.005, difference 8.07 per cent, 95 per cent confidence interval for difference 3.21 per cent to 12.93 per cent). Capillary viscosimetry proved Gentisone HC to be more viscous than normal saline. The benefits are due to Gentisone HC's chemical properties, and Gentisone HC rather than normal saline instillation per-operatively is recommended when tympanostomy tubes are inserted.

Study of acid milk coagulation by an optical method using light reflection

SummaryA turbidimetric method, based on light reflection, was used to study acid coagulation of reconstituted skim milk at low temperature. Capillary viscosimetry, gelograph and laser granulometer techniques were also employed. Acidification of milk was produced by hydrolysis of glucono-δ-lactone. The general shape of the turbidimetric signal as a function of pH or time can be divided into three stages: a lag phase followed by a significant decrease and then a final rise. Two factors have a great influence on the development of milk turbidity, pH and temperature. Dynamic viscosity measurements can be related to the turbidimetric signal while laser granulometrie measurements cannot be correlated with changes in turbidity: the micelle size distribution remains constant until the first signs of gelation. As previous work showed, dynamic viscosity diminishes with acidification until a particular pH is reached (pH 5·9 at 15°C and pH 5·75 at 20°C). We have related this latter period to the turbidimetric lag phase. As milk turbidity became lower than its initial value (pH 5·75 at 15°C and pH 5·55 at 20°C), dynamic viscosity increased significantly. The release of material from micelles (β-casein and Ca) could explain this phenomenon. In the same way, further increase of turbidity at a particular pH value (pH 5·3 at both 15 and 20°C) coulcl be partly due to the reincorporation of soluble casein monomers in the micelle framework. As the onset of gelation was approached, turbidity still increased as a result of gel network formation.