Extra Cross-linking Research Articles

Bioactive oxynitride glasses: Synthesis, structure and properties

The low mechanical strength of bioactive glasses restricts their use to non load-bearing applications. One way to increase strength of glasses is to introduce nitrogen into the silicate network. Oxynitride bioactive glasses in the SiO2–CaO–Na2O–Si3N4 system were successfully prepared. Structural characterization using 29Si MAS-NMR shows that, as nitrogen is substituted for oxygen, formation of [SiO3N] tetrahedra and Q4 units occurs with extra bridging anions at the expense of Q3 units. Glass transition temperature, hardness, Young’s modulus and fracture resistance increase with nitrogen content because of the extra cross-linking of the glass network.CaF2 was substituted for CaO in these glasses which results in decreases in glass transition temperature. Thus, glasses can be melted at lower temperatures while addition of fluorine allows higher solubility of nitrogen and has no effect on the significant increases in mechanical properties induced by nitrogen substitution.Initial assessment of bioactivity suggests that varying the N content may allow tailoring of the level of bioactivity of these glasses.

Oxidative degradation products analysis of polymer materials by pyrolysis gas chromatography–mass spectrometry

Pyrolysis gas chromatography–mass spectroscopy (PGC–MS) has been proved to be a powerful method to analyze both the volatile additives and the macromolecular structure of polymer materials. In this paper, flash evaporation technique was used to analyze the volatile degradation products of polymer materials during natural and artificial aging. In high density polyethylene (HDPE) composites, mainly n-alkanes with carbon number from 14 to 29 were detected after natural aging, while no oxidative product was found. Different composites have different n-alkane distributions. In contrast, various oxidative products including ketones, alcohols, esters and unsaturated species could be found in aged polypropylene (PP) nanocomposites. Nanoparticles accelerated the chain scission of PP and increased the formation of oxidative products significantly. During thermal oxidation of nitrile rubber (NBR) seal rubbers, heat/oxidation-induced extra crosslinking predominated and no volatile degradation products was detected. The main change happened in the volatiles is the decrease of additives, especially paraffins, antioxidant RD and hindered phenol. This resulted in the hardening of the rubber and the weakening of the protection from oxidation. Furthermore, the additive distribution along the depth was investigated, showing different migration speeds of different additives. From the additive levels remained in the NBR rubber, it is possible to predict the degradation status. In summary, PGC–MS can supply abundant information of polymer degradation and is helpful for mechanism research.

How Malaria Parasites Reduce the Deformability of Infected Red Blood Cells

The pathogenesis of malaria is largely due to stiffening of the infected red blood cells (RBCs). Contemporary understanding ascribes the loss of RBC deformability to a 10-fold increase in membrane stiffness caused by extra cross-linking in the spectrin network. Local measurements by micropipette aspiration, however, have reported only an increase of ∼3-fold in the shear modulus. We believe the discrepancy stems from the rigid parasite particles inside infected cells, and have carried out numerical simulations to demonstrate this mechanism. The cell membrane is represented by a set of discrete particles connected by linearly elastic springs. The cytosol is modeled as a homogeneous Newtonian fluid, and discretized by particles as in standard smoothed particle hydrodynamics. The malaria parasite is modeled as an aggregate of particles constrained to rigid-body motion. We simulate RBC stretching tests by optical tweezers in three dimensions. The results demonstrate that the presence of a sizeable parasite greatly reduces the ability of RBCs to deform under stretching. With the solid inclusion, the observed loss of deformability can be predicted quantitatively using the local membrane elasticity measured by micropipettes.

Effects of addition of nitrogen on bioglass properties and structure

Bioglasses have been developed for use in surgery because of their ability to form a hydroxy-carbonate apatite (HCA) layer on their surface which facilitates bonding to natural bone. However, they do not have sufficient strength for use in load-bearing situations and therefore improving their mechanical properties would allow their use in more robust applications. The purpose of this work was to study the effects of nitrogen addition on the physical and mechanical properties and the structure of oxynitride bioglasses based on the system Na2O–CaO–SiO2–Si3N4. The density, glass transition temperature, hardness and elastic modulus were measured and observed to increase linearly with nitrogen content. These increases are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The characterization of these oxynitride bioglasses using solid state nuclear magnetic resonance 29Si MAS NMR and infrared spectroscopy have shown firstly that all the N atoms are bonded to Si atoms and secondly that this increase in rigidity of the glass network can be explained by the formation of SiO3N, SiO2N2 tetrahedra and Q4 units with extra bridging anions at the expense of Q3 units. The oxynitride bioglasses in simulated body fluid form a hydroxy-carbonate apatite (HCA) layer on their surfaces showing that bioactivity is retained.

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Effect of Thermocycling on the Thermal Degradation Kinetics of Goatskin Collagen Matrices

In the present study, the goatskin collagen matrices were tanned by chrome powder and chestnut extract. The samples were then thermocycled in a container at different temperature ranges with a dwell time of 5 h for different cycles. The thermal degradation behaviors of the collagen matrices before and after the thermocycling were investigated. The Coates-Redfern Method was applied to study the thermal degradation kinetics of different samples. The results indicate that the thermocycling exerted more dramatic effect on the native collagen matrices than on tanned samples. The tanning process endows the samples with extra crosslinking structure, and therefore, less sensitivity to thermocycling treatment. It was found that the thermal treatment at moderate temperature (0~50˚̓˹˰̵̵̵̴͈͂̈́˰̵̼̹̼̈́̈́˰̶̵̵̹̼̳̾̾ͅ˰̿̾˰̸̵̈́˰̸̵̱̼̈́͂̽˰̴̵̷̴̱̱̹͂̈́̿̾˰̱̳̹̱̹̈́͆̈́̿̾˰̵̵̷̵̹̾͂̓˰˸ΔE) of the sample. However, for the samples thermocycled at high upper limit temperature (0~150˚̓˹˼˰ΔE was decreased significantly.

SiAlON glasses: Effects of nitrogen on structure and properties

Sialon glasses are effectively alumino-silicates containing modifying cations (Mg, Ca, Y and Lanthanides) in which nitrogen substitutes for oxygen in the glass network. They are found at triple point junctions and as intergranular films in silicon nitride based ceramics. This paper provides an overview of M-Si-Al-O-N glasses and outlines the effects of composition on structure and properties. As nitrogen substitutes for oxygen, increases are observed in glass transition (Tg) and dilatometric softening (T ds ) temperatures, viscosities, elastic moduli and microhardness and decreases can be seen in coefficient of thermal expansion as a result of extra crosslinking of the glass network. The gradients of the linear relationships between properties and nitrogen content are similar for a wide range of different sialon glass compositions and modifier types since each eq.% nitrogen substitution introduces the same number of additional crosslinks into the glass network.

Synthesis of a novel perfluorinated acrylate copolymer containing hydroxyethyl sulfone as crosslinking group and its application on cotton fabrics

An acrylate monomer (2-[(2-hydroxyethyl) sulfonyl] ethyl acrylate) containing hydroxyethyl sulfone as crosslinking group was synthesized and a novel perfluorinated acrylate copolymer (NPAC) was prepared by emulsion polymerization. The average size of the emulsion particles was about 101 nm. NPAC was applied to cotton fabric by a pad–dry–cure process. The finished fabric showed excellent water and oil repellency rating and good washing durability without adding extra crosslinking agent. Some other physical performances of the finished fabrics were examined. The dry wrinkle recovery angle (WRA ( W + F)°) increased to 214°. The tearing and tensile strength retention and whiteness index (WI) of the finished fabric decreased to 70, 63, and 69.7%, respectively, compared with the untreated fabric.

Comparative study of some physico-chemical characteristics of osteoporotic and normal human femur heads

Objective: To compare some of the physico-chemical properties of osteoporotic and normal femur heads — a sample study. Materials and methods: The organic and inorganic parts of human normal (healthy) (N), osteoporotic (OP) femur heads and were separated using conventional methods and their physico-chemical characteristics were compared using infrared spectroscopy (IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results: The data revealed that the extra crosslinking had taken place between the intramolecular alpha chains of collagen of OP bone. This was confirmed by IR spectroscopy and TGA studies. XRD data of the inorganic part of N have shown well-resolved peaks compared to OP revealing the decreased crystallinity in the osteoporotic bone. Conclusions: The extra intramolecular crosslinking of OP bone collagen molecules increases its fragility. The crystallinity of inorganic phase is less in OP and this may be the reason for its brittleness.

Mechano-chemical recycling of sulfur cured natural rubber

The disposal of cured rubber has become a major environmental problem. Discarded rubber was devulcanized by an open two-roll cracker-cum mixing mill both in the presence or absence of diphenyl disulfide at 120°C (Mechano-Chemical Process, MCP), and then the obtained devulcanized mass was revulcanized again by the addition of sulfur and N-cyclohexyl-2-benzothiazyl sulfonamide (CBS). A new look at the devulcanization mechanism and the influence of the devulcanizing agent on the mechanical properties of the ultimate revulcanized rubber are presented in this paper. Rheometric characteristics show that both the scorch time and curing rate were low for revulcanized rubber. One of the most interesting observations is that the mechanical properties of revulcanized rubber obtained by devulcanizing in the presence of disulfide were better than of the revulcanized rubber obtained by devulcanizing in absence of disulfide. The formation of extra crosslinking in disulfide containing revulcanized rubber was confirmed by crosslinking density data. By adopting this devulcanization technique mechanical properties of vulcanized natural rubber were retained in more than 87%.

Solvent-resistant nanofiltration with filled polydimethylsiloxane (PDMS) membranes

The separation of solutions containing non-polar solvents, like toluene, was found to be limited for PDMS membranes, which is due to the extensive swelling of PDMS in those solvents. To improve the performance of silicone-based membranes for separations in non-polar solvents, extra cross-linking was introduced via the introduction of fillers. Of all fillers tested, zeolites were most efficient in decreasing the swelling of the PDMS network. Zeolites induce an increased cross-linking density, which is explained by the interactions between the silanol-groups of the filler and the PDMS-chains. The performance in SRNF of filled and unfilled PDMS membranes were compared, demonstrating increased solute rejection in non-polar solvents and at higher temperatures upon filler addition.

Devulcanization of Automobile Scrap Tyres by a Mechanochemical Process

The de-vulcanization of rubber waste poses a challenging economical, environmental and social problem. We propose a new de-vulcanization process to re-use the rubber waste. It is a mechano-chemical process (MCP), where the waste is de-vulcanized by a combination of mechanical shearing, heat (110 °C) and the use of a de-vulcanizing agent (diallyl disulfide). A new look at the de-vulcanization mechanism and the influence of the de-vulcanizing agent on the mechanical properties of the ultimate re-vulcanized rubber is also presented. One of the most interesting observations is that the retention of tensile strength of the re-vulcanized rubber with respect to the original tyre was 34.9% when de-vulcanized in the absence of diallyl disulfide and 72.4% in its presence. The formation of extra crosslinks in those re-vulcanized rubbers containing disulfide was confirmed from crosslink density data and from TGA results. DMA analysis revealed that the storage modulus also increased for re-vulcanized rubber containing the disulfide.

Analysis of Network Structure of UV-Cured Acrylates by1H NMR Relaxation,13C NMR Spectroscopy, and Dynamic Mechanical Experiments

The network structure of UV-cured acrylates was analyzed by dynamic mechanical experiments, 1H T2 NMR relaxation, and 13C NMR spectroscopy. Photocured mixtures of difunctional (poly(ethylene glycol) diacrylate) and monofunctional (2-ethylhexyl acrylate) were studied. The mean cross-link density and fraction of dangling chains were varied in these networks by changing the content of monofunctional acrylate. Examining networks by 13C NMR spectroscopy, we observed that the conversion is high, and the contribution or the effect of side reactions that generate extra cross-links is negligible. The spatial distribution of cross-links is very heterogeneous in the cured samples; i.e., polyacrylate ziplike network junctions are interconnected by polyether chains. An increase in the content of monofunctional monomer causes a significant decrease in the cross-link density because the monofunctional monomer acts as a chain extender. NMR T2 relaxation method shows good correlation with mechanical tests with respect to molar mass between cross-links, Mc. Obtained values of Mc are significantly smaller compared to molar mass of diacrylate. As anticipated, it is apparent that classical rubber elasticity theories are not applicable for characterization of this type of networks containing ziplike network junctions.

43—THE INTRODUCTION OF AMIDE AND ESTER CROSS-LINKS INTO WOOL

An account is given of the examination of carbodiimides and ethyl chloroformate as cross-linking agents for wool. The level of cross-linking was estimated from the extent of swelling of the treated wool in formic acid. Carbodiimide treatments resulted in the condensation of amino and carboxyl side chains to give amide cross-links; ester cross-links were also formed by condensation of hydroxyl and carboxyl side chains, Hydroxylamine treatments, which cleaved the ester but not the amide cross-links, were used to estimate the relative abundance of the two types of cross-link. N-Hydroxysuccinimide strongly promoted the cross-linking of wool with carbodiimides, most of the extra cross-links introduced being esters. The treatment of wool with ethyl chloroformate introduced relatively few cross-links. The main reactions are believed, on the basis of indirect evidence, to be esterification of carboxyl side chains and conversion of amino side chains to urethanes.