Polymerization of lactams

Summary The following limit (ceiling) temperatures of polymerization were extrapolated from kinetic data for the anionic polymerization of 2-pyrrolidone initiated with potassium salt of 2-pyrrolidone and the initiation systems of optimum compositions: 66°C for the nonactivated polymerization, 68°C and 73°C for the polymerization accelerated with 1-(1-pyr-rolin-2-yl)-2-pyrrolidone and carbon dioxide, respectively, 73°C and 76°C for the polymerization activated with N-benzoyl-2-pyrrolidone and N-acetyl-2-pyrrolidone,respectively.     

Effects of nitrates and nitrites on Lactobacillus helveticus and Lactobacillus casei dairy cultures

 The aim of this work was to observe the effects of nitrites and nitrates on the titratable acidity of milk after addition of Lactobacillus helveticus (TX 121) and L. casei (CAD 154) dairy cultures and on the levels of nitrate and nitrite. After adding L. helveticus and nitrites the increasing concentrations of the latter brought about a marked decrease in titratable acidity. In milk containing 100 mg·kg^–1 nitrite the resulting concentration was 39.33 mg·kg^–1 NaNO₂. Nitrates caused a less obvious decrease in titratable acidity, giving 13.27 g·l^–1 lactic acid. In milk containing 100 mg·kg^–1 NaNO₃ the resulting concentration was 24.99 mg·kg^–1 NaNO₃. Experiments with L. casei and a nitrite additive revealed a decrease in titratable acidity to 8.89 g·l^–1 lactic acid. After incubation, nitrite levels were reduced from 100 mg·kg^–1 NaNO₂ to 37.81 mg·kg^–1 NaNO₂. Nitrates were also stated to inhibit the titratable acidity of the sample, which decreased to 11.42 g·l^–1 lactic acid. Nitrates were reduced to 46.99 mg·kg^–1 NaNO₃. The present study shows that nitrites, more than nitrates decrease the titratable acidity of milk after addition of L. helveticus and L. casei dairy cultures. A reduction of nitrates and nitrites in milk samples by Lactobacillus was also found. The results of this study can be used in the dairy industry in the production of several types of hard cheese as well as fermented milk products that use L. helveticus and L. casei dairy cultures. Received: 31 March 1999 / Revised version: 6 September 1999     

Mechanical properties and morphology of polylactide,linear low‐density polyethylene,and their blends

Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer‐grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882‐91. On the basis of this, LLDPE 80 [80 wt % LLDPE and 20 wt % poly(L ‐lactic acid) (PLLA)] and MA‐g‐low‐density polyethylene 80/4 (80 wt % LLDPE, 20 wt % PLLA, and 4 phr compatibilizer) were found to be an optimum composition. The blends were characterized according to their mechanical, thermal, and morphological behavior. Fourier transform infrared spectroscopy revealed that the presence of compatibilizer enhanced the blend compatibility to some extent. The morphological characteristics of the blends with and without compatibilizer were examined by scanning electron microscopy. The dispersion of PLLA in the LLDPE matrix increased with the addition of compatibilizer. This blend may be used for packaging applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of propylation of starch with different degrees of substitution on the properties and characteristics of starch‐low density polyethylene blend films

Corn starch was modified by propylation and degree of substitution (DS) of four starch modifications were 0.61, 1.56, 2.27, and 2.51. Different films were prepared by blending native and propylated starch with low‐density polyethylene (LDPE). The mechanical properties, thermal properties, water absorption capacity, and biodegradability of the blend films varied with the quantity of starch as well as DS. Tensile strength, elongation, and melt flow index of propylated starch blend films were higher compared to the corresponding native starch blend film. These properties improved with increase in DS from 1.56 to 2.51. Propylated starch blend films were found thermally stable than native starch blend films. There was a decrease in water absorption capacity for the films containing propylated starch at high DS. Enzymatic and soil burial degradation results showed that biodegradability of starch‐LDPE films increased with the increase in the starch concentration but it decreased with increase in the DS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

On the development of natural fiber composites of high‐temperature thermoplastic polymers

A new method is presented for the development of natural fiber composites of high‐performance thermoplastic polymers considering poly(phenylene ether) (PPE) and wood flour as an example system. The large gap between the high processing temperature of PPE, typically between 280 and 320°C, and the low decomposition temperature of wood flour, about 200°C, was reduced by using a reactive solvent, a low molecular weight epoxy. The epoxy formed miscible blends with PPE, which offered much lower viscosity compared to PPE and processing temperatures well below the decomposition temperature of wood flour. In addition, the epoxy component accumulated around the polar wood flour particles upon polymerization during the fabrication step. The composite materials consisted of a thermoplastic continuous phase and two dispersed phases, one of polymerized epoxy and the other of wood flour particles coated with polymerized epoxy. These composites offered a significant reduction in density and better mechanical and physical properties when compared to commercially available grades of engineering polymer blends filled with short glass fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2159–2167, 2002     

Devulcanization of Natural Rubber Vulcanizates by Mechanochemical Process

Using a suitable disulfide-based devulcanizing agent, which cleaved the sulfur cross-links in vulcanized rubber at high temperature, devulcanization of gum natural rubber was carried out. High sulfur and medium sulfur, as well as low sulfur–containing rubber vulcanizates were used to study the cleavage of sulfidic bonds. The cure characteristics and mechanical properties of vulcanized natural rubber and revulcanized natural rubber were studied. Thermal properties of the rubber were analyzed by thermogravimetric analysis (TGA), which indicates that the onset degradation temperature further increased on revulcanization with higher amount of disulfide. The properties of the revulcanized natural rubber increased with increasing disulfide concentration, also the mechanical properties of the devulcanized natural rubber were increased by decreasing the sulfur content in the original rubber vulcanizate. From the rheometric study increases in optimum cure time were observed when ground rubber vulcanizates were treated with higher amounts of disulfide. The scanning electronic microscopy (SEM) study suggested the change in failure mechanism as influenced by the type of cross-linking present and the devulcanizing agent used. From infrared (IR) spectroscopy it was observed that the oxidation of the main polymeric chain did not occur at the time of high temperature milling.     

Removal of textile dyes from single and ternary solutions using poly(acrylamide‐co‐N‐methylacrylamide) grafted katira gum hydrogel

A novel hydrogel poly(acrylamide‐co‐poly‐N‐methylacrylamide) grafted katira gum (KG) was synthesized via free radical copolymerization using a mixture of acrylamide and N‐methylacrylamide in presence of N,N′‐methylene‐bis‐acrylamide as a crosslinking agent. A series of hydrogels (KG‐1 to KG‐6) were prepared by varying amount of acrylamide and N‐methylacryamide. Poly‐acrylamide‐g‐katira gum (PAM‐g‐KG) and poly‐N‐methylacrylamide‐g‐katira gum (PNMA‐g‐KG) hydrogels were also prepared using same crosslinking agent. Swelling characteristics of all the prepared hydrogels in water were evaluated and the hydrogel with best swelling property (KG‐6) was identified. The hydrogel KG‐6 was characterized by FTIR, X‐ray diffractometer, and scanning electron microscopy and was used for the adsorption of textile dyes namely methylene blue (MB), malachite green (MG), and congo red (CR) from single and ternary solutions. Adsorption dynamics, kinetics, isotherm, and thermodynamics of all the prepared hydrogels were studied in the ternary dye solutions. The sorption kinetics data were fitted well to pseudo‐second order and the equilibrium adsorption data were found to follow Freundlich isotherm model. The thermodynamics studies showed that the adsorption process was spontaneous and exothermic in nature. The preferential dye adsorption by the hydrogel was followed in the order MB > MG > CR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45958.     

Vascular Remodeling of Clinically Used Patches and Decellularized Pericardial Matrices Recellularized with Autologous or Allogeneic Cells in a Porcine Carotid Artery Model

Background: Cardiovascular surgery is confronted by a lack of suitable materials for patch repair. Acellular animal tissues serve as an abundant source of promising biomaterials. The aim of our study was to explore the bio-integration of decellularized or recellularized pericardial matrices in vivo. Methods: Porcine (allograft) and ovine (heterograft, xenograft) pericardia were decellularized using 1% sodium dodecyl sulfate ((1) Allo-decel and (2) Xeno-decel). We used two cell types for pressure-stimulated recellularization in a bioreactor: autologous adipose tissue-derived stromal cells (ASCs) isolated from subcutaneous fat of pigs ((3) Allo-ASC and (4) Xeno-ASC) and allogeneic Wharton’s jelly mesenchymal stem cells (WJCs) ((5) Allo-WJC and (6) Xeno-WJC). These six experimental patches were implanted in porcine carotid arteries for one month. For comparison, we also implanted six types of control patches, namely, arterial or venous autografts, expanded polytetrafluoroethylene (ePTFE Propaten^® Gore^®), polyethylene terephthalate (PET Vascutek^®), chemically stabilized bovine pericardium (XenoSure^®), and detoxified porcine pericardium (BioIntegral^® NoReact^®). The grafts were evaluated through the use of flowmetry, angiography, and histological examination. Results: All grafts were well-integrated and patent with no signs of thrombosis, stenosis, or aneurysm. A histological analysis revealed that the arterial autograft resembled a native artery. All other control and experimental patches developed neo-adventitial inflammation (NAI) and neo-intimal hyperplasia (NIH), and the endothelial lining was present. NAI and NIH were most prominent on XenoSure^® and Xeno-decel and least prominent on NoReact^®. In xenografts, the degree of NIH developed in the following order: Xeno-decel > Xeno-ASC > Xeno-WJC. NAI and patch resorption increased in Allo-ASC and Xeno-ASC and decreased in Allo-WJC and Xeno-WJC. Conclusions: In our setting, pre-implant seeding with ASC or WJC had a modest impact on vascular patch remodeling. However, ASC increased the neo-adventitial inflammatory reaction and patch resorption, suggesting accelerated remodeling. WJC mitigated this response, as well as neo-intimal hyperplasia on xenografts, suggesting immunomodulatory properties.     

Coarse and fine-tuning of lasing transverse electromagnetic modes in coupled all-inorganic perovskite quantum dots

Inorganic perovskite lasers are of particular interest,with much recent work focusing on Fabry-P6rot cavity-forming nanowires.We demonstrate the direct observation of lasing from transverse electromagnetic(TEM)modes with a long coherence time-9.5ps in coupled CsPbBr₃ quantum dots,which dispense with an external cavity resonator and show how the wavelength of the modes can be controlled via two independent tuning-mechanisms.Controlling the pump power allowed us tofine-tune the TEM mode structure to the emission wavelength,thus providing a degree of control over the properties of the lasing signal.The temperature-tuning provided an additional degree of control over the wavelength of the lasing peak,importantly,maintained a constant full width at half maximum(FWHM)over the entire tuning range without mode-hopping.