Browse Articles

The group of circular knitting machines with large diameter includes machines with one or two needle-beds with diameters higher than 178 mm and that use knitting process with final loop for stitch forming. The fabrics produced by circular knitting machines with large diameter are designed both for underwear products, clothing products and other destinations items (items for interior decorations, bed linen, technical articles, toys). Manufacturers of circular knitting machines have improved these machines in particular for: increasing productivity and polyvalence of these machines, reducing production costs, increasing quality of knitted fabrics. Appearance and uniformity of knitted fabrics are quality characteristics that directly depend on technological parameters of knitting. The paper presents ways for adjustment of fabric density at knitted fabrics produced by circular knitting machine with large diameter, type interlock, belonging to Mayer & Cie company. Keywords: circular knitting machine, knitted fabrics, fabric density

Platinum nanoparticles with sizes between 10 and 42 nm have been obtained by a sonoelectrochemical method in the presence of a water-soluble polymer, poly(amidehydroxyurethane) (PAmHU), which acted as a coating agent. The PAmHU stabilized Pt nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis and FTIR spectroscopy and dimension distribution and Zeta potential analysis. The analyses showed the fact that these nanoparticles are capped by the polymer, which confers them water-solubility and stability. Keywords: platinum nanoparticles, poly(amidehydroxyurethane), sonoelectrochemical synthesis

This paper presents the preparation by phase inversion of polysulfone and cellulose acetate ultrafiltration membranes (UF1-UF36) with various amounts of PEG additives (1000, 2000, 4000 Da), designed for the whey protein separation. To establish optimal operating conditions for membrane separation and the membrane with the best characteristics for the ultrafiltration of whey, we determined the flow variation of the two types of whey (pH=6.21, pH=4.35) with different parameters: whey temperature, operating pressure, protein retention and clogging phenomenon. All the results indicated that at the same protein separation efficiency (MWCO), the polysulfone membranes present higher flows than cellulose acetate membranes and their use in the acid whey ultrafiltration process lead to a whey protein concentrate with a protein content about 5 times higher than the initial whey content (6.4 kg/m3). The best protein retention 98.73% was obtained for UF18 membrane (20% PS, 2 % PEG 4000), with optimal flow rate (23.9·10-6 m3/m2s) for acid whey, operating at 50oC and 106 Pa. Keywords: membranes, ultrafiltration, proteins, recovery

A series of poly(ester urethane)s were synthesized, containing, poly(e-caprolactone) diol of Mn= 2000 as soft segments. Each series used the same diisocyanate in the hard segment, i.e., 1,6 hexamethylene diisocyanate, with the same content. The polyurethane polymers were prepared by a two-step polymerization in the absence of catalyst, at the molar ratio of OHsoft segment /NCO/ OH chain extenders = 1/2/1. The chain extenders were 1,12-dodecan diol, glycerin and castor oil. For all polymers the structures were determined by FTIR, the physico-chemical and thermal properties were determined by thermogravimetric analysis and additionally tensile properties as well as Shore A hardness were analyzed. Poly(ester urethane)s with castor oil exhibited higher tensile strength (up to 27 MPa vs 30 MPa) and elongation at break (up to ~780% vs. 1000%) in comparison with the corresponding glycerin poly(ester urethane)s. Keywords: polyurethane elastomers, chain extenders, crosslinkers, mechanical properties, thermal behaviour

The paper presents the preparation of two new 3-D nanocomposite porous materials, based on collagen type I (COL) and b-tricalcium phosphate nanopowder (n-b-TCP) and the selection of the best method for their chemical cross-linking using 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC). To our knowledge, no EDC cross-linked COL/n-b-TCP composite materials for orthopedic use were reported. The physico-chemical and biological properties of the cross-linked composite materials were investigated by porosity, dissolution, enzymatic degradation and cytotoxicity analyses. Key words: carbodiimide, nano-beta-tricalcium phosphate, collagen, cross-linking, biocompatibility

The paper presents the results of the research work on the evaluation of the mechanical properties (bending strength, MOE, shearing strength of the adhesive bond) of the laminated wood-textiles composite materials made of wood veneer (beech and poplar wood) and textiles: natural fabric made of jute (sackcloth) and woven fabric with synthetic fiber insertions (MTR-polyester, cotton, staple rayon). The layers of veneer and textiles were glued together by two types of adhesives, successively: a natural one (bone glue) and a polyvinyl adhesive (Jowacoll 107.10). Four types of wood-textile composite samples have resulted, as follows: beech veneer – sackcloth glued with bone glue, beech veneer – sackcloth glued with polyvinyl adhesive, poplar veneer – sackcloth glued with bone glue and beech veneer – woven fabric with MTR glued with bone glue. The samples resulted were loaded to the bending strain and the bending strength and MOE were calculated with the value of breaking force obtained for each tested sample. The shearing strength of adhesive bond has been also experimentally determined in order to establish which adhesive is more appropriate to be used both with wood and textile materials into the composites. The influence of the flexibility of the synthetic fibers on the elastic properties of the resulted composites has been also investigated by determining MOE of the corresponding composites. Based on the results obtained, it is concluded that the synthetic fibers (67%) contained by woven fabric with MTR does not increase MOE of the composites, whilst the natural jute fabric behaviour into the wood-textile composites gives unexpected results in strength and elasticity of the new product. Keywords: synthetic fibers, MOE, bending strength, shearing strength, composite, elasticity

The paper describes aspects concerning the effects of the immersion time in water, on some mechanical characteristics of some composite materials reinforced with E-glass woven fabrics. The specimens were manufactured by reinforcing a polyester resin Copoly 7233 with both woven fabric EWR300 made of E-glass fibres and chopped E-glass fibres. The hand lay-up technology was used to manufacture the specimens with different pressures in the moulding step: low pressure and high pressure, respectively. The first of all, some specimens were immersed in water and the data regarding the moisture content were periodically recorded. Then, the wet composite specimens were subjected to the flexural test (three point method) after 3500 h of immersion and 7417 h of immersion, respectively. Finally, the experimental results obtained in case of the immersed specimens were comparatively analysed with the results recorded in case of the dried specimens subjected to the bending test too. Moreover, the mechanical characteristics of the specimens were analysed taking into account the different manufacture methods used. It is also shown a comparison concerning the results obtained in cases of the two kinds of reinforcements used. Keywords: composite; moisture; absorption; flexural test

An assay on the thermal stability of isotactic polypropylene stabilized with Sanduvor PR 31, a hindered amine (O1-(1,2,2,4,6,6-hexamethyl-4-piperidyl) O3 - (1,2,2,6,6-pentamethyl-4-piperidyl) (2Z) – 2 - [(4-methoxyphenyl) methylene] propanedioate, was performed. The oxidability of modified polymer previously subjected to weathering treatment or UV irradiation was investigated in air by isothermal (1550C) and isobaric (normal pressure) oxygen uptake. The exposure time was sufficient enough to attend a slow degradation rate (281 days for weathering test and 550 h for accelerated UV ageing). The main kinetic parameters, oxidation induction time and oxidation rate, were determined from the dependencies of chemically consumed oxygen on testing time. Comparative results on reference samples (control or stabilized polypropylene) and degraded materials are analyzed for depicting the influence of ageing factors on the polypropylene durability. Keywords: polypropylene, UV degradation, weathering, oxygen uptake, Sanduvor PR 31

Graphite-based Teflon composites find various applications in many engineering fields. For certain applications, the use of composites rather than metals has in fact resulted in savings of both cost and weight. The usage in many fields demands several machining operations to be performed on engineering polymers. The paper deals with two different materials: polytetrafluoroethylene with regenerated graphite (PTFE GR) and polytetrafluoroethylene with 32% carbon and 3% graphite (PTFE CG 32-3). At the beginning of the study it was performed an advanced characterization for both materials that have been used: PTFE GR and PTFE CG 32-3. The chemical composition was determined using X-ray photoelectron spectroscopy (XPS). Complementary information about the chemical structure is obtained with Fourier transform infrared spectroscopy (FTIR). This combination of spectroscopic methods was used to establish individual differences between the chemical structures for the used materials. Second part of the present paper investigates the effect cutting parameters on the cutting force in the turning of PTFE GR and PTFE CG 32-3 materials. The effects of different parameters on cutting force are analyzed and presented in this study. This paper presents that the success of the machining operation is affected by the chemical structure of the work material. Keywords: engineering polymers, spectroscopy analysis, cutting force, turning

The UHMWPE has a plastic behaviour but it is specified only the surface wear, unless the evaluation of the great importance of this behaviour of plasticity for the calculation of the depth of penetration. This work tries to demonstrate the fact that there are components of the wear by plastic deformation. Also, by this type of wear an explanation of smooth surface of the UHMWPE in the contact zone, after millions of gaits cycles may be explained Keywords: hip endoprosthesis, wear, penetration depth, roughness, plastic behavior