Effect of surface modifications of leather on its joint strength with polyvinyl chloride

The treatment of bovine leathers with wetting and lyotropic agents followed by heating produced a strengthening of the leathers which increased their joint strength properties to polyvinyl chloride (PVC). A cohesive failure of leather was always obtained. The highest cohesive strength (or point peel strength) was obtained when the treatment was carried out at 140°C with the surfactant NFOE (8.5) (nonylphenol polyoxyethylene with 8.5 mol of oxyethylene). The lyotropic agents (CaCl₂, urea) gave very high values (a five-fold increase), whereas the water-dimethyl ketone blends and pure water resulted in a smaller improvement in cohesive strength (a three-fold increase). The improved cohesive strength of leather was mainly due to the destruction of the ordered structure of collagen fibres and to the creation of a complex entanglement network among the collagen fibres. The treatments applied to a bovine leather produced a shrinkage of 65%; the degree of shrinkage was not a function of the kind of treatment, but of the structure of the leather. The application of surface treatments to leather prior to its bonding to other substrates may mean that the roughening process of the leather, a tedious and difficult operation which is necessary in order to obtain adequate adhesive joints, can be avoided.     

Nanoscopic investigation on TiO2-SiO2-GLYMO nanocomposite coated and plasma treated leathers

ABSTRACT

In this study, the modification of leather surface by application of TiO₂-SiO₂-GLYMO (3-Glycidyloxypropyltrimethoxysilane) nanocomposite coating and plasma treatment with N₂ gas activation is investigated by using Small and Wide Angle X-ray scattering methods. The protective properties were tried to be developed with TEOS and HMDSO polymers’ usage in the coating process by following and controlling nano scale structural changes. The main aim was the controls of nanoscaled surface modifications and determination of the best coating process by keeping natural structure of the leathers. These scattering methods were useful to investigate the coating effects on the PTLs (Plasma Treated Leathers)’ internal structures including collagen microfibers and nanofibers which are hierarchical structures of triple helix collagen. The main purpose of the work was investigate whether the structural change in the natural form of the leather is present or not in the molecular-nanoscopic and microscopic scales after the coating and the applied physico-bio-chemical processes. On the other hand, the successful protective coatings and surface modifications were determined with SAXS analyses by controlling the shape, size and distance distributions of the appeared nanoglobular aggregations. The observations of structural changes taking place within collagen fibrils as a result of surface modification provides new insight into the nature of finishing and informs future processing developments.     

Dielectric barrier discharge plasma induced surface modification of polyester/cotton blended fabrics to impart water repellency using HMDSO

Continuous treatment of polyester/cotton blended fabric samples was carried with hexamethyldisiloxane (HMDSO) plasma on the pilot scale atmospheric pressure plasma reactor. The mixture of helium and argon was used as carrier gas for generating dielectric barrier discharge plasma. The effect of discharge power and treatment time on the water repellent properties of samples were evaluated with contact angle (CA) and spray test measurements. Spray test and CA results showed improved resistance to wetting with water. The effect of discharge conditions on the surface morphology and surface chemistry of plasma treated samples were investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopic analysis, respectively. The presence of Si‐O‐Si and Si‐CH₃ groups in the structure of plasma polymer deposited at the surface of P/C samples was revealed by FTIR spectroscopy. Further, structural differences in HMDSO plasma polymer deposited under different discharge conditions were reported with reference to organic/inorganic nature of plasma polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

An eco‐efficient rationalized leather process

BACKGROUND: The leather industry is under pressure to develop environmentally efficient leather‐making processes to comply with modern pollution and discharge legislation. Conventional leather‐processing methods are known to contribute significant pollution loads in tannery wastewaters. The rationalized process described here involves a salt‐free curing, lime and sulfide‐free beamhouse process and post‐tanning followed by tanning employing a reverse leather‐processing technique. RESULTS: Scanning electron microscopy (SEM) analysis substantiated that the grain surface, fibre separation and tight packing of fibres are similar for leathers from conventional and rationalized processes. The functional performance of the leathers is found to be on par with that of conventionally processed leathers. The rationalized leather process reduces the usage and discharge of chemicals by 68% and 82%, respectively. It also enjoys the reduction in biochemical oxygen demand (BOD), chemical oxygen demand, Cl^?, SO₄^2? and total solids loads by 58%, 62%, 95%, 66% and 85%, respectively. The rationalized process also results in reduction of water consumption and discharge and energy by 37%, 37% and 38%, respectively. CONCLUSION: The rationalized process utilizes resources efficiently with reduced environmental impact without compromising leather qualities and can be seen as being eco‐efficient compared to the conventional leather process. Copyright © 2007 Society of Chemical Industry     

Investigation of surface pre-treatments for the structural bonding of titanium

This paper evaluates wet-chemical pre-treatments (alkaline etching, anodising) and a plasma treatment for structural bonding of titanium (Ti₆Al₄V). The main objective of this study is the comparison of the applicability of the plasma pre-treatment to wet-chemical treatments on titanium for structural bonding. In this context, an atmospheric pressure plasma device was used to deposit thin functional films from hexamethyldisiloxane (HMDSO) precursor on titanium.X-ray photoelectron spectroscopy (XPS) was employed to assess the chemical composition of the surface after different pre-treatments on the titanium substrate, while the morphology and the film thickness were investigated with scanning electron microscopy (SEM). The adhesion properties on titanium were evaluated by means of a wedge test in hot/wet conditions. After bonding tests the fracture surface and the failure loci were analysed.Using a long arc plasma generator and HMDSO precursor almost stoichiometric SiO₂ coatings were obtained on the titanium substrate. These coatings exhibit good long-term durability and bond strength compared to an alkaline etching in the wedge test. The investigated anodising process leads to oxide layers revealing a highly porous nanostructure. In contrast to the alkaline etching, the plasma derived coatings and the oxide layer produced by the anodising process exhibit a higher micro, respectively nano roughness, and hence a better long-term durability.     

Surface biomedical effects of plasma on polyetherurethane

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N₂ and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N₂ and Ar plasma treatments, and N₂ plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N₂ and Ar plasma treatments broke some of the C-O and C=O bonds at the surface and resulted in oxidation of the surface.     

聚氨酯牛巴革的技术开发与生产加工

简要介绍了聚氨酯牛巴革生产工艺及其影响质量的因素。经过湿法涂层成膜制犁 半成品,再进行表面磨毛和各种后整理,制成的牛巴革产品档次高,质量可以与同类产品相媲美。     

Treatment with Ar–O2 low-pressure plasma of vulcanized rubber sole containing noticeable amount of processing oils for improving adhesion to upper in shoe industry

Vulcanized rubber (L3 rubber) containing intentionally noticeable excess of processing oils in its formulation was treated with Argon–Oxygen (Ar–O₂) (2:1, vol/vol) low-pressure (LP) plasma for achieving a satisfactory level of adhesion to waterborne polyurethane adhesive. The effectiveness of the Ar–O₂ LP plasma treatment of L3 rubber depended on both the configuration of the plasma chamber shelves and the treatment time. Surface modifications were assessed by attenuated total reflectance-IR and X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy. Ar–O₂ LP plasma treatment in direct configuration provided the most effective surface modification of the L3 rubber, and the increase in the treatment time improved the extent of the surface modifications. However, even important surface modifications were produced by Ar–O₂ LP plasma treatment, adhesion of treated L3 rubber was not improved due to the creation of weak boundary layer at the polyurethane–rubber interface after joint formation. Heating at 80 °C for 12 h of the as-received L3 rubber prior to Ar–O₂ LP plasma treatment enhanced the extent of the surface modifications, and improved adhesion was obtained for Ar–O₂ LP plasma treatment times higher than 600 s.     

Styrene and butyl methacrylate copolymers and their application in leather finishing

Homopolymers and copolymers of styrene and butyl methacrylate were synthesized with different ratios by an emulsion polymerization technique with K₂S₂O₈/NaHSO₃ as the redox initiation system and sodium dodecyl sulfate as the emulsifier at 60°C for 3 h. The effects of different monomer ratios on the kinetics of emulsion polymerization and polymer viscosity were studied. These copolymers were applied to leather surfaces with a hand coater to a thickness of 18 μm. The effects of the coatings on the leather surfaces were evaluated through the measurement of physical and mechanical properties of coated and uncoated leather. IR spectra showed new bands characteristic of styrene and butyl methacrylate, which disappeared in the spectrum of uncoated leather. The physical and mechanical results showed that the water absorption content decreased with increasing styrene content, and the water vapor permeability of the coated leather was less than that of the uncoated leather; however, it was still in the acceptable range. The results indicated improvements in the tensile strength and elongation (%) for the coated leather with increases in the butyl methacrylate content. Thermogravimetric analysis showed characteristic improvements in the thermal stability of leather after the coating; its optimum stability was reached when the leather was coated with poly(styrene:butyl methacrylate) (1 : 1). Finally, scanning electron microscopy showed the full grain surface of the leather. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Supercritical carbon dioxide‐assisted loosening preparation of dry leather

The physical modification of the dry leather using supercritical carbon dioxide (SC‐CO₂) was studied in this article. A series of loosening processes of the leather fibers were carried out by changing the experimental conditions such as experimental pressure, experimental temperature, and time. The samples were characterized by scanning electronic microscopy (SEM), Brunauer–Emmett–Teller (BET) and X‐ray diffraction (XRD). SEM images show that samples were loosened by SC‐CO₂ and the leather fibers in micron size arrange more orderly after treatment. The BET surface area of treated samples increase from 1.67 m²/g to 6.33 m²/g with the changing of conditions. The optimal treatment conditions were determined. Moreover, XRD patterns indicate that aggregation structure of collagen fibers in the sample was altered by SC‐CO₂, and it can be found that the loosening of leather mostly happened in amorphous regions of collagen fibers. Besides, the percent breaking elongation of the samples was examined by means of a tensile analyzing test, and it indicates that the elongation at break of all the treated samples in SC‐CO₂ can increase to 128.2% compared with 95.9% of the original ones. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Optimization of Methyl Methacrylate Inductively Coupled Plasma Surface Modification of ZrO2 Particles used in Acrylic Bone Cement Formulations

A response surface methodology was used to optimize the relationships between the time and power of a methyl methacrylate plasma surface modification process for ZrO₂ particles in bone cement formulations. Time and power were varied during the plasma process, and their effect on the mechanical properties of the bone cement was studied. All mechanical properties were improved in all bone cement formulations prepared with modified ZrO₂ particles in comparison to those of bone cement formulated with ZrO₂ particles without plasma treatment.     

Oil extracted from seal hides: Characterization and use as leather fat liquor

Extracting natural grease from leathers and skins is a necessary process designed to avoid the appearance of undesirable blemishes in finished articles. Also, degreasing of pickled skins is an important preliminary step in which excess fats are removed. Fat content of some skins is high. In this paper, we study the characteristics of the extracted fatty substances from seal skins. Extracted fats, which were considered waste, can be used as fat liquors in leather manufacture. The primary function of leather lubricant is to prevent adhesion of the leather fibers and to influence the degree of fiber cohesion that takes place during drying of wet leathers. In mineral tannage or semimineral tannage (e.g., semi-chrome), this is achieved by the fatliquoring of leather, for which purpose mostly anionic emulsifiable oil products are used. Seal oil is made into an emulsifiable anionic product by sulfation or by addition of anionic emulsifiers. We tested these products in lambskin fat-liquoring and we studied the physical properties of leather and fatty spue (white efflorescences that appear sometimes on the surface of leather) formation after aging for 3 mon. The oil extracted from seal skins has good characteristics as fat liquor, and the quality of the resulting leather is comparable to leathers fat-liquored with a commercial reference material.     

Hydrophobic properties of ethylene–vinyl alcohol copolymer treated with plasma source ion implantation

The industrial use of ethylene–vinyl alcohol copolymer (EVOH) film is limited because it is easily degraded by moisture. The plasma source ion implantation (PSII) technique with CF₄ or CH₄ gas was used for the EVOH film to improve the surface hydrophobic properties. Variables examined in implantation were ion energy (0–10 keV), treatment time (5 s–5 min), and ion species. The hydrophobic properties of EVOH films were greatly enhanced after a CF₄ PSII treatment, as evidenced by an increased contact angle from 66° to above 100° at ‐5 keV, and remained relatively unchanged during the period of 28 days. X‐ray photoelectron spectroscopy, atomic force microscopy, and O₂ permeability were used to characterize the surface properties of EVOH films treated with PSII. The improved hydrophobic properties were closely related to the formation of fluorine‐containing functional groups such as CF, CF_2, and CF₃ on the modified surface. The percentage distribution of carbon functional groups supports the role of CF₂ and CF₃ groups in surface modification. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2069–2075, 2004     

Surface modification of natural leather using diffuse ambient air plasma

The aim of this work was to activate the surface of dyed natural leather using a diffuse ambient air plasma treatment. The plasma was generated by the so-called diffuse coplanar surface barrier discharge (DCSBD). It was observed that a 10 s plasma treatment time is enough to decrease the water contact angle from 85° to 45°. Improvement of wettability is important for gluing of dyed leather and better adhesion of glue to leather parts. XPS study indicated that the percentage of oxygen-containing bonds responsible for hydrophilicity is significantly increased by the plasma treatment. Influence of the plasma treatment on mechanical properties of dyed leather was evaluated using tensile strength measurement and no significant changes in the surface morphology and mechanical properties were observed. The results indicate that the DCSBD technique can provide high throughput, technical simplicity and economy required by the leather industry.     

Production of carbon molecular sieves by plasma treated activated carbon fibers☆

Carbon molecular sieves (CMS) are valuable materials for the separation and purification of gas mixtures. In this work, plasma deposition was used aiming to the formation of pore constrictions, by narrowing the surface pore system of commercial activated carbon fibers (ACF). For this reason propylene/nitrogen or ethylene/nitrogen discharges of 80 and 120 W were used. The molecular sieving properties of the plasma treated ACF were evaluated by measuring the adsorption of CO₂ and CH₄. The CO₂/CH₄ selectivity was significantly improved and depended on plasma treatment conditions (discharge gas and power). The optimum CO₂/CH₄ selectivity (26) was observed for C₂H₄/N₂ plasma treated ACF at 80 W. Sample scanning electron microscopy (SEM) analysis after plasma treatment revealed an external film formation and X-ray photoelectron spectroscopy (XPS) analysis showed the incorporation of nitrogen functional groups in the film, which probably interact with CO₂, thereby altering CO₂/CH₄ selectivity.     

Enhancing adhesive joints between commercial rubber (SBS) and polyurethane by low-pressure plasma surface modification

The paper presents research on the two-stage process of low-pressure plasma surface modification of a commercial SBS rubber, improving its adhesion to both the polyurethane adhesive in an organic solvent (PU) and the aqueous polyurethane adhesive dispersion (ADPU). The plasma surface modification process was carried out in a flow reactor with parallel plate electrodes, in which plasma was generated by an RF glow discharge (13.56 MHz). In the first stage of the process, the Ar or O₂ plasma was used, and then, as the second stage of the modification process, the treatment was performed in H₂O plasma. The adhesive properties of the plasma-modified SBS rubber surface were determined using the 180^o-peel strength test (PS). These results were correlated with surface properties investigated using contact angle (CA) measurements, FTIR-ATR spectroscopy, XPS spectroscopy and scanning electron microscopy (SEM). The observed improvement in wettability of the plasma modified surface was attributed to the formation of hydroxyl groups, which was confirmed by spectroscopic methods (FTiR-ATR and XPS). The results of the 180^o-peel strength test showed, in turn, a clear relationship between the capacity of adhesive bonding and the amount of oxygen groups (mainly the hydroxyl groups) as well as the surface roughness, determined by SEM microscopy. It was also found that the effects of the plasma surface modification of the SBS rubber were stable for at least 72 h. The results of this work prove that cleaning and etching of the commercial SBS rubber surface in the first stage of its plasma treatment, followed by chemical modification in the second stage, lead to very strong adhesive joints.     

Comfort,chemical, mechanical,and structural properties of natural and synthetic leathers used for apparel

Natural leather is processed from hides and skins of animals. Synthetic leathers are becoming popular as an alternative material owing to limited availability and varying size of natural leathers. There is a need to understand the properties of natural and synthetic leathers to select proper material for an application. In this study, materials used for apparel application such as natural sheep nappa leather and synthetic polyurethane (PU)‐based leather have been chosen and analyzed for comfort, chemical, physical, and structural properties. It was found that natural sheep nappa leather has enhanced water vapor permeability whereas other comfort properties such as softness and drape ability are comparable to synthetic PU leather. Whereas synthetic PU leather dominated most of the physical properties, especially percentage elongation and stitch tear strength, in specific directions on account of polyester knitted base fabric. Chemical properties of natural sheep nappa leather and synthetic PU leather depended on the individual material composition and characteristics. Scanning electron microscopic (SEM) analysis provided convincing evidence for some of the quantified comfort and physical properties. The results of this study would be useful in selection of proper material for apparel application as well as in providing directions for future research in synthetic leather manufacture. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Double in-situ synthesis of polyacrylate/nano-TiO2 composite latex

Polyacrylate/nano-TiO₂ composite latex was prepared via double in-situ polymerization using acrylamide (AM), vinyl acetate (VAc), butyl acrylate (BA) and methyl methacrylate (MMA) as monomers, tetrabutyl titanate (Ti(OBu)₄) as precursor of TiO₂. The morphology, structure and distribution of composite latex were characterized by Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS) and X-Ray Diffraction (XRD). The thermal stability, anti-yellowing and antibacterial properties of composite latex were also investigated. The results showed that nano-TiO₂ consisted in polyacrylate latex and it was located on the surface of latex particles. The average particle size of polyacrylate/nano-TiO₂ composite latex was 156.6 nm, which was bigger than that of pure polyacrylate (125.1 nm). The introduction of nano-TiO₂ improved the thermal stability, anti-yellowing and antibacterial properties of the latex film. At last, the polyacrylate/nano-TiO₂ composite latex was applied in leather finishing. Compared with polyacrylate latex, the properties of the leather finished by polyacrylate/nano-TiO₂ composite latex were enhanced: water vapor permeability increased by 58% and water uptake decreased by 3.52%.     

Waterborne polyurethane/inorganic hybrid composites: preparation,morphology and properties

Abstract

A series of waterborne polyurethane/inorganic (WPU/TiO₂) hybrid composites were synthesised by a sol–gel process on the basis of isophorone diisocyanate, polyether polyol (GE-210), dimethylolpropionic acid, tetrabutyl titanate (TBT) and 3-glycidyloxypropyl trimethoxysilane as a coupling agent. The physical properties of the WPU and WPU/TiO₂ dispersions and hybrids were measured. Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction were used to assess the fracture surface morphology and the dispersions of the WPU/TiO₂ hybrids. The scanning electron microscopy, transmission electron microscopy and atomic force microscopy results showed that the TiO₂ particles were dispersed homogeneously in the WPU matrix in nanoscale. The prepared hybrids showed good thermal stability and mechanical properties in comparison with pure WPU and showed tunable transparence with the TBT fraction in the film. Through suitable adjustment of TBT content, some thin hybrids have potential applications, such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes.     

Surface modification of polytetrafluoroethylene films by plasma pretreatment and graft copolymerization to improve their adhesion to bismaleimide

BACKGROUND: Polytetrafluoroethylene (PTFE) is utilized in many engineering applications, but its poor wettability and adhesion properties with other materials have limited its use. The study reported was aimed at achieving surface modification of PTFE films by radiofrequency NH₃ and N₂ plasma treatment, followed by graft copolymerization, in order to improve the interfacial adhesion of PTFE and bismaleimide. RESULTS: X‐ray photoelectron spectroscopy results showed that a short‐time plasma treatment had a distinct defluorination effect and led to nitrogen functional group formation. The nitrogen chemical bonding form was different for NH₃ and N₂ plasma treatments. Under the same experimental conditions, the NH₃ plasma exhibited a better etching effect than did the N₂ plasma. Contact angle measurement showed an improvement in both surface energy and wettabliity by short‐time plasma treatment. The concentration of the surface‐grafted bismaleimide on PTFE increased after the plasma pretreatment. The lap shear strength between PTFE and bismaleimide increased significantly after surface modification. CONCLUSION: This study found that plasma treatment caused changes in surface chemistry, thus leading to an increase of the wettability of PTFE surfaces. Hence, the adhesion properties of PTFE with bismaleimide were significantly improved. Copyright © 2008 Society of Chemical Industry