An indirect method which ranks the adhesion in natural rubber filled with different types of cellulose fibres by plots of E(t)/Et=0 versus log t

The suggestion that composites with good bonding between fibres and matrix have a faster stress relaxation rate than composites with poor bonding between fibres and matrix is supported here by measurements on natural rubber filled with untreated cellulose fibres, allyl acrylate grafted cellulose fibres and allyl methacrylate grafted cellulose fibres.     

Effects of electron irradiation on physical properties of rubber/cellulose fibre composites

Short term stress–strain properties were investigated for natural rubber reinforced with short cellulose fibres at various fibre loads. Stress–strain measurements were also performed on natural rubber composites containing cellulose fibres, electron irradiated in the presence of butadiene or N-hydroxymethylacrylamide, where the latter monomer produced the greatest improvement in stress–strain properties. Chemiluminescence analysis indicated the existence of a surface layer on the fibres after irradiation treatments, and water absorption measurements showed a decrease in water uptake for composites containing irradiated fibres. The results demonstrate the improvement of mechanical properties with a reduced sensitivity to moisture.     

Mechanical properties of natural rubber/grafted cellulose fibre composites

Mechanical properties of natural rubber/allyl acrylate and allyl methacrylate grafted cellulose fibre composites are presented. Stress/strain measurements and dynamic mechanical measurements indicate that the adhesion between grafted fibres and matrix is better than that in samples containing untreated cellulose fibres. This makes it possible to vary the composite properties by varying the fibre type and/or fibre amount.     

Characterization of rubber-cellulose-fibre composites by mechanical measurements and electron microscopy

Mechanical measurements, SEM micrographs and crosslink density measurements on cellulose-fibre-filled natural rubber suggest that there are bonds between untreated cellulose fibres and the rubber matrix. Mechanical tests indicate that the dispersion or lack of dispersion of the fibres in the matrix is at least as influential a parameter in determining the strength of the composite as is the adhesion between fibre and matrix. Stress/strain measurements indicate that there is no obvious correlation between adhesion and the shape of the stress/strain curve unless the curve is clearly jagged.     

Ultrasonic cleaning of SBR rubber to improve the performance of subsequent plasma torch treatment

Paraffin wax and other moieties in sulfur vulcanized styrene-butadiene rubber formulations may migrate to the surface, reducing the adhesive strength in joints produced with polyurethane adhesive. In this study, with the aim to remove paraffin wax and other anti-adhesion moieties on the rubber surface to improve adhesion, prior to plasma torch treatment, a methyl ethyl ketone (MEK) cleaning in an ultrasonic bath has been carried out. The surface modifications produced on the rubber surface have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength of treated rubber/polyurethane adhesive joints. Ultrasonic cleaning in MEK resulted in partial removal of paraffin wax on the rubber surface and, thus, lower contact angle values, decreased relative intensity of the infrared bands due to hydrocarbon moieties and lower percentage of carbon assessed from XPS spectroscopy were obtained. The ultrasonic cleaning in MEK of the rubber increased the effectiveness of the atmospheric pressure plasma torch treatment, and surface oxidation was produced. However, the oxidation degree decreased with time after plasma torch treatment, likely due to ageing of the surface treated rubber.     

Influence of chemical treatments on the electrokinetic properties of cellulose fibres

Changes in the surface composition of chemically treated cellulose fibres obtained from the sheath of banana plants were investigated using electrokinetic (ζ-potential) measurements. Scanning electron microscopy (SEM) was used to observe changes in the surface morphology of the fibres. Spectroscopic methods were also used to analyse the changes on the cellulose fibre surface. Chemical treatments such as alkali treatment, acetylation, treatment with a triazine coupling agent, various silanes, etc. reduced the hydrophilicity of the fibres. The surface morphology of the fibres showed considerable changes. Chemical treatments reduced the acidity of the already polar cellulose fibre. The high iso-electric point (IEP) of the silane A1100-treated fibres shows that basic groups dominate at these surfaces. The observations are consistent with the values obtained using solvatochromic measurements.     

Mechanical,morphological and thermal properties of short carbon and aramid fibres-filled bromo-isobutylene-isoprene rubber vulcanised with 4, 4’ bis(maleimido)diphenylmethane

ABSTRACT

This paper describes the use of a combination of 4, 4’ bis(maleimido)diphenylmethane and ZnO as a high-temperature processable vulcanising agent for the short aramid and carbon fibre-filled bromo-isobutylene-isoprene rubber. The fibre breakage analysis, cure characteristics, mechanical, thermal and morphological properties of the composites were evaluated with different fibre loading. The fibre breakage analyses revealed that the aramid fibres have good length retention property compared to carbon fibres. The morphological analysis of the extracted aramid fibres showed severe surface roughness primarily due to fibrillation after shear mixing. The fibrillated aramid fibres lead to aggregation and poor dispersion of the fibres in the rubber matrix. However, fibrillation imparted surface roughness and increased surface area on the aramid fibres which improved the fibre–matrix interaction via mechanical anchoring. On the other hand, the carbon fibre-filled composite showed poor fibre–matrix interaction and inferior strength and modulus.     

Cellulose fibres, nanofibrils and microfibrils: The morphological sequence of MFC components from a plant physiology and fibre technology point of view

During the last decade, major efforts have been made to develop adequate and commercially viable processes for disintegrating cellulose fibres into their structural components. Homogenisation of cellulose fibres has been one of the principal applied procedures. Homogenisation has produced materials which may be inhomogeneous, containing fibres, fibres fragments, fibrillar fines and nanofibrils. The material has been denominated microfibrillated cellulose (MFC). In addition, terms relating to the nano-scale have been given to the MFC material. Several modern and high-tech nano-applications have been envisaged for MFC. However, is MFC a nano-structure? It is concluded that MFC materials may be composed of (1) nanofibrils, (2) fibrillar fines, (3) fibre fragments and (4) fibres. This implies that MFC is not necessarily synonymous with nanofibrils, microfibrils or any other cellulose nano-structure. However, properly produced MFC materials contain nano-structures as a main component, i.e. nanofibrils.     

E.s.c.a. studies of the nitration and denitration of cellulosic materials

The relative rates of the nitration and denitration of cellulose and cellulose nitrate, respectively (in the form of linters paper), have been monitored in the outermost few tens of Angstroms of the fibres using e.s.c.a. (X-ray photoelectron spectroscopy). Important conclusions are drawn on the equilibrium conditions at the surface and it has been shown that in mixed acid nitrations sulphate esters, (often thought to be a cause of instability in cellulose nitrates), are confined to the outermost few tens of Angstroms of the material. Comparison of the degree of substitution at the surface and that determined for the bulk by Kjeldahl methods provides a new insight into this complex problem.     

Mechanical properties of NR/BR/cellulose II composites

Summary Blends of natural rubber (NR) and butadiene rubber (BR) with cellulose filler have been investigated. The coprecipitation of the rubber latex-cellulose xanthate mixtures by acidulation lead to elastomer-cellulose II composites in granular form. In these blends, the NR/BR ratio has been varied from 75/25 to 25/75, and the cellulose content has been increased from 0 to 25 phr. Mechanical tests have been applied to the composite samples, and the results showed that cellulose II may be considered as a reinforcing agent. Those results gave also an insight into the role of NR and BR on the properties of the composite samples.     

Zeta-potential Studies in Cellulose Fibre–Aqueous Electrolyte Solution Systems

Zeta-potential studies of cotton and viscose rayon fibres in aqueous sodium and potassium chloride solutions of different concentrations have been carried out using the streaming-potential method. The Eversole and Boardman equation, which relates the measured zeta potential to the thickness of the electrical double layer, has been found to be valid in all cases. Using the surface-potential values calculated from this equation, the surface-charge densities in these fibres have been estimated. They are in good agreement with the theoretical surface-charge densities calculated from data on the carboxyl-group content of these fibres and the BET nitrogen surface areas for the water-swollen uncollapsed fibres. Two alternative explanations for the apparent increase in surface-charge density with decrease in the zeta potential have been given, without assuming that the anions are absorbed. The variation in zeta potential with increasing carboxyl-group content in samples of oxycellulose has been explained in terms of changes in the degree of dissociation of carboxyl groups with increasing carboxyl content, and an increase in the surface area of the cellulose fibre on oxidation. Studies of the zeta potentials in Form-W and Form-D formaldehyde-crosslinked cotton fibres have indicated that the zeta potential increases with increase in formaldehyde content with Form-D fibres. This result can be explained in terms of the decrease in the surface area of Form-D cottons with increase in the content of bound formaldehyde.     

The effect of chemical treatment on the properties of hemp,sisal, jute and kapok for composite reinforcement

Two chemical treatments were applied to hemp, sisal, jute and kapok natural fibres to create better fibre to resin bonding in natural composite materials. The natural fibres have been treated with varying concentrations of caustic soda with the objective of removing surface impurities and developing fine structure modifications in the process of alkalisation. The same fibres were also acetylated with and without an acid catalyst to graft acetyl groups onto the cellulose structure, in order to reduce the hydrophilic tendency of the fibres and enhance weather resistance. Four characterisation techniques, namely XRD, DSC, FT-IR and SEM, were used to elucidate the effect of the chemical treatment on the fibres. After treatment the surface topography of hemp, sisal and jute fibres is clean and rough. The surface of kapok fibres is apparently not affected by the chemical treatments. X-ray diffraction shows a slight initial improvement in the crystallinity index of the fibres at low sodium hydroxide concentration. However, high caustic soda concentrations lower the fibre crystallinity index. Thermal analysis of the fibres also indicates reductions in crystallinity index with increased caustic soda concentrations and that grafting of the acetyl groups is optimised at elevated temperatures. Alkalisation and acetylation have successfully modified the structure of natural fibres and these modifications will most likely improved the performance of natural fibre composites by promoting better fibre to resin bonding.     

Influence of cellulose as a filler in vulcanized rubber composites

Composites of elastomers and cellulose have been investigated. Copolymers of styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) as well as natural rubber (NR) were compounded with regenerated cellulose (Cellulose II). The technique for the incorporation of filler was based on the coprecipitation of the rubber latex-cellulose xanthate mixture. Cellulose filler was used in the range of 0 to 30 phr. The best results were shown by the natural rubber-regenerated cellulose systems. The different behavior of the systems is explained by experimental evidence. The reinforcement mechanism for NR compositions, which involves an induced crystallizing rubber (NR), seems to be different from the mechanism for SBR and NBR.     

Importance of fullerenic active sites in surface modification of carbon black by plasma polymerisation

Carbon black is widely used as an active filler in rubber to improve the physical properties. The surface energy of carbon black is high compared to that of various elastomers like Styrene-Butadiene rubber, Butadiene rubber and Ethylene-Propylene Diene rubber. Reducing the surface energy and matching its surface chemistry will aid in compatibilising carbon black with various elastomers. Surface modification of carbon black by plasma polymerisation has been attempted earlier in order to reduce the surface energy of carbon black. These studies have shown that for effective surface modification of carbon black, there should be available a sufficient number of surface active sites. The present paper looks into the possibilities of utilizing the surface activity of a by-product of the production of fullerene, the fullerene soot for its use in a plasma modification process. Thermogravimetric analysis, wetting behaviour with various liquids of known surface tension, time of flight secondary ion mass spectrometry and transmission electron microscopy are used to characterise the carbon black before and after surface modification. The study shows that the fullerenic type structures present on the surface of fullerenic soot act as very active growth sites for the plasma polymer.     

Polyolefins–biofibre composites: A new way for an industrial production

Low density polyethylene (LDPE) composites based on cellulose fibres have been processed by high shear extrusion with water injection to help dispersion of fibres and release nanofibres from cellulose. Influence of extrusion parameters as shear, residence time, storage conditions of the matrix, and effect of water injection on the morphological properties of the composites have been studied using microscopy. Optimization of the extrusion parameters is necessary to reach a dispersion of the fibres. Increasing shearing forces and residence time allows limiting the presence of large aggregates of cellulose fibres. Use of powdered LDPE, even for short residence time and low shear, is efficient to produce well‐dispersed composites. Injection of water during the extrusion also improves the quality of the dispersion. However, no nanofibres are observed. The main effect is a spectacular decrease of the discoloration (yellowing) due to cellulose degradation. Mechanical properties of the composites have been investigated. Young modulus increases with cellulose content and reinforcing effect is more important above 10% by weight. For well‐dispersed composites, the extrusion parameters have no significant influence on the stiffness of the composites. However, due to the weakness of the interface, the ductility of composites is reduced compared with LDPE. POLYM. ENG. SCI., 47:467–476, 2007. © 2007 Society of Plastics Engineers.     

SURFACE MODIFICATIONS AND ADHESION OF VULCANIZED SBR RUBBER TREATED WITH RF PLASMAS OF DIFFERENT GASES

The surface modifications produced by treatment of a synthetic vulcanized styrene-butadiene rubber (R1) with oxidizing (oxygen, air, carbon dioxide) and nonoxidizing (nitrogen, argon) RF plasmas have been assessed by ATR-IR and XPS spectroscopy, SEM, and contact angle measurements. The effectiveness of the treatment depended on the gas atmosphere used to generate the RF plasma. In general, acceptable adhesion values of treated R1 rubber were obtained for all plasmas, except for the nitrogen plasma treatment during 15 min, due to the creation of weak layers of low molecular weight moieties on the outermost R1 rubber layer. A toluene wiping of the 15 min N₂-plasma-treated R1 rubber surface removed those moieties, and increased adhesion was obtained. On the other hand, the air, carbon dioxide, and oxygen plasmas produced ablation of the R1 rubber surface, whereas mechanical degradation was not produced by treatment with the Ar plasma.     

Hybridized reinforcement of natural rubber with silane‐modified short cellulose fibers and silica

Natural‐rubber‐based hybrid composites were prepared by the mixture of short cellulose fibers and silica of different relative contents with a 20‐phr filler loading with a laboratory two‐roll mill. The processability and tensile properties of the hybrid composites were analyzed. The tensile modulus improved, but the tensile strength and elongation at break decreased with increasing cellulose fiber content. The scorch safety improved with the addition of 5‐phr cellulose fiber in the composites. The Mooney viscosity significantly decreased with increasing cellulose fiber content. To modify the surface properties of the cellulose fiber and silica fillers, a silane coupling agent [bis(triethoxysilylpropyl)tetrasulfide, or Si69] was used. The effects of Si69 treatment on the processing and tensile properties of the hybrid composites were assessed. We found that the silane treatment of both fillers had significant benefits on the processability but little benefit on the rubber reinforcement. The strength of the treated hybrid composite was comparable to that of silica‐reinforced natural rubber. Furthermore, to investigate the filler surface modification and to determine the mixing effects, infrared spectroscopic and various microscopic techniques, respectively, were used. From these results, we concluded that the fillers were better dispersed in the composites, and the compatibility of the fillers and natural rubber increased with silane treatment. In conclusion, the hybridized use of short cellulose fibers from a renewable resource and silica with Si69 presented in this article offers practical benefits for the production of rubber‐based composites having greater processability and more environmental compatibility than conventional silica‐filler‐reinforced rubber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Acid hydrolysis of cellulose. part i. experimental kinetic analysis

The main objective of this investigation is to obtain experimental data for the sulfuric acid hydrolysis of cotton and mechanically pretreated cotton fibres. These data indicate that some glycosidic bonds of cellulose have very high accessibility to catalytic ions. It was also shown that milling increases the accessibility of some glycosidic bonds of cellulose and decreases the volume of the crystalline regions of cotton. From the glucose yield versus time data, it was found that the effect of milling on the rate of cellulose depolymerization depends on the reactivity and accessibility of the glycon rings of cellulose. It was also found that at 1OO°C, the rate of cellulose depolymerization was not affected by the extraction of cotton wax and this was related to a rolling up process of cotton wax caused by melting. The kinetic constants of glucose degradation and cellobiose hydrolysis have been determined for the stochastic simulation of cellulose depolymerization which is the subject of the second part of this work.     

Adhesion of RFL-coated aramid fibres to sulphur- and peroxide-cured elastomers

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. But the performance of this substance in many cases can be largely affected due to exposure of the coated fibres to air and light. Moreover, most data available in the literature concern sulphur-cured elastomers only. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength compared to other commercial fibres. The adhesion of these fibres in compounds based on sulphur-cured natural rubber and peroxide-cured ethylene propylene diene rubber is investigated after being coated with RFL which is the most common adhesive coating for various sort of fibres, including aramid. The effect of physical interaction between fibres and rubbers is shown to be minor, and the effect of ageing of RFL on its ability to bond with rubbers using peroxide and sulphur curing systems are shown. As a result of ageing, ozone is able to decrease the double bonds of the latex part of the RFL, which negatively affects the RFL–rubber adhesion in sulphur-cured systems, while it has almost no effect in peroxide-cured systems. It is also discussed that, unlike in sulphur vulcanization in which bonding happens just between the latex in the RFL and rubber, peroxide is able to generate bonds between elastomer and the resin structure of the RFL-coating.     

SURFACE MODIFICATIONS AND ADHESION OF VULCANIZED SBR RUBBER TREATED WITH RF PLASMAS OF DIFFERENT GASES

The surface modifications produced by treatment of a synthetic vulcanized styrene-butadiene rubber (R1) with oxidizing (oxygen, air, carbon dioxide) and nonoxidizing (nitrogen, argon) RF plasmas have been assessed by ATR-IR and XPS spectroscopy, SEM, and contact angle measurements. The effectiveness of the treatment depended on the gas atmosphere used to generate the RF plasma. In general, acceptable adhesion values of treated R1 rubber were obtained for all plasmas, except for the nitrogen plasma treatment during 15?min, due to the creation of weak layers of low molecular weight moieties on the outermost R1 rubber layer. A toluene wiping of the 15?min N₂-plasma–treated R1 rubber surface removed those moieties, and increased adhesion was obtained. On the other hand, the air, carbon dioxide, and oxygen plasmas produced ablation of the R1 rubber surface, whereas mechanical degradation was not produced by treatment with the Ar plasma.