Journal- Society of Leather Technologists and Chemists

We report the dynamic mechanical behaviour of leather within the temperature range - 100 to 300°C, where three major viscoelastic transitions were identified, termed α, β and γ. The β transition peak represents the glass transition temperature of the amorphous region of collagen molecules. It also demonstrates that tanning agents act as plasticisers and depress the glass transition temperature to a lower temperature. Thus, the tanning process itself may be viewed as a plasticisation of the collagen molecule: the tanning molecules interpose themselves between the collagen chains, thus reducing the forces holding the chains together. Different tanning agents show differing degrees of plasticisation.

Chrome tanned bovine leather has been dried under uniaxial strain and its relative bending modulus has been determined as a function of the amount of strain applied during drying and of the angle 0 between the test piece and the applied strain axis (long axis of sample). The orientation distribution of collagen fibres in the leather was also examined using wide angle X-ray diffraction at the Synchrotron Radiation Source at Daresbury. It was found that the bending modulus showed a marked dependence on both the amounts of applied strain and the angle 0. This dependence could be understood in terms of the changes in fibre orientation caused by the action of the strain applied during drying.

The utilization of waste collagen as a filler for the rubber compounds was discussed. It was found that such utilization methods could provide products whose price would make up the costs of raw materials and processing. Difficult wastes from the leather industry can be used to produce a leather powder that can be applied as a filler for synthetic isoprene rubbers. The results show that the vulcanizates of synthetic isoprene rubber containing the chrome tanned collagen as a filler were characterized by a good resistance to ageing.

Leather tanning reactions between collagen and dihydroxynaphthalenes (DHNs) or diphenols and oxazolidine have been investigated using hide powder and sheepskin pickled pelt. This investigation showed that some DHNs have a tanning effect on collagen. The measurement of combined and cross-linked DHNs on collagen showed that 30-40% 1,6- and 2,6-DHNs were fixed through covalent bonding. Shrinkage temperature of the leather changed little after the non combined DHNs had been removed from the leather, indicating that the high stability of the combination tanned leather comes from the covalent bonding formed between DHNs and collagen through oxazolidine.

The drying profile of leathers was investigated by analysing the dynamic mechanical properties. The elastic bending modulus, indicating the stiffness, was monitored as a function of time during drying of partially processed leather over a wide range of isothermal conditions, Different phases of drying are explained in terms of residual moisture content of leathers. It is concluded that the drying temperature does not contribute to the stiffness, which is actually controlled by the residual moisture content.

This article was published in the journal, Journal of the Society of Leather Technologists & Chemists [© SLTC] and is also available at: http://www.sltc.org/ Liquid epoxide resins have an obvious potential as collagen crosslinkers, in particular as alternatives to the aldehydic-types used. In the work reported here, some conditions for the effective use of epoxides in tanning systems have been studied and identified based on hide powder trials. Few commercial aromatic epoxides are found to be water-soluble, and also have relatively low reaction rates, proving another disadvantage. In a series of screening tests, it has been found that an epoxide with aromatic groups in its backbone, used to treat collagen, produces higher hydrothermal stability than that treated with aliphatic epoxide. However, of the commercial aliphatic epoxide resins examined in this research, the water-soluble, tetra-functional pentaerythritol polyglycidyl ether, (e.g. Denacol EX 411), has been shown to be suitable for the leather tannage applications. Different types of waterborne epoxide resins, including emulsion and emulsifiable resins based on BDEGA (bisphenol A diglycidyl ether), have been examined but gave disappointing results. It is thought that difficulties here lie in trying to achieve good penetration into the collagen’s fibrous structure, of the particles that make up such emulsions. Late stage tannage, giving a leather product with high shrinkage temperature (Ts = 85ºC) has been achieved; here the system required catalyst to produce acceptable conversion within 3 hr at 50ºC. The important factors influencing the effectiveness of a particular tannage, are discussed.

This article was published in the journal, Journal of the Society of Leather Technologists & Chemists [© SLTC] and is also available at http://www.sltc.org/ An understanding of both the reactive functions of epoxide resins and collagen, suggests that some epoxides could be effectively used in organic tannage systems. As such epoxides may be regarded as alternatives to aldehydic tanning systems, having lower toxicity combined with specific polymerization ability. The commercial and technical potential of epoxides as tanning agents are assessed in this review paper. To this end, an introduction to epoxide chemistry is provided based on the tanning chemist’s viewpoint. The literature survey describes epoxide-protein/collagen addition reaction mechanisms and their kinetics, which in turn are discussed with respect to the potential for future work, where these resins will be utilised in novel tanning technology. The potential risks associated with epoxides and modifications to conventional techniques of tanning, are also discussed.

The recovery of keratin from tannery wastes as a filler for rubber mixes is discussed. It is found that the loading of tannery effluents can be reduced by the separation of keratin. The advantage of the examinations performed is the reduction of pollutants in the leather industry. The optimal content of keratin, to use as a filler in rubber mixes, is also determined.

In the present work, Reactive Red 120-attached poly (2-hydroxy ethyl methacrylate) nanoparticles (PHEMA-RR120) were synthesized as an adsorbent for the removal of the proteins albumin and globulin. PHEMA nanoparticles were first prepared by surfactant-free emulsion polymerisation. The dye ligand Reactive Red 120 was chemically attached to the PHEMA nanoparticles via a nucleophilic substitution reaction. Characterisation of the PHEMA-RR120 nanoparticles was carried out by specific surface area, dry mass weight of the nanoparticle, SEM, FTIR and Zeta Size analysis. Albumin and globulin adsorption of PHEMA-RR120 nanoparticles was investigated with respect to process conditions (temperature, pH, time, initial concentration and ionic strength), and the re-usability of PHEMA-RR120 was also determined. The albumin and globulin protein adsorption of PHEMA-RR120 nanoparticles was found to be respectively 24.60g/g and 3.95g/g at 25°C, 12.58g/g and 3.86g/g at 37°C, 11.45g/g and 2.69g/g at 45°C. The results show that PHEMA-RR120 nanoparticles can be used for the effective, reusable removal of albumin and globulin due to their large surface area and high adsorption capacity. © 2019 Society of Leather Technologists and Chemists. All Rights Reserved.

Certain factors influencing the biodegradation of valonia tannin, ellagitannin, by Endomyces SHQ14 are investigated. The degradation rate of valonia tannin and removal of chemical oxygen demand (COD) are both maximized in a medium containing 25g.l.-1 valonia tannin by shaking the culture at 120 rpm and incubating it at 28°C and pH 4.5-5 for 8 days. Additional carbon sources, particularly sucrose, support the degradation of valonia tannin. Peptone is found to be the most suitable nitrogen source. It is verified that the proper ratio of carbon (sucrose) to nitrogen (sodium nitrate) for the degradation of valonia tannin is about 10:1. Four kinds of compounds that may affect the degradation process were selected for this study; namely, an inducer 2,2'-azinobis (3-ethylbenzothiazolin-6-sulfonic acid) (ABTS), an inhibitor, EDTA and two surfactants SDS (sodium dodecylbenzene sulphonate) and Tween-80 (Tw-80). Note: Tween-80 is polyoxyethylene sorbitan monooleate ester with an HLB value of 14 which is used as an emulsifier / surfactant. The biodegradation process is found to be stimulated by 0.3 × 10-3 M inducer ABTS and 0.2 g.l-1 surfactant Tween-80 and SDS, but is inhibited by EDTA.

In the leather industry, shrinkage temperature (Ts) is determined by the IUP 16 method. However, only microanalytical techniques like the Microscopic Hot Table (MHT) method are appropriate for the Ts of leather objects of historical value. No more than 0.1-0.4mg of sample is needed for the test. The precision and accuracy of the MHT method were investigated taking the official IUP 16 method as a reference. It was concluded that the Ts determined by both methods are in good agreement. The MHT method is precise and sensitive enough to state that small changes of 1.3°C detected in Ts are statistically significant. The method was successfully applied to determine the Ts of several artefacts of the Leather Museum of Igualada.

The retanning process is the main application of formaldehyde in the tanning industry since formaldehyde participates in two groups of synthetic organic tanning agents: syntans and resins. Resins can be hydrolysed with the result that formaldehyde is released. Thus, formaldehyde in leather can be free or from hydrolysis of resins. Due to the carcinogenic character of formaldehyde, its presence in leather should be avoided or should be below allowable limits. The EN ISO 17226 Standard is the Official Standard for the determination of formaldehyde content in leather, which, in the authors' opinion, presents certain ambiguities in the wording of some operations included in their analysis methods and, some of these operations, are susceptible of improvement. Therefore, a revision of the EN ISO 17226 Standard (Parts 1 and) 2 is carried out in this work and, in particular, of the extraction phase of formaldehyde present in leather (possible use of alternative surfactant and shaking method); reaction time between the extracted formaldehyde with the dinitrophenylhydrazine solution (Part 1 of the Standard) and stability of the acetylacetone solution (Part 2 of the Standard). © 2016, Society of Leather Technologists and Chemists. All rights reserved.

The customary diphenylcarbazide (IUC-18) procedure and several modifications thereof have been studied with a view to accommodate coloured extracts and to improve the sensitivity of the procedure for determining the concentration of hexavalent chromium in leather samples. The unmodified IUC-18 procedure is generally inapplicable to leather samples that produce a coloured extract. Even otherwise, the sensitivity of the IUC-18 procedure is limited. We propose here a pre-bleaching procedure that allows reliable analysis of the majority of the samples studied based on results obtained with Induction Coupled Plasma-Optical Emission Spectrometry (ICP-OES) of cation exchanged samples as the reference method. A liquid core waveguide based flow-through absorbance detector deployed in a flow injection format was utilized to significantly improve on the sensitivities normally attainable in the diphenylcarbazide method. Ion exchange of the samples through H+-form cation exchangers has also been found to be essential to prevent gross overestimation of the Cr(VI) concentrations, presumably the interference occurs from the presence of other metals in the extract. Concentrations of Cr(VI) in cation exchanged, bleached leather extracts as low as 1 μg/1 can be readily measured with inexpensive equipment.

In an overview, from the earliest developments of mechanical aids, to sophisticated processing equipment, the rise of machinery within leather manufacture and the interaction of early leather trades' engineers is discussed. The importance of splitting machine development is emphasised as a precursor to the more general introduction of machinery within leather manufacture. Significant British, German and American leather trades' engineers are identified along with their contributions to machinery development. In Part II the impact of early American designed machinery and the principal role of leading British tanners in bringing patented machinery to the British market is also highlighted.

Part II of this paper continues the overview, from the earliest developments of mechanical aids, to sophisticated processing equipment, the rise of machinery within leather manufacture. Attention is turned to American engineers and their role in machinery manufacture and development. The links between US and British engineers are described. The impact of early American designed machinery and the principal role of leading British tanners in bringing patented machinery to the British market is also highlighted. To assist the reader to link the two parts of the work, the figure and reference numbering has been continued from Part 1.

This paper traces the rise of an internationally important engineering concern developed by the Vaughn family in Salem and Peabody, Massachusetts (MA), United States. Initially established to serve the needs of a specific local industry, the Vaughn Morocco Machine Co. Was started in the early 1880s by JosephWarren Vaughn and his three sons. The business name was changed to the Vaughn Machine Co. In 1892, after the company had expanded its sales more generally into leather manufacture. New machinery developments and continuous improvement of the ?Vaughn' product range are detailed and illustrated; machinery which would eventually instigate major changes in leather manufacture worldwide. European demand for the company's equipment justified a sales and service depot being established in Germany with satellite marketing and repair branches in France and Britain. Part 2 pursues new machinery developments and the rise of a specific engineering rival. This new competitor combined with a different approach by management at the Vaughn Machine Co. Ultimately led to the formation of new challenger-the Vaughn-Rood Machine Co. © 2018 Society of Leather Technologists and Chemists. All rights reserved.

The rise of a specific rival to the Vaughn Machine Co. is considered along with major changes in management at the internationally important leather trade engineer, based in Peabody, Massachusetts (MA), United States. By emphasising the essential role of George C. Vaughn in tanning machinery development, it establishes why a new contender – the Vaughn-Rood Machine Co., became a major challenger. It also reflects on the interesting account of how wrangles in the US Courts resulted in the transfer of patents and machinery designs, from the Vaughn Machine Co., to the Turner Tanning Machinery Co. Survival of the old established Vaughn business demanded a change from leather trade machinery into the expanding automotive sector. For a time this seemed to fill the void for the engineering concern. Demise however, soon followed. Subsequent to the brief history of the Vaughn-Rood Machine Co., the paper concludes with the agreed takeover of this business, also by the Turner Tanning Machinery Co., and some of the later enterprises pursued by George C. Vaughn. © 2018 Society of Leather Technologists and Chemists. All Rights Reserved.

Practices in the tanning industry may result in the occurrence of possible damage on the grain surface and grain layer that can spoil the quality of leather. The so called 'large follicle defect,' a natural damage associated with the characteristics of coat and the hair growth cycle, is a defect attracting the attention of researchers because of its morphological characteristic distribution and periodicity in wet-blue, semi-finished, finished, full grain and corrected grain leathers. Due to the lack of information on this defect in journals concerning leather making and to the need to understand the nature of the defect with the purpose of guiding process modifications to minimize its adverse effects, follicle rhythm and details are considered in this report. Knowledge of hair follicle activity and the correlation between coat shedding and the. variation in environmental conditions during the seasons of the year consolidate the hypothesis that the defect is associated with the natural process of hair shedding. This is particularly observed in the phase during which shedding reaches its maximum levels and it is related to the hair deeply anchored in the grain layer during the progress of the Telogen and the Anagen phases (evolution of the shedding hair and expulsion of inactive hair).

This paper analyses information pertaining to notifications of unsafe leather goods submitted to the EU Rapid Exchange of Information System (RAPEX) in the years 2004-2017. The number of leather goods reported in the system has been compared to total number of notifications on dangerous products classified in the category ?Clothing, textiles and fashion items' that includes leather goods. The notifications were analysed for the country of origin of leather goods as well as for the notifying country. This allows identification of countries from which the largest number of dangerous leather goods come, i.e., China, India and Pakistan, as well as countries most active in detecting them in their own domestic markets, i.e., Germany, Spain and Estonia. The article presents also results of surveys related to opinions of Polish consumers towards the safety of leather goods they purchase as well as their awareness about the presence and functioning of the RAPEX system. The research showed that most of Polish consumers cannot clearly indicate whether the leather goods they buy are safe for health or not. Moreover, most of Polish customers have no knowledge of the presence and functioning of the RAPEX system. © 2018 Society of Leather Technologists and Chemists. All rights reserved.

The main causes of deterioration of leather are reviewed, particularly with reference to museums and other heritage collections. Damage caused by bacteria, fungi, insects and vertebrates is described, as are the methods of eradication. Physical damage arising from the hygroscopic nature of leather and other skin products is discussed. The factors leading to the type of chemical decay termed red rot are analysed and the role of oxidation and hydrolysis is considered. The final section deals briefly with the treatment of chemically degraded leather with aluminium alkoxide.

Tannery sludge can contain 70% of organic substances which can have applications as a high-quality fertilizer, however, too high levels of chrome are a major obstacle for tannery sludge in agricultural applications. In this experiment, a study on chrome migration, transformation and resultant chrome levels has been done in the laboratory and expanded to using tannery sludge compost on agricultural land. These studies offer theoretical support for using tannery sludge. The experimental study shows that when Cr3+ levels in soil reach 250mg/kg, the plant absorption of chrome reaches the maximum value, which is 23.33mg/kg. The evidence shows that chrome loading of paddy field soil should be controlled to 350mg/kg.

The role of this lecture is to pay tribute to Henry Richardson Procter, one of the most famous leather scientists. I am, therefore, as a scientist and teacher in tanning technology, deeply honoured by the invitation of SLTC to give the Procter Memorial Lecture today. This is also a pleasure because of the cooperation between Great Britain and Germany in the field of leather technology, especially at this time of increasing collaboration between the British School of Leather Technology (BSLT) and the Lederinstitut Gerberschule Reutlingen (LGR).

The appropriate conditioning time before testing of leathers was discussed. The 48 hour conditioning prior to testing for leathers supplied from areas of relatively low humidity is excessive. Leathers that are from areas of high humidity require times in excess of 48 hours. Leather with a high moisture content pass a lastometer test more easily.

Among the novel collagen crosslinkers currently being studied, polyepoxides (e.g. based on aliphatic polyol glycidyl ether), have shown certain potential in organic tannage applications. The work reported here is a comparison of the tanning abilities of some commercial epoxides with commonly used organic tanning agents, i.e. glutaraldehyde, oxazolidine and THPS. Studies have been based on the progress of tannage followed via crosslink density determination of treated gelatine (i.e. used as a collagen model). The investigation has also been concerned with comparing the physical, chemical, biological and morphological characters of the resultant leather. The results show that the order of tanning ability to be: THPS > oxazolidine > glutaraldehyde ≫ epoxide. Epoxide, when used alone, is a fairly weak crosslinker of collagen and has to be used in relatively large quantities (an offer of 20% of skin weight). The epoxide has a slow reaction rate at room temperature and the resulting leather has lower hydrothermal stability (82°C) with a lower reacted amine content and tensile strength. However, this epoxide treated leather has high apparent density, moisture content and anti-trypsin degradation ability. The differences in tannage mechanisms for these reagents are discussed, in order to interpret the limitations of this type of epoxide.

The emerging new applications of thermochromic pigments in leather industry could give a promising opportunity to create innovative designs of smart thermochromic leathers and these leathers are well known with their colour changing effect depending on thermal activation temperature of the thermochromic pigments. A long product life is also needed for thermochromic leathers due to the demand for additive use which will enhance the fastness properties of the microencapsulated thermochromic pigments. This study aimed at increasing the light and rubbing fastness values of the leathers that change colour with temperature. Touch (magenta; 31°C) and cold (blue; 15°C) activated two thermochromic pigments were used in order to provide the colour change of the finished leathers. UV absorbent and cross-linking chemical additives were used along with thermochromic pigments in the finishing procedure to increase the fastness properties of the leathers. Colour change features, rubbing and light fastness properties of thermochromic leathers were analysed by a spectrophotometric method in addition to ISO standards of related fastness properties. The use of a UV absorbent in the finishing procedure lead to an increase in the light fastness values of touch and cold activated thermochromic leathers. Likewise, it was revealed that the use of cross-linker in the top coat of finishing process improved the rubbing fastness properties of thermochromic leathers.

Besides quality in leather manufacture, another important factor is that the customer should use the product in the long term without any problem. However, a leather product, being a natural structure, can age because of environmental conditions such as UV, temperature, and humidity, and its chemical and physical structure can change with time. Some leather products in particular such as upholstery leathers which are exposed to sunlight can be aged and yellowed by the effects of UV light and temperature. Therefore, there is a need to prevent ageing and yellowing. UV absorbers are often used in various products such as cosmetics and polymeric materials to prevent the destructive effects of ultraviolet radiation. The aim of this work was to study use of the UV absorber benzophenone-4 in reducing yellowing. Chrome-tanned and vegetable-tanned crust leathers were given a coating of hydro lacquer [lacquer emulsion] including the UV absorber benzophenone-4 as a finishing process. After exposure to monochromatic UV light at a wavelength of 340nm for 24, 48, 72, 96, 120, 144 or 168 hours at approximately 80 degrees C. The results were investigated by CIE Lab Colour measurement and by FTIR-ATR spectrophotometer.

The effect of ultraviolet absorbers on the stability and quality of nitrocellulose topcoats on leather was investigated. Stabilisation was carried out with three differently substituted hydroxybenzophenone derivatives. Samples from unstabilised and stabilised nitrocellulose coated leather were simultaneously exposed to a monochromatic UV light of 300nm wavelength for a maximum period of 168 hours. Results of analysis of the products show that the stabilisers impart good resistance to UV degradation to the nitrocellulose finish on the leather. The stabilisation also improved the adhesion of finish, light fastness, flexing endurance, dry rub fastness and heat fastness properties of the top coated leather. Di substituted hydroxybenzophenone was found to be most effective.

Gelatin is used as a model for collagen, chloroacetic acid is a good candidate as a modification agent to introduce additional carboxyl groups with methanol being used as a termination agent to block carboxyl groups - using these parameters, we investigated the effect of the carboxyl group content of collagen on the chromium(III) absorption. When Gelatin is modified with chloroacetic acid or methanol, the Zeta potential decreases from 4.8 to 2.8 for the former and increases from 4.8 to 6.2 for the latter also, the total organic carbon (TOC) contents increase by 9% and 12%, respectively. Studies on chromium(III) absorption reveals that hide powders modified in the same way show quite different chromium(III) absorption capacity, for the carboxyl-group-added samples the maximum absorption capacity of chromium (III) (Amax) increased from 42.44mg/g to 87.65mg/g (Cr3+/collagen) at 40°C at pH=4. The carboxyl-group-blocked samples lose their affinity for cationic chromium due to the inactivation of carboxylic groups, the Amax decreased from 42.44mg/g to 16.34mg/g under the same conditions. Further study indicates that the action of blocking carboxyl-groups or adding carboxyl groups only changes the chromium absorption capacity and does not change the traditional chromium tanning mechanism, the effects of pH value, temperature and time on the chromium absorption process are still as the same as for the traditional chromium tannage.

In this paper, volatile low molecular weight aldehydes and ketones in samples of leather shoes were collected by static absorption with water, analyzed and detected by 2,4dinitrophenylhydrazine precolumn derivatization of high performance liquid chromatography(HPLC). Firstly, the sampling temperature and time of the volatile aldehyde and ketone in leather shoes were optimized and then the volatile aldehyde and ketone in absorption liquid were determined. The experiment result shows that the optimal temperature is 45°C, the sampling time is 24 hours. The collected sample was derivatized by purified sulfuric acid acidulated 2,4dinitrophenylhydrazine. The volatile aldehydes and ketones in absorption liquid of leather shoes were formaldehyde, acetaldehyde, acetone, propionaldehyde, butyraldehyde, benzaldehyde, cyclohexanone and hexanal. the average concentrations of which are: 0.252mg/shoe, 0.061mg/shoe, 0.079mg/shoe, 0.053mg/shoe, 0.037mg/shoe, 0.011mg/shoe, 0.09mg/shoe, 0.018mg/shoe respectively. This method is suitable for determination of volatile aldehydes and ketones in leather shoes.

In this article, the influence on finished leather properties of five different waterproofing agents has been examined. Wet-salted bovine hide (weight category 35 kg) was treated in an half-industrial environment by conventionally used liming, tanning and retanning processes. 9% offers of five different waterproofing agents were used for the waterproofing process. The levels of water vapour, fats, ash and Cr2O3 were determined for the crust leather. The water vapour permeability, leather porosity to water vapour and absorption of water (measured on both the Kubelka apparatus and the Bally penetrometer) were determined. The water repellency properties of each waterproofing agent were estimated from the results.

The relationship between the single technological parameter and chrome absorptivity [percentage of total chrome absorbed] based on laboratory tests and process manual data was studied. Stepwise regression analysis was employed to obtain the quantitative correlation between tanning parameters and chrome absorptivity, on the basis of establishing a relationship between multi-process parameters and comprehensive factors of chromium binding capacity using commercial tanneries actual measurements as contrast. The results showed that, the quantitative calculation of chrome absorptivity through technological parameters could absolutely reflect the actual situation in the tanning process amongst the multiple steps in the heterogeneous and mixed systems contained in the leather making processes.