Stabilization of chromium: an alternative to make safe leathers.

Flame retardant and its influence on the performance of asphalt – A review

Hexavalent chromium release from leather over time natural ageing vs accelerated ageing according to a multivariate approach.

In preparing the second edition of ‘Tanning Chemistry. The Science of Leather.’, the literature was updated and the content was revised and reviewed. Here, the new findings are presented and discussed. Notable developments include the necessary rethinking of the mechanism of sulfide unhairing because of new understanding of the aqueous chemistry of sulfide species. Revision upwards of the value of the second pKa for sulfide species ionisation means that S2− cannot exist in an aqueous medium, so the unhairing species in hair burn reactions is HS−. Although the technology remains the same, this means the mechanisms of associated reactions such as immunisation must be revised. Rawstock preservation has benefitted from studies of the potential role of materials from plants which accumulate salt, but which also contribute terpene compounds. There is also further discussion on the continuing issue of chromium (VI) in the leather industry. The application to processing of new solvents, ionic liquids and deep eutectics, is the coming technology, which offers transforming options for new chemistries and products. Renewed interest in vegetable tanning and methods of wet white processing are current trends. Also, within the topic of reagent delivery is processing in a solid medium of plastic beads.

/pdf/current-trends-in-leather-science-atuw4cuj8t.pdf

Current trends in leather science

Exploration of the binding between ellagic acid, a potentially risky food additive, and bovine serum albumin.

This study assesses the role of hydroxyl radicals (•OH) on the formation of Cr 6+ in leather. To avoid the complexity of composition of chemicals produced in leather fatliquors, •OH produced from the oxidation of lipids in leather fatliquors was replaced by •OH produced by a Fenton reagent. At room temperature, Fenton reagent was reacted with solutions of CrCl 3 , CrCl 3 - benzoic acid, chrome tanning agent and chrome tanning agent-benzoic acid, respectively. The amount of Cr 6+ in each solution was measured at different time intervals. The effect of •OH on the amounts of Cr 6+ was explored and the effect of adding an •OH scavenger(benzoic acid) on inhibiting the formation of Cr 6+ was also studied. Using ultraviolet spectrometry, the molecular structure of benzoic acid was analysed both before and after oxidation by Fenton reagent or potassium dichromate. The oxidization of Cr 3+ by Fenton reagent was initially explored. The results showed that the •OH group can oxidize Cr 3+ to Cr 6+ in both systems of CrCl 3 and chrome tanning agent and the •OH scavenger can inhibit the production of Cr 6+ . When the amount of benzoic acid was 3wt.% of the chrome the Cr 6+ concentration was decreased by 99.3% in 90 minutes.

Oxidation of Cr3+ to Cr6+ by hydroxyl radicals in leather

It is known that the oxidation of Cr(III) into Cr(VI) in leather is caused by the oxidation process of unsaturated oil. Breaking down the oxidation of unsaturated oil with hydroxybenzene [phenol] so as to prevent Cr(III) from oxidizing into Cr(VI) has been investigated In our previous work PVC sponge was used as a reactant carrier, taking advantage of the sponge's porous character similarly to that of leather. The oleic acid, chrome liquid and various phenols such as pyrocatechin, hydroquinone, gallic acid and pyrogallic-oleic acid were absorbed on to the sponge and then placed in a container at constant temperature and humidity to oxidize. The iodine value, peroxide value of oils and the contents of chrome (VI) were determined at regular intervals. The structural changes of oleic acid were analysed by IR. The results showed that phenolic compounds had an inhibitiory effect on the oxidation of oleic acid and so as to influence the oxidation of Cr(III) into Cr(VI); the greater the hydroxyl number of the single ring polyhydroxy phenol, the stronger the inhibitory effect on α-H oxidation, and the less formation of Cr(VI). When the hydroxyl numbers of the single ring polyhydroxy phenols were the same, the o-hydroxy phenol had stronger inhibition than p-hydroxy phenol; meanwhile the structure change of oleic acid indicated that Cr(VI) formation was mainly caused by hydroxyl radicals from a series of radical reactions derived from α-H autoxidation of oleic acid.

Antioxidant effects of phenolic compounds on unsaturated lipids preventing the oxidation of chome (III)

The influence of relative humidity of the environment on the level of Cr(VI) in chrome-tanned leather was studied. The experiments were carried out as follows: a leather sample was cut into pieces which were stored in different relative humidities followed by determination of Cr(VI). Subsequently, these same pieces were stored at different relative humidities followed by re-determination of the Cr(VI) levels. To confirm the influence of relative humidity, pieces of leather soaked in dichromate solution were dried and then subjected to similar treatment as was given to the earlier leather samples. The results showed that there is a close relationship between the stored humidity and Cr(VI) levels in leather. The higher the relative humidity, the lower the level of Cr(VI) and vice versa.

Influence of relative humidity on the level of Cr(VI) in chrome-tanned leather

Mechanism of leather flame retardant was introduced in detail.And several kinds of flame retardants were held forth for making leather fit and clarified requirementsof flame retardant.In the end,methodologies of verification were simply interpreted.

Mechanism of Leather Flame Retardant and Selection of Flame Retardant Materials

This work has broken free from the framework of the traditional leather-making process and taking a new method, has explored the influence of the double bonds of unsaturated lipids on the level of chromium(VI) in chrome-tanned leather The following parameters were controlled during the experiment: temperature, humidity, time and the pH Checking the iodine value and peroxide value of the lipids regularly and determining the structural changes by infrared, the experiment demonstrates the oxidation mechanism of chromium(III) to chromium(VI) by unsaturated lipids in chrome-tanned leather

Yu Congzheng

Papers

Oxidation of Cr3+ to Cr6+ by hydroxyl radicals in leather

Antioxidant effects of phenolic compounds on unsaturated lipids preventing the oxidation of chome (III)

Influence of relative humidity on the level of Cr(VI) in chrome-tanned leather

Mechanism of Leather Flame Retardant and Selection of Flame Retardant Materials

Exploring the Oxidation of Chromium (III) to Chromium (VI) by Unsatured Lipids in Leather