Content: It is acknowledged that conventional chrome tanning in leather processing discharges significant amounts of chromium, dissolved solids and chlorides. The recycling technology is one of the effective solutions to reduce the environmental impact of chrome tanning waste water at source. In this work, a novel closed recycling technology of chrome tanning wastewater was applied in the tanning process of the goat skins at a pilot scale level. The properties of chrome tanning liquors obtained by the recycling technology and the resultant crust were analyzed. The results show that this close recycling process works well. The contents of Cr2O3, total organic carbon, ammonia nitrogen and chloride ion in the waste water tend to accumulate with the increase of recycling times, and finally reach a balance after 5 times of recycling. The obtained leather sample is full, soft and having a shrinkage temperature comparable to that of conventional chrome tanned leather. SEM images indicate that the resulting leather samples by this recycling technology show fine and clean grain and well-dispersed fibrils. TG and DSC results show that the thermal stability of wet blue leathers tanned by the circular process are similar to those tanned by conventional chrome tanning process. Compared with conventional chrome tanning technology, water, salt and chrome tanning agent are saved in this process, and the zero emission of chrome tanning wastewater is realized. The cleaner production technology exhibits promising application prospect for its economic and environmental benefits. Take-Away: 1. A novel closed recycling technology of chrome tanning wastewater was applied in the tanning process of the goat skins at a pilot scale level. 2. The chrome tanning liquors obtained by the recycling technology and the resultant crust were analyzed. 3. Water, Sodium chloride and chrome tanning agent are saved by the closed recycling technology, and the zero emission of chrome tanning wastewater is realized.

Content: In leather making processes, the thermal and non-thermal effect of microwave, especially non-thermal effect, strengthen the combination between collagen and chemicals. Although tanning under microwave makes the leather have better thermal stability, the tanning process and leather properties have not been studied in detail. For illustrating the influence of microwave on chrome tanning process, pickled skin was tanned for 6h as penetration procedure and then basified for another 4h as fixation procedure. The tanning under microwave heating (MW) was experimental sample and under water bath heating was control. UVVis, ICP-OES and pH meter were used to measure the changes of tanning effluent during tanning, and Shrinkage temperature meter, DSC, TG, FT-IR, SEM, XRD and XPS were applied to determine the differences between MW and WB in aspect of leather property and structure. The results indicated microwave accelerated chrome tanning agent penetration and had better promotion effect on chromium complex hydrolysis and olation. The leather tanned with microwave assisting had special effect on improve tanning effect which led better thermal stability and resistance of leather, but the collagen structure, including triple helix structure, stayed as WB and the combination mechanism between collagen and chromium was also same with conventional. In sum, microwave had positive effect on accelerating tanning rate and resulting in better leather without any negative effect on leather structure. Therefore, microwave would be a potential for achieving clean and sustainable chrome tanning by making tanning much faster and more efficiency. Take-Away: Microwave promotes chrome tanning agent penetration and combination Microwave has positive effect on tanning effect further as the leather tanned by microwave assisting has higher thermal stability. Although microwave promotes chrome tanning process, the collagen structure and tanning mechanism remained as normal.

Content: Pre-treatments are widely used during tanning processes as to improve the performance of the main tannage. Synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to study four common types of pre-treatments, viz. monodentate complexing agent (sodium formate, SF), chelating agent (disodium phthalate, DSP), covalent cross-linker (glutaraldehyde, GA) and nanoclay (sodium montmorillonite, MMT) about their effects on chromium-collagen cross-linking reaction during tanning. Based on the results, the performance of chromium-collagen cross-linking with and without pre-treatments was presented considering five aspects: cross-linking, the level of hydration, hydrothermal stability, uniformity through leather cross-section and the uptake of chrome. Comparing to the original ThruBlu chrome tanning, at the same chrome offers, leather pre-treated using SF, DSP and MMT showed improved hydrothermal stability, uniformity and the level of hydration, while GA showed decreased hydration. All of the pre-treatments reduce surface fixation by decreasing the reactivity of chromium with collagen. Changes in the reaction performance can influence the properties of the leather products as well as the efficiency of the leather manufacturing processes. Insights into the structural changes of collagen during tanning with varied reaction conditions can guide the design of novel, benign tanning processes to reduce environmental impact. Take-Away: 1. Uniformity of the hydrothermal stability through leather cross-section were improved by all of the studied pre-treatments. 2. Reactivity of chromium to cross-link with collagen was reduced as a result of the complexing, covalent cross-linking, or preferential adsorption. 3. Complexing agents and nanoclay pre-treatments tend to retain collagen bound water, while covalent cross-linker causing decrease in the level of hydration of collagen.

Content: Leather and leather products are known for its durability and luxuries which makes it more unique among the other synthetic materials. Breathability and visco-elastic properties make leather unique choice of biomaterial. Utilization of leathers in marine based applications is limited owing to reactivity of leather towards salt and weather conditions. Moreover, the choice of raw materials and chemicals used during leather manufacture has greatly influence the properties of the leather. An attempt has been made to understand the influence of sea conditions on leathers. Conventional chrome tanned and vegetable tanned leathers were incubated in sea water and subsequently processed into post tanning to evaluate the physical properties. To understand, the leaching of chemicals, dyed leathers are incubated at different humidity and saline conditions. Interestingly, chrome tanned leathers found to be friendlier to marine conditions whereas, vegetable tanned leathers lead to leaching of chemicals. Furthermore, leaching of chromium is negligible, and crust leathers resulted in soft leathers. Prolonged exposure of chrome tanned leathers under salt stress leads to more softness. This might be due to saline stress to the skin matrix. Moreover, the computability of conventional leather chemicals were also tested using sea water. The research provides a new insight on fine tuning the chemicals to suit marine based applications. Take-Away: A new insight on fine tuning the chemicals to suit marine based applications.

Läder som material har använts av människor i århundraden och är ett av de mest tåliga materialen som finns idag. Detta leder till att det produceras extremt höga mängder läder där den högsta andelen som produceras är kromgarvat läder, som står för cirka 90 procent av den totala läderproduktionen. I och med dagens medvetenhet kring miljö och hur läder påverkar denna efterfrågas alternativa material. Piñatex är ett material där man använt sig av bladen på ananasplantan för att sedan producera ett nonwoven-material som är likt läder, trots att det inte skapats som ett substitut till läder, men användningsområdena är desamma. Piñatex kan vara ett alternativt material när det gäller hållbarhet över tid men även ur miljösynpunkt. I denna rapport är syftet att studera tillverkningsprocesserna för Piñatex, kromgarvat läder och vegetabiliskt garvat läder för att ge ökad förståelse för deras miljöpåverkan. Dessutom utförs materialtester för att se hur de tekniska egenskaperna skiljer sig mellan materialen. Testresultaten i denna studie visar på att materialen har olika för- och nackdelar beroende på vilket test som utförts. Vidare är det svårt att veta exakt hur stor miljöpåverkan de olika tillverkningsprocesserna har, men kromgarvning är den process som med största sannolikhet leder till störst inverkan på miljön. I slutändan handlar ett materials önskvärdhet om preferenser från användarna och i vilket syfte ett material ska användas. / Leather has been used by humans for centuries and it is one of the most resistant materials that exists today. This leads to a high production of leather, where the largest part comes from chrome tanning, which stands for approximately 90 % of the total leather industry. Because of today’s awareness surrounding the environment and how leather affects it, demand for alternative materials are increasing. Piñatex is a material based on the leaves of the pineapple plant, which is turned into a non woven material, looking alot like leather. Although it is not created as a substitute for leather, the areas of use are the same. Piñatex can be an alternative material when it comes to durability but also from an environmental point of view. The purpose of this report is to study the manufacturing processes for Piñatex, chrome tanned leather and vegetable tanned leather to yield a higher understanding for their environmental impact. Futhermore, material testing is carried out to see how the technical properties differentiate between the materials. Test results from this study show that the materials have different advantages and disadvantages depending on which test has been carried out. It is hard to know exactly how big the environmental impact from the different manufacturing processes are, but chrome tanning is probably the one with the highest impact. In the end, the desirability of a certain material all comes down to user preferences and for which purpose the material will be used.

Content: Synchrotron small-angle X-ray scattering (SAXS) technique was applied to leather research to understand the changes in molecular-level collagen structure during tanning and denaturation (shrinkage), which can help reduce the environmental impact from the extensive chrome usage. Based on SAXS results from realtime denaturation experiments on leather samples, we established a mechanistic model of chrome tanning indicated by the structural changes of collagen. It suggests that only a low level of chromium species is effectively involved in the cross-linking with collagen, which highlights the overuse of chrome during conventional tanning processes. Any extra amount of chrome added, however, can support the stabilisation of collagen possibly via a non-covalent mechanism. Such mechanism points towards a more environment-friendly tanning method by using suitable supplementary reagents to benefit tanning effect non-covalently instead of chrome. By pre-treating with complexing agents such as sodium formate and disodium phthalate, as well as nanoclay (sodium montmorillonite), the uniformity through bovine hide collagen matrix were improved significantly. These pre-treatments effectively reduce the reactivity of chromium during its cross-linking reaction with collagen while retaining its bound water. However, collagen pre-treated with a covalent cross-linker (glutaraldehyde) results in a decrease in both chromium-collagen cross-linking and bound water while improving uniformity. These molecular-level insights can be developed into metrics to guide us towards a more sustainable future for the leather industry. The coating on collagen fibrils can provide a pseudo-stabilisation effect of increasing the heat resistance of collagen. A group of tanning experiments were also conducted in situ on the SAXS beamline to observe the different mechanisms of free-of-chrome alternative tannages as potential replacements. Overall, synchrotron SAXS provides valuable information about collagen structure changes that could lead to more efficient use of chrome (or other tanning agents) in the global leather tanning industry. Take-Away: 1. Kinetics of hydrothermal denaturation and collagen crosslinking mechanism proceed through different pathways 2. Alternative chemistries to enhance chrome uptake at low offers. 3. The role of collagen structure studies in understanding tanning mechanims

Content: Tannery effluent with high salinity and chromium have a serious environmental impact. The traditional chrome tannage that involved the use of sodium chloride, acid and chromium is one of the main origins of salt and chromium pollution. In this study, a non-pickling, low-chrome tanning technology was developed. The novel Chrome-free agent SL can be directly employed to tan bated cattle pelts and the wet white was obtained. Then the shaved wet white was pre-treated by Poly-carboxylate auxiliary agent and tanned by chrome powder. It was tested that the shrinkage temperature of the wet white, the initial pH of chrome tanning, the consumption of chrome powder, the shrinkage temperature of the chrome-tanned leather, the content of Cr2O3 in effluent, the absorption of chromium and the other properties of the chrome-tanned leather. It was found that the shrinkage temperature of the wet white tanned by SL reached over 80oC, the optimal consumption of Poly-carboxylate auxiliary agent was 2wt% based on the weight of the shaved wet white, the better low-chrome tanning conditions were that the wet white was tanned by 4wt% chromium powder for 150～180min at room temperature when the initial pH value was 3.5. The next processes were same as traditional chrome tannage. Meanwhile, the shrinkage temperature of the leather tanned by the low-chrome tannage reached more than 95oC, the absorption of chromium was 96%, the content of Cr2O3 in the effluent was under 200mg/L. For the low-chrome tanned leather, the absorption of dyestuff, fat-liquor reached 99.5%, 82.5% respectively. Compared with the traditional chrome tanned process, not only the conventional pickling process was eliminated, the process was been shorten and reduce the pollution of sodium chloride, but it can reduce 50% of the consumption of Chrome powder, improve the absorption of chromium and can reduce content of Cr2O3 in effluent. Take-Away: 1. LUO JIAN-XUN, LI JING, LIAO XUE-PIN,etc.Cleaner Chrome Tanning – A Non-Pickling Process Using an Aliphatic Aldehyde as Pre-tanning Agent. J. Soc. Leather. Technol.Chem. 2012,96 (1):21-26. 2.LUO JIAN-XUN,FENG YANJUAN.Cleaner Processing of Bovine Wet-white: Synthesis and Application of a Novel Chrome-free Tanning Agent Based on an Amphoteric Organic Compound. J. Soc. Leather. Technol.Chem. 2015,99 (4):190-195. 3.XU JIA-LI, LUO JIAN-XUN.Synthesis and application of a polycarboxylate auxiliary agent. China Leather.2017,46(3):35-41.