| Leather as a kind of natural polymer composite material which is processed by a series of physical and chemical methods,plays an important role in human life.After treatments,the thermal properties,softness,twists and turns resistance,tear resistance,weather resistance and storage stability of raw hide have been significantly improved.Among them,the thermal properties of leather are particularly important,which affect the processability,durability and functionality of leather in industry.The study on the thermal degradation kinetics of leather and collagen has significant value on high-performance leather.It also provides an important theoretical basis for the pyrolysis treatment and recycling of leather wastes,the identification and protection of leather cultural relics.But in the previous work,there are less systematic analysis of the kinetic behavior of leather products,and also lack of kinetic mechanism of leather and collagen within.In this paper,the pyrolysis behavior and mechanism of several kinds of leather and leather waste were studied by means of kinetic analysis,including:the pyrolysis mechanism of cashmere samples and leather samples in different processes was studied by means of iso-conversion method and master-plot method;the method of simulating the thermokinetic parameters of chromium waste by means of simulated annealing algorithm and global optimal annealing algorithm was put forward innovatively;and the effects of graphene oxide and nano silver on the thermal properties of leather were studied.The details are as follows:1.Thermogravimetry?TG?was used to characterize the weightlessness of sheep fur waste samples in nitrogen atmosphere at different heating rates.TG results showed that the degradation process of the samples was divided into three stages.The apparent activation energy?E?of the main pyrolysis stage is 275.6 k J/mol calculated by the improved Kissinger-Akahira-Sunose?MKAS?method.Due to the pyrolysis process of sheep fur waste can not be described by one-step reaction,the experimental differential thermogravimetry?DTG?curve of sheep fur waste is deconvoluted into three independent peaks,and then the TG curves corresponding to the three pseudo-components are reconstructed.The average activation energy of these pseudo-components were 234.7 k J/mol,176.4 k J/mol and 186.2 k J/mol,respectively.The generalized principal curve method shows that the pyrolysis process of sheep fur waste samples may follow the random nucleation growth mechanism?Am?.The reaction model functions f???of these pseudo components are respectively expressed as:f???=3.1?1-??[-ln?1-??]0.67?f???=3.6?1-??[-ln?1-??]0.72and f???=3.9?1-??[-ln?1-??]0.74.2.In nitrogen atmosphere,the leather samples of raw hide,tanned,retanned and fatliqued leather sample were analyzed by TG at heating rate of 5,10,20,30°C/min.The average activation energies of the four samples were 163.8 k J/mol,385.4 k J/mol,332.5 k J/mol and 345 k J/mol,respectively.Thermal degradation of leather samples after tanning,retanning and fatliquoring can not be described by one-step reaction,so the DTG curvea are divided into two peaks by deconvolution,respectively.The results show that the kinetic process of each single peak after peak separation is most likely described by Avrami erofeev equation?Am model?in the integral form of g???=[-ln?1-??]0.1,which shows that the kinetic models of these pseudo-components follow the random nucleation and growth mechanism.Scanning electron microscopy?SEM?and energy dispersive X-ray?EDX?were used to analyze the morphology and composition of tanned,retanned and fatliquored leather samples.The evolution of gas products was identified and analyzed by TG-FTIR.3.The pyrolysis of chrome shavings is one of the most important methods for the harmless treatment of leather waste.Based on the compound kinetic method,the pyrolysis kinetics of chrome shavings was studied.By using the analysis of the thermogravimetric data of chrome shavings by simulated annealing algorithm,it is found that the optimal reaction mechanism of one-step pyrolysis of chrome shavings is348.4 k J/mol.Due to the pre-exponential factor is not a fixed value,the pyrolysis of chromium wastes can not be described by a simple one-step reaction.The experimental data of pyrolysis are well fitted by using the three parallel reaction model of composite kinetics.The reaction mechanism of three pseudo components is f???=?-4.2?1-??4.4[-4.The effect of graphene oxide on the thermal stability and decomposition kinetics of raw hide powder and the effect of nano silver on the thermal properties of wet blue leather were studied by thermogravimetry.The results show that raw hide powder doped with graphene oxide?GO-HP?does good in thermal stability.The activation energies of GO-HP and raw hide were 283.30 and 226.88 k J/mol,respectively.The comparn of the experimental and theoretical curves showed that when the conversion was lower than 0.5,the most likely decomposition mechanism of raw hide powder and GO-HP was D1.Above 0.5,the decomposition mechanism of raw hide powder and GO-HP is most likely to be described by A3 and R3 models respectively.The addition of nano silver decreased the thermal stability of leather,and the activation energy was 293.4 k J/mol,which was less than 385.4 k J/mol of blue wet leather.This may be due to the existence of nano silver particles play a role of thermal catalysis,which makes leather materials more prone to degradation under the effect of heat. |
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