【作者】 曾慧；

【导师】 石碧；

【作者基本信息】 四川大学 ， 生物质化学与工程， 2021， 硕士

【摘要】 铬鞣法是目前制革工业中最成熟、产品质量最可靠、应用最广泛的鞣法。然而受传质和化学反应平衡的限制,使用传统铬鞣法鞣制皮革时铬鞣剂的吸收利用率只有65%⁷5%,导致铬鞣废水中铬含量远超国家排放标准。大量排放的铬不仅会导致环境污染,也造成了铬资源的严重浪费。近年来,无铬鞣剂的研发与应用一直是制革领域的研究热点,但现有的无铬鞣剂在实际应用中尚存在诸多不足,其中最常见的问题是无铬鞣剂所制鞣革的湿热稳定性较低。鉴于铬鞣革具有其它鞣革难以比拟的优良性能,因此开展高吸收清洁化铬鞣研究依旧是实现制革清洁化和可持续发展的有效途径。本研究首先初步构建了两步升温鞣制工艺。第一步对裸皮进行预鞣以获得一定的湿热稳定性,第二步则升温鞣制3 h以促进铬鞣剂与皮胶原充分反应,从而提高铬鞣剂的吸收利用率和鞣制效果。以铬鞣革的收缩温度（Ts）、Cr₂O₃含量、铬鞣剂的吸收利用率、粒面的细致程度及力学性能等性能为指标,对比了常规鞣制、两步常温鞣制和两步升温鞣制三种不同工艺所制鞣革的差异,并考察了第一、二步鞣制工艺的铬鞣剂用量配比及第二步鞣制温度对两步升温铬鞣法鞣革性能的影响规律。研究发现:当第一、二步铬鞣剂用量配比为2%:4%,第二步升温鞣制温度为60℃时,铬鞣革的Ts由常规铬鞣革的107.2℃提高至118.8℃;铬鞣剂的吸收利用率由69.8%提高至91.3%;铬鞣革的综合性能最佳。在此基础上,进一步优化了第二步鞣制时铬鞣剂的用量。最终确定两步升温铬鞣技术的最佳铬鞣剂用量配比为2%:2%,第二步最佳鞣制温度为60℃。在此条件下,铬鞣革的Ts为111.1℃;铬鞣剂的吸收率为95.7%;铬鞣革的Cr₂O₃含量为24.24 mg/g。上述研究表明,通过两步升温铬鞣技术可以达到“高吸收,少铬鞣”的目标。为了进一步提高两步升温铬鞣工艺的清洁化效果,对两步升温铬鞣法中第二步鞣制的升温时间进行了优化。通过研究模拟鞣制升温时间对铬鞣液的pH值、平均水解配聚速率、电导率、铬鞣液的紫外可见吸收光谱（UV-Vis）和傅里叶红外吸收光谱（FT-IR）的影响规律,探究了升温时间对铬鞣液中铬配合物的水解配聚程度和配合物的结构造成的影响。同时以铬鞣革的Ts、Cr₂O₃含量、铬鞣剂的吸收利用率、粒面细致程度及力学性能等为指标,探究和考察了第二步鞣制过程的升温时间对两步升温铬鞣法鞣革性能的影响。研究发现:升温后,铬鞣液中鞣剂的水解配聚速率加快,水解配聚程度增大,使铬配合物的结构更加稳定。这使得升温鞣制的铬鞣革的湿热稳定性更高,铬鞣剂在革内的分布更加均匀,铬鞣剂的吸收利用率更高,鞣剂与胶原纤维的交联程度更大。在第一步和第二步鞣制均采用2%铬鞣剂的条件下,第二步鞣制时将升温时间控制在1.5 h内,能够提升多项鞣制性能。铬鞣革的Ts大于105°C;革中Cr₂O₃含量在30 mg/g左右;铬鞣剂吸收利用率大于90%;铬鞣革的热稳定性、力学性能等均得到提高,且不存在粗面问题。在此条件下,第二步鞣制的升温时间由3 h缩短至1.5 h以下,既降低了工艺能耗,又提升了鞣制效果,进一步提高了两步升温铬鞣法的清洁化程度。此外,研究了在两步升温铬鞣法第二步鞣制工艺的鞣制末期（提碱后）升温对鞣制效果的影响。首先探究和考察了模拟鞣制末期升温及不同升温时间对铬鞣剂的水解配聚反应造成的影响。并以典型的鞣制性能参数为指标,研究了鞣制末期升温以及升温时间对两步升温铬鞣法鞣革性能的影响。研究发现:采用鞣制末期升温的方法,能够提高铬鞣剂的吸收利用率和铬鞣革的湿热稳定性等性能。但由于铬鞣剂的水解配聚程度过大,导致铬配合物分子尺寸过大,收敛性过强,引起铬鞣革的粒面平细度、纤维分散程度以及力学性能下降,铬鞣革的整体鞣革性能不理想。综上所述,两步升温铬鞣法的优化工艺参数确定为:第一步预鞣和第二步升温鞣制的铬鞣剂用量配比2%:2%,在第二步先常温鞣制,后升温至60℃鞣制0.5¹.5 h。在此条件下,铬鞣革的Ts大于105°C;革中Cr₂O₃含量在30mg/g左右;铬鞣剂吸收利用率大于90%;铬鞣革的热稳定性、力学性能等均得到提高,并且粒面均匀细致。通过本研究发现,两步升温铬鞣法能够实现“高吸收,少铬鞣”的目标,综合鞣革性能优良,该工艺技术具有一定的应用前景。更多还原

【Abstract】 At present,chrome tanning is the most mature,reliable and widely used tanning method in leather industry.However,due to the limitation of chemical mass transfer and chemical reaction equilibrium,the absorptivity of chrome tanning agent in leather is only 65 % 75 % under the traditional tanning conditions,which leads to the chrome content in chrome tanning wastewater far exceeding the national discharge standard.The chrome emission in leather industry will not only lead to the pollution of environment,but also cause serious waste of chrome resource.Thus,in recent years,the research and development of chrome-free tanning agents have always been the focus of tanning field.However,there are still many shortcomings in the existing chrome-free tanning agents,such as low hydrothermal stability（Ts）of chrome-free leather.In view of the excellent properties of chrome tanned leather,it is still an effective way to realize the clean and sustainable development of leather industry by researching on high-absorption and clean chrome tanning.In this study,a two-step temperature change chrome tanning process was initially established.In this novel technology,the pickle hide was pre-tanned at first step to obtain basic hydrothermal stability,and then tanned under higher temperature for 3 h in the second step to promote the full reaction between chrome tanning agent and collagen,thus improving the absorptivity of chrome tanning agent and the tanning effects.The differences of chrome tanned leathers made by conventional chrome tanning,two-step chrome tanning under normal temperature and two-step temperature change chrome tanning were compared based on their shrinkage temperature（TS）,Cr₂O₃ content,grain surface fineness,mechanical properties,distribution uniformity of chrome,and tanning effectiveness.The effects of the dosage ratio of chrome tanning agent in the first and second steps,and the tanning temperature in the second step on leather properties were investigated.The results showed that,when the dosage ratio of chrome tanning agent was 2 %:4 %,and the tanning temperature in the second step was 60 ℃,the Ts of chrome tanned leather increased from 107.2 ℃ to 118.8 ℃,and the absorptivity of chrome tanning agent increased from 69.8 % to 91.3 % in comparison with traditional chrome tanned leather.Meanwhile,the comprehensive properties of leather are satisfactory.On this basis,the dosage of chrome tanning agent in the second step was further optimized.The optimal dosage ratio of chrome tanning agent in the first and second steps was determined to be 2%:2%,and the optimal tanning temperature in the second step was 60 ℃.Under these conditions,Ts of chrome-tanned leather is 111.1 ℃.The absorptivity of chrome tanning agent was 95.7 %.The content of Cr₂O₃ in chrome tanned leather is 24.24 mg/g.These results indicate that the two-step temperature change chrome tanning process can realize the objective of less-chrome tanning with high absorption.In order to make the two-step temperature change chrome tanning process more effective,the heating time in the second step was optimized.Firstly,the influence of simulated heating time on properties of chrome tanning liquor were investigated,like pH change of solution,average hydrolysis and polymerization rates of Cr complexes,conductivity,UV-Visible absorption spectrum（UV-Vis）and Fourier infrared absorption spectrum（FT-IR）.Then the effect of the heating time in the second step on the degree of hydrolysis and polymerization and chemical structure of chrome complexes in chrome tanning liquor was explored and surveyed.In addition,the effects of various heating time in the second step on the leather properties were investigated based on the indexes of thermal stability and mechanical properties of leather,and absorptivity of chrome tanning agent.It was found that heating led to increase of hydrolysis and polymerization rates of Cr in chrome tanning liquor,which made the chrome complexes more stable.Therefore,tanning under heating produced leathers with higher Ts and more uniform chrome distribution,accompanied by higher absorptivity of chrome tanning agent and more efficient cross-linking of collagen fiber.By using 2% chrome tanning agent in the first and the second steps respectively,most of leather properties were improved when heating（60 ℃）time in the second step was within 1.5 h.Under these conditions,the Ts of chrome tanned leather was greater than 105 °C.The content of Cr₂O₃ in leather was about 30 mg/g.The absorptivity of chrome tanning agent was more than 90 %.The thermal stability and mechanical properties of leather were also considerably improved while fine grain was presented.Obviously,energy consumption of the two-step temperature change chrome tanning process can be reduced when heating time in the second step is shortened from 3 h to within 1.5 h,in addition to improvement of tanning effect and environmentally friendly of this technology.The effects of temperature change in the final stage of the second step（after basification）in the two-step temperature change chrome tanning process on leather properties were also investigated.Firstly,the influences of simulated heating time in the final stage of the second step on hydrolysis and polymerization degree of chrome complexes were explored.Then,the effects of heating time in the final stage of the second step on the tanning properties of the two-step temperature change chrome tanning process were investigated.It was found that the absorptivity of chrome tanning agent and Ts of leather were increased by rising temperature to 60 ℃ in the final stage of the second step.However,due to the excessive degree of hydrolysis and polymerization of chrome tanning agent at the relatively higher pH,the molecular size of the chrome complexes and their astringency were drastically increased,which led to the decrease of grain surface fineness,fiber dispersion and mechanical properties of leather,and the overall tanning effect of the chrome-tanned leather is not ideal.In summary,the optimal process parameters of the two-step temperature change chrome tanning process are determined as follows.The dosage ratio of chrome tanning agent in the first step and the second step is 2 %:2 %.After pre-tanned by the first step,the wet-blue is tanned under room temperature first,and then at 60 ℃ for 0.5 1.5h.In this case,Ts of chrome tanned leather is higher than 105 °C.The content of Cr₂O₃ in leather is about 30 mg/g.The absorptivity of chrome tanning agent is more than 90 %.Meanwhile,the thermal stability and mechanical properties of leather are also improved,and the grain is fine.This study demonstrates that the two-step temperature change chrome tanning process can achieve a less-chrome tanning with high chrome absorption and satisfactory comprehensive performances of leather,and thus present a good prospect of application in practice.更多还原