| Our country is rich in wild silkworm resources,which is the world’s first country to use the resources.Bombyx mandarina(B.mandarina)silkworm is widely accepted as an ancestor of the Bombyx mori(B.mori)silkworm,and it has formed the different geographic population by the long-term natural selection.Yellow B.mori silk with B.mandarina silkworm consanguinity can be obtained thorough the hybridization between B.mori silkworm and B.mandarina silkworm.Antheraea assama(A.assama)silk has a natural color,and the hygroscopicity and mechanical property are very excellent.An important prerequisite for extending fibers’ application fields is the comprehensive fundamental research.Most of current research on the B.mandarina silkworm resources is about biology,and the basic research on the structure and property is few.The development and utilization of A.assama silk is mainly in India for this material is difficult to be obtained.B.mandarina and A.assama silks are both precious wild silk resources.To make a better use of these precious green materials,morphology,aggregation structure,thermal property and mechanical property of B.mori silk,yellow B.mori silk with B.mandarina silkworm consanguinity,B.mandarina silk and A.assama silk are compared and analyzed in this paper.In the meantime,the influence on the secondary structure,thermal properties and mechanical properties of the four types of silks after being chemical reagent and thermal ageing treatment are studied.The research results show that:1.A.assama silkworm cocoon has irregular shape,and it is difficult to reel silk.The content of glycine for mulberry silks(B.mori,yellow B.mori and B.mandarina silks)is higher than that of alanine,but A.assama silk is just the opposite.B.mori silk has the highest degumming loss,and A.assama silk,with the lowest degumming loss,has excellent hygroscopicity.Both sericin and fibroin of A.assama silk have natural color.2.The aggregation structures in the four types of silks are predominantly β-sheet structure with an addition amount of α-helix structures and random coil secondary conformation.A.assama silk has calcium oxalate crystal absorption peak,which is consistent with the result of scanning electron microscope(SEM).Mulberry silks and A.assama silk have different primary structure,and the corresponding crystalline structure is also different.Mulberry silks have polyalanine glycine series absorption peak,while A.assama silk,with the highest crystallinity,has polyalanine series absorption peak.3.A.assama silk has the best thermal stability with the thermal decomposition temperature of 378.4 ℃.B.mori,yellow B.mori and B.mandarina silks have similar thermal stability as well as the thermal degradation process.B.mandarina silk is the finest fiber,and A.assama silk is the roughest.Yellow B.mori silk has the highest breaking strength,but B.mori silk has the lowest.A.assama silk has good breaking strength,best elongation at break and initial modulus,revealing the coexistence of tenacity and flexibility in A.assama silk.4.With the acid treatment conditions strengthening,crystallinity of yellow B.mori,B.mandarina and A.assama silks are firstly increasing and then increasing,as well as the thermal degradation temperature of yellow B.mori and B.mandarina silks.While the thermal stability of A.assama silk essentially remains unchanged.Breaking strength of all the silks gradually reduces,but breaking elongation increase at first and decrease afterwards after being acid treatment.Strong acid with high temperature and high concentration has extremely significant influence on the mechanical property of silk fibers.5.Crystal types of all the silks do not change after being alkali treatment,and thermal stability roughly shows a reducing trend.Crystallinities of yellow B.mori and B.mandarina silks gradually decrease with the enhancement of treatment conditions.Alkaline liquor concentration and temperature significantly affect the strength of yellow B.mori and B.mandarina silks.Temperature has a greater destructive effect on A.assama silk than alkaline liquor concentration.6.Crystallinity and thermal stability have been less affected by oxidizing agent treatment.The higher the temperature,the better the bleaching effect..A.assama silk can be bleached under the condition of 60 °C,while B.mori and B.mandarina silksneed 80 °C.Strength retention rates of yellow B.mori and B.mandarina silks are more than 80% after being treated by oxidizing agent under high temperature and high concentration,while A.assama silk can keep over 90%.7.Calcium salt treatment makes crystallinity and thermal decomposition temperature of yellow B.mori and B.mandarina silks increase firstly and then decrease.Dissolve-loss rate of A.assama silk is the lowest,and the crystal structure and thermal stability are less influenced.Treatment time has insignificant influence on the strength of A.assama silk,while has extremely significant effect on the strength and breaking elongation of yellow B.mori and B.mandarina silks.8.With the heat treatment conditions strengthening,crystallinities of all the silks are first rose and the dropped,while thermal stability gradually reduces.100 °C heat treatment has little impact on the aggregation structure of all the silks,and 150 °C heat treatment has prominent influence on the tensile properties.Crystal structures of yellow B.mori and B.mandarina silks change significantly after being 200 °C treatment,and crystal types reduce.Thermal degradation temperature of yellow B.mori and B.mandarina silks are decreased by 20 °C and 15 °C,respectively.Mechanical properties of silks can not be test because 200 °C continuous heat treatment made silk brittle and hard.In conclusion,A.assama silk have better properties,and chemical resistance and heat resistance properties are the best among all the silks.Yellow B.mori and B.mandarina silks have similar tolerance for heat treatment and chemical agent.This study shows that domesticated selection has no remarkable influence on the structure and properties of mulberry silk,but hybridization breeding can improve and enhance some properties of mulberry silk.A.assama silk,with distinct structure and properties,has an important exploitative prospect. |
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