Research On Permeation Effect Of Cocoon In Pretreatment Process Of Cocoon Cooking Based On The Contact Angle

The moisture osmotic effect of cocoon shell in cooking affects directly the silk reeling and the quality of raw silk, but cocoon shell is hardly infiltrated by water molecules for its surface with natural moisture resistance and overlapping reticular structure. In order to improve the yield and quality of raw silk, cocoons have to absorb some moisture and be infiltrated uniformly through the pretreating process of cocoon cooking. Then the evenness of gumming force among silk and silk dissociation in reeling is considerably improved. But in the traditional characterization methods of cocoon layer penetration effect, the methods of testing water absorption just reflect the water contents of cocoon layers and it is not useful when hardly any water, that not showing the penetration condition of between gumming area and not gumming area and the change of hydrophilic and hydrophobic of cocoon shell. In the other method of dye, coloring agent which is chemical substances could do damage to silk. Overcoming that weakness, penetration of cocoon layers will be analyzed by the new characterization method of testing contact angle in this study.This paper mainly studies on the penetration and hydrophilicity of cocoon layer after direct steaming pretreatment and vacuuming penetration based on the contact angle of cocoon shell. The permeation effect of water to cocoon layer will be analyzed in the pretreating process of cocoon cooking by the contact angle value of cocoon layers after processing, combining this process changes with surface tension of osmotic solution. Firstly, testing the surface tension of different osmotic solutions including 0.01% FCL-41(fluorocarbon surfactant) solution, 0.02% JFC(penetrant) solution and deionized water at 20, 25, 30, 35 and 40℃ respectively. Secondly, the cocoons were treated with different direct steaming time including 20, 40, 60 minutes and different direct steaming temperature including 65, 85, 105℃ respectively in the pretreating process of direct steaming. The dried cocoons not treating were compared with those cocoons after treating. The penetration effect of moisture to cocoons under different direct steaming time and temperature in direct steaming process was analyzed by testing the contact angle of those treating cocoons and dried cocoons and recording the contact morphology of droplet with that cocoon shells. Finally, under vacuum degree of-0.09 Mpa, dried cocoons and treated cocoons after direct steaming were treated with that above different osmotic solution at above five different temperatures respectively. Then penetration effect of cocoon shells were researched under different osmotic solution and osmotic temperature in vacuuming permeation processes, through determining contact angle and contact morphology of droplet with those treated cocoon, combining with surface tension of osmotic solutions. And the influence of direct steaming pretreatment process on permeation effect of cocoons in vacuuming permeation processes were also analyzed and the relevance of contact angle to penetration effect of cocoon layer in pretreating process of cocoon cooking. This study objectively shows the wetting and permeation of cocoon layers in that process by combination of qualitative and quantitative.The results showed that, when the direct steaming time was 60 minutes and temperature was 105℃ in the direct steaming pretreating process, the contact angle value of droplet with cocoon layer was the lowest, the contact area between droplet and cocoon layer was the largest, the droplet was in almost hemispheric shape, so was when osmotic solution was 0.01% FCL-41 and infiltration temperature was 40℃ in the process of vacuum osmotic cocoon cooking. That reveals the hydrophilicity of those cocoons and permeation of moisture to cocoon layer is best in this process. That increasing direct steaming temperature and time properly in the pretreating process of direct steaming and adding very little surfactants and increasing penetration temperature properly in the process of vacuum osmotic cocoon cooking could obviously the hydrophilicity of cocoon layer and penetration effect of water to cocoon layers. The contact angle value of water to cocoon layer treated with vacuuming permeation after direct steaming was smaller than that no treating with direct steaming. This shows that appropriate direct steaming have obvious affect on the permeation of cocoons and could improve the wetting and infiltration of water to cocoons. The permeability effect of water to cocoons treated under different pretreating process of cocoon cooking can be directly evaluated through measuring contact angles of droplets with cocoon layer.