Study About The Influence Of Plasticizing Factors On Mechanical Properties Of Collagen Casing Film

In the industrial making process of collagen casing,tubular collagen pastes are usually plasticized by immersing into glycerol solution.Glycerol is a kind of plasticizer and can improve the ductility of collagen film.At present,in addition to pure glycerol solution,the mixed solution of glycerol and carboxymethyl cellulose(CMC)is also used in the plasticizing process to soften collagen pastes.However,the mechanism and influence of this mixed plasticization on the film properties are not clear,including the influence of the mixed composition on the adsorption content and its relationship with the performance of collagen casing film.Therefore,this research was focused on the glycerol/CMC plasticizing process,studying the relationship between adsorption content and film characteristics,as well as the structure change of collagen pastes in plasticizing solution.Besides,in order to improve the wet mechanical property,multivalent salt was used to cross link.The relationship between CMC and glycerol adsorption in collagen film.After immersing in different plasticizing solutions,the final contents of CMC and glycerol in collagen film were tested.Results showed that CMC could reduce the glycerol content in the film.Compared with the collagen film immersed in 4%(w/v)pure glycerol solution,the glycerol content decreased by 50% after immersing in 0.5%(w/v)CMC and 4%(w/v)glycerol mixed solution.The influence of mixed plasticization on the structure and properties of collagen film.Compared with samples without plasticizing,pure CMC immersing could improve the dry mechanical properties(50.69 MPa~60.16 MPa,p < 0.05).However,due to the water absorbing properties of CMC,the swelling rate of collagen film increased(129.0%~166.1%,p < 0.05),leading to the decline of its wet mechanical properties(2.90 MPa~2.40 MPa,p < 0.05).After immersing in pure glycerol solution,the molecular spacing of collagen increased,the dry tensile strength(TS)of collagen film decreased,and the elongation at break(EAB)increased.Meanwhile,the content of collagen triple helix decreased,and the thermal denaturation temperature of collagen film decreased from 115.09°C to 91.3°C.After adding CMC,the adsorption content of glycerol reduced,thus affecting the mechanical and thermodynamic properties of collagen film.CMC could make collagen pastes dehydrate and shrink,and reduce drying time,while glycerol had no such effect.The mechanism and regularity of dehydrate and shrinkage of the collagen pastes in CMC solution were studied.This study discussed from three aspects,including electrostatic interaction,salting-out effect and osmotic pressure.Collagen paste could dehydrate in acidic,neutral and alkaline CMC solutions and the dehydration rate was about 40%~50%,indicating that dehydration has nothing to do with the charged property of collagen paste.0.1%(w/v)of NaCl solution dehydrated collagen paste to a small extent(about 5%),implying that salting-out effect is not the main reason for the dehydration.The greater the CMC concentration,degree of substitution and molecular weight are,the higher the micelle dehydration rate will be.However,by increasing the ionic strength of CMC solution,the dehydration rate reduced to 20%,indicating that the osmotic pressure effect of CMC polyelectrolyte may be the reason for dehydration.In addition,microstructure images showed that CMC could lead to the contraction of surface collagen fibers aggregates,which was caused by the inability of macromolecules CMC to enter into the collagen fibers.After decreasing the MW of CMC,the dehydration rate reduced.Calcium alginate improves the wet mechanical properties of collagen membrane.Sodium alginate(SA)was used to replace CMC,and the effect of calcium alginate on the wet mechanical properties of collagen membrane was investigated through calcium ion spraying.The results showed that SA/ glycerol mixed plasticization reduced the wet mechanical properties of collagen membrane.After SA/ glycerol plasticized,calcium spray can effectively improve the wet mechanical properties of collagen membrane,up to 4.61Mpa(p < 0.05).After plasticized by CMC/ glycerol mixed solution,aluminum spray cross-linking can improve the wet mechanical properties of collagen membrane,up to 3.71Mpa(p < 0.05),which is still lower than the wet TS of calcium alginate collagen membrane,indicating that calcium cross-linking can replace aluminum cross-linking and improve the wet mechanical properties of collagen membrane.