Effects Of External Forces On The Structure And Properties Of Glutaraldehyde Retanned Cattlehide Upper Chrome-leather

Different kinds of external forces may be applied to the leathers in leathermaking. However, because of the shortage in the basic study on effect of externalforces on the structure and property of leathers, the related influence and mechanismare not clear. No exact theoretical direction may be found and used in leather making.For example, many mechanical processes are used in leather making, such asmechanical softening, staking, togging, drum milling, stretching, ironing andpressing, etc. By applying various external forces, we may get the leathers with goodperformance by control the structure of leathers. So much more attention should bepaid to the effects of the external forces on the structure and properties of leathers.Therefore, the study in the field is of theoretical significance and application value.The paper are focused on the simulation of external forces in leather making,which contains three parts. The first is the simulation of uniaxial and biaxial stressstates, the second part says the simulation of dynamic stretching, and the last is thesimulation of mechanical softening.After being chrome tanned, the wet blue was glutaraldehyde retained,neutralized, and fat liquored to get different crust samples. Uniaxial stress andbiaxial stress were applied to the leather samples under the condition of ambientdrying and vacuum drying. The influences of different stress state on leatherstructure and performance were studied by changing the stretch level. And theleather yield and water vapor permeability was investigated. The samples were thenstudied from viewpoints of mechanical properties, the grain smoothness and crosssection. Finally, the hydrothermal stability, dry heat resistance and thermaldegradation of the various samples were studied and infrared spectra was applied inthe analysis of the change of hydrogen bonds before and after stretching. The resultsshowed that after being dried with stretching, the yield and water vapor permeabilityare both increased, no matter uniaxial stretching or biaxial stretching mode is used.Under the biaxial stretching, the leather yield and water vapor permeability is betterthan that of the uniaxial stretching. The leather yield is related with the leatherthickness change ratios, and there is a close relationship between the water vapor permeability and the final thickness of the samples. Meanwhile, after drying andstretching, the tensile strength of the samples is increased while the elongation atbreak is decreased. Compared with the sample being biaxial stress processed, thesample with uniaxial stress history is higher in tensile strength and lower in breakelongation. After being stretched, the surface of the samples becomes smoother.Uniaxial stretching increases the orientation degree of the collagen fiber in thesample, while biaxial stretching separates some fiber bundles in it. On the basis ofthe work, a simplified fiber structure model during stretching was proposed. It wasindicated that stretching while being dried decreases the hydrothermal stability, dryheat resistance. The dry heat resistance of leather sheet is better than that of collagenfibers in leather. It was found that stretching while being dried improved the stabilityof thermal degradation of samples. The stretching process is accompanied with thebreak of some hydrogen bonds in the samples.The effects of dynamic stretching on the structure and performance of sampleswere studied by changing the streching time and releasing time. There were threestretching methods which were paralleled stretching, vertical stretching and crossedstretching. The leather yield, water vapor permeability, mechanical properties, thegrain smoothness and cross section of samples were investigated. Finally, the workwas focused on the hydrothermal stability, dry heat resistance and thermaldegradation of the various samples, and infrared spectra was applied in the analysisof the change of hydrogen bonds before and after stretching. The results showed thatthe crossed stretching samples possess the best yield of all, the less yield are theparalleled one, the vertical ones’ yield are the least. The paralleled samples have themaximum tensile strength and minimum elongation at break just the opposite to thevertical ones’. The crossed one falls in the between of them. It was indicated thatdynamic stretching containing the paralleled and crossed ones while being drieddecreases the hydrothermal stability, especially for the samples stretched all the time.But for the vertical ones, the hydrothermal stability is improved, and to all thedynamic samples the heat stability is increasing.The effects of mechanical softening on the structure and performance ofsamples were studied. In this work, drying and finishing were simulated in laboratory and different forces were applied on leather so that they were in adifferent stress state, i. e., uniaxial stress state and plane stress state. And then, halfof the samples were mechanical softened. And the mechanical properties, watervapor permeability, porosity, hydrothermal stability and dry heat resistance wereinvestigated. The results showed that mechanical softening may improve themechanical properties. It can increase both the tensile strength and the elongation atbreak of samples, while the porosity and water vapor permeability were decreased. Itwas indicated that stretching while being dried improves the hydrothermal stabilityof stretched samples, but the contrastive samples’ are decreased.