Laminuotos odos reologinės elgsenos tyrimas ; Investigation of laminated leather rheological behaviour
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Laminuotos odos reologinės elgsenos tyrimas ; Investigation of laminated leather rheological behaviour

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KAUNAS UNIVERSITY OF TECHNOLOGY INSTITUTE OF PHYSICAL ELECTRONICS OF ECHNOLOGY Daiva Milašien ė INVESTIGATION OF LAMINATED LEATHER RHEOLOGICAL BEHAVIOUR Summary of doctoral dissertation Technological Sciences, Materials Engineering (08 T) Kaunas, 2005 The scientific work was carried out in 2000 – 2004 at Kaunas University of Technology, Faculty of Design and Technologies, supported by Lithuanian State Science and Studies Foundation. Scientific supervisor: Assoc. Prof. Dr. Virginija JANKAUSKAIT Ė (Kaunas University of Technology, Technological Sciences, Materials Engineering – 08 T). Council of Materials Engineering Sciences trend: Prof. Dr. Habil. Rimgaudas ABRAITIS (Institute of Architecture and Construction of Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T); Dr. Viktoras GRIGALI ŪNAS (Institute of Physical Electronics of Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T); Prof. Dr. Habil. Matas GUTAUSKAS (Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T) – chairman; Prof. Dr. Habil. Sigitas TAMULEVI ČIUS (Institute of Physical Electronics of Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T); Prof. Dr. Vaclovas TRI ČYS (Šiauliai University, Technological Sciences, Materials Engineering - 08 T). Official opponents: Dr.

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Publié le 01 janvier 2005
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KAUNAS UNIVERSITY OF TECHNOLOGY INSTITUTE OF PHYSICAL ELECTRONICS OF KAUNAS UNIVERSITY OF TECHNOLOGY        Daiva Milaienė    INVESTIGATION OF LAMINATED LEATHER RHEOLOGICAL BEHAVIOUR       Summary of doctoral dissertation  Technological Sciences, Materials Engineering (08 T)           Kaunas, 2005
The scientific work was carried out in 2000  2004 at Kaunas University of Technology, Faculty of Design and Technologies, supported by Lithuanian State Science and Studies Foundation.  Scientific supervisor:  Assoc. Prof. Dr. Virginija JANKAUSKAITĖ University of (Kaunas Technology, Technological Sciences, Materials Engineering  08 T).  Council of Materials Engineering Sciences trend:  Prof. Dr. Habil. Rimgaudas ABRAITIS (Institute of Architecture and Construction of Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T); Dr. Viktoras GRIGALIŪ of Physical Electronics of KaunasNAS (Institute University of Technology, Technological Sciences, Materials Engineering -08 T); Prof. Dr. Habil. Matas GUTAUSKAS (Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T) chairman; Prof. Dr. Habil. Sigitas TAMULEVIČIUS (Institute of Physical Electronics of Kaunas University of Technology, Technological Sciences, Materials Engineering 08 T); -Prof. Dr. Vaclovas TRIČ University, Technological Sciences,YS (iauliai Materials Engineering - 08 T).  Official opponents:  Dr. Rimantas LEVINSKAS (Lithuanian Energy Institute, Technological Sciences, Materials Engineering - 08 T); Assoc. Prof. Dr. Eugenija STRAZDIENĖ(Kaunas University of Technology, Technological Sciences, Materials Engineering - 08 T).  Public defence of the Dissertation will take place at the open meeting of the Council of Materials Engineering Sciences trend at 11 a.m. on 31 th. May 2005 in Dissertation Defence Hall at the Central Building of Kaunas University of Technology. Address: K. Donelaičio g. 73  403, 44029, Kaunas, Lithuania. Tel.: (370) 37 300042; fax (370) 37 324144; e-mail: mok.skyrius@ktu.lt. The summary of the Dissertation is sent on 30 April, 2005. The dissertation is available at the libraries of Kaunas University of Technology (K. Donelaičio g. 20, Kaunas) and Institute of Physical ecEls icontr of Kaunas University of Technology (Savanoriųpr. 271, Kaunas).
KAUNO TECHNOLOGIJOS UNIVERSITETAS KTU FIZIKINĖS ELEKTRONIKOS INSTITUTAS         Daiva Milaienė    LAMINUOTOS ODOS REOLOGINĖS ELGSENOS TYRIMAS       Daktaro disertacijos santrauka  Technologijos mokslai, mediagųininerija (08 T)         Kaunas 2005
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Disertacija rengta 2000  2004 metais Kauno technologijos universitete, Dizaino ir technologijųfakultete ir remta Lietuvos valstybinio mokslo ir studijų fondo.  Mokslinėvadovė:  Doc. dr. Virginija JANKAUSKAITĖ technologijos universitetas, (Kauno technologijos mokslai, mediagųininerija - 08 T).  Mediagųininerijos mokslo krypties taryba:  Prof. habil. dr. Rimgaudas ABRAITIS (Kauno technologijos universiteto Architektūros ir statybos institutas, technologijos mokslai, mediagų ininerija  08T); Dr. Viktoras GRIGALIŪ technologijos universiteto FizikinNAS (Kaunoės elektronikos institutas, technologijos mokslai, mediagųininerija - 08 T); Prof. habil. dr. Matas GUTAUSKAS (Kauno technologijos universitetas, technologijos mokslai, mediagųininerija - 08 T) pirmininkas; Prof. habil. dr. Sigitas TAMULEVIČIUS (Kauno technologijos universiteto Fizikinės elektronikos institutas, technologijos mokslai, mediagųininerija - 08 T); Prof. dr. Vaclovas TRIČYS (iaulių universitetas, technologijos mokslai, mediagųininerija - 08 T).  Oficialieji oponentai:  Dr. Rimantas LEVINSKAS (Lietuvos energetikos institutas, technologijos mokslai, mediagųininerija - 08 T); Doc. dr. Eugenija STRAZDIENĖ (Kauno technologijos universitetas, technologijos mokslai, mediagųininerija - 08 T).   Disertacija ginama vieame Mediagų mokslo krypties tarybos ininerijos posė gegudyje 2005 m.ės 31 d., Kauno technologijos universiteto val. 11 centriniųrūmųcitaeris Djųgynimo salėje. Adresas: K. Donelaič73  403, 44029, Kaunas, Lietuva.io g. Tel.: (370) 3 300042; faks.: (370) 37 324144; el. patas: mok.skyrius@ktu.lt  Disertacijos santrauka isiųsta 2005 m. balandio 30 d. Su disertacija galima susipainti Kauno technologijos universiteto (K. Donelaič Kaunas) ir Kauno technologijos universiteto Fizikinio g. 20,ės elektronikos instituto (Savanoriųpr. 271, Kaunas) bibliotekose. k
Introduction Relevance of the research. Phenomenological prediction of the mechanical behaviour of various materials and their systems is a fundamentally important problem for engineering application. Recently the multi-component polymeric products from the materials with different nature and properties are widely used into variety applications. One of them, the soft laminated polymeric materials composing microporous or hydrophilic film or membrane, is used for sport, tourist, military and professional clothing products. Such heterogeneous materials often show absolutely new properties and sometimes combine wide range of them, for example, high temperature and chemical resistance, improved permeability properties. On the other hand, the rheological behaviour of laminated materials differs from the rheological behaviour of the separate components. Different elastic properties of laminated materials layers influenced the increase of internal stress and determine the final properties of the composites, too. One of such soft laminated polymeric materials  microporous film laminated leathers. Microporous polyurethane coat protects leather from various external ambient aggressions very good withal provide good vapour permeability, but in the other hand, it changes leather rheological properties whose are very important in technological aspect. It means that the new manufacture technologies of products from laminated leather are need. Therefore the investigations allowed to predict the behaviour of deformability and relaxation properties of microporous film laminated leather are relevant. The goal of the workwas to investigate the rheological properties of laminated leather and predict the relaxation behaviour in order to select and substantiate the shaping regime. During the research the followingtasks are approached:  to determine the peculiarities of mechanical properties of polyurethane (PU) film laminated leather and its layers;  to investigate the stress relaxation process of laminated leather and its layers and compare with others kinds of leather; chose and adapt the simple and rigorous theoretical model for  to mathematical description and phenomenological interpretation of investigated materials stress relaxation behaviour;  to determine the influence of some environment and loading parameters on laminated leather and microporous film relaxation process. Scientific Novelty and Practical Significance.The substantially different relaxation process of macrolayers with very different structure (leather and microporous elastomeric film) mainly determines the relaxation process of heterogeneous materials (laminated leather). As our investigations have shown, the microporous polyurethane (PU) film substantial changes the intensity and behaviour of stress relaxation process of the microporous PU film laminated 5
leather. Relaxation process of laminated leather was approximated by various mathematical models, but the highest precision of approximation is obtained by generalised Maxwell model. The two stages with different rates of the relaxation process is characteristic for various leathers and PU film were used for prediction of stress relaxation process of this materials till 10 000 s. Stress relaxation of laminated leather and microporous PU film was described by the time-rate analogy, which creates possibility to predicts influence of loading rate on stress relaxation of laminated leather and microporous film in wide interval of relaxation time and loading rate. The obtained results can be used for prediction of microporous PU film laminated leather relaxation behaviour in order to optimize the leather products technological regimes of formation and increase their shape stability at wearing. Approbation of the research results.The results of the research were presented in the 10 scientific publications. Structure of the dissertation. This dissertation consists of: introduction, five chapters, conclusions, list of references and list of scientific publications. The materials of the dissertation are presented in 106 pages, including 60 figures and 13 tables. Content of the dissertation Introduction the relevance of the research, definition of the presents research aim and objectives, survey of the scientific novelty and practical value of the dissertation. Chapter 1.Literature review gives the view of relevant publications related to the theme of dissertation. The information about leather, elastomers and heterogeneous materials structure, environment, and loading parameters influence on their mechanical and relaxation behaviour have been reviewed. The analysis of mathematical description methods of polymeric materials relaxation process has been carried out, too. Chapter 2presents the materials and methods of investigations. The leathers of various processing technology (tanning and coating) manufactured in AB iaulių and microporous PU film StumbrasPermair (Porvair have been used for investigation.plc., UK) The methods of specimens preparation, tensile properties determination, stress relaxation process and leather shaping investigations are presented. Stress relaxation tests were carried out at 20 % level of deformation and held in this position. The influence of deformation rate on stress relaxation process was determinate by changing loading speed up to 300 mm/min. Chapter 3presents the experimental and theoretical investigations. Investigation of various leathers tensile properties. The mechanical behaviour of tanned leather in great deal depends on leather structure, topographical zone, nature and size of defects, sort and age of cattle, tanning 6
and finishing process, etc. Tanned leather is usually coated with thin pigmented or lacquer coatings. The structure of laminated leather imitates leather with natural grain (Fig. 1).  Microporous film Adhesive Corium of leather
1/3 h h 2/3 h
 Fig. 1. Microporous PU film laminated leather It was determined that the tensile strength of laminated leather (σt is close to strength of semifinishing crust leather15.5 MPa  22.5 MPa) and is approximately twice higher then this property of elastic leather. Herewith the variation of properties results is lower in compare with values of other types leathers. That can be explained by influence of homogeneity of synthetic PU film structure on properties of hybrid material. The investigations show the evident dependence of laminated leather tensile properties upon thickness. The difference of values of different thickness laminated leathers (LO1and LO2) is 17%- 36%, the difference of elasticity modulus at break Etr is 36%, and elongations at breakεtr 23%. It is possible to suppose that the main influence on presented properties of laminated leather has split leather. Therefore, was important to study the mechanical properties of each layer of leather separately and to determine their influence on hybrid leather properties. Investigation of laminated leather layers tensile properties. Mechanical properties of laminated leather were compared to such properties of semi-finishing products at the different stages of laminate manufacturing: S1  chrome-tanned split leather 1.2 ± 0.1 mm of thickness, S2  split leather grounded with acrylic ground (in amount of 20 g/dm2  grounded leather), S3 coated with adhesive layer (polyurethane water-born dispersion in amount of 12  15 g/dm2) and microporous PU film (PL). Such properties as tensile strengthσt, elongation at breakεb elasticity modulus at break E andb were determined. Besides, in the footwear manufacturing the moment atσ1=9.8 MPa is important; this value of stress appears in the leather at the time of its shaping by deformation in order to give the desirable shape. Therefore, elongationε1 and elasticity modulus E19.8 MPa of stress was determined as well.at It was determined that the influence of grounding on the tensile properties of split leather is very low, while the adhesive layer increases deformation of split leather (Table 1). The differences in the leather strength properties can be related not only to the finishing procedure, but also to initial properties of the 7
sample, topographical zone of leather, defects, etc. Meanwhile, th ofσt e value of the hybrid leather is higher (σt22 MPa), although it is laminated with low strength PU film (σt2.3 MPa). Table 1.Mechanical properties of laminated leather and its layers Strain, %: Elasticity modulus, MPa: Sampleσtr, MPa ε1,εtr,E1,Etr, .8 MPa at break whenσ when break at=9.8 MPaσ=9 S1 20.6±1.9 20±2.0 38±2.6 52.0 55.2 S2 19.1±1.3 21±1.8 38±2.3 47.3 51.4 S3 15.9±1.2 37±2.3 53±3.0 26.7 28.8 PL 7.5±0.2  326±14  2.3 LO 21.9±1.7 16±1.3 37±2.3 68.8 58.9  It can be attributed to the combinative strengthening of laminated system, when the tensile strength of hybrid system is higher than that of the separate layers even at the low cohesion strength of the medium layer. This effect can be evaluated by the coefficient of the strengtheningKS:  Ks= σ1−σ0, (1) σ0 whereσ1is experimentallyvalue of the tensile strength of laminated obtained system,σ0is theoretically calculated tensile strength: σt1SS1k1t2SS2k2+...tiSSiki= σ0   (2) whereσti andSi are the tensile strength and the cross-section ofi-th layer, respectively; ki is the ratio of elasticity modulus ofi-th layer with highest modulus. The evaluation of laminated leather mechanical properties shows that the lamination of microporous PU film considerably increases the strength of laminated system:KS= 14 % - 23 %. It may be attributed to the leather surface defects repairing by the adhesive layer. Another possible explanation of these results may be related to the effect of defects locking, i.e. to the dissipation of kinetic energy that releases during the elementary failure. From the character ofσ-ε curve it follows that mechanical properties of different structure layers such as leather and elastomeric PU film differs radically (Fig. 2). The adhesive increases the elongation at break of the split leather about 1.5 times (sample S3 in Table 1). It may be considered that low viscosity elastomeric adhesive penetrates in the leather pores and other gaps, affects as plasticizing agent and repairs the surface defects at the moment of failure under the loading. 8
The deformation properties of the laminated leather LO are very similar to that of the split or grounded leathers. However, it should be pointed out that at the beginning the deformability of the hybrid leather is slightly lower (atσs=9.8 MPa for LOεs=15%-17%comparing to 19%-22%of S1 and S2). It may be attributed to the interaction between two layers that effects the increase of surfaces layers stiffness. 25 2034 152 10 5 1 0 0 100 200 300 400 ε,%  Fig. 2.Stress-strain curves for laminated leather and its layers: 1 PU film (PL); 2  split leather with adhesive layer (S3); 3  grounded leather (S2); 4  laminated leather (LO) As can be seen from data, presented in Table 1, for PU film also it is characteristic markedly higher elasticity modulus at low strain, i.e. Young modulus comes up toEJ=18 MPa, when modulus at break - onlyEb=2.3 MPa. Thus, as was mentioned above variation of hybrid leather modulus can be explained by the influence of elastomeric PU film on its mechanical behaviour. The polymeric film has significantly higher elongation at break (higher than 300%) comparing to that of the leather (36%-40%). On the other hand, high elastic deformation is characteristic to PU film. It was determined that the residual elongation even after 1 min of relaxation is only 30 %. This property creates problems for laminated leather products formation process and shape stability in wear. Since the mechanical properties of laminated leather depend on the separate leather layer, it is important to determine the peculiarities of relaxation process of laminated leather and its individual layers (leather split, PU film) contribution on this process. Mathematical methods for stress relaxation prediction of leather and PU film. For the comparison and modelling it is often necessary to fit experimental relaxation data to an analytic function. The objective of the fitting process is to determine parameter values that in some sense represent the best fit of the approximating function to the experimental data. In order to define the most effective method of mathematical description of stress relaxation in investigated materials four analytical functions were used: power function (Eq. (3)), Kohlrausch equation (Eq. (4)) and two rheological 9
models such us twin Maxwell - Wiechert (Eq. (5)) and generalized Maxwell. Generalized Maxwell model of five Maxwell elements and a single elastic Hookean spring in parallel (Eq. (6)). σ = σ+atb (3) σ = σ+(σ0σ)emt (4) tt σ(t) =Dsε0eτs+Dwε0eτw (5) * n−εtt σ = σ+ ∑σi=D0εt+vtDτievtτieτi, (6) i=1i=n1i1wheret* is the time counted from the instant, at which the strain reaches the limit valueεt, i.e.t*=t−εtvt. The regular discrete spectrum, proposed in literature, was used to eliminate influence of external factors on the relaxation time and its intensity. In this case relaxation periods always have constant values, which can be obtained according to the relation: τ =ai1τ1, (7) i whereτ1is a minimal time of relaxation,ais constant (a>1). In order to ensure that within certain time rangest*relaxation is reflected by one Maxwell element solely, constantaadmitted to be equal to 10. The value ofD0, which defines the equilibrium stressσon the model, can be calculated from Eq. (8) using two experimental values of stress:σn1 that corresponds to the timet*1≈τn andσn2t*2 t*u (t*u is real time of observation): t*2t1*σn2−σn1expτ = D0εt1expt2*τnt1*n  Correspondingly: D Dn= σn10εt*, t vtτnGnexpτ1nεt whereGn=1evtτn.
10
 
 
 
 
 (8)
 (9)
The visual examination of the theoretical curves permits to conclude that Kohlrausch method and generalized Maxwell one only successfully describe stress relaxation behaviour in the non - linear regions of leathers (Fig. 3,b, d). Power function and Maxwell - Wiechert model representing approximating functions fit to the experimental data in worse manner (Fig. 3,a, c).  12 12 10 10 8 8 6 6 4 4 1 100 10000 1 100 10000 t, st, s  a b 1212 1010 88 66 44 1 100 10001 100 10000 t, st, s  c d Fig. 3.Stress relaxation of various leathers approximated by different theoretical models: a according to Eq. (3), b  according to Eq. (4), c according to Eq. (5), d  according to Eq. (6); hydrophobic, elastic, laminatedPermair, and-S  split leathers experimental data The same tendency is observed in the case of microporousPermair film: experimentally determined and predicted stress relaxation behaviour changes in the same manner using Kohlrausch and generalized Maxwell models. Adequacy of the approximating curves to the experimental data may be evaluated by the magnitude of inadequacy dispersion. The next consideration is the selection of a measure of the error between approximating function and the experimental data. One convenient measure is the Euclidean norm of the deviations at theN data points. However, since the stress decays over several orders of magnitude, this error measure artificially weights the error at short 11
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