Scanning acoustic microscopy investigation of melted collagen in thermoplastic leather
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Scanning acoustic microscopy investigation of melted collagen in thermoplastic leather A. Wylera) Jerusalem College of Technology, POB 16031, Jerusalem, Israel
G. Golan Open University of Israel (Received 10 August 1998; accepted 8 February 1999)
A scanning acoustic microscope (SAM) has been used to investigate the structure of thermoplastic leather. This material is formed by pressing fibers of leather under high pressure and moderate temperature. The result is a matrix from transformed, melted fibers in which leftover fibers act as reinforcement. Unlike the scanning electron microscope (SEM), the SAM is able to distinguish between completely and incompletely transformed fibers and also to penetrate the material beneath the surface. The results show that the matrix is built as a domain structure. The advantages of the SAM over the SEM for organic materials are indicated. I. INTRODUCTION
Scanning acoustic microscopy is a useful technique for imaging and investigating the properties of materials such as metals, ceramics, and composites, as well as integrated circuits and biological samples.1–5 It has also been used for organic composites to image the fibers in the matrix material.6 The method is based on the fact that the elastic constants for various constituents in the material differ at least 10%, which leads to a difference in the reflection and absorption of acoustic wave pulses. This led us to believe that acoustic microscopy could be useful in the investigation of internal structures in certain natural materials that are built in composite-like form. Thermoplastic leather is a composite material that we have produced under high pressure and moderate temperature, from leather fibers. This compressed fiber material comprises melted collagen in which leather fibers act as reinforcement. We have previously reported on this kind of matrix auto reinforced composite.7 We have described how fibrous organic material can be ground and then compressed under high pressure and moderate temperature. Most of the fibers transform into a polymerized matrix and the leftover fibers act as reinforcement. The produced material is very strong under compression. The maximum compression strength of the material, about 180 MPa, depends on the production parameters which determine the quality and quantity of the matrix material and the number and distribution of leftover fibers. Further investigation on leather and collagen has made it clear that the transformation is a process of dry melting of the collagen molecules during the application of the pressure and temperature. The influence of a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 6, Jun 1999
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temperature and pressure on the structure as seen in the SEM has been published elsewhere.8 In order to get more exact information about the distribution of the melted collagen and the fibers, compressed leather fiber mater
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