|Khalili, S. - SWEDISH UNIV OF AG PROD|
Submitted to: Vibrational Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 1998
Publication Date: N/A
Interpretive Summary: The stem of the flax plant is the source of linen fiber that is of commercial importance in Europe and Asia. The growing and processing of flax for fiber is gaining interest in the United States. However, the United States has essentially no means of processing flax for fiber or any means of assessing quality of this material. In order to assess processing methods and quality of materials, better knowledge of the chemistry and structure of this plant tissue is needed. This study demonstrated the ability to use near-infrared generated Raman signals to produce images that provide this knowledge. This was accomplished by exposing sections of flax plant stems to a low power near-infrared laser and collecting the Raman scattered light from the sample. From this response, images of the chemical components were produced. Specific images were produced for cellulose, hemicellulose, pectins, aromatics, and wax components. Thus, all of the major chemical components in flax stems could be imaged by the Raman method. The results obtained indicated that this type of imaging could be used to provide a means of quality assessment of native plant materials. The method is particularly sensitive for detecting aromatic components that lead to processing problems and are a quality factor in linen textile production. The use of this technique, as shown in this work, will permit the selection of the proper raw materials and the assessment for potential problems that occur in the processing of flax for textile production.
Technical Abstract: NIR-FT Raman microscopy was employed to image and subsequently produce in situ maps of the distribution of chemical components in flax (Linum usitatissimum) stem tissue. Thick (ca. 80 um) cross-sections of flax were cryotomed, thawed, equilibriated at 85% RH for >3 hr and sealed under cover glasses on gold mirrored microscope slides. Spectra for each image pixel were collected from selected tissue sections over the Raman shifted region 3600-300 cm-1 at 16 cm-1 with 256-512 scans and employing ca. 185 mW of focused laser power at the sample. A computer controlled automated microscope stage was used to collect area maps of 50-150 um in rectangular dimensions in 6-10 um steps and register them to the visible images that were captured using a CCD camera. Data collection required 8-10 hr per image. Chemical profiles were produced from area integrations of specific spectral regions. The chemical profiles showed the location of all of the major components of flax by anatomical cell type. A sharp shoulder at 285 cm-1 in the CH stretch region provided evidence of waxes in the cuticular/epidermal tissue. The bands occurring around 1600 cm-1, due to aromatic ring stretching vibrations, gave evidence of lignin in core tissue and pigments in epidermal tissue. Bands occurring between 1180-1045 cm-1, due to COC heavy atom mixed mode vibrations, showed the greatest concentration of carbohydrate in fiber cells with lesser (but significant) amounts indicated in core tissue. In addition, bands occurring between 870-800, 515-476, and 400-360 cm-1 gave specific evidence for the presence of pectins, other non-cellulosic polysaccharides and cellulose (respectively) in parenchyma tissue.