W. Herbert Morrison

Chemical and instrumental characterization of maturing kenaf core and bast

Abstract A limiting factor in the production of bast fiber from kenaf is retting, the process by which the fiber is freed from the non-fibrous tissue. An objective of this study was to evaluate the variation in cell wall chemistry with maturity for different cultivars, particularly in relation to lignin and retting. Two cultivars of kenaf (Hibiscus cannabinus), Tainung-1 (T-1) and Everglades-41 (E41), were harvested at 96 and 151 days post planting (DPP), and the top and bottom 15 cm of the stems were excised for analysis. The hand-separated core and bast portions were analyzed for guaiacyl and syringyl groups (indicative of lignin), and arabinose, xylose, mannose, galactose, glucose, and uronic acids. Cell walls from bast were examined for aromatics by ultraviolet (UV) absorption microspectrophotometry. Bottom core contained significantly higher amounts of aromatics. Results suggested that the top bast tissue was not completely lignified by the early harvest. Cellulose deposition, as indicated by the glucose content at 96 DPP, also was not fully complete until the later harvest. UV absorption microspectrophotometry demonstrated that, while the entire bast fiber cell walls were all lignified, the middle lamella had higher absorbance indicative of more aromatic compounds. The λmax at 274–276 nm was consistent with a predominance of syringyl lignin. In a second study, three cultivars of kenaf, Tainung-2 (T-2), E41, and SF459, were harvested at 30, 60, 90, 120, and 180 DPP. The center 15 cm of the stems was excised for analysis. All three cultivars were similar to each other in components within a maturity period. Bast and core fractions were relatively high in lignin even at 30 DPP, and both secondary layers and middle lamellea contained lignin. The core had more lignin than fiber at maturity. Plants increased in lignin to ca 60 DPP and did not increase thereafter, while carbohydrates continued to vary with maturity. Glucose concentrations became stable at about 90 DPP and xylose concentrations remained constant at 60 DPP. Bast fibers had unusually high syringyl:guaiacyl ratios (6.3–9.4). Principal component analysis (PCA) of the mass spectral data of the bast indicated that 30 DPP samples were distinctly different from those harvested at 60–120 DPP, with the 180 DPP sample different from all others. In enzymatic retting studies of Everglades-41 bast from younger plants, i.e. 30–60 DPP were more easily retted than other harvests and mechanical disruption improved retting of more mature bast. Enzymatic retting resulted in separation of fiber bundles, rather than ultimate fibers.

A new approach for estimating purity of processed flax fibre by NIR spectroscopy

Flax must be retted, in which bast fibres are separated from non-fibre components, and then mechanically processed to clean the fibres before industrial application. In the USDA Flax Fiber Pilot Plant, flax is first cleaned through four separate modules and then passed through a Shirley Analyzer to further clean fibres for high-value applications such as textiles. Often, multiple passages through the Shirley Analyzer are employed to obtain higher quality fibres, but it is difficult to determine when the limit for cleanliness is reached by this method. Further, it is clear that materials other than the woody shive components are being removed by Shirley-cleaning, and a method is needed to assess cleanliness beyond the measure for shives. In this study, we attempted to establish an index to determine the degree of purity of flax fibre during the secondary cleaning stage for high quality fibre. Dew-retted (DR) flax and enzyme-retted (ER) flax, which had been first processed through the USDA Flax Fiber Pilot Plant and assessed for shive content, were processed with 10 repetitions of cleaning through the Shirley Analyzer. For both flax samples, absorbances at 1730, 1766, 2312 and 2350 nm decreased with successive Shirley-cleaning steps. These wavelengths appeared to originate from the epidermal layer (EL) that was associated with the flax fibre, an index was calculated using 11 training samples and validated using 10 independent test samples from the same flax samples. Index values gradually decreased with successive Shirley-cleaning steps for both retted flax samples; a lower index value indicated cleaner fibre. Different curves were apparent for the two flax samples, suggesting variations in the cleanliness of the starting material or perhaps differencess in fibre composition. The results suggest it is possible to determine the extent of cleaning of flax fibre using NIR spectroscopy beyond that for shive content based on the epidermal layer of the plant.

Variation in the wax content of sunflower seed with location and hybrid

Three genetically different types of oilseed sunflower hybrids grown at six different locations were evaluated for the influence of hybrid and location on wax content of hull and oil. Analysis of variance showed that differences in the amount of hull and wax content of the hull were related to both location and hybrid. However, location and hybrid were not found significantly to influence wax content of the oil.

Prediction of shive content in pilot plant processed flax by near infrared reflectance spectroscopy

Shive is the main contaminant in flax fibre and affects fibre quality. In this study, we developed a calibration for determining shive content in flax using near infrared (NIR) spectroscopy and applied the model to pilot plant processed flax to predict shive content. The model based on “ground” mixtures performed best from multiplicative scatter correction after a second derivative treatment of the spectral data, giving a standard error of cross-validation of 0.35% using five factors. Prediction samples were Jordan enzyme-(ER) and Natasja dew-retted (DR) flax that was collected after various stages of processing. When the model was applied to the “ground” flax, a high correlation was obtained between the NIR predicted value and actual shive content, giving a correlation coefficient of > 0.98 for both retted flax samples. However, when the model was applied to the “as-is” flax, a slope and bias were observed. These deviations were corrected by a linear regression between predicted values of “ground” and “as-is” flax. For the NIR analysis of ER flax, the shive content decreased rapidly by the third processing step to 4 to 5% and almost 0% after the last step. For the DR flax, the shive content continuously decreased with processing to about 5% after the last step. The results indicate that it is possibile to measure shive in flax on a commercial processing line.

Pyrolysis mass spectrometry of coastal Bermudagrass (Cynodon dactylon (L.) Pers.) and ‘Kentucky-31’ tall fescue (Festuca arundinacea Schreb.) cell walls and their residues after ozonolysis and base hydrolysis

Cell walls from coastal Bermudagrass (Cynodon dactylon (L.) Pers.) (CBG) and ‘Kentucky-31’ tall fescue (Festuca arundinacea Schreb.) (K-31) were treated with ozone and the resulting residue with sodium hydroxide. The aromatics and polysaccharides of the treated cell walls and the residues from ozone and ozone/base treatments were studied by pyrolysis mass spectrometry. Ozone effectively removed lignin from the cell walls of both grass species. The residue from ozone-treated CBG cell walls showed mass markers characteristic of condensed lignin whereas the base-treated residue from ozone-treated K-31 cell walls showed no lignin remaining in the sample and principally polysaccharides being left. This difference may be due to the type of lignin present in the two grasses which, in turn, may relate to CBG cell walls being less digestible by rumen microorganisms.

Partial least squares regression calibration for determining wax content in processed flax fiber by near-infrared spectroscopy

The quality of flax fiber in the textile industry is closely related to the wax content remaining on the fiber after the cleaning process. Extraction by organic solvents, which is currently used for determining wax content, is very time consuming and produces chemical waste. In this study, near-infrared (NIR) spectroscopy was used as a rapid analytical technique to develop models for wax content associated with flax fiber. Calibration samples (n = 11) were prepared by manually mixing dewaxed fiber and isolated wax to provide a range of wax content from 0 to 5%. A total of fourteen flax fiber samples obtained after a cleaning process were used for prediction. Principal component analysis demonstrated that one principal component is enough to separate the flax fibers by their wax content. The most highly correlated wavelengths were 2312, 2352, 1732, and 1766 nm, in order of significance. Partial least squares models were developed with various chemometric preprocessing approaches to obtain the best model performance. Two models, one using the entire region (1100–2498 nm) and the other using the selected wavelengths, were developed and the accuracies compared. For the model using the entire region, the correlation coefficient (R2) between actual and predicted values was 0.996 and the standard error of prediction (RMSEP) was 0.289%. For the selected-wavelengths model, the R2 was 0.997 and RMSEP was 0.272%. The results suggested that NIR spectroscopy can be used to determine wax content in very clean flax fiber and that development of a low-cost device, using few wavelengths, should be possible.