Roy B. Dodd

Enzyme-retting of flax and characterization of processed fibers

Enzyme-retting formulations consisting of Viscozyme L, a pectinase-rich commercial enzyme product, and ethylenediaminetetraacetic acid (EDTA) were tested on Ariane fiber flax and North Dakota seed flax straw residue. Flax stems that were crimped to disrupt the outer layers were soaked with various proportions of Viscozyme-EDTA solutions, retted, and then cleaned and cottonized with commercial processing equipment. Fiber properties were determined and crude test yarns were made of raw and Shirley cleaned flax fibers and cotton in various blend levels. Cleaned fibers were obtained from both seed and fiber flax types, but with variations due to treatment. Retting formulations produced fibers having different properties, with enzyme levels of 0.3% (v/v as supplied) giving finer but weaker fibers than 0.05% regardless of EDTA level. Experimental yarns of blended flax and cotton fibers varied in mass coefficient of variation, single end strength, and nep imperfections due to sample and formulation. With cost and fiber and yarn quality as criteria, results established a range in the amounts of components comprising retting formulations as a basis for further studies to optimize enzyme-retting formulations for flax. Under conditions examined herein, Viscozyme L at 0.3% (v/v) plus 25 mM EDTA produced the best test yarns and, therefore, established a base for future studies to develop commercial-grade, short staple flax fibers for use in textiles.

Chemical and structural analysis of fibre and core tissues from flax

Samples of flax (Linum usitatissimum) stems from the cultivars ‘Natasja’ and ‘Ariane’ were separated into fibre and core fractions and analysed by gas–liquid chromatographic methods, 13C CPMAS NMR spectrometry, histochemistry, electron microscopy and UV absorption microspectrophotometry to assist in determining the structure and composition of these cell walls in relation to quality and utilisation. Analyses from chromatography and NMR gave similar results for carbohydrate and phenolic constituents in various samples and in the lower, more mature regions of the stem. Amounts of uronic acids and xylose were lower while amounts of mannose, galactose and glucose were higher in fibre vs core fractions. Quantities of phenolic constituents were significantly higher in the core than the fibre, with groups representative of both guaiacyl and syringyl lignins; amounts of phenolic acids were low. NMR showed a low intensity signal for aromatics in fibre, and it is possible that such signals arise from compounds in the cuticle rather than the fibre. Microscopic studies indicated that aromatic constituents were present in core cell walls, cuticle of the epidermis, and cell corners and middle lamellae of some regions within the fibre tissues. The lignin in fibre appeared to be of the guaiacyl type and may be too low in concentration to be unambiguously detected by NMR. Aromatic compounds were not observed in the epidermis or parenchyma cell walls. Similar analyses of dew-retted (unscutched) samples indicated that core tissues were mostly unchanged from unretted samples. Retted fibre tissues still contained lignified cell corners and middle lamellae in some regions. The cuticle, which was associated with retted fibres, was not degraded by dew-retting fungi. Fungi removed interfibre materials in some places and at times degraded the secondary wall near the cell lumen of fibre cells. Results indicate that microspectrophotometry and histochemistry are useful to identify the location and type of aromatics in fibre cell walls.

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.

Influence on Flax Fibers of Components in Enzyme Retting Formulations

A series of formulations with varying enzyme and chelator components is tested for flax fiber yield and properties using a recently developed enzyme retting system on Ariane flax grown as a winter crop in southeastern South Carolina. The levels of Viscozyme L, a commercial pectinase-rich enzyme mixture, and Mayoquest 200, a commercial chelator containing 38% ethylenediaminetetraacetic acid (EDTA) as tetrasodium salt, are varied. Enzyme retted flax straw is hand-carded and passed one time through a Shirley Analyzer for cleaning. The chelator level determines the fine fiber (i.e., Shirley cleaned) yield. Fiber strength measured by Stelometer is inversely proportional to enzyme level and not affected by chelator level. Fiber fineness measured by air flow methods is better with higher enzyme levels, and within enzyme levels the higher chelator levels tend to produce fibers with the highest degree of fineness. Relative cost calculations, taking into account fiber yield with costs of enzyme and chelators, provide a framework for determining retting efficiency and fiber quality. Results indicate that fiber properties can be tailored by enzyme or chelator levels. Further, commercial enzyme mixtures and chelators effectively ret flax and can serve as a basis for large scale retting tests.

Processing techniques for improving enzyme-retting of flax

Information is needed to optimize enzymatic-retting of flax (Linum usitatissimum L.) based on a pectinase-rich mixture and chelators. Seed flax straw from North Dakota in 1998, ‘Natasja’ fiber flax straw from South Carolina in 1993, ‘Ariane’ fiber flax straw field-aged and dried from South Carolina in 1999, ‘Ariane’ fiber flax straw shed-dried from South Carolina in 1999, and Canadian seed flax straw in 1997 comprised diverse samples that were subjected to various tests to improve absorption of enzyme formulation by stems or to evaluate clean fiber yield. Mechanical disruption by crimping stems through fluted rollers at about 80 Newtons gave optimum fiber yield in conjunction with enzymatic-retting and was, therefore, used in further tests to evaluate enzyme absorption. Enzyme absorption was increased significantly for uncrimped flax stems with increased pressure of about 310 kPa or with a vacuum around 88 kPa. Increased pressure was effective more than the vacuum treatment. Samples with minimal post harvest handling were affected more by pressure alterations than samples that had considerable disruptions, such as seed flax straw or field-aged straw. Crimped stems showed little increase in enzyme absorption with alterations in applied pressure. Mechanical treatment of stems by crimping gave the largest increase in enzyme absorption and increased significantly the fiber yields. Based on a variety of sample types, the results suggest that normal atmospheric conditions are satisfactory for penetration of enzyme formulation into crimped stems, and that extraordinary measures are not required to expedite the enzyme-retting process.

Sprayer control by sensing orchard crop characteristics: orchard architecture and spray liquid savings

The performance of a control system for an orchard air-carrier sprayer was evaluated. The sprayer control system used spray target information obtained from an ultrasonic measurement system. Based on the target measurements, three three-nozzle manifolds on each side of the sprayer were controlled by an on-board computer. Field tests were conducted to investigate the spray volume savings achieved through use of the control system. The relationships between spray volume savings and orchard target architecture were analysed for row sections in peach and apple orchards. Spray volume savings ranged from 28 to 52% and were strongly related to the target architecture.

Enzyme-Retted Flax Fiber and Recycled Polyethylene Composites

Municipal solid wastes generated each year contain potentially useful and recyclable materials for composites. Simultaneously, interest is high for the use of natural fibers, such as flax (Linum usitatissimum L.), in composites thus providing cost and environmental benefits. To investigate the utility of these materials, composites containing flax fibers with recycled high density polyethylene (HDPE) were created and compared with similar products made with wood pulp, glass, and carbon fibers. Flax was either enzyme- or dew-retted to observe composite property differences between diverse levels of enzyme formulations and retting techniques. Coupling agents would strengthen binding between fibers and HDPE but in this study fibers were not modified in anyway to observe mechanical property differences between natural fiber composites. Composites with flax fibers from various retting methods, i.e., dew- vs. enzyme-retting, behaved differently; dew-retted fiber composites resulted in both lower strength and percent elongation. The lowest level of enzyme-retting and the most economical process produces composites that do not appear to differ from the highest level of enzyme-retting. Flax fibers improved the modulus of elasticity over wood pulp and HDPE alone and were less dense than glass or carbon fiber composites. Likely, differences in surface properties of the various flax fibers, while poorly defined and requiring further research, caused various interactions with the resin that influenced composite properties.

Progress in enzyme-retting of flax

Abstract New methods for retting flax are sought to overcome problems in the current method of dew-retting of flax. Published data are reviewed and new data presented on the development and testing of a method to ret flax using pectinase-rich enzyme mixtures plus chelators based on cost and fiber yield and properties. In spray enzyme retting (SER), flax stems are crimped to physically disrupt the plants protective barrier and then sprayed until soaked with, or briefly immersed in, an enzyme/chelator formulation. Flax is then incubated at temperatures optimal for enzyme activity, washed, and dried. Pilot scale tests, conducted with 10 kg samples of flax retted with a series of formulations, showed that this method effectively retted flax stems from a variety of sources, including fiber flax, mature fiber flax, and linseed straw. Fiber yield, strength, and fineness were significantly influenced by variations in enzyme-chelator amounts. Cellulases inpectinase mixtures appeared to preferentially attack dislocations in fibers and fiber bundles resulting in loss of fiber strength. Polygalacturonases alone effectively separated fiber from non-fiber components. The SER method proved to be an effective framework for further tests on enzyme-chelator formulations that now must be integrated with physical processing to optimize the extraction of flax fibers based on cost and fiber yield and properties.

Color of Enzyme-Retted Flax Fibers Affected by Processing, Cleaning, and Cottonizing

Twenty-seven samples representing variations of retted flax fibers are analyzed using a color spectrophotometer and CIELAB models. Variables included enzyme or dew retting, fiber or seed flax, enzyme and chelator concentrations, and sequential cleaning steps. In addition to differences in color with enzyme or dew retting, the variables involved in enzyme retting also contribute to differences in the lightness, redness-greenness, and yellowness-blueness of the resulting fibers. Dew retted fiber flax, as well as seed flax that has weathered during storage prior to enzyme retting, is significantly darker than non-weathered, enzyme retted fiber flax. Pairwise comparisons show that lower enzyme concentrations (0.05% v/v as commercially supplied) produce redder and yellower fiber samples than those retted with higher (0.3% v/v) enzyme levels. Higher chelator levels, (i.e., 50 versus 25 mmol ethylenediaminetetraacetic acid) produce redder fibers. Fiber lightness significantly increases with additional cleaning steps. Results indicate that objective color measurements and color standards can define important fiber properties in order to tailor raw materials for specific industrial applications.

Production of Flax Fibers for Biocomposites

Natural fibers for many and varied industrial uses are a current area of intense interest. Production of these fibers, furthermore, can add to farmer incomes and promote agricultural sustainability. Flax (Linum usitatissimum L.), which has been used for thousands of years, is unparalleled in supplying natural fibers for industrial applications as diverse as textiles and paper, providing high value linseed and fiber from a single plant, and maintaining sustainable agriculture in temperate and subtropical climates for summer or winter production, respectively. As a value-added replacement for glass fiber from a renewable resource, flax fiber is recyclable, biodegradable, and sustainable for the economy, ecology, and society. To the point, DaimlerChrysler reported that natural fibers for automotive components required 83% less energy and were 40% less expensive than glass fiber components. A better understanding of the fiber characteristics that influence composite performance could lead to the development of additives, coatings, binders, or sizing suitable for natural fiber and a variety of polymeric matrices. Stems of flax require retting to separate fiber from nonfiber components and rigorous mechanical cleaning to obtain industrial-grade fibers. Considerable work has been undertaken to improve the retting process using specific cell-free enzymes, especially pectinases, to control and tailor properties for industrial applications. Fiber processing and use in composites are affected by variables such as length, uniformity, strength, toughness, fineness, surface constituents, surface characteristics, and contaminants. One of the main concerns for the composite and other industries in incorporating natural fibers, such as flax, into production parts is the fiber variability resulting from crop diversity, retting quality, and different processing techniques. Standardized methods to assess flax fiber properties, therefore, are needed to maintain quality from crop to crop and provide a means to grade fibers for processing efficiency and applications. Other parts of the plant stalk, notably the waste shive and dust, can potentially be utilized as coproducts to offset costs for producing the major products of fiber and seed.