High Volume Instrument and Advanced Fiber Information System were used to determine cotton fiber properties, like micronaire, strength, maturity ratio, fineness and so on. HVI is a bundle test instrument which checks bunch of fiber samples at the same time and determines an average value (Parthasarathi, 2008). Under normal operating conditions, HVI can completely evaluate a group of fiber samples in approximately 20 seconds (Parthasarathi, 2008). HVI is useful to test the following fiber properties:
Micronaire. Micronaire detection is based on the relationship between a specific area and airflow (Apex Enterprises). Micronaire is an indirect indication of fineness and maturity. It affects textile processing, spinning performance, neps formation, and dyed fabric appearance (Estur & Knappe, 2007).
Strength and Elongation. The strength acquired in HVI is bundle strength, which refers to the ratio of breaking load in pounds to unit bundle weight in mg (Stewart et al. 2010). Before testing, a bundle of fiber samples are randomly selected and automatically prepared; they are subjected to comb in order to remove loose fibers and foreign materials, straighten the clamped fibers, as well as to remove crimps (Negahdari & Salehi, 2012). During fiber strength measurement, a bunch of fibers are clamped between two pairs of clamps at a certain distance; a pair of clamps pulls away the fibers from the other pair at a constant speed to break the bunch fibers (Parthasarathi, 2008; Stewart et al. 2010). The fibers traveled right before the breakage point is known as the elongation (Parthasarathi, 2008). The whole testing process is automated and quick.
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Length. The HVI system provides a fiber length distribution in quick. It employs a fibro- sampler to grad a part of fibers from the whole sample; the subsample is to be automatically created parallel and scanned to measure the length (Kelly, Hequet, & Dever, 2012). The length measured by HVI is called upper half mean length (UHML), which is an average length of the longest one-half fibers within a sample (ASTM, 1994b). The HVI system doesn't look over the short fibers. In commercial practices, the UHML measured is a supplement for raw cotton classification; however, the limitation of the approach is that the results are normalized.
AFIS method works with an aeromechanical processing, which measures fiber samples under almost the exact same conditions as the real-world processing (Hequet & Ethridge, 2000). The AFIS system measures essential cotton fiber properties, like maturity ratio, length, neps, nep size, short fiber content, fineness, immature fiber content, and trash content (Bragg & Shofner, 1993). In this discussion part, we particularly focus on fineness and maturity ratio. AFIS fineness is generally defined as a gravimetric fineness or linear density, which is the cell wall area times a constant (Ramey, 1982). Maturity ratio retrieved form AFIS is expressed as the cell wall area divide by the squared parameter of the same circle (Lord & Heep, 1988).
3.2.1 HVI micronaire
Micronaire readings provide us with a composite of fiber cross-section and relative wall thickening; it is often treated as the fiber maturity measurement in classing-office data (Bradow & Davidonis, 2000). A bundle of fiber sample with known weight is compressed and examined at one time in a given volume chamber; a steam of air will be passing through the plug of fibers. The volume of air we acquired is the micronaire (Parthasarathi, 2008), which is a combination of maturity and fineness. Maturity and fineness are highly correlated within the same cotton cultivar (Gillham et al., 1995). Inclement weather has an adversely impact on fiber maturity and fineness; immature fibers contribute to poor dye uptake and less fine fibers will affects yarn appearance, yarn uniformity, and yarn strength (Bradow & Bauer, 1997). Figure X and Figure Y summarize the results of irrigation treatments on four different cotton cultivar micronaires in 2010 and 2011, respectively. They show a change in micronaire as a function of genotype and irrigation level. The variance analysis in Table X show there is no statistically significant effects of cultivar, treatment, and there is no interaction effect on HVI micronaire of 2010 crop. For 2011 cotton fiber samples, Table Y show there is a significant effect of treatment, cultivar, and interaction effect between treatment and cultivar on the HVI micronaire. The different result is probably due to that it is very dry in 2011; however, in 2010 we got a lot of rains in Lubbock (USDA-ARS weather data). To better verify the results, we need conduct one more year field research. Another possible reason is that HVI instrument is not highly sensitive to the cotton fiber differences compared to the FTIR analysis.
3.2.2 HVI strength
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The strength of cotton fibers is attributed to the highly ordered crystalline structure, the rigidity of the cellulosic chains, and the extensive intermolecular and intramolecular hydrogen bonding (Moon, Martini, Nairn, Simonsen, & Youngblood, 2011; Siqueira, Bras, & Dufresne, 2010). The crystalline regions are essential to give fibers the required strength. Fiber strength refers to the force required to break a bundle of fibers or a single fiber (Bradow & Davidonis, 2000). The strength acquired in HVI system is bundle strength. A group of fibers are randomly selected and automatically prepared; HVI will test fiber strength by clamping and breaking the beard with 1/8-inch gage spacing between two clamp jaws (Parthasarathi, 2008). The strength reported is the force in grams required to break a bundle of fibers that is one tex unit in size; the tex unit represents the weight in grams of 1000 meter of the fiber (Chiparus, 2004). Measurement of fiber strength is of great importance because of the significant relationship between fiber strength and yarn strength. In textile industrial processing, cotton fibers with higher strength endure more vigorous mechanical handling than the fibers with lower strength (Faerber, 1995). Figure X and Figure Y give the results of different irrigation level treatments on four different genotypes cotton strength of 2010 and 2011, respectively. They show a change in strength as a function of cultivar and irrigation level. No significant effects (P-value> 0.05) were found from treatment, cultivar, and the interaction between treatment and cultivar for 2010 cotton fibers. The statistical analysis of the effect of irrigation treatment and cultivar on 2011 cotton fiber strength is shown in Table X the results demonstrate that there is a significant effect of treatment and the interaction between treatment and cultivar (P-value> 0.05); but there is no statistically significant effect of cultivar. As mentioned before, fiber is made of crystalline structure and amorphous regions, mature fibers are inherently stronger than immature fibers due to more crystalline cellulose structure, but this is sometimes hardly seen clearly in the HVI bundle strength test. For immature fibers, it is also possible to produce a good bundle strength value because of the improper assessment of fiber linear density and bundle weight as well as more fiber ends and surface area in immature fibers. Due to the insensitivity of the HVI bundle strength test, we need conduct more sensitive FTIR test to analyze the crystalline cellulose structure changes in the fibers.
3.2.3 HVI length
The HVI system measures the upper half mean length in quick. The principle of HVI is to measure light attenuation produced by scanning a sample of parallel fiber beard and output the fiber length distribution (Harzallah & Drean, 2011). Dividing the mean fiber length by the UHML, the ratio obtained is uniformity index (UI) (Azzouz, Ph, Hassen, & Sakli, 2008). The disadvantage of HVI is that it doesn't measure the short fibers that have length less than 0.15 inch (ASTM Standards, 1994). AFIS method is another helpful way to measure fiber length. The fiber length measured by AFIS is the individual length by number or by length as defined by ASTM standards; nevertheless, the shortcoming of the system is that it overestimates the short fiber content, fiber breakage and underestimates fiber length (Bragg & Shofner, 1993). Figure X shows the results of different irrigation level treatments on four different genotypes cotton length of 2010. The statistical analysis demonstrates that there are no significant effects of cultivar and no interaction between cultivar and irrigation levels. It reveals significant from the irrigation levels, because fibers from well irrigated field are normally longer. Figure Y presents the irrigation treatments on four cultivars cotton length of 2011. Statistically significant effects were observed from cultivars, treatment, and the interaction between cultivar and treatment.
3.2.4 HVI elongation
The amorphous regions in cotton fibers are essential for elasticity and flexibility, as well as enduing fibers the ability to absorb water, dyes, and chemical finishes. HVI, FAVIMAT, and stelometer are three commonly methods that are adopted to measure fiber elongation properties in the cotton industry. FAVIMAT is used for individual fiber testing, while stelometer and HVI are adopted to bundle testing. In practical applications we are according to different needs to choose the right method. FAVIMAT, an automatic single fiber-testing instrument, is used to provide researchers tensile properties distribution of single fibers from limited materials; it is helpful for fineness testing as well (Cui & Thibodeaux, 2010). The distributions of sample properties are readily obtained when single fiber testing is performed which may allow for more data available for cotton breeders; therefore, FAVIMAT is a satisfactory tool for measuring cotton elongation property and to aid breeders in making more informed decision (Cui & Thibodeaux, 2010). The shortcoming of the FAVIMAT is tedious and time-consuming because we need examine the samples one by one. Stelometer is a bundle test method which provides a constant rate of load and a measurement of fiber elongation as well as the breaking strength at both 1/8 inch and 0 gauge lengths (ICAC report, 2006). Stelometer testing results are well correlated with FAVIMAT results (Cui & Thibodeaux, 2010). HVI is another bundle test method which is faster than Stelometer. Benzina et al. (2007) confirmed the ability of the HVI system to produce reliable elongation data in their work. Backe (1996) reported that the higher the cotton fiber bundle elongation, the better the yarn's quality and resistance to the stresses during textile processing. Based on fiber bundle test, HVI checks many fibers at the same time and the average value determines. The results of HVI elongation from four cultivars as a function of irrigation level treatment from 2010 and 2011 were summarized in Figure X and Figure Y. Significant effects were found from the cultivar and their irrigation levels, however, no interaction effect was observed for 2010 crop. There are statistically significant effects of cultivar, their irrigation level, and the interaction between cultivar and irrigation level on 2011 cotton fiber elongations.
3.2.5 AFIS maturity ratio
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"Maturity ratio is the ratio of fibers with a 0.5 or more circularity divided by the amount of fibers with a 0.25 or less circularity; the higher the maturity ratio, the more mature fibers are and more high quality fibers are for dyeing and processing." (Anthony, 2005). Figure X presents the results of different irrigation level treatments on four cultivars maturity ratio of 2010. Statistically there are no significant effects of cultivar, their irrigation treatment, and the interaction between cultivar and treatment. Figure Y shows the irrigation treatments on four genotype cotton maturity ratio of 2011. The statistical analysis demonstrates that the cultivar and irrigation level both have significant effects on AFIS maturity ratio. The significant effects from interaction between cultivar and irrigation level are also observed.
3.2.6 AFIS fineness
Fineness is generally expressed as gravimetric fineness or linear density. Fineness is a relative property arising from the diameter, perimeter, and cross-sectional area (Hsieh et al, 1995). The fineness or linear density of a fibers is calculated by multiplying the know cell wall density (Ï = 1.52 g/cm3) by the cell wall area of the fibers, that is H = ÏAw. The area of fiber cell wall depends on maturity, the degree of secondary cell wall thickness (or theta). AFIS is a reliable individual fiber quality measurement. AFIS is required to be checked, cleaned, and calibrated before measuring samples to provide for good data. Gravimetric fineness measured by AFIS is defined as the mass per unit length expressed as millitex (Hequet & Wyatt, 2001); a millitex equals to 1000 meters of fibers with a mass of 1 milligram (Ramey,1982; Munro, 1987). Figure X and Figure Y show the results of different irrigation level treatments on four different cultivars AFIS fineness of year 2010 and 2011, respectively. For 2010 crop, there are no significant effects of cultivar, irrigation level, and the interaction between cultivar and irrigation treatment on AFIS fineness. For 2011 cotton fibers, the statistical analysis shows that there is no significant effect of cultivars on fineness; however, the analysis of variance reveals significant from the irrigation levels and the interaction between cultivar and irrigation treatments.