Evidence and potential explanation of the influence of fiber length on the High Volume Instrument measurement of cotton fiber strength

Abstract

This study explores the influence of cotton fiber length characteristics on the High Volume Instrument (HVI) strength measurement. A set of cotton samples cut at different lengths from a common parent sliver was used. HVI strength data exhibited a consistent trend as a function of the fiber length properties. This data was analyzed using the working hypothesis that the HVI estimates the total mass of fiber at a position between the jaws, rather than the true mass, which contributes to the breaking force. A quantitative model was developed to correct for this overestimation based on the shape of the Fibrogram. It was demonstrated that the Fibrogram can be adequately modeled as a straight line in the region of the HVI strength measurement. Based on this, it was found that the required correction factor is a function of the mean fiber length and various geometrical parameters of the HVI instrument (i.e. (a) the distance from the base of the beard to the inside edge of the clamp nearest the base of the jaws, and (b) the actual position of the beard's fiber length determination relative to the clamping jaws). Importantly this correction factor is independent of the shape of the fiber length distribution. Application of this correction factor approach was able to remove the effect of fiber length on the corrected strength values. The same model was also applied to other published data and, again, a simple correction factor based on mean fiber length adequately 'removed' the observed bias.Cotton length and strength are two important fiber quality parameters that are commonly measured using the Uster High Volume Instrument (HVI) (e.g. ASTM Test method D 4605-86 1 ). For example, the Agricultural Marketing Service of the United States Department of Agriculture (USDA) specifies a range of cotton fiber quality parameters, including fiber strength and length characteristics based on HVI measurements.Average length and strength values of US cotton have both steadily improved, 2 and it is assumed that these values reflect real and separate improvements in both characteristics. Indeed, plant breeders develop strategies for new varieties with improved length and strength on the assumption that both are separate parameters that require attention.Cotton fiber length is generally quite variable within a sample and description of the length distribution has been the subject of a wide range of studies (recent work includes Krifa 3,4 and Lin et al. 5 ). Fiber breakage during ginning is a major contributor to the broadening of the length distribution, and as Krifa 3 notes, modeling of the length distribution is dominated by applications of 'breakage models'. 6-8 Krifa 4 demonstrated that a mixture of two Weibull probability density functions adequately fits the experimental length distribution data.

Development of the correction procedure for High Volume Instrument elongation measurement

“…These shorter fibers will not be broken in HVI tensile property testing. 25,26 Another contrast between the devices is that the HVI uses a constant rate of elongation and the Stelometer use a constant rate of loading. 27 In addition, the Stelometer has an estimated instrument breaking speed of 0.3 cm/min, while the HVI presents an estimated breaking speed of 12.3 cm/min.…”

Reflectivity and fluffiness coupled optical algorithm for colored cotton fibrogram of random-beard image method

“…3,20,21 Although its principle was unclear, 22,23 it was proved to have high consistency with HVI using the beard for raw cotton. 24,25 It was often employed as a standard method for other methods in the literature. 26–29 As AFIS can measure colored fiber length in principle, it could also be applied as a reference for the new method.…”