An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer

TLDR

The study develops an empirical X‑ray diffractometer method to determine native cellulose crystallinity using focusing and transmission techniques. The method measures the 002 peak and amorphous scatter at 2θ = 18° to compute a crystallinity index, which is then correlated with acid‑hydrolysis crystallinity, moisture regain, density, degree of polymerization, and IR absorbance for cotton cellulose treated with ethylamine solutions. The crystallinity index proved to be a rapid, reliable proxy for relative crystallinity, with a standard error of 6.5 % across over 40 samples.

Abstract

An empirical method for determining the crystallinity of native cellulose was studied with an x-ray diffractometer using the focusing and transmission techniques. The influence of fluctuations in the primary radiation and in the counting and recording processes have been determined. The intensity of the 002 interference and the amor phous scatter at 2θ = 18° was measured. The percent crystalline material in the total cellulose was expressed by an x-ray "crystallinity index." This was done for cotton cellulose decrystallized with aqueous solutions containing from 70% to nominally 100% ethylamine. The x-ray "crystallinity index" was correlated with acid hydrolysis crys tallinity, moisture regain, density, leveling-off degree of polymerization values, and infrared absorbance values for each sample. The results indicate that the crystallinity index is a time-saving empirical measure of relative crystallinity. The precision of the crystallinity index in terms of the several crystallinity criteria is given. Based on over 40 samples for which acid hydrolysis crystallinity values were available, the standard error was 6.5%.