1. Scope

1.1 This practice covers the accelerated drying of flax fibers using combinations of drying temperatures and durations to prepare material for use in processes or test methods where: chemical changes to the flax fiber during drying are to be minimized or avoided and the required moisture content of the flax fibers is such that it should be in equilibrium at 0%RH at the temperature the processing or testing will occur. 1.2 The practice includes two methods to dry material. Method selection depends on the percentage of moisture present in the flax when received and the level of chemical composition preservation required for subsequent testing. 1.3 While the practice will dry flax fiber, the practice does not include a test method for the determination of the amount of moisture in the material. For moisture content testing, other standards for cotton, wool or wood (ASTM D2495 Standard Test Method for Moisture in Cotton by Oven-Drying, ASTM D1576 Standard Test Method for Moisture in Wool by Oven-Drying, and ASTM D4442 Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials, respectively) should be consulted.

Keywords

The scope has all the keywords needed::Oven; Drying; Flax; Equilibrium

Rationale

The chemical, physical and mechanical properties of flax fibers can be significantly altered with exposure to elevated temperatures and/or changes to the moisture content. In most cases it is preferable to not expose the flax fibers to elevated temperatures or extreme humidities prior to testing and conditioning following methods in ASTM D1776 Practice for Conditioning and Testing Textiles is appropriate. However, in some applications an equilibrium condition of 0% relative humidity is preferred, such as composite manufacturing where the presence of moisture in the fibers can interfere with bonding to a matrix or in test methods such density or FTIR analysis where the presence of moisture adversely affects the accuracy of the results. In those applications it is also desirable that the fibers are not subjected to any unintentional chemical changes which might affect later analysis such as that of lignin or acid detergent insoluble nitrogen. This practice offers time efficient methods of drying materials to an equilibrium condition of 0% relative humidity using elevated temperatures and durations known to be sensitive towards the chemical stability of flax. Currently, research papers published on topics where fibers were dried dont have a standard that can be cited. Many are using different temperatures and different durations, making comparing work challenging. Commonly, temperatures over 100C are used, likely originating from temperatures set in moisture content testing standards. While they effectively dry the fibers for moisture analysis, these temperatures have a significant, negative impact on fiber performance, making them inappropriate for secondary processing or many follow-on tests. In addition to the above, the composites industry is looking to utilize flax fibres as a source of reinforcement. Its anticipated that drying fibers practically and without damage in larger than test quantities is going to increase in demand. The temperatures and durations proposed are intended to be a resource for flax fibre or mat suppliers to composite fabricators. This work is drawing from already known information in the forage industry where drying organic matter is required before chemical assessment and being developed for flax.

The title and scope are in draft form and are under development within this ASTM Committee.