ISO 248-2:2019 pdf download – Rubber, raw – Determination of volatile-matter content
1.1 This document specifies two thermogravimetric methods for the determination of moisture and other volatile-matter content in raw rubbers by using an automatic analyser with an infrared drying unit.
1.2 These methods are applicable to the determination of volatile-matter content in synthetic rubbers (SBR, NBR, BR, IR, CR, IIR, halogenated IIR and EPDM) listed in ISO 1629 and to various forms of raw rubber, such as bale, block, chip, pellet, crumb, powder and sheet. These methods might also be applicable to other raw rubbers only when the change in mass is proven to be due solely to loss of original volatile matter and not to rubber degradation.
1.3 The methods are not applicable to raw rubbers which need homogenizing as specified in ISO 1795.
1.4 The hot-mill method and the oven method specified in ISO 248-1 and the methods specified in this document might not give identical results. In cases of dispute, therefore, the oven method, procedure A, specified in ISO 248-1:2011, is the referee method. NOTE These methods can be useful for routine determinations, e.g. quality control, when the measurement conditions for the automatic analyser are fixed for a particular raw rubber or grade of raw rubber.
7 Sampling and preparation of test portion
Take a laboratory sample in accordance with the method specified in ISO 1795, and then prepare a test portion of between 2 g and 15 g from the laboratory sample. The actual mass of the test portion depends on the type of analyser, the expected volatile-matter content, and the form of the sample. For raw rubbers in bale form, the test portion shall be cut into small pieces of volume less than about 350 mm 3 (in the ideal case of a cubic piece, the length of a side should be about 7 mm). This operation shall be carried out as quickly as possible so as not to lose volatile matter.
8.1 General
Either method A (which uses a pre-defined drying time) or method B (in which drying ends when the mass loss rate has decreased to a pre-defined level) can be chosen, provided the automatic analyser used offers the choice. The endpoint (the pre-defined drying time for method A or the pre-defined mass loss rate for method B) shall be determined for each of the two methods for each type or grade of rubber to be analysed. Examples of test conditions are given in Annex A.
8.2.2 Then, for method A, take a test portion of between 2 g and 15 g and weigh it to the nearest 1 mg. Operating the automatic analyser in accordance with the manufacturer’s instructions, set a drying temperature (preferably between 100 °C and 120 °C) and obtain a drying profile (X-axis: time in min, Y-axis: volatile matter lost, in %). From the drying profile (see Figure 1), determine the time at which the volatile- matter content determined by the automatic analyser is equal to that determined in 8.2.1. Take this drying time as the pre-defined drying time to be used in method A for this particular type or grade of rubber.
8.2.3 For method B, take a test portion of between 2 g and 15 g and weigh it to the nearest 1 mg. Operating the automatic analyser in accordance with the manufacturer’s instructions, set a drying temperature (preferably between 100 °C and 120 °C) and obtain a drying profile (X-axis: time, Y-axis: mass). From the drying profile (see Figure 2), determine the mass loss rate at the point on the profile where the volatile-matter content corresponds to that determined in 8.2.1. Take this value of the mass loss rate as the endpoint for use in method B for this particular type or grade of rubber. NOTE The automatic analyser can be programmed to calculate this value automatically.