GB/T 44307-2024 Carbon-fibre-reinforced composites - Determination of fibre weight content - Thermogravimetry (TG)
1 Scope
This document specifies a thermogravimetric method for the determination of fibre weight content by weight percent, of carbon fibre reinforced composites.
This method applies to prepregs and carbon fibre reinforced composites.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 291 Plastics - Standard atmospheres for conditioning and testing
Note: GB/T 2918-2018 Plastics - Standard atmospheres for conditioning and testing (ISO 291:2008, MOD)
3 Terms and definition
For the purposes of this document, the following terms and definitions apply.
3.1
fibre weight content
Wf
ratio of fibre weight to total weight of fibre based composites
Note: same as fibre content by weight, expressed as a percentage
4 Principle
A weighed test specimen is heated following a pre-set programme in a known atmosphere.
Initial pyrolysis in an inert atmosphere (nitrogen) is followed by combustion in an oxidizing atmosphere.
Generally, the reactions that generate mass variations are decompositions, oxidations, or reactions volatilizing a constituent.
Plotting the loss of mass as a function of temperature gives a quantitatively analysis on the carbon fiber content of prepreg or composite material.
5 Reagents
5.1 Nitrogen gas, of minimal purity 99.995 % mass fraction, with an oxygen content of less than 10 mg/kg (ppm) and hydrocarbon content less than 1.5 mg/kg(ppm).
5.2 Dry air, with no detectable trace of oil.
The air used may be reconstituted nitrogen and oxygen of purity minimum 99.5 % mass fraction. In some cases, pure oxygen may be used.
6 Apparatus -Thermogravimetric analyser
6.1 General
Various types of analyser are commercially available. The basic components of an analyser are listed in 6.2 to 6.8.
6.2 Thermogravimetric balance, comprising a microbalance provided with a pan made from a non- oxidizable material, that can weigh up to 50 mg, is readable to the nearest 1 μg, and equipped with an oven capable of being maintained at temperatures from room temperature to approximately 1000℃.
6.3 Furnace, allowing the sample to be heated under a specified atmosphere and temperature.
6.4 Pan or crucible, with a size suitable to accommodate the sample and small enough to reduce the influence of buoyancy, and without melting to 1000℃. Pan or crucible made of platinum or almina is recommended.
6.5 Temperature-control system, allowing heating rates to be controlled from 10℃/min to 50℃/min.
6.6 Gas selector, allowing successive introduction of the inert gas and oxidizing gas while controlling the flow rate.
6.7 Flow valve control and meter, for controlling gas flow rate in the range 10 mL/min to 250 mL/min.
6.8 Data acquisition and processing system, allowing temperature and weight data to be recorded and to be analysed during all the operating steps.
7 Samples
7.1 Conditioning of samples
Test samples shall be conditioned in standardized laboratory conditions of temperature and humidity. A quantity of material sufficient to complete the tests is taken as the test sample and conditioned for a sufficient time to re-establish temperature equilibrium. This conditioning shall be carried out in one of the standard humidity and temperature specified in ISO 291.
7.2 Preparation of samples
Prepare a test specimen of 10 mg±2 mg mass cut it as a single piece. They shall be less than 1 mm in thickness and shall be 3 mm to 5 mm in length and width. A number of test specimens shall be prepared according to the type of carbon fibre-reinforced plastic type of and purpose of measurement.
The test portion should be carefully prepared, since the test portion can influence the kinetics of the phenomena.
A number of test pieces depend on the type of CFRP or purposes of measurement. Standard deviation of fibre content measured by thermogravimeter for type of CFRP with weave clothes is almost the same as that measured by combustion (see Annex B). Three samples or more can be enough for CFRP with weave clothes. More than five of test portions can be required for the analysis of distribution of fibre content or CFRP with short fibres.
8 Test procedure
8.1 Operating steps
Table 1 gives details of the operating steps for the procedure.
8.2 Test processes
8.2.1 Connect the apparatus and adjust (6.6) the gas flow to a rate between 20 mL/min-250 mL/min (6.7). Set the parameters according to the chosen process. In the absence of equipment manufacturer' recommendation, use a flow rate of 100 mL/min.
8.2.2 Before the test, ensure that the pan (6.4) or the crucible is clean.
8.2.3 Close the thermogravimetric balance oven (6.2), purge with a nitrogen (5.1) flow at the preset rate. Wait until stabilization. Adjust the zero to compensate for the mass of the pan or the crucible.
8.2.4 Place the test piece prepared in accordance with Clause 7 in the pan or the crucible and weigh it under the conditions specified in 8.2.3. Record the mass, m0 after the reading is stable.
8.2.5 Conduct the test by following the operating steps specified in Table 1.
8.2.6 At the end of the test, allow the oven to cool to room temperature, open it and clean the pan or the crucible.
