ISO 15040 pdf download.Composites — Prepregs — Determination of gel time
1 Scope
This International Standard specifies a method for the determination of the gel time of prepregs made of continuous reinforcement impregnated with epoxy and/or unsaturated-polyester resin. The method is applicable to most prepregs with a width in the range 300 mm to 1 000 mm. It is not suitable for very narrow prepregs (for example narrow tape), nor for prepregs with a low resin content. NOTE Other methods of measuring gel time exist. These methods are based on principles which differ from those described in clause 4, and the results obtained using such methods may be different from those obtained with this International Standard. The method described below is the traditionally used one and is widely accepted, even though it may be somewhat obsolete.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 291 :1 997, Plastics — Standard atmospheres for conditioning and testing. ISO 472:1 999, Plastics — Vocabulary. ISO 8604:1 988, Plastics — Prepregs — Definitions of terms and symbols for designations .
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 472 and ISO 8604 apply.
4 Principle
A test specimen is prepared by laying up square pieces cut from the prepreg sample and wrapped in an impervious film or foil. The resin is squeezed out by applying pressure to the specimen in a hot press preheated to the test temperature. The gel time of the resin is measured as the point at which it can no longer be spun or drawn into a thread.
5 Apparatus
5.1 Cutting template, made of a hard metal such as steel, or ceramic material, measuring 50 mm by 50 mm and about 2,5 mm thick. 5.2 Knife, single-edge. 5.3 Notched plate for measuring gel time, as shown in Figure 1 for example. The plate shall be sufficiently flat to ensure a uniform temperature distribution. 5.4 Heated-platen press, capable of raising the temperature to 200 °C and maintaining the pressure at 300 kPa to 600 kPa over a 50 mm by 50 mm area. The platens shall be sufficiently flat to ensure a uniform temperature distribution. 5.5 Release film, heat-resistant, for example tetrafluoroethylene-hexafluoroethylene copolymer (FEP). 5.6 Stopwatch, capable of measuring seconds. 5.7 Pick, 2 mm to 3 mm in diameter and about 1 50 mm in length, made of heat-insulating material such as wood or bamboo. 5.8 Wrapping material: aluminium foil about 1 5 µm thick or polymer film which is chemically inert towards the prepreg resin and has a melting point higher than the anticipated test temperature, for example tetrafluoroethylene- hexafluoroethylene copolymer (FEP) or polyimide.
6 Preparation of test specimens
6.1 A minimum of three specimens shall be tested from each sample. 6.2 Using the cutting template (5.1 ), carefully cut out pieces 50 mm by 50 mm square in one or more rows across the width of the prepreg. Cut out sufficient pieces so that, when they are placed one on top of the other, they will give specimens about 2,5 mm thick. If the necessary number of pieces cannot be cut out across the width of the prepreg (as with narrow tape, for example), they may be cut out in the longitudinal direction. The edges and selvedges of the prepreg shall not be included in any of the pieces.