Fishing and Gear Technology

Unit 2 - Fishing gear materials

2.4.4. Solubility test
This relatively simple chemical test does not require any particular skill in chemistry, or any equipment or complicated equipment. Safety precautions common for chemical laboratories should be observed, especially when working with boiling reagents. The requirement for the test are 25 ml test tubes, a heat source (e.g. Bunsen burner of alcohol lamp) a holder to hold the test tube into the flame, and the chemical reagents quoted in the table. If an electric hot plate is used instead of test tubes, glass beakers of 50 to 100 ml in size and glass stirring rods are used.

The fibres of the sample to be tested should be loose as possible. Therefore, the netting yarn is untwisted and the fibres are cut in to pieces of about 1cm in length. Coarse material, like split fibres, and monofilaments, should be reduced to very small pieces. Small samples of the material and 10 to 15 ml of the solvent should be put into the test tube. Further directions for the application of the solubility test may be taken from Table. The reagents quoted have been selected so that only one reaction needs to be observed i.e soluble or not soluble.

In most cases it will not be necessary to conduct the test with all reagents given in Table

• Polyamide (PA) fibres are soluble in the reagents (a) and (e). If it is desirable to separate the two types from one another, (c) can be used, it which PA 6 is soluble but not PA 6.6
• Polyester (PES) fibres are not soluble in (a),(f) and (g).
• Polyethylene (PE) and polypropylene (PP) fibres are not soluble in (b) and (c).
• Polyvinyl chloride (PVC) (not after-chlorinated; see note(3) in table 2 is the only synthetic fibre here mentioned which is soluble in reagent (g) at room temperature.
• Saran (PVD) may be identified by its solubility in (f) and (c).
• Polyvinyl alcohol (PVAA) (after – treated with formaldehyde; see note (4) in Table 2) is soluble in (a) but not in (e).
• PE and PP cannot be distinguished from one another by a solubility test. The burning test (Table) shows some differences in the reactions of these two synthetics but it is not always sufficient for identification. The most reliable method to distinguish PE from PP is to determine the melting point.

Table-identification of synthetic fibres by solubility tests

Reagent\kind of fibre	PA 6.6	PA 6	PES	PE	PP	PVC	Saran	PVA (A)
(a) Hydrochloric acid/HCL (37%) 30 minutes at room temperature	+	+	O	O	O	O	O	+
(b) Sulphuric acid/H2SO4 (97-98%) 30 minutes at room temperature	+	+	+	O	O	O	(+)	+
(c)Dimethylfomamide/HCON(CH3)(1) 5 minutes boiling	O	+	+	O(2)	O(2)	+(3)	+	O
(d) Formic acid/HCOOH(96-100%) 30 minutes at room temperature	+	+	O	O	O	O	O	+
(e) Glacial acetic acid/CH3-COOH 5 minutes boiling	+	+	O	O	O	O	O	O
(f) Xylene/C6H4(CH3)2 5 minutes boiling(inflammable!)	O	O	O	+	+	O(2)	+	O
(g) Pyridine 30 minutes at room temperature	O	O	O	O	O	+	(+)	O

+ = soluble O = not soluble; (+) = soluble only if boiled, but not at room temperature.

(1) Dimethylformamide is decomposed by exposure to light even when store in a brown bottle. It should be stored away from light and preferably in a cool place. (2) Destroyed but not soluble. (3) Soluble already at room temperature.