GMW GMW17224 PDF

Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. Measure the percent silica producing volatiles present in liquid injection molded silicone, heat cured silicone rubber or one component room temperature vulcanizing (RTV) silicone sealant regardless of cure system.

Applicability. Silica producing volatiles are contributors to the fouling of oxygen sensor systems used to control vehicle exhaust emissions. Encapsulating electronics in silicone liquid injected molded products may result in these low molecular weight extractable (cyclic dimethyl-siloxane) disrupting electrical function. As a contributing source of contamination, the volatile potential of silicone can be accurately monitored using this procedure. Utilizing this procedure in conjunction with a realistic maximum volatility tolerance level for end use silicones can minimize risk of component dysfunction.

Consistency. To avoid variation in measurements to production parts or sealant, and when comparing test results, the following must be strictly controlled:

• Time from molding to test (3.3).

• Extraction or shake time (5.2.1).

• Specific gravity (5.3.2) of the silicone part or sealant evaluated must be used to determine compliance to the maximum percent specified on the release print.

Remarks. This procedure consists of the following four (4) basic steps:

1.The silicone sealant is cured to its elastomeric form and molded parts are sampled.

2.The volatiles (cyclic dimethyl-siloxane) are extracted from the cured silicone.

3.The extract is separated and measured by gas chromatography (GC).

4.The GC results are quantified using a siloxane standard solution calibration.