ASTM D3749 Vinyl Chloride Monomer determination in PVC by Gas Chromatographic Headspace technique

Scope:

ASTM D3749 test method helps determine the amount of unreacted vinyl chloride monomer in a PVC resin. It measures RVCM, which is essential for specifying purposes, manufacturing control, and accepted application principles. The sample equilibration and temperature maintenance are also studied, which enhances the durability of the PVC resin.

Procedure:

In ASTM D3749, the sample is prepared by mixing the resin with water and it is then placed in an analyzer turntable. The sample is equilibrated, and a gas chromatographic technique is applied to pack the sample with polymer beads which are then passed through a stream of carrier gas resulting in the purification of the VCM (vinyl chloride monomers). A standard sensing device records its retention time and relative concentration.

Specimen size:

As per ASTM D3749, the nominal concentrations of vinyl chloride in nitrogen gas should be 5, 50, and 500 ppm by volume (vppm).

Data:

In ASTM D3749, the headspace equation for the VCM/PVC resin system is as follows:

Where: C_vcm = concentration of the residual vinyl chloride in the resin, ppm by weight
Aₛ = VCM peak area in sample, counts,
Pₐ = atmospheric pressure, mm Hg,
R_f = average response factor counts per vppm,
T₁ = laboratory temperature, °K
M_v= molecular weight of VCM (62.5 g/mole), and
V_g = free vapor volume of the vial, cm3.

Conclusion:

ASTM D3749 test method determines the residual vinyl chloride monomer content of PVC resins, with the range for this test being 0.1 to 400 ppm residual vinyl chloride monomer (RVCM).