Resistance to stress cracking by wetting solution is one of the selected properties together with the corresponding test method FNCT and tolerances for a comparison of polyethylene grades of one design type in the procedural rule on suitability proof for alternative plastic resins used for packagings and intermediate bulk containers (IBCs) for the transport of dangerous goods.
The environmental stress crack resistance determined by Full Notch Creep Test (FNCT) represents the impacts from the stacking tests at 40 °C performed with standard liquid wetting solution (without pre-storage) and with normal butyl acetate saturated wetting solution (pre-storage with normal butyl acetate).
Environmental stress crack resistance determined with FNCT for the polyethylene grades was related to the times to failure of different jerrican samples made of these grades in stacking tests with 5% wetting solution and a n-butyl acetate saturated wetting solution (pre-storage with n-butyl acetate) at 40 °C. The FNCT is suitable for comparison of polyethylene grades in relation to environmental stress crack resistance independent of their use as drum, IBC or jerrican material. The stiffness of polyethylene grades should be taken into account to the comparison as jerricans are not only chemically but also mechanically stressed.
Resistance to stress cracking by wetting solution is one of the selected properties together with the corresponding test method FNCT and tolerances for a comparison of polyethylene grades of one design type in the procedural rule on suitability proof for alternative plastic resins used for packagings and intermediate bulk Containers (IBCs) for the transport of dangerous goods.
The environmental stress crack resistance determined by Full Notch Creep Test (FNCT) represents the impacts from the stacking tests at 40 °C performed with Standard liquid wetting solution (without pre-storage) and with normal butyl acetate saturated wetting solution (pre-storage with normal butyl acetate). Environmental stress crack resistance determined with FNCT for the polyethylene grades was related to the times to failure of different jerrican samples made of these grades in stacking tests with 5 % wetting solution and a n-butyl acetate saturated wetting solution (pre-storage with n-butyl acetate) at 40 °C. The FNCT is suitable for comparison of polyethylene grades in relation to environmental stress crack resistance independent of their use as drum, IBC or jerrican material. The stiffness of polyethylene grades should be taken into account to the comparison as jerricans are not only chemically but also mechanically stressed.
The material parameters melt flow rate MFR, density D, notched impact strength N.I.S. at -30 °C, stress crack resistance FNCT and resistance to oxidative degradation Ox (determined by the increase of MFR) have been selected for a comparison of polyethylene grades for one design type in the “European Standard EN 15507 - Transport packaging for dangerous goods - Comparative material testing of polyethylene grades”. The parameters have a systematic relationship with design type tests. The notched impact strength at -30 °C and the resistance to oxidative degradation of polyethylene grades determined with test specimens of compression moulded sheets are directly comparable with drop tests at -18 °C of design types produced of these grades after pre-storage with 55 % nitric acid for 21 days at 40 °C. The impact of the pre-storage time of jerricans with 55 % nitric acid at 40 °C and 23 °C on the marginal drop heights in drop tests at -18 °C, on the MFR and on the tensile properties tensile strength, breaking elongation and the elastic modulus were investigated. Packaging design types (jerricans) made of three polyethylene grades from different producers were pre-stored with 55 % nitric acid for 21,42 and 84 days at 40 °C as well as for six months at 23 °C. The MFR and tensile properties of test specimens taken from the design type side walls as well as the marginal drop heights of the jerricans in drop tests at -18 °C were determined.
The values of the notched impact strength at -30 °C of polyethylene grades are not comparable with the marginal drop heights determined in drop tests at -18 °C. The oxidative damaging impact of nitric acid has a greater effect on the grade with lower resistance to oxidative degradation by reducing more significantly the marginal drop heights with increasing pre-storage time.
Pre-damage with 55 % nitric acid for 21 days at 40 °C, as recommended in ISO 16101 and EN 15507 caused an increase in the marginal drop heights of most design types in drop tests when compared with design types without pre-damage. The test results demonstrated clearly that pre-storage of the jerricans for six months at 23 °C caused a higher increase in the MFR and lower marginal drop heights of the jerricans in drop tests at -18 °C compared with pre-storage of the jerricans for 21 days at40 °C.
The mechanical properties change as a result of diffusion of nitric acid into the polyethylene grades and the reaction of the nitric acid with the polymers. The percentage decrease and increase in the tensile strength, breaking elongation and elasticity modulus of test specimens taken from the design type side walls after different pre-storage times were only partly comparable with the marginal drop heights in drop tests at -18 °C.