Processing of HDPE by compression moulding: study of the volatile substances content

According to the most recent European directive, any organic compound with a boiling temperature lower than 250 °C at atmospheric pressure must be considered as a volatile organic compound (VOC). These substances can migrate from the matrix in which they are contained, such as food packaging. In the case of food contact materials, regulation (EC) 1935/2004 2 provides a harmonized EU legal framework and establishes the general principles of safety and inertness for all materials intended to come in contact with food. Therefore, the design of any product that will have such use must be suitable to minimize the release by the polymeric material of all the substances mentioned in the European directives. In this study, the compression moulding process (a technology developed by SACMI Imola S.C.) was evaluated from the point of view of volatile organic compounds profile. Compression moulding offers numerous advantages, including a low extrusion temperature and low mechanical stress applied to the polymeric material. We have implemented different VOCs extraction methods and gaschromatographic analysis for quali-quantitative studies of such compounds. In particular, GC-MS analysis were carried out on HDPE samples subjected to a thermodesorption by analyzing the substances produced. This type of analysis is necessary for the identification of different compounds in the polymer matrix. In order to quantify the VOCs, a more accurate GC-FID determination with internal standard has been run on microwave assisted extracts. Afterwards, compression moulding tests were conducted with two types of commercial HDPE. Two process parameters are evaluated in the tests, namely the temperature profile of the extruder zones and the cycle time (productivity). Finally, the volatile compounds present in the molten polymer at the extruder outlet and in the caps moulded with the most robust analytical techniques (GC-FID) were analyzed. The results show that the passage in extruder, in the condition used for subsequent compression moulding, implies a decrease in volatile compounds, and the subsequent compression molding increases this effect. Moreover, for both polyolefin matrices processed, any type of processing used does not lead to a degradation of the material, but to a reduction of volatile substances already present in the starting material (linear chains oligomers with even number of carbon atoms). Continuous Compression Moulding (CCM) is therefore a packaging manufacturing process that does not modify the characteristics of polymeric starting materials. This process could prove to be important, even fundamental whenever the starting material shows to be subject to significative degradation.