Extrusion International 4-2024

44 Extrusion International 4/2024 PLASMA COATING – FROM THE RESEARCH garding to their applications e.g. ad- ditives were introduced. Through, a broad spectrum of contaminants, migration mechanisms and effects can be investigated related to the barriers and the plastic itself. The evaluation of the contamination procedure will be covered with sev- eral analytical techniques in terms of qualification, quantification and effects of the model substrates on PP properties to enable the concept of an efficient contamination pro- cedure, migration evaluation and thus barrier developments. The suc- cessful introduction of one of the predetermined model substrates into PP can be qualitatively observed in the Infrared spectra of the cor - responding extracts of the samples ( see Picture 5 ). Respectively for the differentia - tion of virgin and blank PP, blank PP is the processed version through compounder without adding any chemical. Seeing no absorption for the extracts of the virgin and blank PP respectively to the cor- responding absorption bands of the extract from the compounded butyl benzoate in PP, a successful qualitative contamination can be observed by comparing the visible absorption bands to the originat - ing absorption bands of pure butyl benzoate. A quantitative validation for the contamination procedure can be observed demonstratively in the thermogravimetric analysis (TGA) results for one of the model substrate butyl benzoate in PP in comparison to blank and virgin PP samples ( see Picture 6 ). A decrease of the weight percent- age and peaks of derivate ther- mogravimetry (DTG) curves of all samples can be seen at 430°C until 440°C, indicating a complete deg- radation of all samples. The weight percentage and DTG curve of the butyl benzoate in PP shows a de- viation to the other samples below 268°C. Since the boiling point of butyl benzoate is 250°C the de- crease before 268°C can be attrib- uted to the evaporation of the bu - tyl benzoate proving a successful introduction in PP. After complete evaporation at 268°C indicated by the merging DTG curves of all PP samples only the remaining PPs are degrading. Therefore, the differ- ence of the weight curves of the PP samples at 268°C can be assigned to the weight of evaporated butyl benzoate which is around 5 percent. The resulting smaller contamination amount than the desired 10 weight percent could be explained trough evaporation during the contamina - tion procedure, uneven distribution of the model substrates in the gran - ules and evaporation during stor - age trough migration. Migration analysis Under the aspects of an efficient barrier development, a respective barrier evaluation by a valid analy - sis chain is essential to understand the migration mechanisms of con - taminants in the polymer, plasma barrier and food matrixes [FHP94, KBD22]. Regarding the barrier mi- gration characterisation, a meth - odology needs to be introduced to assure a targeted analysis of all in - troducedmodel substrates after mi - gration processes. The methodolo- gy needs to be in accordance to the regulatory authorities in order to ensure the future applicability and authorization of the proven barriers [EU 11, EU 23, EU 22, Foo21]. The EU and EFSA regulations determine the scope of food contact plastics in terms of application, applicable functional barriers and both of their testing procedures regarding over - all migration limits and specific mi- gration limits for a broad spectrum of substances [Pfa22, EU 11, EU 23, EU 22]. According to the food contact testing, the experiments need to be performed through a contact to a specific food simulant [OLH+21, SWB07, RBS09]. Including, certain testing procedures related to sample preparation and contact conditions [RBS09]. By the quantita- tive and qualitative analysis regard - ing the migrated substances to the food simulant, the accordance to the migration limits is determined and an approval procedure for a certain food contact material can be induced [EU 11, EU 23, EU 22]. After the novel contamination procedure to introduce the model substrates to the corresponding polypropylene samples followed by barrier deposition, a migration testing including a purification and characterization of the surrogate mixture in the food simulant by gas chromatography coupled mass spectrometry (GC/MS) is supposed to be suitable to quantify and qual - ify the migrated substances and en - able a barrier development ( see Picture 7 and Picture 4 ). Achieving a basic understanding of migration mechanisms inside the polymer matrix, the plasma bar - rier structure and at the interface to the barrier layer is from high rel - evance to modify coating properties and to inhibit migration processes [PWNC22]. Therefore, all interacting layers will be characterized in terms of physical and chemical properties to display interactions correspond - ing to the migration behaviors of the model substrates inside the material matrixes as a basis for the barrier development. To ensure the previous mentioned understanding of mechanisms and development of plasma-based barriers, the migra- tion needs to be analyzed. Beside, enabling the transfer of the model approach results to recycled con - sumer plastics. Picture 7: Quantitative and qualitative migration analysis via GC/MS