Extrusion International 4-2024

43 Extrusion International 4/2024 sumer plastic is of urgent need. Only through control of plasma processes a sufficient barrier can be applied on various surfaces [KBD22, AAB+23, PWNC22]. Includ- ing different barrier characteristics in relation to changing material sur - face properties to enable migration barriers [KBD22, AAB+23, SHT+23]. To address the challenges of bar - rier deposition on varying surface qualities of recycled materials, due to impurities, differing rough nesses and molecular distributions a mul - tilayer coating approach is consid - ered. The decoupling of SiOx barrier efficiency from deposition on surfac- es with varying properties is impor- tant, since the barrier properties are coupled to the deposition quality [KBD22, VPA+22, JHB+17]. Previous study has been conducted to over - come the challenges by the use of a organosilicon (SiOCH) intermediate coatings to decouple the properties of SiOx barrier coatings from the varying above mentioned surface properties of the underlying sub - strates [KBD22]. Organic SiOCH lay- ers containing high organic carbon amount are considered to be weakly crosslinked, elastic, ductile and rela- tively soft barriers with low perme- ability and high surface roughness, enabling them to act as optimal in - termediate layers [KBD22, VPA+22]. Hence, the SiOCH layer acts as a sur - face promoter and stress reliver for the brittle SiOx layer deposition since the SiOCH layer can be designed pri - or to efficient SiOx deposition and decouple the challenges of direct SiOx deposition on the correspond - ing substrate [VPA+22, JHB+17]. For the SiOCH layer deposition the same monomer as for the SiOx under dif - fering lower to none oxygen input is applied [KBD22, JHB+17]. Further, a low fragmentation is desired to de- posit a high organic content compo - sition. Therefore, low energy input is required proper to lower monomer defragmentation [KBD22, VPA+22]. The applied SiOCH interlayer pro - motes the adhesion and decouples the resulting barrier properties for SiOx of the applied barrier compos - ite to the surface [VPA+22, JHB+17, KBD22]. Further having a lower en- ergy input in combination to lower oxygen contents for SiOCH coat - ings as compared to SiOx coatings, etching processes of the substrate surfaces can be inhibited to protect weakly structured substrate surfaces [AAB+23, KBD22, CLW01]. Addition- ally, dyad barrier systems consist - ing of SiOx with SiOCH interlayers were conducted, relieving the layer stresses without reaching the critical layer thickness to increase the total thickness of SiOx barriers and further improving the barrier properties [KBD22]. The previous conducted multilayer coating study in combi - nation to the novel contamination approach and proposed character - ization chain will be the basis for the barrier developments and evalua - tion of migration mechanisms. Results from a novel contamination approach FDA or EFSA guidelines require an introduction of model contami - nants in which the virgin plastics are stored under certain environmental conditions with the contamination surrogates and then purified before testing [Foo21, EU 22]. A novel con- tamination approach of PP at the IKV is conducted by a direct introduction of the contaminants in virgin poly - propylene [Moplen HP640J] sam- ples. Due to this novel approach, a higher concentration of certain suit - able contaminants can be efficiently achieved. For an effective barrier evaluation on PP various chemicals based on volatility and polarity re - Picture 5: Infrared spectra of extracts in DCM from virgin PP, blank PP and butyl benzoate in PP and of pure butyl benzoate Picture 6: Thermogravimetric and derivative thermogravimetric curves of virgin PP, blank PP and butyl benzoate in PP