Extrusion International 4-2024

42 Extrusion International 4/2024 PLASMA COATING – FROM THE RESEARCH possess efficient barrier functional- ities, leading to their widely distri- bution in packaging industry as gas barriers, reducing the permeations from packaging [CLW01]. Based on layer structures e.g. cross-linkage, porosity and op- tical transparen- cies various macroscopic properties with permitting permeation of dif- fering molecules can be achieved [AAB+23]. In order to deposit SiOx barriers with efficient barrier properties a high fragmentation is desired according to literature [AAB+23]. A higher fragmentation can be initiated by a higher oxygen environment in combination to high energy input [KBD22]. Resulting na- noscale SiOx layers are attributed to hard, highly crosslinked and brittle glassy structured efficient gas barri- ers containing low organic content with smooth low ductile surfaces [JHB+17, VPA+22]. Further, na- noscale PECVD coatings on plastics can be introduced into existing re - cycling processes without any nega- tive influences [VPA+22]. Transfer- ring the idea of gas permeation barriers to migration barriers ap - plied to PCR, a migration limitation of hazardous contaminations could be potentially carried out by SiOx coatings ( see Picture 3 ) [KBD22, WF11]. Generation of model-recyclates for barrier development Prior to initiating the develop - ment of effective barrier layers, it is imperative to consider post-con- sumer recyclates sourced from vari - ous disposals, recycling strategies and environmental factors [KBD22, PWNC22]. The dynamic life cycle factors of recyclates inherit varia - tions in chemical compositions and physical properties, resulting in an inhomogeneous products stream quality and challenges in barrier de - velopment [Pfa22, KBD22]. Consid- ering differences not only in terms of a contamination perspective but also regarding the processing of post-consumer materials, as well as their applications, especially with- in the realm of food-related sec- tors, is associated with limitations [PWNC22, RDv17, Ber22]. Taking the contaminations in a complex matrix respectively to the physical and chemical properties of the recy - cled post-consumer plastics into ac- count, the quantification and quali- fication of the migration behaviour of contaminants in those matrices is necessary. Therefore, not only the barrier development is from urgent need but also the implantation of an analysis chain to determine the effi- ciency of these barriers and meeting the desired migration requirements ( see Picture 4 ) [YLC+21, FHP94]. To reduce the complexity and ac - celerate barrier development, virgin materials can be contam- inated with determined chemicals prior for barrier evaluation. The barrier evaluation contains the introduc - tion of the contaminants into virgin plastics, followed by barrier devel- opments, migration testing and analysis. The migration testing pro- cedures and analysis are determined by official regulations in relation to the specific application fields. Prior for barrierdevelop-ments the analy- sis is designed appropriate to the introduced chemicals. This general process is similar to the evaluation of recycling processes based on the regulation of the FDA or EFSA, where so-called challenge test chemicals are introduced into pris - tine plastics to evaluate their decon - tamination during recycling [Foo21, EU 22]. Insufficiant quality and immense application potential for food pack- aging of post-consumer polypropyl- ene are the key motivation points of the research at the IKV to ad- dress and overcome challenges as - sociated by contamination, herby implementing effective migration barriers especially to reintegrate post-consumer polypropylene [Sys- talen PP-C14900 gr000] to the circu- lar economy. Challenges in development of functional barriers on recyclates Beneath the challenges of migra - tion analysis to corresponding SiOx plasma barriers, a fun- damental understanding to the plasma de - position on virgin and recycled con - Picture 3: PECVD coatings as potential migration barriers Picture 4: Proposed migration evaluation process for barrier developments