Tuning The Surface Structure Of BOPP Film With An Atmospheric Pressure Plasma

BOPP?Biaxially Oriented Polypropylene?film is widely used in packaging and printing field for its perfect properties,such as colorless,odorless,non-toxic,high tensile strength,impact strength,toughness and good transparency.However,the surface energy of BOPP film is very low,which limits its applications in some industry.Therefore,it is very necessary to improve the surface hydrophilic properties of BOPP film for the functionalization of BOPP materials.The low temperature plasma technology has been widely used for modifying the polymer materials because of its advantages,such as no damage to matrix,no need of c hemical solvent and dry-method modification.However,the traditional low-temperature plasma cannot be applied to modify the film with low value-added because the expensive vacuum systems are normaly applied.In addition,the aging problem of plasma treatment also limits its application in the field of film treatment.In this paper,we innovatively modified the BOPP film with the plasma polymerization under an atmospheric conditions or the plasma-coating mode to achieve a permanent modification of BOPP film,which is expected to be used for environmental-friendly printing and packaging.In order to achieve the hydrophilic modification of BOPP films,two treating protocols were used.The method 1: BOPP films were firstly pretreated by D BD plasma,secondly the PVA/SF/PEG mixture was homogeneously coated on the modified BOPP film.Finally,the functional PVA/SF/PEG was cured by ethanol to improve the anti-water property of complex coating.Meanwhile,the hydrophilic characteristics of modified BOPP film were exp lored by printing water-based ink on the coating.Method 2: The biocompatibility of BOPP film modified with the acrylamide polymer by using Ar/O₂ and He/O₂ plasma jets was investigated.The polar functional groups,such as COOH and –OH,were successfully grafted on the BOPP surface when it was pretreated by the dielectric barrier discharge plasma at ambient conditions.The grafted polar groups greatly improved the combining intensity between the BOPP film and the mixed coating?PVA/SF/PEG?,therefore,the stability of the modified BOPP increased obviously.Moreover,the tensile properties and optical properties of pretreated BOPP film with DBD plasma still maintained an excellent performance.The results show that the surface free energy of BOPP film can be improved obviously by grafting O-C and N-C functional groups on the surface of BOPP film.The contact angle of modified BOPP decreased from 105 °to 20 °.When the silk fibroin solution?SF?was mixed into the coating and treated by 60% ethanol,the silk fibroin solution was transformed from ?-helix to ?-sheet,causing that the transparent ratio of modified BOPP reached nearly 100%.Meanwhile,the PEG in the coating can increase the softness of PVA/SF/PEG coating.The other method for increasing the hydrophilic property of BOPP film is achieved by polymerizing acrylamine with an inert gas plasma jet.When the inert gas flow rate is 0.4 m³/h and O₂ gas flow rate is 0.1 m³/h,for the Ar plasma jet,its polymerization rate is about 200 nm/min,and the polymerization rate of He plasma jet is about 40 nm/min.At the same time,the amine film deposited by Ar plasma torch has better water resistance than that fabricated by He plasma jet.The size and density of the polymer nano-nodes are affected by the discharge gas?Ar/O₂ or He/O₂?type,and the gas flow rate.Under the same discharge conditions,the content of C-N/C=N and N-C=O/C=O bonds on the surface of modified BOPP film with Ar/O₂/ALA plasma jet was 14.5% and 17.3%,respectively.Compared to the He/O₂/ALA plasma polymerization,the functional bond contents were about 2.8 and 1.7 times.This result is attributed to the fact that the higher ion density of the Ar/O₂ plasma produced higher concentrations of ALA,leading to higher density carbonyl functional groups being grafted onto the BOPP surface.Cytotoxicity and adhesion measurement showed that the ALA polymer is friendly,and the modified BOPP surface adhered a large number of cells.Compared to the He/O₂/ALA plasma,the number of cells adhered on the modified BOPP was about higher 1.5 × 105/mm² when the original BOPP was treated by Ar/O₂/ALA plasma.This protocol not only overcomes the hydrophobic problems of the original BOPP film,but also improves its biocompatibility.