Surface Modification Of Graphene And Its Application In Barrier PET

Barrier polyethylene terephthalate?PET?has wide application prospects in the fields of packaging,solar cells,flexible wearable devices,etc.,but its insufficient barrier performance limits its application in these fields.Graphene?GNs?modified polymer to improve its barrier performance has been a research hotspot in recent years,but due to insufficient interface between GNs and polymer matrix,it is usually difficult to exert the excellent barrier performance of GNs.Therefore,the surface of GNs is modified to enhance its Interaction with a polymer matrix to improve the performance of composite materials is the focus of attention in the art.In view of the deficiencies of the existing GNs surface modification technology that requires a large amount of organic solvents,this paper uses green and environmentally friendly supercritical carbon dioxide?SC-CO₂?as the reaction medium to combine the GNs surface structure design with the micro-nano laminated co-extrusion processing technology.Several silane coupling agents with different structures were used to adjust the surface properties of GNs,and the effects of different surface properties on the structure and properties of micro-nano laminated PET composites were studied to clarify the relevant mechanism.It can be a high-performance GNs/polymer composite The structural design and preparation of materials provide theoretical guidance.The main research contents and results of the paper are as follows:1.Using SC-CO₂as the reaction medium,three different structures of silane coupling agents KH550,KH560,KH570 were used to graft-modify the surface of GNs.The structure of silane coupling agent,the content of silane coupling agent and the reaction time on the form of GNs were studied.Influence of structure and surface properties.The results showed that KH550,KH560,and KH570 were successfully grafted onto the surface of GNs.The size of GNs aggregates modified by silane coupling agent was significantly reduced compared to unmodified GNs,and the aggregate structure was significantly fluffy.The aggregate structure of sexual GNs is the most fluffy.With the increase of the content of silane coupling agent,the grafting amount of modified GNs showed a tendency to decrease after the increase.When the ratio of graphene to silane coupling agent was 1:15,the grafting amount of modified GNs was the largest at 1.3513 mequi/g,the structure of the modified GNs aggregate is the most fluffy.With the increase of SC-CO₂reaction time,the grafting amount of modified GNs also showed a trend of decreasing after the increase.When the reaction time was 2h,the grafting amount of modified GNs was the largest,up to 1.4593mequi/g,modified GNs aggregates are small in size and fluffy in structure.2.The effects of GNs modified by silane coupling agents with different structures on the structure and properties of PET composites were studied.The results show that the dispersibility of GNs in the PET matrix is significantly improved after modification.The dispersion of GNs modified by silane coupling agents with different structures in PET groups is different.The dispersion of GNs modified with KH560 in PET is the best.After the modification,the interface between GNs and PET matrix is enhanced,and the interface between GNs modified with KH560 and PET matrix is the strongest.The crystallization behavior and crystal structure research results show that GNs has obvious heterogeneous nucleation effect on PET.After modification,the heterogeneous nucleation effect of GNs on PET is not obvious,but the initial nucleation rate is significantly enhanced,and the crystallinity change is not obvious.In the GNs/PET composites before and after modification,spherulites with a size of about 30 nm are formed.The results of the barrier performance study show that the oxygen barrier properties of the modified GNs/PET composites are significantly improved.The oxygen permeability of the composites prepared with GNs modified by KH550,KH560,and KH570 has been reduced by 57.9%compared to pure PET.36.9%and 58.0%;the water barrier performance is greatly affected by the structure of the silane coupling agent.For composite materials prepared with GNs modified with KH550 and KH560,the water vapor permeability is reduced by 62.2%and 90.1%,respectively,but modified with KH570 The composite material prepared by GNs has no improvement in water vapor permeability;the improvement of barrier performance is mainly due to the integrated effect of the dispersion structure of GNs and its interface with the PET matrix and the interface bonding bond on the affinity of gas ions.The mechanical properties research results show that the GNs/PET composites before and after modification show good strength and toughness,and the strength and toughness of the composites prepared by the modified GNs are further improved,the tensile strength of the composites can reach 59.2?65.5MPa,and the fracture Elongation up to 612?730%.3.The effect of the amount of silane coupling agent grafted on the surface of GNs on the structure and properties of PET composites was studied.The results show that as the grafting amount of silane coupling agent increases,the dispersibility of GNs in PET matrix gradually improves,and the interface between GNs and PET matrix shows an increasing trend and then decreasing trend.The crystallization behavior and crystal structure research results show that with the increase of the silane coupling agent grafting amount,GNs has no obvious effect on the heterogeneous nucleation of PET,but the crystallinity of the composite material increases with the increase of the silane coupling agent grafting amount.And a small amount of crystal structure appears.The results of the barrier performance show that with the increase of the grafting amount of the silane coupling agent,the oxygen permeability of the composite decreases first and then rises.When the grafting amount is 1.0354 mequi/g and 1.3513 mequi/g,the oxygen permeability of the composite is respectively 2.13084cc/[m2-day]and 2.11063 cc/[m2-day],the improvement of oxygen barrier performance is mainly due to the improvement of the dispersion of GNs and its interaction with the polymer and the formation of a small amount of crystalline structure in the matrix.The mechanical property research results show that with the addition of silane coupling agent,the tensile strength and elongation at break are improved by 10%?22%and 32.5%?67.2%respectively compared with GNs/PET composites.