High Performance Hybridized Cellulose/epoxy Resin Composites For Light Emitting Diode Encapsulation

Epoxy resin is the main types of resins for light emitting diode(LED)encapsulation owing to its good integrated performances such as adhesion,sealing and manufacturability.However,as LED encapsulation material,epoxy resin has two bottlenecks,that are big internal stress and poor UV resistance,which greatly deteriorate the service life and limit its application field.Additionally,to meet the requirements of electronic information materials,it is necessary to enhance the comprehensive performances of EP resin.Studies have shown that internal stress of EP resin for LED encapsulation can be effectively reduced by reducing thermal expansion coefficient(CTE)or increasing the toughness.However,only one of them was used in most existing researches.In addition,the reduced stress usually brings degraded protective capacity of the encapsulation materials.The second drawbacks of EP resin is the poor UV resistance,which often tend to degrade the properties such as mechanical properties.Therefore,it is significant subject to develop EP resin for LED encapsulation with low internal stress,high UV weatherability and low moisture absorption while maintaining transparency and heat resistance of LED packaging material.This is the target of our project reported herein.First,aiming to reduce the internal stress and improve UV resistance,isocyanatopropyl triethoxysilane(IPTS)reacted with cellulose(CNC)to get m CNC,on which Si O2 particles were then formed through st?ber method.Si O2 particles not only bring mechanical riveting effect between CNC and EP resin,but also endow CNC with excellent UV resistance.Several methods were used to characterize the structure of hybridized cellulose(m CNC@Si O2).TGA tests show that m CNC@Si O2 has higher thermal degradation temperature(Tdi,270°C)than m CNC and CNC,indicating that silane modification and coating of Si O2 can significantly improve the thermal stability of CNC.Secondly,m CNC@Si O2 and EP resin were used to develop a series of composites(coded as m CNC@Si O2/EP resin).The influences of the content of m CNC@Si O2 on the structures and comprehensive performances(internal stress,UV resistance,dielectric properties,moisture resistance,heat resistance,transparency and hardness)of m CNC@Si O2/EP resin were systematically investigated.Results show that the presence of m CNC@Si O2 not only greatly reduces the internal stress and improves UV resistance,but also increases moisture resistance while maintaining high heat resistance.When the content of m CNC@Si O2 is only 2.0wt%,the internal stress is reduced by 62%,thanking to the significant decrease in thermal expansion coefficient,and curing stress derived from the flexibility of Si-O-Si segment in m CNC@Si O2.KIC and impact strength of 2.0m CNC@Si O2/EP resin are about 1.7 and 1.5 times of that of EP resin,respectively.In addition,m CNC@Si O2/EP resin has good transmittance,proving that the presence of m CNC@Si O2 can effectively alleviate yellowing and improve UV resistance.2.0m CNC@Si O2/EP resin has the most excellent overall performance,solving the bottlenecks of available EP resin for LED encapsulation.