Enhanced toughness and thermal conductivity for epoxy resin with a core-shell structured polyacrylic modifier and modified boron nitride

Abstract

A new epoxy-based composite with higher toughness and thermal conductivity was developed. First, a poly(n-butyl acrylate)/poly(methyl methacrylate-co-glycidyl methacrylate) (PBMG) core-shell structured latex was prepared by seeded emulsion polymerization to toughen the epoxy resin (EP). Second, boron nitride particles were modified into nano-scale sheets and added to the epoxy/PBMG blend to improve the thermal conductivity of the resulting composite material. The properties of the constituent materials were determined prior to fabrication and testing of the composite product. The monomer conversion in the emulsion polymerization process of the PBMG was checked by determining the solid particle content. The PBMG particle size was characterized by dynamic laser scattering, and the morphology of the particles was characterized by scanning and transmission electron microscopy. The exfoliation of the modified boron nitride (MBN) flakes was verified by TEM and Raman microscopy. The mechanical properties and the thermal conductivity of the EP/PBMG/MBN composite were determined at various constituent contents. Results showed that the unnotched impact strength of the composite increased by 147%, the flexural strength increased by 49.1%, and the thermal conductivity increased by 98% compared with pristine EP at a PBMG content of 5 wt% and MBN content of 7 wt%. With the enhanced properties and ease of fabrication, the developed composite has good potential for application in high-end industries such as microelectronics packaging.

Fig. 1. Preparation procedure of PBMG.

Fig. 2. Emulsion polymerization of PBMG (a) monomer conversion vs. reaction time; (b) theoretical and measured diameter of latex particles vs. reaction time; and (c) particle size distribution and morphology of the final PBMG.

Fig. 3. PBMG latex (a) TEM core–shell structure; (b) SEM particle distribution.

Fig. 4. SEM images of h-BN and MBN (a) lateral size of h-BN, 3–5 μm; (b) thickness of h-BN, 300 nm; (c) lateral size of MBN, 1–2 μm; (d) thickness of MBN, 30 nm.

Fig. 5. TEM images of MBN (a) & (b) low resolution; (c) HRTEM; (d) electron diffraction pattern; and (e) photos of h-BN and MBN dispersed in ethanol solvent for 24 h.

Fig. 6. XRD patterns of h-BN and MBN.

Fig. 7. Raman spectra of h-BN and MBN.

Fig. 8. Impact and flexural strengths of epoxy composites with various MBN contents.

Fig. 9. SEM images of the fracture surface of samples: (a) neat EP; (b) EP/PBMG/h-BN (3 wt%) composite; (c) EP/PBMG/MBN (3 wt%) composite; (d) EP/PBMG/MBN (10 wt%) composite.

Fig. 10. Thermal conductivity improvement of EP/PBMG/BN composites with different BN contents.