Effect Of Hexagonal Boron Nitride On Crystallization Properties And Related Properties Of Polyketones

Hexagonal boron nitride（h-BN）is a two-dimensional lamellar material with excellent mechanical properties,high thermal conductivity,good chemical stability and dielectric properties.h-BN could be added to the polymer to enhance and functionalize it.The modification of polyketone（PK）by h-BN has not yet been reported.In this paper,h-BN with different particle sizes was introduced into PK by melt blending.The crystallization behavior,crystallization structure and morphology,microscopic morphology,mechanical properties and heat resistance of the PK/h-BN system were studied by POM,DSC,SEM,XRD and universal electronic testing machine.First,the effects of h-BN-1（particle size:2.2μm）,mica,talc,organic montmorillonite and flake graphite on the crystallization and mechanical properties of PK were compared.It was found that none of these five inorganic nucleating agents changed the crystallization structure and form of PK.Among these,talc,flake graphite and h-BN-1 all had a certain induced nucleation effect on PK,which made the crystallization temperature of PK move to high temperature and refines the PK grains.Among them,h-BN had the strongest inducing nucleation effect.Then,we systematically studied the non-isothermal crystallization kinetics of the PK/h-BN system.The effects of the content and particle size of h-BN on the crystallization of PK were investigated,and the Jeziorny equation and Mo equation were used for analysis.The results showed that different particle sizes of h-BN played a role in heterogeneous nucleation of PK,increasing crystallization temperature of PK.The smaller the particle size,the higher the crystallization temperature of the PK/h-BN system,and the more obvious the nucleation promotion effect of PK.The increase of h-BN content had little effect on the crystallization temperature.The Jeziorny equation and the Mo equation were suitable to study the non-isothermal crystallization process of PK and the PK/h-BN system.The values of F（T）,Z_c and half-crystallization time(t_1/2)showed that the addition of h-BN with different particle sizes reduced the crystallization rate of PK.The larger the particle size of h-BN,the faster the crystallization rate of the PK/h-BN system.When h-BN-1 and h-BN-4（26.4μm）were0.5wt%and 0.3wt%,respectively,the crystallization rate of the PK/h-BN system was the fastest.Avrami’s exponent n values showed that pure PK crystallization consisted of homogeneous nucleated three-dimensional growth.The n value of Avrami exponent showed that pure PK crystallization was composed of three-dimensional growth of homogeneous nucleation.The addition of h-BN changed the nucleation and crystallization growth process of PK,which made the crystallization process of PK more complicated.Finally,the effects of h-BN content and particle size of h-BN on the mechanical properties,heat resistance and rheological behavior of PK were studied.The results showed that only h-BN-4 with the largest particle size had a significant enhancement effect on PK.When the content of h-BN-4 was only 0.3wt%,the tensile strength and flexural strength of PK/h-BN-4 were 64.3MPa and 66.6MPa,respectively,which increased by 7.2%and 35%as compared to pure PK.However,the mechanical properties of the system were not further improved by continuing to increase the content of h-BN-4.h-BN-4 also significantly increased the heat deflection temperature of PK.The heat distortion temperature of pure PK was 163.4°C and after adding 0.8wt%h-BN-4,the heat distortion temperature increased to 175°C.In contrast,the heat distortion temperature of h-BN-1 with smaller particle size decreased after adding PK.In this paper,the enhancement mechanism of a small amount of h-BN on PK was discussed.It was believed that the large-area rigid h-BN sheet with multiple PK spherulites attached to the surface forms a physical cross-linked network structure in the PK matrix,which was beneficial to improve flexural performance,tensile properties and heat distortion temperature.However,h-BN with smaller particle size only played the role of nucleus due to its smaller or equivalent size than PK spherulites,and could not form a cross-linked network,which could not have a significant strengthening effect.