The effect of melt temperature on interfacial bonding strength in the thermoplastic CF-PAEK (PEEK) coating process.
The previous text described the impact of mold temperature on the interfacial bonding strength between thermoplastic carbon fiber polyaryletherketone (CF-PAEK) and polyetheretherketone (PEEK) during the coating process. It was understood that an increase in temperature not only improves the interfacial bonding strength but also enhances shear strength. This article will continue to discuss the effect of resin melt temperature on the interfacial bonding strength of the two composite materials after the coating process.
The effect of melt temperature on the interfacial bonding strength of thermoplastic CF-PAEK (PEEK) composites.
1.Shear Strength of Coated Composite Materials at Different Melt Temperatures: The figure above shows the shear strength of PEEK/CCF-PAEK and SCF-PEEK/CCF-PAEK samples at different melting temperatures. The shear strengths of PEEK/CCF-PAEK are 69 MPa, 67 MPa, 71 MPa, 67 MPa, and 66 MPa, respectively, while the shear strengths of SCF-PEEK/CCF-PAEK samples are 84 MPa, 84 MPa, 85 MPa, 87 MPa, and 83 MPa, respectively. Comparing the shear strength data of the two thermoplastic resin-coated composite samples reveals that when the mold temperature is 260 degree , increasing the melt temperature initially improves the interfacial bonding strength of PEEK/CCF-PAEK, but then leads to a decline.
2.Interfacial Bonding Performance of SCF-PEEK/CCF-PAEK Samples at Different Melt Temperatures: The figure above illustrates the interfacial bonding state of SCF-PEEK/CCF-PAEK composites at various melt temperatures. When the mold temperature is 260 degree , the boundary between PAEK and PEEK becomes unclear. As the melt temperature increases, an increasing number of short carbon fibers from SCF-PEEK penetrate into the PAEK resin. As indicated by the red circles in the figure, the short carbon fibers bridge the boundary between the two matrix resins, enhancing the interfacial bonding strength. When a resin blending zone forms at the interface, the flowability of the SCF-PEEK resin can be improved by raising the melt temperature, allowing more short carbon fibers to be inserted into the resin-rich region to strengthen the interface.
According to experimental data, when the mold temperature is 260 degree and the melt temperature of PEEK/CCF-PAEK is 400 degree , the shear strength of the coated composite material reaches its highest point at 71 MPa. Conversely, for SCF-PEEK/CCF-PAEK, the maximum shear strength of the composite sample is reached at 87 MPa when the melt temperature is 410 degree .
As shown in the figure above, PAEK resin is colored brown and PEEK resin is colored green. The specific process of coating and molding the two thermoplastic composites is observed using scanning electron microscopy, allowing for the examination of molecular diffusion and interfacial formation. The results indicate that mold temperature significantly affects interfacial bonding strength, while melt temperature has almost no impact. Therefore, mold temperature is set as the core factor for simulation observation in the experiment, with the injection molding temperature established at 400 degree and mold temperatures set at 220 degree , 240 degree , 260 degree , and 280 degree , respectively.
The data shows that as the mold temperature increases, some molecular chains penetrate the interface and entangle with the chains of the other layer. In the coating and molding process of PEEK/PAEK thermoplastic composites, the formation of the interface depends not only on the mutual movement of the two molecular chains but also on the self-movement of the molecules.
Figure a shows the rotational radius at the interface between PAEK and PEEK resins under different mold temperatures. Under various processing conditions, when a stable state of 300 degree is reached, the rotational radius of the entire system gradually increases. Figure b displays the average azimuthal displacement-time curve at the interface between PEEK and PAEK resins under different mold temperatures. The overall average azimuthal displacement increases rapidly over time, indicating that as the temperature rises, molecular motion accelerates, leading to an enhancement in interfacial bonding strength. However, when the temperature exceeds 280 degree , the average azimuthal displacement stabilizes, and the interfacial bonding strength also ceases to increase.
The figure shows the interfacial bonding energy and diffusion coefficient of the two systems at different mold temperatures. It can be observed that as the mold temperature increases from 220 degree to 280 degree , the diffusion coefficient rises from 7.3 × 10^-10 m²·s^-1 to 14.0 × 10^-10 m²·s^-1, while the absolute value of the interfacial energy sharply increases from 233.4 kcal·mol^-1 to 450.8 kcal·mol^-1. Compared to other temperature changes, the diffusion coefficient exhibits a significant variation when the mold temperature is raised from 220 degree to 240 degree . At this point, the molecular diffusion rate increases, which aligns with the trend observed in the shear strength of the samples.
