Synthesis Of PA6-b-PU Copolymers And The Study Of Compatibility Of The PA6/TPU/ PA6-b-PU Blends

PA6-b-PU copolymers powder were synthesized with the method of anionic suspension polymerization using caprolactam as a monomer, sodium hydroxide as a catalyst, the PU prepolymer terminated with isocyanate as macroactivator, and the dimethicone as reaction media. And the content of PU in the block copolymers respectively was 15%, 20% and 25%(PA6-b-PU15%, PA6-b-PU20% and PA6-b-PU25%). The structure and properties of the block copolymers were studied using the different techniques such as FTIR, DSC, TG, WAXD and SEM. Then PA6-b-PU copolymers were added into PA6/TPU blends as compatibilizer for the blends by melt blending. The structure and properties of the blends were researched using the test techniques such as SEM, DSC, and mechanical tests. The factors such as the content of PA6-b-PU copolymer and the block ratio of PA6-b-PU copolymer were studied, which had effects on the two phase structure, crystallization behavior and mechanical properties of the PA6/TPU/ PA6-b-PU blends. In addition, the study also was carried out of the PA6-b-PU25% copolymer as compatibilizer for the PA66/TPU blends. The structure and properties of the blends also were researched.The results of FTIR, DSC and TG showed the PA6-b-PU copolymers were synthesized successfully with the method of anionic suspension polymerization. The melting temperature,crystallization temperature, crystallinity and thermal stability of the PA6-b-PU copolymers dramatically decreased with the increase of the PU content compared to these of the PA6 homopolymer. The PA6-b-PU copolymers were relatively homogeneous microspheres, and the surface was smooth under the observation by SEM. However, the results of WAXD showed the crystal form of the block copolymers didn’t change, and there were α crystal form.The two phase structures of PA6/TPU/PA6-b-PU blends were observed by SEM. The results showed the size of TPU dispersed phase decreased obviously, and the TPU phase dispersed more uniformly with the increasing of PA6-b-PU copolymer content. When the content of PA6-b-PU copolymer increased to a certain value, the TPU dispersed phase size reached the minimum, and then continued to increase the content of PA6-b-PU copolymer, the size of dispersed phase increased. Compared two phase structures of PA6/TPU/PA6-b-PU blends with different PU content of PA6-b-PU copolymer, when the content of PA6-b-PU copolymers with the PU content of 15% and 20% were 7 phr, the size of TPU dispersed phase reached the minimum. When the content of PA6-b-PU copolymer with the PU content of 25% was 5 phr, the size of TPU dispersed phase reached the minimum. These results indicated that the increase of the PU content of PA6-b-PU copolymer could improve the compatibilizing effect of PA6-b-PU copolymer.The crystal and melting behaviors of PA6/TPU/PA6-b-PU blends were researched by DSC. After adding the PA6-b-PU copolymer in the PA6/TPU blends, the crystallinity of the blends decreased in different degree compared to the PA6/TPU blends without compatibilizer. When adding the content of PA6-b-PU copolymer was made the size of TPU dispersed phase reached the minimum, the crystallinity of the blends was the lowest. Because the PA6-b-PU copolymer could reduce the interfacial tension to make the size of TPU dispersed phase decreased, and TPU phase dispersed more uniformly. On the other hand, the amphiphilic PA6-b-PU copolymer increased the degree of the combination of TPU and PA6. When the blends crystallized, these factors made the movement of chains of PA6 more difficult, thereby reduced the crystallinity of the blends.The results of mechanical tests showed adding PA6-b-PU copolymer in the PA6/TPU blends could improve the tensile strength and the notched impact strength synchronously. The tensile strength and the notched impact strength increased to the maximum, and then decreases with the increase of the content of PA6-b-PU copolymer. When the content of PA6-b-PU copolymers with the PU content of 15% and 20% were 7 phr, the tensile strength and the notched impact strength reached the maximum. The tensile strength of PA6/TPU/PA6-b-PU15% blend and PA6/TPU/PA6-b-PU20% blend increased 25.3% and 28.1% respectively, and the notched impact strength increased 132.8% and 148.4% respectively compared to the PA6/TPU blends without the compatibilizer. When the content of PA6-b-PU copolymer with the PU content of 25% was 5 phr, the tensile strength and the notched impact strength reached the maximum. The tensile strength of PA6/TPU/PA6-b-PU25% blend increased 29.0%, and the notched impact strength of it increased 159.4% compared to the PA6/TPU blends without the compatibilizer. These results indicated that PA6-b-PU copolymers could improve the mechanical properties of PA6/TPU effectively, and achieved the effects of strengthening and toughening at the same time. The results were consistent with the researches of compatibility and crystallization of the PA6/TPU/PA6-b-PU blends above.The results showed PA6-b-PU25% copolymer also could decrease the size of TPU dispersed phase effectively and the crystallinity of the blends. PA6-b-PU25% copolymer could also improve the mechanical properties of PA66/TPU effectively. These reseaches indicated PA6-b-PU copolymers could improve the compatibility of the PA66/TPU blends. When the content of PA6-b-PU25% copolymer was 5 phr, the tensile strength and the notched impact strength reached the maximum. The tensile strength of the PA66/TPU/PA6-b-PU25% blend increased 17.4%, and the notched impact strength of it increased 104.4%.