Effect and origin of the structure of hyperbranched polysiloxane on the surface and integrated performances of grafted Kevlar fibers

Highlights: • Four new hyperbranched polysiloxanes (HPSis) with various structures were prepared. • HPSis have different molecular weights and contents of active groups. • Four grafted Kevlar fibers (HPSi-g-KFs) were facilely prepared with different HPSis. • The structure and properties of HPSi-g-KF depend on the structure of HPSi. • The origin behind greatly improved integrated properties of HPSi-g-KF is discussed. - Abstract: Four hyperbranched polysiloxanes (HPSis) with different molecular weights and concentration ratios of double bonds to epoxy groups (1:6.5–1:0.7) were synthesized and characterized. Each HPSi was facilely grafted onto surfaces of Kevlar fibers (KFs) to develop novel modified fibers (HPSi-g-KFs). The structures and integrated properties of HPSi-g-KFs as well as the origin behind were systematically investigated. Results show that HPSi-g-KFs have much rougher surface morphologies, and their surface free energies are as high as about 1.7 times that of KFs, showing greatly improved wettability. Besides, HPSi-g-KFs have excellent UV resistance after 168 h UV irradiation, the retentions of tenacity, energy to break, modulus and break extension are as high as 92, 86, 95 and 96%, respectively, while those of KFs are 66–85%. In addition, compared with KFs, HPSi-g-KFs have higher tensile tenacity and energy to break with similar modulus and break extension, much better thermal stability and flame retardancy. The nature of HPSi has different influence on different property of fibers, the HPSi with smaller molecular weight and more epoxy groups is beneficial to prepare HPSi-g-KFs with better wettability, while that with larger molecular weight and more double bonds tends to prepare HPSi-g-KF with better flame retardancy and UV resistance