The Preparation Of Carboxyl Starch And Carboxyl Linen By Hydrogen Peroxide And Their Application In Flame Retardance Of Epoxy Resin

Epoxy resins are widely used in laminating, adhesive, coating, and casting fields due to their dimensional stability, satisfactory mechanical properties, suitable weather, chemical and thermal resistance. However, its lack of flame retardancy limits its more extensive applications where high thermal stability and flame retardancy are needed. In order to improve the flame retardant properties of EP, oxidized starch(OST) and oxidized linen(OLF) was prepared by starch and linen using hydrogen peroxide as the oxidant, respectively. Due to their high char yield and low flammable gas, OST and OLF were used as carbonization agent for increasing the flame retardant properties of EP. Based on compact and the expansion of the carbon layer structure, the compact char reduced the EP flammability by retarding the diffusion of oxygen and heat when EP was burning, as a resule, IFR-EP composites exhibited significantly enhanced flame retardant properties.Novel c-6 position oxidized corn starch(OST) with high carboxyl contents(26.3-54.5%) was prepared by a green method, using hydrogen peroxide as the oxidant. The as-obtained OSTs were then used as flame-retardant carbon sources with microencapsulated ammonium polyphosphate(MFAPP) in epoxy resin(EP). Compared to EP, EP/MFAPP/OST composites obtained exhibit significantly enhanced flame retardancy. The introduction of only 6.25 wt% OSTs and 6.25 wt% MFAPP results in remarkably increased limiting oxygen index and decreased heat release rate, and all composites can reach UL94 V-0 rating. Thermogravimetric analyses and Cone calorimeter results suggest both OSTs and MFAPP have good catalytic charring effects, and the increased carboxyl content benefits to the char formation of the composites. Owning to the formation of compact char on the sample surface during combustion, the transfer of oxygen, heat and flammable gas products is inhibited; the flame retardancy of EP/MFAPP/OST composites is thus remarkably enhanced.In order to develop novel carbonization agent with more excellent performance, hydrogen peroxide was used to oxidize pretreated linen with carboxylic content(CC) ranging from 12.2% to 34.5% depending on the H2O2/cellulose molar ratios used. The structure of OLF was characterized by FT-IR, 13C-NMR, XRD, TG and TG-IR. The results revealed that the primary hydroxyl at C6 site in glucose units of linen was selectively oxidized to carboxyl group by H2O2, and the notable characteristic peaks of carboxyl groups appeared at 173±2 in the spectra of 13C-NMR. With the increase of CC, the crystallinity of OLF decreased. The result revealed the oxidation occurred in the amorphous region of linen firstly, and then in crystalline region. TG-IR showed that with the increase of CC, the content combustible gases such as methanol of OLF released decrease, while the residual carbon increased. The as-obtained OSTs were then used as flame-retardant carbon sources with microencapsulated ammonium polyphosphate(MFAPP) in epoxy resin(EP). Compared to EP, EP/MFAPP/OST composites obtained exhibit significantly enhanced flame retardancy. The introduction of only 5 wt% OLFs and 3.75 wt% MFAPP results in remarkably increased limiting oxygen index and decreased heat release rate, and all composites can reach UL94 V-0 rating. Thermogravimetric analyses and Cone calorimeter results suggest both OLFs and MFAPP have good catalytic charring effects, and the increased carboxyl content benefits to the char formation of the composites. THR and TSP of EP/MFAPP/OLF27.4 were 13.4 MJ/m2 and 5.85 kg/m2, respectively, which decreased to 35.0% and 21.6% respectively compared with PER as carbonization agent. Owning to the formation of compact char on the sample surface during combustion, the transfer of oxygen, heat and flammable gas products is inhibited; the flame retardancy of EP/MFAPP/OLF27.4 composites is thus remarkably enhanced.To evulate the effect of OST and OLF on water resistance and mechanical properties of IFREP, water adsorption, surface contact angle and mechanical properties test were employed. The water adsorption rario and surface contact angle of EP/MFAPP OLF27.4 was 4% and 46.6°, respectively. Compared with those of EP/MFAPP OST47.6, EP/MFAPP OLF27.4 achieved higher hydrophobicity. The reasos were attributed to the less amount of flame retardants and high hydrophobic properties of OLF. The tensile strength and the impact strength of the EP/MFAPP OLF27.4 was 36.9MPa and1.78KJ/m2, respectively, which was 85% and 130% of pure epoxy resin. SEM analysis results showed that OLF can obtain the flexible fiber with a certain length to diameter ratio, it could effectively absorb energy to improve the mechanical properties of EP/MFAPP OLF27.4l. This work demonstrates OLF is not only a good flame retardant but also an excellent carbon source, much better than PER and ST, OST, it can enhance the flame retardancy of epoxy resins containing MFAPP.