Study On The Crystallization Properties And Flame-Retardant Modification Of Poly (Butylene Succinate)

As a kind of quickly developed and novel biodegradable polymer, poly(butylene succinate) (PBS) has attracted more and more attention owing to its good overall performances. As a semi-crystallized polymer, We can control or improve PBS's processing, mechanical and biodegradable properties to adapt to different usage requirements by the investigating its crystallization properties. However, PBS is flammable and melt dripped seriously during combustion, which would ignite something else and then result in a fire hazard, making the application area of PBS limited. Experiments of this thesis were carried out in two ways. Firstly, we investigated in the crystallization properties of PBS and its inorganic nanocomposites. Secondly, using intumescent flame retardants and nano-synergists, we made a flame retardant PBS, and related mechanisms were discussed in detail. The detailed outline is elaborated as follows:1. We have prepared PBS/titanium dioxide nano-tubes (TNTs) and PBS/ hydroxyapatite nanorods (HAP) nanocomposites, and studied their crystallization and melting performances. In the system of PBS/TNTs, TNTs acted as a heterogeneous nuclear agent to increase the crystallization temperature and rate. However, the presence of tubular TNTs would limit mobility and movement of the molecular chains, resulting in a decrease in the crystallinity and an increase in the activation energy of crystallization. For the nanocomposite of PBS/HAP, the hydrogen bonding effect between HAP and PBS weakened the nucleation activity of PBS, reduced the crystallization temperature and rate, but favored the crystal growth leading to a lower crystallization activation energy. We have found that there's a"double melting peaks"phenomenon for the DSC melting curves of PBS and its nanocomposites, and we attributed it to the theory of"melting- recrystallization-melting". Furthermore, we analyzed the non-isothermal crystallization processes by methods of Jeziorny, Ozawa and Mo, and found that the method proposed by Mo could successfully analyze the non-isothermal crystallization kinetics of PBS and its nanocomposites.2. Intumescent flame retardant PBS was prepared by using ammonium polyphosphate (APP) as the acid source, melamine (MA) as the gas source, and PBS itself as macromolecular carbon source. The ratio of APP/MA exerted a great impact on the material's flame retardant property, and the best ratio was set at 5:1. IFR catalyzed the thermal degradation of PBS, making the maximum weight loss temperature decreased. But at the same time, IFR could significantly improve PBS's thermal stability at higher temperature and the char yield. It was indicated from the results of in situ FTIR that the outer char of IFR-PBS was covered by a layer of non-combustible glassy film which was composed of the phosphoric acid spicies such as pyrophosphate and polyphosphoric acid as well as the pyrolysis products of the flame retardants containing nitrogen. Thus the inner polymer matrix was well protected. Finally, an intumescent flame retardant mechanism of PBS was proposed. The escape of a large number of non-flammable gas products and the formation of a dense carbon layer with graphite structure played a heat and oxygen barrier effect, which could effectively improve the flame retardancy and thermal stability of PBS.3. Nano-fumed silica could further improve the flame retardant efficiency and anti-dripping performance of IFR-PBS, making a more pronounced swelling effect. The best addition level of silica was 2 wt%. TG-IR experimental results showed that silica could reduce the rate and degree of the thermal degradation of IFR-PBS to a certain extent, making the total amount of pyrolysis gas products decreased. Finally, the possible synergistic flame retardant mechanism of silica was suggested. In pyrolysis or combustion process of IFR-PBS/silica, the esterification/trans-esterification crosslinking reactions and the presence of hydrogen bonding interactions led to the formation of a stable three-dimensional interpenetrating network-like structure in the carbon layer, which could greatly increase the viscosity of carbon layer in the gel or cured state as well as the melt of PBS. In the meanwhile, fumed silica was prone to migrate and accumulate on the the sample surface, acting as thermal insulation layer. A complex Char/Silica intumescent char layer was generated at last. It could not only effectively prevent the molten drop, but also could play as a barrier blocking oxygen and heat diffusion into the matrix and the migrating of flammable thermal degradation gas products to the combustion zone of the surface. Thus the chain reactions of combustion of PBS was broken off.