The Synthesis Of Novel Phosphorus Contained Flame Retard Ants And Their Application On Improving The Fire Resistance Of Poly (Lactic Acid) Composites

The conventional halogenous flame retardants have been faced increasing pressure under the restriction of new legislations (WEEE/RoHs). Novel phosphorus contained flame retardants have exhibited good flame retardancy with reduced toxic effect and have been regarded as the most promising alternatives to the current used halogen-contained flame retardant formulations. Poly (lactic acid) (PLA) as a bio-base polymer has been widely used in many industrial areas such as transportation and electronic equipments, however, its inflammability cannot meet the fire resistant requirements in many end use cases.In this work, several novel organic and inorganic flame retardants have been synthesized by versatile methods, and flame retardancy formulations have been used to enhance the flame retardancy of PLA composites (PLA/polycarbonate (PLA/PC), PLA/polyamide 11 (PLA/PA11)). The mechanism of the synthesized reactions and the flammability, thermal properties and mechanical properties of PLA composites have been investigated. The main works have been summarized as follows:1. The phosphazene-phosphaphenanthrene compound (HPAPC) has been synthesized by reacting hexa-aminophenoxy-cyclotriphosphazene (C2) with DOPO using classical Atherton-Todd reaction and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and element analysis (EA). HPAPC as a phosphorus/nitrogen contained flame retardant have been introduced into PLA by melting blending. The different influence in enhancing the flammability of PLA/HPAPC and PLA/C2/DOPO composites were explored. The flammability test results have indicated that the LOI value was increased to 34.7 and UL-94 grade was improved toV-0 at the presence of 5 wt%HPAPC. The FTIR spectra of the char after cone calorimeter test shows that the phosphorus acids and P-N crosslinking compounds have been formed, which can promote the char formation and hence isolate heat and oxygen in combustion. The evolved gas products of PLA composites were analyzed by FTIR-thermo gravimetric analysis (FTIR-TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and it was demonstrated that the release of ammonia gas during combustion, which was beneficial to the formation of an intumescent char structure; the release of PO free radical could capture OH free radical to inhibit the combustion chain reactions.2. A series of phosphazene-phosphaphenanthrene compounds (HPHAPC, compound 3 and compound 4) which have multiple hydroxyl groups have been synthesized by Kabachnik-Fields reaction, and their structures were characterized by FTIR, NMR and EA. HPHAPC and trisilanollsobutyl polyhedral oligomeric silsesquioxane (POSS) were introduced into PLA/PC (60/40) composites by melting blending. It was demonstrated that the LOI value was increased to 31.5, UL-94 grade was improved to V-0, and the PHRR value was reduced from 748 kW·m-2 to 520 kW·m-2 at the presence of 3 wt% HPHAPC and 3 wt% POSS. Differential scanning calorimetry (DSC) results showed that the introduction of POSS could enhance the compatibility of PLA/PC system. The X-ray photoelectron spectroscopy (XPS) of PLA/PC/HPHAPC/POSS shows that the cross linking between HPHAPC and POSS during processing was responsible for the promoted char formation during combustion. The evolved gas products analyzed by TGA-FTIR and Py-GC/MS could capture the free radical of combustion.3. A series of flame retardants HEDP-MEL, EDTMPA-MEL and ATMP-MEL were synthesized by reacting melamine (MEL) with phosphorous acid complexing agent (1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP), ethylene diamine tetra (methylene phosphonic acid) (EDTMPA) and amino trimethylene phosphonic acid (ATMP)) respectively. The structure of HEDP-MEL was characterized by FTIR, solid NMR and EA. HEDP-MEL and aluminium hypophosphite (OP 1230) was introduced into PLA by melting blending. The LOI value of PLA was increased to 33.9 and UL-94 grade was improved to V-0 which showed that the mixed additives could effectively enhance the flammability of PLA composites. HEDP-MEL and OP1230 were then introduced into PLA/PA11 (40/60) composites. It was demonstrated that the LOI value was increased to 33.5 from 22.9, UL-94 grade was improved to V-0 and the PHRR value was reduced from 430 kW·m-2 to 303 kW·m-2 at the presence of 2.5 wt% HEDP-MEL and 17.5 wt% OP1230. It was proposed that the formed polyphosphoric acid and P-N crosslinking structure could enhance char formation in the condensed phase, and the ammonia and PO free radical generated by the degradation of HEDP-MEL could dilute the flammable gas and capture free radical in the gas phase.4. Sepiolite (SEP) was surface modified by grafting with 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) via the condensation between amino groups and salicylaldehyde. The chemical structure characterized by FTIR, Solid NMR, TGA and transmission electron microscope (TEM) showed that DOPO had been successfully grafted onto the surface of sepiolite and the grafting ratio was around 12.8%. The DOPO modified sepiolite (DOPO-SEP) was then introduced into PLA to improve the fire performance of the composites. It was demonstrated that the LOI value was increased to 31.5 and UL-94 grade was improved to V-0 at the presence of 10 wt% SEP-DOPO, which is better than PLA/10 wt%(SEP/DOPO) composite. The synergetic effect between DOPO and SEP was evaluated. The results of TGA-FTIR and py-GC/MS showed that un-grafted DOPO was degraded earlier than polymer matrix, which cannot enhance the flame retardancy of PLA composite. The formed Si-O-Si and P-N crossl inking structure could enhance char formation in the condensed phase.5. The effect of the PLA/SEP/DOPO mixture on the LOI and PHRR values was investigated by an experimental design methodology which was chosen to support a quadratic regression model to estimate a potentially complex response function. The correlation coefficients R2 (LOI)= 0.98 and R2 (PHRR)= 0.91 which showed that the quadratic model was well fitted by multiple linear regression, which were obtained according to MODDE 10.1 software. The thermal properties and mechanism of PLA composites with different ratio between DOPO and SEP were investigated. The introduction of SEP can enhance the initial temperature and char amount of PLA composites. The condensate depression of PLA/SEP/DOPO was reduced which showed that SEP and DOPO can promote the grow rate of PLA crystallization. The solid NMR of the char after cone test showed that different Si-O-Si structure were formed during the combustion of PLA composite containing different ratio between DOPO and SEP. The water vapor formed by the degradation of SEP could diluted flammable gas in the gas phase.