Nano filler synergistic intumescent flame retardant (IFR) system is an effective way to improve the flame retardant properties of polymer. In this study, the effects of montmorillonite (MMT) on the flame retardant properties of polylactic acid/layered double hydroxides (PLA/LDH) and PLA/IFR/LDH were investigated. The results show that both LDH and LDH/IFR can reduce the peak heat release rate (HRR) of PLA and prolong the combustion time of PLA; When a proportionate MMT is introduced into PLA/LDH and PLA/IFR/LDH systems, respectively, MMT will not only affect the degradation process of PLA composites during combustion, but also the PLA composites can form a more stable carbon layer during combustion, which could decrease the peak HRR and prolong combustion time of PLA composite. Furthermore, when 0.5 wt% MMT is incorporated, the peak HRR of LDH/IFR/LDH composite is reduced by 16.17% and the combustion time is prolonged by about 70 s. This study can provide an opportunity to further optimize the properties of intumescent flame retardant polymer.
Polylactic acid (PLA), as a nonpetroleum based environmentally friendly biodegradable plastic, is a non-toxic, nonirritating thermoplastic polyester. It has the advantages of good transparency and high strength [
Intumescent flame retardant (IFR) is the most promising halogen-free flame retardant, which has the advantages of halogen-free environmental protection, low toxicity and low corrosion. It plays a flame retardant role by forming a dense and continuous expanded carbon layer to block the entry of oxygen and heat [
Based on the above studies, the main researchers used a single synergistic to improve the flame retardant performance of IFR, and did not further optimize the performance after synergistic modification. The research shows that both MMT and LDH can improve the flame retardant performance of IFR. At the same time, LDH and MMT have relevant laminate charges [
PLA (REVODE101) was purchased from Zhejiang Haizheng Biomaterials Co., Ltd., China. Pentaerythritol phosphate ester (PEPA) was provided by Hubei Jinleda Chemical Co., Ltd., China. Organically modified montmorillonite (MMT) was produced by Sichuan Santai Fine Bentonite Co., Ltd., China. Sodium hydroxide (NaOH), magnesium nitrate (Mg(NO3)2⋅6H2O), aluminum nitrate (Al(NO3)3⋅9H2O), melamine (MA) were obtained from Chengdu Jinshan Chemical Reagent Co., Ltd., China.
Firstly, Mg (NO3)2⋅6H2O (0.18 mol) and Al (NO3)3⋅9H2O (0.06 mol) were dissolved in deionized water and recorded as solution I. Secondly, a certain amount of sodium dodecyl sulfate (SDS) was dissolved in deionized water and added to solution I with mixing evenly, and it is recorded as solution II. And the pH value of solution II was adjusted to 10 by NaOH solution; Thirdly, the mixed solution was stirred at 70°C for 12 h under a nitrogen atmosphere [
Firstly, 25 g of Na-MMT was dispersed in 250 g of deionized water under vigorous stirring for 0.5 h, and the solution remained still for 1 h. Secondly, removed supernatant and bottom sediment, so purified Na-MMT solution was obtained. Finally, 15 g of CTAB was dispersed into purified Na-MMT solution and heated to around 70°C under continuous stirring for 2 h [
PLA, MMT, LDH, PEPA were dried at 80°C overnight before use. PLA composites with the desired amount of MMT, LDH and PEPA were melted compound using a two-roll mill at 160°C for 10 min. Adjusting the mass ratios of PLA/LDH/MMT to 99.5/0.5/0, 99.25/0.5/0.25, 99/0.5/0.5, 98.5/0.5/1, 97.5/0.5/2 were designated as PLAx (x = 1, 2, 3, 4, and 5), respectively. The mass ratios of PLA/PEPA+MA/MMT/LDH to 75/25/0/0, 74.5/25/0.5/0, 74.25/25/0.5/0.25, 74/25/0.5/0.5, 73.5/25/0.5/1, 72.5/25/0.5/2 were designated as PLAx (x = 6, 7, 8, 9, and 10), and the mass ratio between PEPA and MA was 4/1.
X-ray diffraction (XRD) characterization was carried out on a panalytical x’pert Pro X-ray diffractometer equipped with a copper anode (Cu Kα radiation, λ = 1.54187 Å). The X-ray source was operated at 40 kV and 40 mA.
The morphology of all electrocatalysts was investigated by field emission scanning electron microscope (FESEM, UItra55, Carl zeissNTS GmbH, Germany) and transmission electron microscope (TEM, Libra200, Carl zeiss irts Co., Germany).
Q5000IR (TA instrument, USA) thermal analyzer was used for thermogravimetric analysis (TGA). Nitrogen atmosphere mode was used with a temperature range from room temperature to 500°C with a heating rate of 20 °C/min.
Cone calorimeter 6180 (Siemens analyzer) was used to test the combustion properties of composites according to ISO5660-1 standard. The sample size was 100 mm × 100 mm × 3 mm, and the radiation flux was 35 kW/m2.
The X-ray photoelectron spectroscopy (XPS) was carried out with a VG Escalab Mark II spectrometer (Thermo-VG Scientific Ltd., UK), using Al Kα excitation radiation (hv = 1486.6 eV).
The XRD of LDH and MMT before and after modification was shown in
Cone calorimetry is one of the most effective ways to analyze the combustion properties of various polymer materials [
The heat release rate (HRR) is a very critical parameter, and can be used to express the intensity of a fire. From
The char residues of PLA1 and PLA4 showed in
When 25 wt% IFR was introduced into PLA/LDH system (
To further investigate the synergistic mechanism between MMT and LDH/IFR in PLA, the morphologies of surface char residues of PLA6 and PLA9 were performed by SEM, as shown in
CO and CO2 are the main culprits, causing fatalities in a fire scenario because of their asphyxiant characteristics. Therefore, it is significant to research the emission evolution of CO and CO2. The CO and CO2 production profiles were presented in
The mass loss rate reflects the pyrolysis rate and pyrolysis behavior of the material under a certain fire intensity.
This study investigated the effect of MMT on the flame retardant properties of PLA/LDH and PLA/IFR/LDH composites. The results indicated that LDH and MMT were well dispersed in PLA; MMT could improve the stability of char for PLA/LDH or PLA/IFR/LDH composites during combustion, but did not change the carbon formation process of polymers; During the combustion of PLA composites, MMT could cooperate with LDH or IFR/LDH system to reduce the peak HRR, prolong the combustion time and reduce the fire risk of PLA composites. The above research work can provide a new strategy for the development of multifunctional synergistic intumescent flame retardant PLA composites.