Novel fire‐resistable PUF/APP/Gelatin composites from wasted PET bottles: Synthesis and processing

Flame retardant efficiency of KH-550 modified urea-formaldehyde resin cooperating with ammonium polyphosphate on polypropylene

In this work, ammonium polyphosphate (APP) was microencapsulated by UV-curable epoxy acrylate (EA) resin. The resulting novel EA-microencapsulated APP (EA-APP) was characterized by Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, granulometry, and thermogravimetric (TG) analysis. EA-APP was used to flame retard polypropylene (PP). The water solubility of EA-APP and the water resistance of PP/EA-APP systems were investigated. The thermal stability and combustion behaviors of PP/EA-APP composites were studied through TG and cone calorimeter (CC) tests, respectively. The water resistance test showed that the EA shell could significantly improve the water resistance of PP/APP. TG data illustrated that the char residue of EA-APP greatly increased by 149% compared with uncoated APP, and the thermal stability of PP/EA-APP composite was improved because of the microencapsulation of APP, with an increment of 248% for the char residue compared with PP/APP. CC test results indicated that the peak value of heat release rate, the total heat release, and the peak of smoke production rate of PP/EA-APP decreased in comparison with PP/APP. The mechanism for the improvement of flame retardancy in CC test was discussed based on the experimental results. EA resin containing a large number of hydroxyl groups might promote the dehydration reaction in EA-APP, which facilitated the formation of char residue and the stabilization of APP. Consequently, the flame-retardant efficiency for APP was improved because of the presence of EA shell. Copyright © 2014 John Wiley & Sons, Ltd.

An N, P co‐doped carbon quantum dot (NP‐CQD) was prepared using citric acid as the carbon source and hexachlorotripolyphosphonitrile as the nitrogen and phosphorus source. The structure and morphology of NP‐CQD were characterized. Subsequently, NP‐CQD was blended with ammonium polyphosphate (APP) to come into being a synergistic phosphorus‐nitrogen flame retardant system (SPFRS). The SPFRS was applied in epoxy resin (EP) to enhance the flame retardancy of EP. Thermal stability, flame retardancy, combustion behavior, and char residue morphology of the EP samples were determined by multiple testing methods such as thermogravimetric analysis, vertical burning (UL‐94) and limiting oxygen index (LOI) tests, microscale combustion calorimetry test, and scanning electron microscopy. When the weight ratio of NP‐CQD to APP was kept at 1:9 and 8% SPFRS was added to EP, the obtained flame‐retardant EP (EP/CQD‐APP 2:18 ) passed the UL‐94 V‐0 level and the LOI value of EP/CQD‐APP 2:18 reached 33.2%. The MCC test showed that the heat release capacity (HRC) of EP/CQD‐APP 2:18 was reduced by 48.7% compared with pure EP. Morphology observation on the char residue of EP/CQD‐APP 2:18 after the UL‐94 test indicated that the addition of SPFRS promoted the formation of the dense char residue layer to improve the flame retardancy of EP. Highlight An N, P co‐doped carbon quantum dot (NP‐CQD) was prepared and applied as a flame retardant. NP‐CQD and ammonium polyphosphate (APP) showed synergistic flame retardancy in epoxy resin. The proper weight ratio of NP‐CQD to APP was 1:9.

Carbon nanotubes (CNTs) and ammonium polyphosphate (APP) was used to improve the flame retardancy of linear low-density polyethylene/nylon-6 (LLDPE/PA6) blends. It was observed that APP or CNTs tended to be dispersed in the PA6 phase of the blends when all components were melt-blended together. CNTs dispersed in the PA6 phase caused the decrease of flame retardancy. Different processing methods were used to tailor the localization of APP and CNTs in the blends. The results showed that the localization of CNTs or APP strongly influenced the flame retardancy of blends. APP-incorporated CNTs had antagonism in blends with APP localized in the LLDPE phase and CNTs in the PA6 or LLDPE phases. A synergism between APP and CNTs was exhibited only in blend with the localization of APP in the PA6 phase and CNTs in the LLDPE phase. SEM observation showed that the residual char layer in blends with poor flame retardancy was either discontinuous or continuous but porous. A continuous and compact-residue char layer was observed in blends with excellent flame retardancy. Different morphologies of the residual char layer could be attributed to the difference of residual char mass and network structure.

A novel intumescent flame retardant (IFR), containing ammonium polyphosphate (APP) and poly(hexamethylene terephthalamide) (PA6T), was prepared for acrylonitrile–butadiene–styrene (ABS). Limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA) were used to investigate the flammability property and thermal stability of the IFR/ABS systems. It was found that the flame retardancy of the IFR/ABS systems was improved significantly. When the components of the IFR were 25% APP and 5% PA6T, the LOI value of IFR/ABS system reached to the maximum of 29, but only UL-94V-1 rating was passed. Thus, Al(H2PO2)3 was incorporated into ABS/APP/PA6T system as a synergistic agent, it was found 2% addition of Al(H2PO2)3 caused PA6T/APP/PA6T/Al(H2PO2)3 (70/23.3/4.7/2) to pass V-0 rating of UL-94 test. Meanwhile, the TGA curves indicated that PA6T could be effective as a charring agent and there was a synergistic reaction between PA6T and APP, which effectively promoted the char formation of IFR/ABS composites. Moreover, the residual char obtained after the LOI test of the IFR/ABS was characterized by Fourier transform infrared spectra (FTIR). Results indicated that P–O–C chemical bond was formed in the residual char, which could indicate the cross-linking reaction between PA6T and APP could occur. Furthermore, scanning electron microscopy (SEM) was used to investigate the morphology of the residual char formed in the LOI tests. It was revealed that both ABS/APP/PA6T (70/25/5) and PA6T/APP/PA6T/Al(H2PO2)3 (70/23.3/4.7/2) formed uniform and compact intumescent charred layers.

Polyethylene terephthalate (PET) is of excellent mechanical properties and melt processability and is widely used as raw material for textile fibers and engineering plastics. However, its flame retardant properties are rather poor, and its melt-dripping behavior during burning hasn’t been handled properly. In this work, coal powder and ammonium polyphosphate (APP) were blended with PET, and the thermal degradation, flame retardancy, char formation and mechanical properties of the modified PETs were investigated. All results show that, the initial thermal degradation was accelerated remarkably with APP but to less extent with coal. The gasification of carbonaceous residues was suppressed by the two additives at higher addition levels. The oxygen indice of the modified PETs with APP were increased whereas unchanged with coal unexpectedly. APP/Coal synergistically improved the flame retardancy of PET. There existed some physical and chemical interactions among PET, APP and coal during combustion process. The mechanical properties of the modified PETs were worse than those of virgin PET.

Ammonium polyphosphate (APP) and inorganic fillers were applied for improving flame retardancy and mechanical performance of recycled poly(ethylene terephthalate) (RPET). RPET was compounded with 5–10 wt% of talc and glass bead using twin screw extruder then were injection molded with 2 wt% of APP. The effects of fillers contents and APP on properties and flame retardancy of RPET composites were investigated. The incorporation of talc and glass bead as well as the adding of APP significantly improved tensile and flexural modulus of RPET composites. Scanning electron microscope micrographs indicated good distribution of talc, while glass bead was agglomerated on the RPET matrix. Flame‐retardant property of neat RPET and the RPET composites revealed V‐2 of UL‐94 flammability rating. It can be noted that the composites were less dripping because of the synergistic effect of adding talc and glass bead with APP. From thermogravimetric analysis results, larger of residual char contents and lower values of the activation energy were considered for enhancing flame retardancy in the RPET composites. Copyright © 2015 John Wiley & Sons, Ltd.

In order to improve the flame retardancy of knitted cotton fabrics and investigate the flame-retardant mechanism of the system formed by ammonium polyphosphate (APP) and chitosan (CS), flame-retardant knitted cotton fabrics coated with APP and CS were successfully prepared by layer by layer assembly. APP and CS formed the intumescent flame-retardant system, in which CS acted as the carbon source agent and APP acted as both the acid source and foaming agent. The surface micromorphologies before and after flaming of coated knitted cotton fabrics were exploited by scanning electron microscopy. The flammability, combustion behaviors, thermal degradation properties and flame-retardant mechanism of this system were investigated by vertical burning test, cone calorimetry test and thermogravimetric analysis coupled with Fourier transform infrared analysis in N2 atmosphere, respectively. Compared with the control sample, the deposition of APP and CS endowed the knitted cotton fabrics with improved flame retardancy, higher residual chars, lower heat release rate and total heat release, while increased the smoke production. Improved flame-retardant behaviors are attributed to the thermally stable residual chars, more release of inflammable gases and potential free radical scavengers (PO·) in the gaseous products, named the combination of the condensed-phase and gaseous-phase flame-retardant mechanism.

Synthesis of a novel PEPA-substituted polyphosphoramide with high char residues and its performance as an intumescent flame retardant for epoxy resins

SummaryA new halogen‐free flame retardant was developed by integrating β‐cyclodextrin, triazin ring, and nanohydroxyapatite (BSDH) into a hybrid system. A β‐cyclodextrin was grafted to a commercially available SABO®STAB UV94 via an aromatic deanhydrate. The BSDH was prepared in situ in the presence of β‐cyclodextrin‐grafted nitrogen‐rich precursor. The resulting hybrid was applied as a flame retardant for poly(lactic acid) (PLA) and compared for performance with ammonium polyphosphate (APP). PLA composites containing BSDH and APP, individually or simultaneously, were examined for thermal degradation and flammability by TGA, cone calorimeter, and pyrolysis‐combustion flow calorimetry. TGA results confirmed enhancement of thermal stability of PLA with assistance of BSDH compared to APP. The gases evolved during thermal degradation were assessed by a thermogravimetric analysis and Fourier infrared spectroscopy device. APP revealed catalytic effect to initiate PLA degradation, while BSDH continued to release some gases at elevated temperatures. The flame retardancy of PLA/APP/BSDH blend containing only 10 wt.% of additives was significantly improved. In cone calorimetric tests, a significant fall in peak of heat release rate was observed for this sample, 49% more than that of neat PLA, which was indicative of more gas and condensed phase reflected in more char residue. The corresponding PLA/APP sample, however, showed 17% improvement, as compared to neat PLA. Also, total heat release rate of PLA/APP/BSDH was 45 MJ.m−2, whereas those of PLA and PLA/APP were 89 and 65 MJ.m−2, respectively. BSDH and APP showed a synergistic effect on improving the flame retardancy of PLA composites.

Three citrates, which incorporate cobalt citrate (CoC), copper citrate (CuC), and yttrium citrate (YC), were combined with ammonium polyphosphate (APP) as a flame retardant to improve the flame retardancy and thermal stability of thermoplastic polyurethane (TPU). The cone calorimeter test (CCT) results demonstrated that the PHRR (peak heat release rate) values of TPU‐2, TPU‐3, and TPU‐4 were decreased from 271.4 kW/m2 for TPU‐1 to 188.0, 256.9, and 219.0 kW/m2, respectively. Besides, compared with TPU‐1, the release of CO and CO2 of TPU composites that containing citrate were decreased. The limiting oxygen index (LOI) value for TPU‐1 (containing 8.0 wt% APP) was 26.5% while that of TPU‐4 was increased to 27.5% and reached to V‐0 rating on the vertical burning test. Thermogravimetric analysis (TG) indicated that containing both APP and citrate accelerated the degradation of TPU composites but increased the char residue. In detail, the char residue of TPU‐0 was 6.3 wt% at 685°C, while that of TPU‐3 was reached to 45.2 wt% at N2 atmosphere. Laser Raman spectroscopy (LRS) showed that the degree of graphitization of TPU composites had been increased after adding the citrates. X‐ray photoelectron spectrometer (XPS) and gas chromatography/mass spectrometry (GC‐MS) illustrated that citrate and APP exerted barriers effect in the condensed phase. This work provided a new way of flame retardant that integrated with citrate and APP for TPU composites.

In this research, expandable graphite (EG) and ammonium polyphosphate (APP) were incorporated into water-blow semirigid polyurethane foam (SPUF) as flame retardants. The synergistic flame retardant effects of EG with APP in SPUF had been studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI), horizontal burning test, polarizing microscope, and scanning electron microscopy (SEM). The results indicated that APP and EG used together in SPUF could effectively improve the flame retardancy of SPUF. When the EG to APP ratio reached 2 : 1 under the total content of flame retardants was kept constant as 20%, the LOI value was increased by about 51% compared to pure SPUF, 2.9% to SPUF/EG and 16.3% to SPUF/APP. Besides, the residual char was increased up to 27.7% displayed by TG test results. SEM shows that burned residues of EG/APP/SPUF present more compact char and worm-like structure. Furthermore, EG shows negative effect on the mechanical property of SPUF with 21.7% decrease in compression modulus, but the mechanical property can be improved by the addition of appropriate content of APP.

In order to investigate the effect of guanylurea phosphate-ammonium polyphosphate-silica sol on the combustion and pyrolysis characteristics of Masson Pine, UL-94 horizontal and vertical burner, LOI tester, cone calorimeter, and thermogravimetric analysis were used to study the flame retardant wood, and Coats-Redfern model was used to analyze its pyrolysis kinetics. The results showed that the combined use of guanylurea phosphate-ammonium polyphosphate-silica sol had a significant synergic flame retardant effect on Masson pine. When the mass ratio of guanylurea phosphate, ammonium polyphosphate, and silica sol was 2:1:1, the heat release rate and total heat release of flame retardant pine were decreased by 54.7% and 44.7% compared with pure Masson pine, and the LOI was increased by 77.8% compared with the control group. In addition, the addition of silica sol in the flame retardant reduces the effect of flame retardant on the mechanical properties of wood. Raman analysis of carbon layer showed that the R-value of char residue decreased by 5% and 13% when the mass fraction ratio of guanylurea phosphate, ammonium polyphosphate, and silica sol was 5:1:2 and 2:1:1, respectively, indicating that the compound flame retardant effectively promoted the conversion of amorphous carbon into graphite structure. The TG results of the 5:1:2 and 2:1:1 ratios of guanylurea phosphate, ammonium polyphosphate, and silica sol groups showed that the pyrolysis temperature of flame-retardant pine advanced by about 100°C at the heating rate of 15 ℃/min, and the final char residue rate and apparent activation energy were 15.22%, 18.61%, 24.35 kJ/mol, and 23.76 kJ/mol, respectively. These results indicated that the synergistic flame retardant system of guanylurea phosphate-ammonium polyphosphate-silica sol reduced the apparent activation energy of pine pyrolysis, effectively inhibited the pyrolysis of Masson Pine, and enhanced the thermal stability, char forming ability, and flame retardant property.

Gemin-surfactant modified montmorillonite (G-MMT) was successfully prepared by an ion exchange reaction and characterized via Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The P(BA-VAc)/G-MMT emulsion was prepared via an in-situ polymerization method using potassium persulfate (K2S2O8, KPS) as an initiator. Ammonium polyphosphate (APP) was introduced for obtaining P(BA-VAc)/APP/G-MMT flame-retardant latex with a constant total content of 15 wt% of APP and G-MMT in P(BA-VAc). The flame retardancy and thermal behavior of the latex films were investigated by limiting oxygen index (LOI), vertical burning test (UL-94) and thermal gravimetric analysis (TG/DTA). Compared with the P(BA-VAc)/APP composite, the LOI value of P(BA-VAc)/APP/G-MMT containing 0.5 wt% G-MMT at the same total additive loading increased to 29.1 from 20.0 and its UL-94 increased from no rating to V-0. Thermal gravimetric (TG) data showed that the amount of residues increased significantly with the loading of G-MMT. In addition, the LOI values increased with the increase in char residues. The morphology and microstructure of the residues generated during LOI testing were investigated by scanning electron microscopy (SEM). The outer surfaces of P(BA-VAc)/APP/G-MMT charred layers were more continuous and compact than those of P(BA-VAc)/APP.

Preparation and characterization of a novel oligomeric charring agent and its application in halogen-free flame retardant polypropylene