Mechanical properties,thermal stability,sound absorption,and flame retardancy of rigid PU foam composites containing a fire‐retarding agent: Effect of magnesium hydroxide and aluminum hydroxide

Isocyanate, polyether polyol, a flame retardant (10 wt%), and aluminum hydroxide/magnesium hydroxide (0, 5, 10, 15, and 20 wt%) are used to form the rigid polyurethane (PU) foam, while nylon nonwoven fabrics and a polyester aluminum foil are combined to serve as the panel. The rigid PU foam and panel are combined to form the rigid foam composites. The cell structure, compressive stress, combustion resistance, thermal stability, sound absorption, and electromagnetic interference shielding effectiveness (EMI SE) of the rigid foam composites are evaluated, examining the effects of using aluminum hydroxide and magnesium hydroxide. Compared with magnesium hydroxide, aluminum hydroxide exhibits superior performance to the rigid foam composites. When aluminum hydroxide is 20 wt%, the rigid foam composite has an optimal density of 0.153 g/cm³, an average cell size of 0.2466 mm, a maximum compressive stress of 546.44 Kpa, an optimal limiting oxygen index (LOI) of 29.5%, an optimal EMI SE of 40 dB, and excellent thermal stability and sound absorption.     

Sound absorption and compressive property of PU foam‐filled composite sandwiches: Effects of needle‐punched fabric structure,porous structure,and fabric‐foam interface

The flexible polyurethane (PU) foam‐filled composite sandwiches are constructed using three types of needle‐punched fabrics (upper layer), PU foam (core layer), and nylon (bottom layer). Different contents of deionized water were used to adjust the pore size and bulk density of PU foam by free‐foaming. Effects of needle‐punched fabric components, cell structure, and fabric‐foam interface on sound absorption and compressive property of the composite sandwiches were investigated. Fabric‐foam interface contributes to improve high‐frequency sound absorption efficiency. When containing 0.5 wt% water in the core and nylon‐glass grid needle‐punched composite fabric (NPUN‐G) in the upper face, the composite sandwiches exhibited optimal sound absorption of 0.78 at low frequency of 450 Hz, and optimal compressive strength of 14.4 kPa. Combination of needle‐punched composite fabric improved the sound absorption coefficient and compressive strength, as high as 223% and 121%, respectively, compared with pure PU foam. This study provided an important basis for the preparation of high‐strength composite sandwiches with low‐frequency sound absorption.     

Effects of structural design including cellular structure precision controlling and sharp holes introducing on sound absorption behavior of polyimide foam

This paper aims to effectively improve acoustic property of polyimide foam (PIF) by regulating cellular structure of PIF on a large scale and introducing sharp hole structure simultaneously, adopting a special mold with split structure in a closed-mold foaming route. In this work, PIF with same split structure but different pore cell sizes, density, and windows opening rate were produced in the first time. Due to the stepwise transition principle, the impedance of the air acoustic medium and the acoustic material was well matched. In addition, the characterization results showed the effectively effects of microporous structure and split structure characteristics of PIF on the acoustical absorption coefficient. For PIF-4, sound absorption coefficient kept around 0.9 from 900 to 6300 Hz. Especially, the resonance sound absorption characteristics was basically eliminated, which ensured the high efficiency sound absorption behavior of PIF in the broadband range from 600 to 6300 Hz region.     

Melamine,silica, and ionic liquid as a novel flame retardant for rigid polyurethane foams with enhanced flame retardancy and mechanical properties

Rigid polyurethane (PU) foams were successfully filled with different weight ratios of melamine (1 wt%, 5 wt%, 10 wt%), silica (0.1 wt%) and ionic liquid, 1-Ethyl-3-methylimidazolium chloride, [EMIM]Cl (0.3 wt%). The aim of this study was to improve the flame retardancy of PU foams and to develop the synergistic effect between melamine, silica and ionic liquid on the flame-retardant PU foams. The influence of different loadings of the fillers was examined. The results showed that in comparison with unfilled foam, all modified compositions are characterized by higher density (41–46 kg m⁻³), greater compression strength (134–148 kPa), and comparable thermal conductivity (0.023–0.026 W m⁻¹ K⁻¹). Moreover, the reaction to fire of the PU composites has been investigated by the cone calorimeter test. The results showed that the fire resistance of PU foams containing as little as 1 wt% of melamine is significantly improved. For example, the results from the cone calorimeter test showed that the incorporation of the melamine, silica and ionic liquid significantly reduced the peak of heat release rate (pHRR) by ca. 84% compared with that of unmodified PU foam. SEM results showed that incorporated fillers can form an intumescent char layer during combustion which improves the reaction to fire of the composite foams.     

Effect of aluminum diethylphosphinate on flame retardant and thermal properties of rigid polyurethane foam composites

Rigid polyurethane foam/aluminum diethylphosphinate (RUPF/ADP) composites were prepared by one-step water-blown method. Furthermore, scanning electron microscope (SEM), thermal conductivity meter, thermogravimetric analysis (TGA), limiting oxygen index, Underwriters Laboratories vertical burning test (UL-94) and microsacle combustion calorimetry were applied to investigate thermal conductivity, thermal stability, flame retardancy and combustion behavior of RPUF/ADP composites. Thermogravimetric analysis–Fourier transform infrared spectroscopy (TG–FTIR) was introduced to investigate gaseous products in degradation process of RPUF/ADP composites, while SEM and X-ray photoelectron spectroscopy were used to research char residue of the composites. It was confirmed that RPUF/ADP composites presented well cell structure with density of 53.1–59.0 kg m^?3 and thermal conductivity of 0.0425–0.0468 W m^?1 K^?1, indicating excellent insulation performance of the composites. Flame retardant test showed that ADP significantly enhanced flame retardancy of RPUF/ADP composites, RPUF/ADP30 passed UL-94 V-1 rating with LOI of 23.0 vol%. MCC test showed that ADP could significantly decrease peak of heat release rate (PHPR) of RPUF/ADP composites. PHPR value of RPUF/ADP20 was decreased to 158 W g^?1, which was 21.8% reduced compared with that of pure RPUF. TG–FTIR test revealed that the addition of ADP promoted the release of CO₂, hydrocarbons and isocyanate compound in first-step degradation of RPUF matrix while inhibited the release of CO in second step degradation. Char residue analysis showed that the addition of ADP promoted polyurethane molecular chain to form aromatic and aromatic heterocyclic structure, enhancing strength and compactness of the char. This work associated a gas–solid flame retardancy mechanism with the incorporation of ADP, which presented an effective strategy for preparation of flame retardant RPUF composites.

     

Vanillin‐derived phosphorus‐containing compounds and ammonium polyphosphate as green fire‐resistant systems for epoxy resins with balanced properties

Flame retardants from vanillin when utilized together with ammonium polyphosphate (APP) yield excellent synergistic flame retardancy toward epoxy resins. Bisphenol A epoxy resins have been widely used due to their excellent mechanical properties, chemical resistance, electrical properties, adhesion, etc., while they are flammable. Environment‐friendly and bio‐based flame retardants have captured increasing attention due to their ecological necessity. In this paper, 3 bio‐based flame retardants were synthesized from abundant and more importantly renewable vanillin, and their chemical structures were determined by ¹H NMR and ¹³C NMR. They were used together with APP (an environment‐friendly commercial flame retardant) to improve the fire resistance of bisphenol A epoxy resin. With the addition APP content of 15 phr, the modified bisphenol A epoxy resin could reach UL‐94V0 rating during vertical burning test and limit oxygen index values of above 35%, but reducing APP content to 10 phr, the flame retardancy became very poor. With the total addition content of 10 phr, the epoxy resins modified by 7 to 9 phr APP and 1 to 3 phr bio‐based flame retardants with epoxy groups or more benzene rings showed excellent flame retardancy with UL‐94V0 rating and limit oxygen index values of around 29%. The T_gs of the epoxy resins could be remained or even increased after introducing bio‐based flame retardants, as the control; those of APP alone‐modified epoxy resins compromised a lot. The green synergistic flame‐retardant systems have a great potential to be used in high‐performance materials.     

Preparation and burning behaviors of flame retarding biodegradable poly(lactic acid) nanocomposite based on zinc aluminum layered double hydroxide

A flame retarding biodegradable polylactic acid (PLA) nanocomposite based on flame retardant composites (containing ammonium polyphosphate (APP), pentaerythritol (PER) and melamine cyanurate (MC) by controlling the weight ratio was 2:2:1) and organomodified zinc aluminum layered double hydroxide (Zn-Al-LDH) has been prepared by melt-compounding directly. The morphology and burning behaviour of nanocomposite with 2 wt% Zn-Al-LDH loadings were investigated. The extent of dispersion of LDH was quantified by wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM), illuminating the good dispersion state for ZnAl-LDH in the PLA matrix. Significant improvements in fire retardant performance were observed for the nanocomposite from microscale combustion calorimeter (MCC) and cone calorimetry (reducing both the heat release rate and the total heat released). It revealed that incorporation of FR and ZnAl-LDH was very efficient in improving the flame retardance of PLA composite.     

Biobased porous acoustical absorbers made from polyurethane and waste tire particles

The production of flexible polyurethane foams (FPF) with good acoustical performance to control sound and noise and incorporating bio/recycled raw materials is an interesting alternative to conventional acoustic absorbent materials. In this sense, biobased polyols like glycerol (GLY) or hydroxylated methyl esters derived from tung oil (HMETO) as multifunctional polyols, and waste tire particles (WTP) as fillers of low thermal conductivity and good capability for acoustical absorption, are prospective feedstocks for FPF preparation. In this work, FPF were prepared by adding different amounts of these components to a formulation based on a commercial polyether polyol. Results of scanning electron microscopy (SEM) analysis, compression tests and normal-incidence sound absorption coefficient (α_N) measurements are presented and discussed. The addition of WTP or GLY to the commercial formulation enhanced both the modulus and yield stress of the obtained FPF in all cases. Moreover, a high recovery of the applied strain (>90%) was attained 24 h after the compression tests. On the other hand, the normal-incidence sound absorption coefficient, α_N, reached high values mostly at the highest evaluated frequencies (α_N ∼0.62–0.89 at 2000 Hz and α_N ∼0.70–0.91 at 5000 Hz). SEM micrographs revealed that the foams obtained present a combination of open and closed cell structure and both the modifiers and particles tend to decrease the cell size.     

Effects of melamine polyphosphate and halloysite nanotubes on the flammability and thermal behavior of polyamide 6

Melamine polyphosphate (MPP) and halloysite nanotubes (HNT) were introduced to polyamide 6 (PA6) by melt blending in order to improve the fire resistance. PA6 composite containing 12% flame retardants with good spinnability was obtained. The flammability of PA6 composite was characterized by limiting oxygen index (LOI), UL‐94 vertical burning and cone calorimeter (CONE) tests. The results indicated that the LOI value could reach 24.0 vol.% and UL‐94 rating could achieve V2 level at the presence of 12% flame retardants. CONE data demonstrated that peak heat release rate was significantly reduced from 554 kW/m² of neat PA6 to 368 kW/m² of the sample containing flame retardants. Thermal analysis indicated that the thermal stability and char formation were improved by the presence of flame retardants. The morphology of residue char was characterized by scanning electron microscopy; and it suggested that a network‐structured protective char layer had been formed. The possible synergism between MPP/HNT and their flame retardant mechanism was also analyzed and discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Nutmeg filler as a natural compound for the production of polyurethane composite foams with antibacterial and anti-aging properties

Polyurethane (PU) composite foams were successfully reinforced with different concentrations (1 wt%, 2 wt%, 5 wt%) of nutmeg filler. The effect of nutmeg filler concentration on mechanical, thermal, antimicrobial and anti-aging properties of PU composite foams was investigated. PU foams were examined by rheological behavior, processing parameters, cellular structure (Scanning Electron Microscopy analysis), mechanical properties (compression test, impact test, three-point bending test, impact strength), thermal properties (Thermogravimetric Analysis), viscoelastic behavior (Dynamic Mechanical Analysis) as well as selected application properties (thermal conductivity, flammability, apparent density, dimensional stability, surface hydrophobicity, water absorption, color characteristic). In order to Disc Diffusion Method, all PU composites were tested against selected bacteria (Escherichia coli and Staphylococcus aureus). Based on the results, it can be concluded that the addition of 1 wt% of nutmeg filler leads to PU composite foams with improved compression strength (e.g. improvement by ~19%), higher flexural strength (e.g. increase of ~11%), improved impact strength (e.g. increase of ~32%) and comparable thermal conductivity (0.023–0.034 W m⁻¹ K⁻¹). Moreover, the incorporation of nutmeg filler has a positive effect on the fire resistance of PU materials. For example, the results from the cone calorimeter test showed that the incorporation of 5 wt% of nutmeg filler significantly reduced the peak of heat release rate (pHRR) by ca. 60% compared with that of unmodified PU foam. It has been also proved that nutmeg filler may act as a natural anti-aging compound of PU foams. The incorporation of nutmeg filler in each amount successfully improved the stabilization of PU composite foams. Based on the antibacterial results, it has been shown that the addition of nutmeg filler significantly improved the antibacterial properties of PU composite foams against both Gram-positive and Gram-negative bacteria.     

Synthesis of a novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano zinc oxide and its application in poly (lactic acid) resin

A novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano ZnO (A4‐d‐ZnO) was synthesized and applied in poly (lactic acid) (PLA). Fourier transform infrared (FTIR), solid state nuclear magnetic resonance (SSNMR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive spectrometer (EDS) were used to confirm the chemical structure of A4‐d‐ZnO. The thermal stability and the flame‐retardant properties of the PLA composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning test (UL‐94), and micro combustion calorimeter (MCC) test. The results of XPS showed that A4‐d‐ZnO has been synthesized, and the doping ratio of ZnO was 7.2% in flame‐retardant A4‐d‐ZnO. TGA results revealed that A4‐d‐ZnO had good char forming ability (40 wt% at 600°C). The results of LOI, vertical burning test, and MCC showed that PLA/5%A4‐d‐ZnO composite acquired a higher LOI value (24%), higher UL94 rating, and lower pk‐HRR (501 kW/m²) comparing with that of pure PLA. It indicated that a small amount of flame‐retardant A4‐d‐ZnO could achieve great flame‐retardant performance in PLA composites. The catalytic chain scission effect of A4‐d‐ZnO could make PLA composites drip with flame and go out during combustion, which was the reason for the good flame‐retardant property. Moreover, after the addition of A4‐d‐ZnO, the impaired mechanical properties of PLA composites are minimal enough.     

Fire behavior of flame retarded unsaturated polyester resin with high nitrogen content additives

The novel flame retarded unsaturated polyester resins have been developed and prepared by introduction of high nitrogen content additives into the polymer matrix in order to verify their effectiveness in the formation of swollen carbonaceous char inhibiting the burning process of the polymer. The intumescent flame retardants (IFRs) based on mixture or metal complex were developed and characterized by particle size distribution, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), powder X-ray diffraction (XRD), elemental analysis (CHN) and thermogravimetric analysis (TGA). The evaluation of the efficiency of IFRs addition on the flammability and smoke emission of the unsaturated polyester resins (UP) was carried out using the fire hazard (UL-94), limiting oxygen index (LOI) and cone calorimeter (CC) tests, as well as smoke density chamber tests. The volatile compounds evolved during the burning of materials were determined using a steady state tube furnace and a gas chromatograph with mass spectrometer. Furthermore, the prepared materials were subjected to differential scanning calorimetry (DSC), thermogravimetric analysis and water resistance tests. The mechanical properties of the materials were investigated using Shore D hardness and dynamic mechanical thermal analysis (DMA). The structural evaluation of the manufactured materials and samples after the cone calorimetry tests was carried out using scanning electron microscopy (SEM). It was found that the incorporation of new intumescent flame retardants led to the formation of carbonaceous char layers’ inhibiting the decomposition process and limiting the smoke emission. The most promising results were obtained for the resin containing complex designated as ZN3AT, for which the highest reduction in maximum values of heat release rate (419 kW/m²) compared to unmodified polymer (792 kW/m²) were recorded. Apart from that, the prepared intumescent flame retardants affect the cross-linking process as well as the thermal and mechanical properties of the UP.     

A facile strategy to fabricate intumescent fire-retardant and smoke suppression protective coatings for natural rubber

As flammable natural rubber (NR) becomes more ubiquitous in industrial fields, there is a growing need for safe and effective flame retardant treatments through efficient techniques. Remarkably, our developed highly efficient natural tannic acid (TA)-based intumescent flame-retardant system (AGT) has the unique function in the rubber flame retardant aspect. Meanwhile, the developed coating method through polyurethane elastomer (PU) both as adhesive medium and a carbonforming agent can not only minimize the influence of flame retardant on the desirable intrinsic properties of base polymer and also maximize the efficiency of flame retardant. The flame-retardant coating (AGT/PU) exhibits highly efficient flame retardant performances reflected by a 31.9% reduction in peak heat release rate and a 27.3% reduction in total heat release and a 26.2% reduction in total smoke production with 50 wt% loading in 1 mm thick coating due to synergistic flame retardant effects. More importantly, the excellent flame retardancy performance are obtained by the PU@AGT10, as reflected in flame retardancy index (FRI) value of 11.88 makes it as excellent flame retardancy performance. While many physically mixed flame retardants are usually seriously detrimental to mechanical properties of NR, the influence of AGT/PU coating on mechanical properties of NR decreases obviously because fire retardant just directly impacts on PU adhesive layer rather than NR matrix, and the reinforcement function of graphene is also much significant. Moreover, the coating method requires just less flame retardant to achieve high flame retardant effect for NR. These findings suggest that significant opportunities for flame retardant polymer materials in industry.     

Polyaniline-coated coconut fibers: Structure,properties and their use as conductive additives in matrix of polyurethane derived from castor oil

Electrically conducting fibers based on coconut fibers (CF) and polyaniline (PANI) were prepared through in situ oxidative polymerization of aniline (ANI) in the presence of CF using iron (III) chloride hexahydrate (FeCl_3.6H₂O) or ammonium persulfate (APS) as an oxidant. The PANI-coated coconut fibers (CF-PANI) displayed various morphologies, electrical conductivities and percentages of PANI on the CF surface. For both systems, a PANI conductive layer was present on the CF surface, which was responsible for an electrical conductivity of around 1.5 × 10⁻¹ and 1.9 × 10⁻² S cm⁻¹ for composites prepared with FeCl₃.6H₂O and APS, respectively; values that are similar to that of pure PANI. In order to modify the structure and properties of polyurethane derived from castor oil (PU) both CF-PANI and pure PANI were used as conductive additives. The PU/CF-PANI composites exhibited higher electrical conductivity than pure PU and PU/PANI blends. Additionally, the PU/CF-PANI composites showed a variation in electrical resistivity according to the compressive stress applied, indicating that these materials could be applied for pressure-sensitive applications.     

Sound absorption properties of polyurethane foams derived from crude glycerol and liquefied coffee grounds polyol

The main objective of this study was to evaluate the sound absorption properties of rigid polyurethane foams (PUFs) produced from crude glycerol (CG) and/or liquefied coffee grounds derived polyol (POL). The lignin content of POL proved to have a major influence on the structure and mechanical properties of the foams. Indeed, the POL content increased the cell size of the foams and their stiffness, which subsequently influenced the sound absorption coefficients. The POL derived foam has slightly higher sound absorption coefficient values at lower frequencies, while the CG foam has higher sound absorption coefficient values at higher frequencies. In turn, the foam prepared using a 50/50 mixture of polyols presents slightly higher sound absorption coefficient values in the medium frequencies range due to a balance between the cell structure and the mechanical properties. The results obtained seem to suggest that the mechanisms involved in sound wave absorption depend on the formulation used to prepare the foams. Additionally higher POL contents improved the thermal stability of PUFs as well as their mechanical properties. From this work the suitability of CG and/or POL derived PUFs as sound absorbing materials has been proven.     

Recent Progress in Two-dimensional Nanomaterials Following Graphene for Improving Fire Safety of Polymer (Nano)composites

The high fire safety of polymer nanocomposites is being pursued by research institutions around the world. In addition to intrinsic flame retardancy strategy, the additive-type flame retardants have attracted increasing attention due to low commercial cost and easy fabrication craft. However, traditional additive-type flame retardants usually need high addition amount to achieve a desirable effect, which causes many side-effects on the overall performance of polymer materials, such as deteriorated mechanical property and processability. At present, two-dimensional(2 D) nanomaterials have also been applied to reduce the fire hazards of polymer(nano)composites with the coupling of barrier function and catalysis as well as carbonization effect. Even though most research work mainly focus on graphene-based flame retardants, more emerging two-dimensional nanomaterials are taking away research attention, due to their complementary and unique properties, mainly including hexagonal boron nitride(h-BN), molybdenum disulfide(MoS_2), metal organic frameworks(MOF), carbon nitride(CN),titanium carbide(MXene) and black phosphorene(BP). In this review, except for graphene, the flame retardant mechanism involving different layered nanomaterials are also reviewed. Meanwhile, the functionalization method and flame retardancy effect of different layered nanomaterials are emphatically discussed for offering an effective reference to solve the fire hazards of polymer materials. Moreover, this work objectively evaluates the practical significance of polymer/layered nanomaterials composites for industrial application.     

“One‐pot” synthesis of crosslinked silicone‐containing macromolecular charring agent and its synergistic flame retardant poly(l‐lactic acid) with ammonium polyphosphate

A crosslinked silicone‐containing macromolecular charring agent (CSi‐MCA) was synthesized via “one‐pot” process, and it was combined with ammonium polyphosphate (APP) to synergistically improve the flame retardancy of poly(l ‐lactic acid) (PLA). The chemical structure of synthesized CSi‐MCA was characterized by Fourier transform infrared spectroscopy and solid‐state ¹³C nuclear magnetic resonance. The thermal gravimetric analyzer indicated that the CSi‐MCA displayed good thermal stability and high residue via the catalytic crosslinking. Furthermore, the flame retardant effect of CSi‐MCA and APP as intumescent flame retardants in PLA system was investigated by limited oxygen index, UL94, and cone calorimeter test. When the content of CSi‐MCA was 5 wt% and APP was 10 wt% (CSi‐MCA/APP = 1/2), the limited oxygen index value of composites was 33.6 and UL94 classed a V‐0 rating. The peak heat release rate and total heat release of PLA composites containing both APP and CSi‐MCA decreased significantly in comparison with those with APP or CSi‐MCA alone. The flame retardancy mechanism was investigated via analyzing residual chars by scanning electron microscopy and X‐ray photoelectron spectroscopy as well as the possible chemical reaction between APP and CSi‐MCA by thermal gravimetric analyzer and Fourier transform infrared spectroscopy. The results showed that the enhanced flame retardancy was attributed mainly to synergistic effect of CSi‐MCA and APP, which could form a compact, continuous, and protective layer during combustion. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of surface chemical modification for aluminum hypophosphite with hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene on the fire retardancy,water resistance,and thermal properties for polyamide 6

The surface chemical modified aluminum hypophosphite (AHP) defined as MAHP was successful prepared through P–H bonds on AHP surface reacted with the aldehyde groups in hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene made in our lab. The wettability of the flame retardants was evaluated by water contact angle tests, and the water contact angle of the prepared MAHP dramatically increased from 0° for AHP to 145°, which indicated the surface modification made the superhydrophilic AHP into superior hydrophobic MAHP. The prepared MAHP and AHP, respectively, incorporated into polyamide 6 (PA6) matrix to prepare flame retardant PA6 composites and the fire retardancy and thermal degradation behavior of flame retardant PA6 composites were investigated by limiting oxygen index, vertical burning test (UL‐94), cone calorimeter, and thermogravimetric analysis tests. The morphologies and chemical compositions of the char residues for PA6 composites were investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy, respectively. The water resistant properties of flame retardant PA6 composites were evaluated by putting the samples into distilled water at 70°C for 168 hr, and the mechanical properties for flame retardant PA6 composites were investigated by the tensile, flexural, and Izod impact strength tests. The results demonstrated that the PA6/MAHP composites successfully passed UL‐94 V‐0 flammability rating, and the limiting oxygen index value was 27.6% when the loading amount of MAHP was 21 wt%. However, there is no rating in vertical burning tests for PA6/AHP composite with the same amount of AHP, which indicated the surface modification of AHP enhanced the flame retardancy efficiency for PA6 composites. The morphological structures and analysis of X‐ray photoelectron spectroscopy of char residues revealed that the surface modification of AHP benefited to the formation of a sufficient, flame retardant elements rich, more compact and homogeneous char layer on the materials surface during combustion, which prevented the heat transmission and diffusion, limit the production of combustible gases, inhibit the emission of smoke and then led to the reduction of the heat release rate and smoke produce rate. The mechanical properties results revealed that the surface modification of AHP enhanced the mechanical properties, especially the Izod impact strength comparing with that of PA6/AHP composites with the same amount of flame retardant. After water resistance tests, the PA6/MAHP composites remained superior flame retardancy and presented continuous and compact char layer after cone calorimeter tests; however, the fire retardancy for PA6/AHP composite obviously decreased, and the char layer was discontinuous with big hole caused by the extraction of AHP by water during water resistance tests. Copyright © 2017 John Wiley & Sons, Ltd.     

Compressive response of composite ceramic particle-reinforced polyurethane foam

Quasi-static and dynamic compressive tests are undertaken on the polyurethane (PU) foam and fumed silica reinforced polyurethane (PU/SiO₂) foam experimentally. The ceramic microspheres with varying mass fractions are adopted to mix with the PU/SiO₂ foam to fabricate the composite particle-reinforced foams. The effects of strain rate and particle mass fraction are discussed to identify and quantify the compressive response, energy-absorbing characteristic, and the associated mechanisms of the composite foams. The results show the initial collapse strength and plateau stress of the foams are improved significantly by reinforcing with the ceramic microsphere within 60 wt% at quasi-static compression. The rate sensitivity is observed on all the foams, but in different patterns due to the influence of ceramic microsphere. The compressive response affected by ceramic microsphere can be attributed to the particle cluster effect and stress wave propagation. Together with the deformation, the compressive characteristic experiences non-monotonic change from the low to high strain rates. The specific energy absorption (SEA) of the foam with 41 wt% ceramic microsphere show the largest magnitude at quasi-static compression. With the increasing strain rate, the ceramic reinforced foam exhibits superior energy absorption efficiency at high strain rates to that of the pure foams.     

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin

A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.