LLDPE／EAA共混体系结晶行为及相容性

通过ＤＭＡ、ＤＳＣ、偏光显微镜（ＰＬＭ）、ＷＡＸＤ及力学性能测试等方法，对线性低密度聚乙烯（ＬＬＤＰＥ）／乙烯－丙烯酸共聚物（ＥＡＡ）共混体系的研究表明，ＬＬＤＰＥ与ＥＡＡ的非晶相可部分相容，结晶相不能形成共晶；共混物结晶时，两组分相互影响，ＬＬＤＰＥ的结晶速度高于ＥＡＡ，两者结晶没有进入对方晶胞中．还发现ＬＬＤＰＥ与ＥＡＡ力学性能上相容．低含量ＥＡＡ共混体系显示出较佳的力学性能．     

EAA增容LLDPE/PEO共混物及其增容机理

以乙烯-丙烯酸共聚物(EAA)为增容剂, 研究了它在线性低密度聚乙烯(LLDPE)/聚环氧乙烷(PEO)共混物中的增容作用及其增容机理。采用电子显微镜(SEM)、动态力学分析(DMA)、DSC和红外光谱(IR)对共混物形态及其微观结构进行了表征。结果表明, EAA对LLDPE/PEO共混物有一定的增容作用; 其增容机理为: EAA和LLDPE两者的非晶区部分相容, 而EAA分子中的羧基与PEO分子中的醚氧基相互作用形成了分子间氢键。     

EAA增容LLDPE／SAN共混物的形态及力学性能

采用SEM及力学性能测试等方法，研究了乙烯－丙烯酸共聚物（EAA）含量对其增容线性低密度聚乙烯（LLDPE）／苯乙烯－丙烯腈共聚物（SAN）共混物形态及性能的影响．发现少量的EAA可使共混物中SAN相的相尺寸减小，共混物模量、拉伸强度及断裂伸长率提高．当EAA的含量增加至11．7％时，它在共混物中两相界而的分布达到饱和，即增容剂饱和浓度Cs=11．7％；此时，共混物形态及性能的变化趋势出现明显转折．明显过量的EAA主要起增韧作用．EAA的增容机理为，它与LLDPE组分的非晶区可部分相容，同时又与SAN相存在着分子间特殊作用.     

The effects of irradiation cross-linking on the thermal degradation and flame-retardant properties of the HDPE/EVA/magnesium hydroxide composites

High-density polyethylene/ethylene vinyl-acetate copolymer/magnesium hydroxide composites were crosslinked via high-energy electron beam irradiation in the presence of triallylisocyanurate. The structure of the cross-linking network was determined with the help of rheological measurements through advanced rheological extended systems (ARES). The thermal and flame-retardant properties of the irradiated composites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cone calorimetry. Results showed that the cross-linking network structure could enhance the thermal stability of composites, and did favor to smoke suppression. However, the peak heat release rate (PHRR) increased and the time to PHRR shortened, inferring that the composites after irradiation cross-linking were easier to combust. The char microstructure after cone calorimetry test was observed and used to give explanation of the above results.     

Synergistic effects and mechanism of multiwalled carbon nanotubes with magnesium hydroxide in halogen-free flame retardant EVA/MH/MWNT nanocomposites

The synergistic effects and mechanism of multiwalled carbon nanotubes (MWNTs) with magnesium hydroxide (MH) in halogen-free flame retardant EVA/MH/MWNT nanocomposites have been studied by cone calorimeter test (CCT), limiting oxygen index (LOI), thermogravimetric analysis (TGA), torque test, morphological evolution experiment, and scanning electron microscopy (SEM). The data obtained from the CCT, LOI, and TGA show that suitable amount of MWNTs has synergistic effects with MH in the EVA/MH/MWNT nanocomposites. The MWNTs can considerably decrease the heat release rates and mass loss rate by about 50-60%, prolongate the combustion time to near two times, and increase the LOI values by 5% when 2 wt% MWNTs substitute for the MH in the EVA/MH/MWNT samples. The TGA data also show that the synergistic effects of MWNTs with MH apparently increase the thermal degradation temperatures and final charred residues of the EVA/MH/MWNT samples. The experimental observations from the torque, morphological evolution tests, and SEM give positive evidences that the synergistic mechanism of MWNTs with MH can be described to: (i) the increase of melt viscosity because of network structure formation of MWNTs in the EVA/MH matrix; (ii) the enhancement of thermo-oxidation stability due to the MWNTs' mechanical strength and integrity of the charred layers in the EVA/MH/MWNT nanocomposites; (iii) the formation of compact charred layers promoted by MWNTs acted as heat barrier and thermal insulation. All the above-mentioned factors efficiently enhance thermal and flame retardant properties and protect the EVA/MH/MWNT nanocomposite materials to be burning.     

A novel zinc chelate complex containing both phosphorus and nitrogen for improving the flame retardancy of low density polyethylene

A novel metal chelate complex containing phosphorus, nitrogen and zinc (II) ion was synthesized and used as the flame retardant of low density polyethylene (LDPE). The zinc chelate complex was synthesized by reacting zinc acetate with the ligand of tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (TEPAPM). The chemical structure of the target Zn-TEPAPM was confirmed by FTIR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra. The flame retardancy and thermal behavior of LDPE containing various amount of Zn-TEPAPM were investigated by limiting oxygen index test, thermogravimetric (TG) analysis and cone calorimetry. The results show that Zn-TEPAPM can greatly increase the thermal stability, the char formation and smoke suppression ability of LDPE. The TG curves show that even when the filler content of Zn-TEPAPM is as low as 1 wt% in LDPE, the onset degradation temperature of LDPE is increased from 429 °C to 442 °C, and the maximum degradation temperature is increased from 469 °C to 488 °C. Also, a reduction of 32% for the peak heat release rate (PHRR) is obtained in the cone test. Moreover, Zn-TEPAPM is demonstrated to be a very effective synergist of ammonium polyphosphate (APP). When 1 wt% of Zn-TEPAPM was introduced into the LDPE/APP (mass ratio 80/19) blend, the PHRR value is reduced by 32%, compared with that of LDPE/APP blend without Zn-TEPAPM, and the char layer becomes more compact and intact.     

Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene-acrylic acid copolymer

Two grades of low density polyethylene (LDPE) were blended with polyamide-6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene-acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrillation is increased, especially for the blends with the higher molar mass LDPE grade. The mechanical properties of the latter blends were found to be considerably enhanced by the addition of EAA, whereas the improvement was relatively modest for the blends with the lower molar mass LDPE. The fracture properties of double end notched samples of the ribbons prepared with the blends containing the lower molar mass LDPE grade were also studied. It was shown that, despite of the increased interfacial adhesion caused by the presence of EAA, the latter plays a measurable positive effect on the fracture properties only for the blends with LDPE as the matrix.     

Synergistic effect of graphene oxide and boron-nitrogen structure on flame retardancy of natural rubber/IFR composites

In this paper, GO-BN(graphene oxide grafted boron nitride) was synthesized from graphene oxide and boron nitride by silane coupling agent KH550. Furthermore, GO-BN and intumescent flame retardant (IFR) were added into natural rubber (NR) simultaneously to improve its flame retardancy. The structure of GO-BN was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The analysis showed that GO-BN was successfully synthesized. The enhanced flame retardancy performance of flame retardant natural rubber (FRNR) was evaluated by limiting oxygen index (LOI) and UL-94 tests. Moreover, the combustion action of FRNR in fire was evaluated by cone calorimetry. Notably, the results showed that the sample with a GO-BN content of 12 phr showed the best flame retardancy performance. The heat release rate (HRR) and total heat release rate (THR) were remarkably decreased by 42.8% and 19.4%, respectively. Carbon residues were analyzed by infrared spectroscopy and scanning electron microscopy, which showed that GO-BN and IFR had a synergistic catalytic effect. The formation of compact thermal stable carbon layer after combustion was the key to protect engineering materials from combustion.     

聚氯乙烯／线性低密度聚乙烯共混体系的相容性

用动态力学分析（ＤＭＡ）和傅利叶变换红外光谱（ＦＴＩＲ）研究了氢化聚丁二烯－ｂ－聚甲基丙烯酸甲酯（ＨＰＢＤ－ｂ－ＰＭＭＡ）共聚物增容剂对聚氯乙烯（ＰＶＣ）与线性低密度聚乙烯（ＬＬＤＰＥ）共混体系的增容作用．增容剂使共混物中两相的玻璃化温度发生变化，说明其相容性增加．ＦＴＩＲ的结果表明，增容剂中羰基与ＰＶＣ的α氢形成氢键，使ＣＯ，Ｈ─Ｃ及Ｃ─Ｃｌ的振动频率变化，峰形加宽．     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.     

Effect of gamma irradiation on linear low density polyethylene/magnesium hydroxide/sepiolite composite

Radiation crosslinking is generally used to improve the thermo-mechanical properties of the composites. A study has been carried out to investigate the effect of gamma radiation on the thermo-mechanical properties of linear low density polyethylene containing magnesium hydroxide (MH) and sepiolite (SP) as non-halogenated flame retardant additives. The developed composites are irradiated at different doses upto maximum of 150 kGy. Infrared spectra of the irradiated composites reveal the reduction in the intensity of O-H band with increase in the absorbed doses, thus indicates a distinct structural change in MH at higher doses. The thermogravimetric analysis results of unirradiated and composites irradiated at low doses (≤75 kGy) show two steps weight loss, which is changed to single step at higher doses with lower thermal stability. The melting temperature (T_m) and crystallization temperature (T_c) of irradiated composites are lowered with irradiation whereas Vicat softening temperature (VST) is increased. The increasing trend in gel content with increase in the absorbed dose confirms the presence of crosslinked network. The mechanical properties, results show significant improvement in the modulus of irradiated composites. The results also confirm that MH gradually loses its OH functionality with irradiation.     

Dynamic mechanical properties of ethylene-acrylic acid copolymers neutralized with copper(II), manganese(II) and nickel(II) acetates

Dynamic mechanical properties of ethylene-acrylic acid copolymer (mole% ofAA is 9.3) neutralized with copper(II), manganese(II) and nickel(II) acetates were measured in a temperature range of –150 to 80 °C at 3.5, 11, 35 and 110 Hz. The and relaxations are observed around 30 and –140 C, respectively, which are attributed to a micro-Brownian molecular motion of segments and a local molecular motion of short segments, respectively. In the relaxation, the relaxation temperature increased with increasing degree of neutralization,x, and the peak height decreased, which were independent on the species of counter ions. The relaxation which is ascribed to molecular motion of rather short segments between ion-clusters was observed at high ion concentrations. The effects ofx on the and relaxations were different from those of the preceding dielectric results. This discrepancy between the mechanical and the dielectric results can be explained by the assumption that the segments responsible for the mechanical relaxations are different of those for the dielectric relaxation. In the relaxation, the relaxation temperature and the peak height were almost independent ofx and the species of counter ions. The relation between the molecular motion and the structure of the transition metal salts (complex structure and formation of ion-clusters) was understood well by examining the mechanical and dielectrical results together.     

Surface treatment of LLDPE and LDPE blends by nitric acid,sulfuric acid,and chromic acid etching

Surface treatment of linear low density polyethylene and low density polyethylene blends is investigated herein using nitric acid, sulfuric acid, and chromic acid. These chemical treatments not only make the surface rough but also introduce polar groups. A new method, “sulfonic groups index” (SI) is employed to quantify the newly generated polar groups in the wavenumber of 1,250–840 cm⁻¹ in the Fourier transform infrared spectra. The SI values effectively indicate that the most polar groups are incorporated into the chromic acid-etched samples among the three inorganic acids, which is also confirmed by scanning electron microscopy and roughness tests. Besides, annealing treatment can enhance the crystallinity X _c of all etched samples which plays a predominant role in the increase of roughness within 2 h. As etching time increases, chain scission and destruction of amorphous parts happen and roughness increases a lot for chromic acid-treated samples, but for sulfuric acid- and nitric acid-treated samples, the destruction of amorphous parts may not happen so that the roughness has not many changes.     

Effect of a novel charring-foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene

A new triazine polymer was synthesized by using cyanuric chloride, ethanolamine and ethylenediamine as raw materials. It is used both as a charring agent and as a foaming agent in intumescent flame retardants, designated as charring-foaming agent (CFA). Effect of CFA on flame retardancy, thermal degradation and mechanical properties of intumescent flame retardant polypropylene (PP) system (IFR-PP system) has been investigated. The results demonstrated that the intumescent flame retardant (IFR) consisting of CFA, APP and Zeolite 4A is very effective in flame retardancy of PP. It was found that when the weight ratio of CFA to APP is 1:2, that is, the components of the IFR are 64 wt% APP, 32 wt% CFA and 4 wt% Zeolite 4A, the IFR presents the most effective flame retardancy in PP systems. LOI value of IFR-PP reaches 37.0, when the IFR loading is 25 wt% in PP. It was also found that when the IFR loading is only 18 wt% in PP, the flame retardancy of IFR-PP can still pass V-0 rating, and its LOI value reaches 30.2. TGA data obtained in pure nitrogen demonstrated that CFA has a good ability of char formation itself, and CFA shows a high initial temperature of the thermal degradation. The char residue of CFA can reach 35.7 wt% at 700 °C. APP could effectively promote the char formation of the APP-CFA system. The char residue reaches 39.7 wt% at 700 °C, while it is 19.5% based on calculation. The IFR can change the thermal degradation behaviour of PP, enhance T_max of the decomposition peak of PP, and promote PP to form char, based upon the results of the calculation and the experiment. This is attributed to the fact that endothermic reactions took place in IFR charring process and the char layer formed by IFR prevented heat from transferring into inside of IFR-PP system. TGA results further explained the effective flame retardancy of the IFR containing CFA.     

Effect of a phosphorus-containing flame retardant on the thermal properties and ease of ignition of poly(lactic acid)

An aryl polyphenylphosphonate, poly(9-oxa-10-(2,5-dihydro-xyphenyl) phospha-phenanthrene-10-oxide) phenylphosphonate (WLA-3), was used to prepare a flame-retardant poly(lactic acid) (PLA) by direct melt compounding. The thermal behaviour, burning behaviour and mechanical properties of the flame-retardant PLA systems have been investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), vertical burning test (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT) and tensile test. The flame retardance mechanism has been studied via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and P content analysis. The UL-94 ratings of PLA’s containing 7phr (W_7P) and 10phr (W_10P) of WLA-3 were enhanced to V-0 from no rating for neat PLA. However, the cone calorimetry of flame-retardant PLA (W_7P) only showed a little decrease in heat release rate (HRR), peak of heat release rate (PHRR) and total heat release (THR) compared to neat PLA. TGA results showed that the PLA containing different amounts of WLA-3 presented more complicated thermal decomposition behaviours than neat PLA. Additionally, the results from DSC and tensile tests showed that the addition of WLA-3 into PLA had a slight impact on the crystallization behaviours and tensile properties.     

Effects of carbon nanotubes on the thermal stability and flame retardancy of intumescent flame-retarded polypropylene

Flame retardant mixtures of carbon nanotubes (CNTs) and intumescent flame retardant (IFR) were embedded in polypropylene (PP) to investigate what will happen if the additives exhibit two different flame retardation mechanisms. TEM tests showed that CNTs dispersed homogenously in PP matrix without any visible agglomeration. The effects of CNTs on thermal stability and flammability of PP were investigated by thermogravimetry (TG) and cone calorimetry tests, respectively. Results indicated that the introduction of CNTs only enhanced thermal stability of materials in a certain temperature range, but caused a severe deterioration of flame retardancy due to the interaction of the network structure and the intumescent carbonaceous char. Furthermore, conditions for an intumescent flame retardation system to behave with high efficiency were also discussed by a secondary combustion test.     

Photocrosslinking and related properties of intumescent flame‐retardant LLDPE/EVA/IFR blends

The photoinitiated crosslinking of halogen‐free flame retarded linear low density polyethylene/poly(ethylene‐co‐vinyl acetate) blends (LLDPE/EVA) with the intumescent flame retardant (IFR) of phosphorous‐nitrogen compound (NP) in the presence of photoinitiator and crosslinker and their characterization of related properties have been investigated by gel determination, heat extension test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), Fourier transfer infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), mechanical properties measurements, limiting oxygen index (LOI), UL‐94, and water resistance test. The data from the gel content and heat extension rate (HER) show that the LLDPE/EVA/IFR blends filled with NP are readily crosslinked to a gel content of above 75% and the HER values reach about 50% by UV‐irradiation of 5 sec under suitable amount of photoinitiator and crosslinker. The data obtained from the CCT and LOI indicate that photocrosslinking can considerably decrease the heat release rates (HRR) by 10–15%, prolongate the combustion time, and increase two LOI values for the LLDPE/EVA/NP blends UV irradiated for 5 sec. The results from TGA and the dynamic FTIR spectra give the evidence that the photocrosslinked LLDPE/EVA/NP samples show slower thermal degradation rate and higher thermo‐oxidative degradation temperature than the uncrosslinked LLDPE/EVA/NP samples. The morphological structures of charred residues observed by SEM give the positive evidence that the compact charred layers formed from the photocrosslinked LLDPE/EVA/NP samples play an important role in the enhancement of flame retardant and thermal properties. The data from the mechanical tests and water‐resistant measurements show that photocrosslinking can considerably improve the mechanical and water‐resistant properties of LLDPE/EVA/NP samples. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Thermal stability and flame retardancy of PET/magnesium salt composites

Nano-Mg(OH)₂ (nanometre magnesium hydroxide, nano-MH) was successfully introduced into the esterification and polycondensation system by in situ polymerization to obtain PET/magnesium salt composites (PETMS). The thermal properties and flame retardancy of PETMS were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UL-94 vertical burning and limited oxygen index (LOI) test. The DSC and TGA results show that magnesium salts in the PET matrix have little effect on the thermal properties of PET, but a significant effect on the thermal stabilities of the composites. The results of LOI and UL-94 test show PETMS have higher LOI values (≥25%) and V-0 rating without melt dripping in the UL-94 test, indicating that PETMS have good flame retardancy and anti-dripping property. Moreover, the residues of magnesium salts and composites after TGA test were also studied by Fourier transform infrared spectroscopy (FTIR) to better understand the mechanism of flame retardancy, which reveals that magnesium salts accelerate the degradation of PET and catalyze the formation of char. The SEM results show the morphological structures of the char effectively protect the composites’ internal structures and inhibit the heat, smoke transmission and reduce the fuel gases when the fire contacts them.     

The flame retardancy of alginate/flame retardant viscose fibers investigated by vertical burning test and cone calorimeter

The smoldering weakness of alginate fibers can be effectively suppressed by simple blending with flame retardant viscose fibers. The char formed by flame retardant viscose fibers can prevent the heat transmission and suppress the smoldering of alginate.