Advances in Nylon 6,6 Flame Retardancy

Abstract

The development of an ecologically safe flame retardant system for nylon 6,6 remains to be a major problem of polymer industry. This study reviews three approaches: the increase of char by addition of polyvinylalcohol (Part I), the suppression of combustion in gaseous phase by addition of melamine cyanurate (Part II), and the combination of char increase and flame suppression by addition of various Si-inorganic systems (Part III).     

Compatibility of nylon 6 with poly(vinyl alcohol), hydroxylated poly(vinyl acetate) and poly(vinyl acetate)

Summary The compatibility of nylon 6 with poly(vinyl acetate)(PVAc) and poly(vinyl alcohol)(PVA) was investigated in terms of the melting-temperature depression. In order to vary the compatibility systematically, a hydroxylated poly(vinyl actate)(m-PVAc) was prepared by hydrolyzing PVAc with KOH in CH₃OH. It was found that the compatibility with nylon 6 is better in the systematic order PVA> m-PVAc> PVAc.     

Characterization of flame-retarded polymer combustion chars by solid-state 13C and 29Si NMR and EPR

We report here on the results of our continuing effort to study the flame-retardant mechanism of silica gel and potassium carbonate. These additives reduce the flammability of a wide variety of common polymers such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), and cellulose. In an effort to determine how these additives reduce polymer flammability, we have used electron paramagnetic resonance spectroscopy and solid-state ¹³C and ²⁹Si nuclear magnetic resonance spectroscopy to characterize the combustion chars or residues. These data indicate that, in the case of poly(vinyl alcohol), the additives do not change the type of char formed, but they do change the rate of char formation relative to the rate of fuel generation. We also found that, using only CP/MAS ¹³C NMR, there can be significant intensity distortions which complicate interpretation, if the char is hydrogen depleted and contains paramagnetic centres. © 1998 John Wiley & Sons, Ltd.     

Pervaporation of ethanol—water mixture by Co60 γ-ray irradiation-modified nylon 4 membrane

The ethanol—water separation by pervaporation with γ-ray irradiation-modified nylon 4 membrane was investigated. The membrane was prepared by homografting γ-ray irradiation of vinyl acetate (VAc) monomer onto nylon 4, poly(vinyl acetate) (PVAc)-homo-g-nylon 4 followed by hydrolysis treatment, poly(vinyl alcohol) (PVA)-homo-g-nylon 4. The homografting method shows significant improvement in the degree of grafting of (VAc) onto nylon 4 over the heterografting method. For example, the degree of grafting of the VAc with 30 vol % and total dose of 2 Mrad for the heterografted method and for the homografted method are 14.1 and 42.2%, respectively. The effects of irradiation with or without oxygen in solution, irradiation time, VAc content, degree of grafting, crystallinity, feed concentration, and operating temperature on performances of the PVA-homo-g-nylon 4 membrane were carried out. Comparison of the separation factor of sorption in membrane (α_sorp) and that of pervaporation (α_perv) was made. A separation factor of 7.3 and a 0.691 kg/m² h permeation rate can be obtained by the PVA-homo-g-nylon 4 membrane with a degree of grafting of 42.2% for 90 wt % ethanol feed concentration. Compared with the unmodified nylon 4 membrane, which has the separation factor of 4 and permeation rate of 0.350 kg/m² h, the PVA-homo-g-nylon 4 membrane shows improved a separation factor and permeation rate. © 1993 John Wiley & Sons, Inc.     

Development of new sustainable inorganic flame retardant additive system for polyamide 6,6 with improved performance

We report the effect of new sustainable inorganic phosphate glass (P‐glass) flame retardants for polyamide 6,6 (PA6,6). Three P‐glasses differing in chemical composition and glass transition temperature (T_g) were prepared and their flame retardant effect on PA6,6 was studied by cone calorimetry, thermogravimetric analysis, and SEM‐EDX. The effect of high and intermediate T_g P‐glasses on the thermal stability of PA6,6 was negligible as compared to that of the low T_g P‐glass due to the hygroscopic nature of the latter. However, the char formation was independent of the P‐glass composition and was observed to increase by 30% in the presence of P‐glass. The low T_g P‐glass composition (i.e., ILT‐1) was found to be a promising flame retardant for PA6,6 at a concentration of up to 15% by weight. Cone calorimetry data showed that the ILT‐1 decreased both the peak heat release rate and the total heat amount released from the PA6,6/ILT‐1 hybrids, resulting in an efficient formation of a glassy char layer. In contrast to the intermediate and high T_g P‐glasses of this study, SEM‐EDX indicated that the ILT‐1 P‐glass was well dispersed in the PA6,6 matrix to yield a typical droplet‐in‐matrix phase morphology in the melt‐blended binary immiscible P‐glass/PA6,6 hybrids. POLYM. ENG. SCI., 55:1741–1748, 2015. © 2014 Society of Plastics Engineers     

Mass transfer study of chlorine dioxide gas through polymeric packaging materials

The mass transfer profile (permeability, diffusion, and solubility coefficients) of chlorine dioxide (ClO₂), a strong oxidizing agent that is used in food and pharmaceutical packaging, was determined through various common polymeric packaging materials. A continuous system for measuring permeation of ClO₂, using an electrochemical detector, was developed. It was observed that biaxially‐oriented poly(propylene), poly(ethylene terephthalate), poly(lactic acid), nylon, and a multilayer structure of ethylene vinyl acetate and ethylene vinyl alcohol were better barriers for gaseous ClO₂, as compared to polyethylene, poly(vinyl chloride), and polystyrene. The activation energies of permeation for ClO₂ through poly(ethylene terephthalate) and poly(lactic acid) were determined to be 51.05 ± 4.35 and 129.03 ± 2.82 kJ/mol, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, , 2009     

Spider-net within the N6, PVA and PU electrospun nanofiber mats using salt addition: Novel strategy in the electrospinning process

Electrospun nanofibers are promising candidates in the nanotechnological applications due to the advantages of the nanofibrous morphology. Therefore, many attempts were reported to modify the electrospun mats to gain more beneficial properties. In the present study, we are introducing a strategy to synthesize electrospun polymeric nanofiber mats containing spider-net binding the main nanofibers. Addition with long stirring time of a metallic salt having tendency to ionize rather than formation of sol–gel in the host polymer solution reveals to synthesize a spider-net within the electrospun nanofibers of the utilized polymer. Nylon6, polyurethane and poly(vinyl alcohol) have been utilized; NaCl, KBr, CaCl₂ and H₂PtCl₆ have been added to the polymeric solutions. In the case of nylon6 and poly(vinyl alcohol), addition of the inorganic salts resulted in the formation of multi-layers spider-network within the electrospun nanofibers mats. The synthesized spider-nets were almost independent on the nature of the salt; the optimum salt concentration was 1.5 wt%. The metallic acid led to form trivial spider-nets within both of nylon6 and poly(vinyl alcohol) nanofibers. In a case of polyurethane, few spider-nets were formed after salt addition due to the low polarity of the utilized solvents. According to TEM analysis, the synthesized spider-net consisted of joints; the later issued from the main nanofibers at Taylor's cone zone. The spider-net improved the mechanical properties and the wetability of the nylon6 nanofiber mats, accordingly a mat having amphiphilic feature has been prepared.     

Highly Efficient Dye Removal from Aqueous Solutions Using Simple Chemical Modification of Wood Sawdust

Abstract

This study examined the efficiency of oxidized wood meal for removal of methylene blue (MB) as a typical basic dye from aqueous waste streams. The adsorption process was performed using sawdust treated with KMnO₄, K₂Cr₂O₇, and H₂O₂ oxidants. Among the tested chemical oxidants, KMnO₄ was found to be more effective for modification of sawdust for dye uptake. Based on the breakthrough analysis, the highest column capacity of 227 mg g^?1 was obtained for the KMnO₄/SD. Sorption capacity of KMnO₄ treated sawdust for dye uptake was about seven times that of untreated sawdust (SD). The nature and morphology of adsorbents were characterized by SEM, XRD, and FTIR analysis. The adsorption behavior of KMnO₄/SD was found to be a strongly pH-dependent process and the maximum adsorption efficiency was obtained at pH 10. Dye-loaded KMnO₄/SD sorbent can be regenerated using low-cost chemicals.     

Synthesis of nylon 6,6 copolymers with aromatic polyamide structure

In this article, flexible nylon 6,6 was reinforced with rigid‐chain aromatic polyamides based on poly(4,4′‐diphenylsulfone terephthalamide) (PSA), poly(p‐diphenyl oxide terephthalamide) (POA), poly(p‐diphenylmethane terephthalamide) (PMA), and isophthaloyl chloride (IPC). Various high molecular weight block copolyamides were synthesized by solution polymerization using p‐aminophenylacetic acid (p‐APA) as a coupling agent. Their thermal properties show that the block copolyamides exhibit higher values of T_g and T_m and better thermal stability than those of nylon 6,6, especially the IPC‐modified nylon 6,6. The order of increased thermal properties of copolyamides is IPC > POA > PMA > PSA. From wide‐angle X‐ray diffraction patterns, it was found that nylon 6,6 has two diffraction peaks, that is, 2θ = 20.5° and 23°, while the multiblock copolymers showed only one at 2θ = 20°, indicating a different crystal structure. It was found that the mechanical properties of the IPC‐modified nylon 6,6 were improved more than those of the semirigid copolyamides. The order of tensile strength was IPC > PSA > PMA > POA, but for elongation, it was POA > PMA > PSA > IPC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2167–2175, 2001     

Polymer flame retardancy: A new approach

New types of ecologically friendly polymer flame-retardant systems were proposed for Nylon 6,6 and polypropylene [high temperature polymer–organic char former, poly(vinyl alcohol), and silicon–inorganic system]. These systems can act in condensed and gaseous phases. The cone calorimeter and LOI tests indicated the improvement of fire-retardant properties for compositions of flame retardants with Nylon 6,6 and polypropylene in comparison with pure polymers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:715–725, 1998     

Using Green Process for the Synthesis of Poly(Vinyl Alcohol)/α-Al2O3-Thiamine Nanocomposite: Thermal,Mechanical, Contact Angle,and Morphological Studies

Hydrophilic surface of α-Al₂O₃ nanoparticles was treated with thiamine as a green modifier for better compatibility with poly(vinyl alcohol) matrix. In this regard, poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites with different ratios of modified α-Al₂O₃ (3, 5, and 7?wt%) were prepared through ultrasonic irradiation and their properties were compared with the pure poly(vinyl alcohol). Many techniques were used to study the properties of poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites. Morphology images of poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites showed the good dispersion of the α-Al₂O₃ nanoparticles in poly(vinyl alcohol) matrix in nanometer-scale. The results demonstrated that poly(vinyl alcohol)/α-Al₂O₃-vitamin B₁ nanocomposites give better thermal stability, strain, and E-modulus than the pure poly(vinyl alcohol.     

Fire-retardant additives for polymeric materials—I. Char formation from silica gel–potassium carbonate

Silica gel combined with potassium carbonate is an effective fire retardant for a wide variety of common polymers (at mass fraction of only 10% total additive) such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), cellulose, and to a lesser extent polystyrene and styrene-acrylonitrile. The peak heat release rate is reduced by up to 68% without significantly increasing the smoke or carbon monoxide levels during the combustion. © 1997 by John Wiley & Sons, Ltd.     

Synergistic effect between hollow glass beads and aluminium hydroxide in flame retardant EVA composites

Abstract

Flame retardant ethylene vinyl acetate (EVA) composites were prepared based on different contents of hollow glass beads (HGBs) and aluminium hydroxide (ATH) in this paper, and the flame retardant properties were studied using limiting oxygen index, UL-94 test and cone calorimeter test respectively. The results showed that EVA-4 with 1·0 wt-%HGBs has the lowest heat release rate, total heat release and smoke production rate among all samples, and HGBs could promote to form a compact char layer on the surface of the sample. It indicates that there is an obvious synergistic flame retardant effect between HGBs and ATH in this composite.     

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H₂O₂, KMnO₄ and HNO₃. Their physicochemical properties were investigated by BET N₂ adsorption, laser particle examination, Boehm’s titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g⁻¹, while it reaches 2.6, 5.1 and 11.0 mg g⁻¹ for the H₂O₂, HNO₃ and KMnO₄ oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg l⁻¹. Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO₃ and KMnO₄ oxidized CNTs is more obvious than that of the as-grown and H₂O₂ oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO₄ oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H₂O₂ and HNO₃ oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO₄ oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent.     

Flame retardant flexible poly(vinyl chloride) compound for cable application

ZnO/MgO, ZnO/CaO, and ZnO/CaO/MgO can form solid solutions. The solid solution for we as flame retardant (SSFR) was obtained by annealing at 1023 K for 4.5 h in a muffle furnace. Flexible poly (vinyl chloride) (PVC) filled with SSFR and Sb₂O₃ was investigated by differential thermal analysis thermogravimetry. Limiting oxygen index (LOI), mechanical properties, and electrical properties were studied. The surface of the char formed after combusting of the PVC compounds was observed through scanning electron microscopy and the effect of the surface area to the LOI was also studied. The data suggested that a small amount of SSFR and Sb₂O₃ have good synergy and can greatly increase the LOI and the char yield, and that the thermal degradation temperature and the activation energy decreased. It can be concluded that the mechanism of SSFR is a condensed‐phase mechanism. Moreover, one can conclude that the surface area can enhance the LOI. All the results showed that SSFR is effective and safe as a flame retardant in flexible PVC. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3137–3142, 2003     

Effect of chlorine dioxide gas on physical,thermal, mechanical,and barrier properties of polymeric packaging materials

The effects of gaseous chlorine dioxide (ClO₂) on properties and performance of 10 selected polymeric packaging materials, including polyethylene (PE), biaxially oriented poly(propylene), polystyrene, poly(vinyl chloride), poly(ethylene terephthalate) (PET), poly(lactic acid), nylon, and a multilayer structure of ethylene vinyl acetate (EVA)/ethylene vinyl alcohol (EVOH), were evaluated. Physical, mechanical, barrier, and color properties as well as infrared (IR) spectra were assessed before and after polymer samples were exposed to 3600 ppmV ClO₂ gas at 23°C for 24, 168, and 336 h. The IR spectra of the ClO₂‐treated samples revealed many changes in their chemical characteristics, such as the formation of polar groups in the polyolefin, changes in functional groups, main chain scission degradation, and possible chlorination of several materials. The ClO₂‐treated PE samples showed a decrease in tensile properties compared with the untreated (control) films. Decreases in moisture, oxygen, and/or carbon dioxide barrier properties were observed in the treated PE, PET, and multilayer EVA/EVOH/EVA samples. A significant increase (P < 0.05) in the barrier to O₂ was observed in the ClO₂‐treated nylon, possibly the result of molecular reordering, which was found through an increase in the crystallinity of the material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Properties of films and fibers obtained from Lewis acid-base complexed nylon 6,6

A nylon 6,6 complex with GaCl₃ in nitromethane (4-5 wt% nylon 6,6) was prepared at 50-70 °C over 24 h for the purpose of disrupting the interchain hydrogen bonding between nylon 6,6 chains, resulting in amorphous nylon 6,6, and increasing the draw ratio for improving the performance of nylon 6,6 fibers. After drawing, complexed films and fibers were soaked in water to remove GaCl₃ and regenerate pure nylon 6,6 films and fibers. FTIR, SEM, DSC, TGA, and mechanical properties were used for characterization of the regenerated nylon 6,6 films and fibers. The amorphous complexed nylon 6,6 can be stretched to high draw ratios at low strain rates, due to the absence of hydrogen bonding and crystallinity in these complexed samples. Draw ratios of 7-13 can be achieved for complexed fibers, under low strain rate stretching. This study indicates that nylon 6,6 fibers made from the GaCl₃ complexed state, using a high molecular weight polymer, can reach initial moduli up to 13 GPa, compared to initial moduli of 6 GPa for commercial nylon 6,6 fibers. Lewis acid-base complexation of polyamides provides a way to temporarily suppress hydrogen bonding, potentially increasing orientation while drawing, and following regeneration of hydrogen bonding in the drawn state, to impart higher performance to their fibers.     

Rheology of a textured fluid consisting of poly(ethylene terephthalate) and nylon 6,6

The rheology and development of the texture of immiscible polymer blends based on poly(ethylene terephthalate) (PET) and nylon 6,6 at composition ratios of 75/25, 50/50, and 25/75 w/w PET/nylon 6,6 were studied. The blends were prepared by mixing in an extruder and by dry blending and mixing between cone-and-plate fixtures in a nitrogen atmosphere. The rheology of these blends was found to be a function of both polymer degradation and the two-phase morphology. An accelerated degradation rate in air was observed for the 75/25 and 50/50 w/w PET/nylon 6,6 blends relative to the neat polymers while the blend at a weight ratio of 25/75 w/w PET/nylon 6,6 displayed a rate of degradation similar to that of the neat polymers. The values of the steady shear viscosity (η), |η^*| storage modulus (G′), and steady-state first normal stress difference (N₁) for melt-blended 75/25 and 50/50 w/w PET/nylon 6,6 samples were lower than those of the neat polymers and were determined to be a consequence of the higher rate of degradation of these blends during extrusion relative to that of the neat polymers. The role played by the two-phase nature on the blends was observed for all samples prepared by dry blending and mixing in cone-and-plate fixtures under a nitrogen atmosphere and for the melt-blended 25/75 w/w PET/nylon 6,6 blend. The two-phase nature of the dry-blended samples and the extruded 25/75 w/w PET/nylon 6,6 sample resulted in values of |η^*|, η, G′, and N₁ which were higher than those of the neat polymers. Transient behavior observed for the blends using stepwise changes of shear rate was found to superimpose when plotted in reduced form, indicating that at rates lower than the longest relaxation time of the neat polymers there was no intrinsic time constant associated with the deformation of the interface in the blends. © 1996 John Wiley & Sons, Inc.     

Some physicochemical properties of methyl methacrylate-grafted nylon 6. II.

Graft copolymerization of methyl methacrylate on nylon 6 was investigated using KMnO₄ as initiator at 60°C. The optimum conditions of the grafting process using various amounts of methyl methacrylate have been utilized. Physical and chemical properties of the grafted nylon such as moisture regain, density, and infrared spectra are studied. Furthermore, the dyeing behavior of the grafted nylon toward acid and direct dyes is also investigated. The rate of graft copolymerization (R_p) of methyl methacrylate with this system was evaluated and expressed by the following equation depending upon the potassium permanganate concentration used: The degree of polymerization of isolated poly(methyl methacrylate) from the grafted nylon was found to be a first-order dependence.     

Polymer Nanocomposites based on Modified ZrO2 NPs and Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) Blend: Optical,Morphological, and Thermal Properties

Nanocomposite films were prepared successfully by simple solution casting method from the blend of poly(vinyl alcohol) and poly(vinyl pyrrolidone) as the polymer matrix and functionalized ZrO₂ nanoparticles as nanofiller. To prevent aggregation and improve the dispersion of nanoparticles into the matrix, ZrO₂ nanoparticles were functionalized with citric acid and ascorbic acid. Then, nanocomposites were fabricated by adding different contents of modified nanoparticles into the poly(vinyl alcohol)–poly(vinyl pyrrolidone) matrix. Thermal stability of the obtained nanocomposite films was improved in comparison to the pure blend. Furthermore, optical property of nanocomposites makes them a potential candidate for ultraviolet shielding material.