Polymer Degradation and Stability (v.118, #C)
Editorial Board (IFC).
Innovative controllable photocatalytic degradation of polystyrene with hindered amine modified aromatic polyamide dendrimer/ polystyrene-grafted-TiO2 photocatalyst under solar light irradiation by Yonglin Lei; Hong Lei; Jichuan Huo (1-9).
A novel hindered amine modified aromatic polyamide dendrimer/polystyrene-grafted-TiO2 hybrid photocatalyst (HADPG-TiO2) was synthesized. And a new kind of controllable photodegradable polystyrene (PS) composite was prepared by embedding the HADPG-TiO2 into the commercial polystyrene. Solid-phase photocatalytic degradation of the PS-HADPG-TiO2 composite was carried out in ambient air at room temperature under solar light irradiation. The HADPG-TiO2 was characterized by FT-IR and scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–vis diffuse reflectance spectroscopy, in comparison with reference materials (plain TiO2). The properties of PS-HADPG-TiO2 films were compared with those of the pure PS films and PS-TiO2 films by methods such as weight loss measurement, SEM and tensile properties measurement. The results showed that the HADPG-TiO2 had a better dispersion in PS polymer and could absorb the visible light. The PS-HADPG-TiO2 films had better tensile properties, compared with the pure PS films and PS-TiO2 films. Moreover, the as-prepared PS-HADPG-TiO2 films showed more excellent photostability under solar light irradiation for 0–250 h and higher photodegradable efficiency under the solar light irradiation for 600 h than the pure PS films and PS-TiO2 films. The photocatalytic degradation mechanism of the films was briefly discussed. The novel fabrication method of composite polymer provides a valuable way for developing highly efficient and controllable photodegradable plastics.
Keywords: Aromatic polyamide dendrimer; Hindered amine; Photocatalytic degradation; Polystyrene; TiO2;
Comparison of the UV stabilisation effect of commercially available processing stabilizers Irganox HP 136 and Irganox 1010 by Jozef Rychlý; Katarína Mosnáčková; Lyda Rychlá; Agnes Fiedlerová; György Kasza; Attila Nádor; Zsófia Osváth; Timea Stumphauser; Györgyi Szarka; Klaudia Czaníková; Štefan Chmela; Béla Iván; Jaroslav Mosnáček (10-16).
Infrared and UV spectroscopy were used for estimation and mutual comparison of action of Irganox HP 136 and Irganox 1010 in UV stabilisation of polypropylene films. The instantaneous stability state of polypropylene after the different time of UV treatment was also tested by the non-isothermal chemiluminescence so that the actual resistance of sample against the thermal oxidation has been established. It was ascertained that Irganox HP 136 as a weak thermo-oxidation stabiliser is an excellent UV stabiliser of polypropylene, the fact that was not described in the literature until now. This stabilising efficiency was proposed to be provided by photochemical transformation of Irganox HP 136 to 2-hydroxy benzophenone moieties, the compound with ability to absorb the light as well as efficiently scavenge reactive free radicals.
Keywords: Polypropylene; Increased UV stability due to Irganox HP136; Chemiluminescence; FTIR spectroscopy;
Efficiency of curcumin, a natural antioxidant, in the processing stabilization of PE: Concentration effects by Balázs Kirschweng; Dóra Tátraaljai; Enikő Földes; Béla Pukánszky (17-23).
The stabilising efficiency of curcumin was studied in polyethylene during processing and under oxygen at high temperature. The effect of the natural antioxidant was investigated at concentrations of 0–1000 ppm in combination with a phosphonite secondary antioxidant (Sandostab P-EPQ) of 1000 and 2000 ppm, respectively. The polymer was homogenized with the additives then processed by six consecutive extrusions taking samples after each processing step. The samples were characterized by FT-IR spectroscopy, melt flow index, colour, and OIT measurements. Compared to the effect of pure phosphorous antioxidant, the melt stability of PE is increased already at 5 ppm curcumin content. The melt as well as the high temperature oxidative stability (OIT) of the polymer are controlled by both types of antioxidants. Curcumin hinders the oxidation of polyethylene and the formation of long chain branches during processing, which can be attributed to the fact that curcumin is not only a hydrogen donor but its unsaturated linear moiety can also scavenge alkyl and oxygen centred macroradicals. Curcumin discolours polyethylene already at small concentrations but the colour fades with increasing number of extrusions.
Keywords: Curcumin; Natural antioxidant; Polyethylene; Stabilisation; Phosphonite;
Improvement of the photo-stability of polystyrene-block-polybutadiene-block-polystyrene through carbon nanotubes by Nadka Tzankova Dintcheva; Rossella Arrigo; Francesco Catalanotto; Elisabetta Morici (24-32).
The photo-stability of Polystyrene-Polybutadiene-Polystyrene (SBS) based nanocomposites containing bare multi-walled carbon nanotubes (CNTs) and carbon nanotubes bearing carboxylic functional groups (CNTs-COOH) in comparison to that of pristine SBS has been studied. The photo-oxidation of pristine SBS occurs through crosslinking reactions and oxidized species formation and both these processes begin at early stage of exposure. The formation of crosslinking, formerly in polybutadiene phase, assessed by spectroscopical (FTIR), mechanical, dynamic mechanical and rheological analysis, leads to occurrence of internal mechanical stresses in the solid state and the SBS samples become prematurely unable to stretch. SBS-based nanocomposites showed a significant improved photo-stability to the respect to pristine matrix, due to the presence of CNTs and even more, of CNTs-COOH, that are able to protect efficiently SBS against UVB exposure. All obtained results suggest that the used nanotubes are able to delay the degradation process because of their acceptor-like electron properties and their ability to shield UV-light. Besides, the CNTs act as radical traps, hindering the crosslinking and slowing down the oxidation process. The presence of carboxylic functional groups onto CNTs outer surface enhances the protection ability of CNTs due to the presence of a larger amount of surface defects, that improves their radical scavenging activity.
Keywords: Polystyrene-polybutadiene-polystyrene copolymer; Carbon nanotubes; Photo-stability; Structural changes;
Green flame retarding bismaleimide resin with simultaneously good processing characteristics, high toughness and outstanding thermal stability based on a multi-functional organic boron compound by Yanjing Zhu; Li Yuan; Guozheng Liang; Aijuan Gu (33-44).
Multi-function and green are two keywords of developing new flame retarding thermosetting resins, however, to achieve this target is still a big challenging today. Herein, a new kind of flame retarding bismaleimide resins with simultaneously good processing characteristics, high toughness and outstanding thermal stability were prepared by copolymerizing 4,4′-bismaleimidodiphenylmethane (BDM) with allyl triphenylborate (ATPB). The structure and integrated performances of BDM/ATPB resins were systematically studied and compared with the BDM/o,o′-diallylbisphenol A resin (coded as BD) that is almost known to be the best modified bismaleimide resin available. Results show that BDM/ATPB resins are solids with low softening points; they can be dissolved in acetone and have wide processing window, completely overcoming the poor processing characteristics of BDM. The properties of the BDM/ATPB system are dependent on the molar ratio of imide and allyl groups, and BDM/ATPB3 resin of which the molar ratio of imide to allyl groups (1:0.85) is the same as that of BD resin not only has significantly improved flame retardancy, reflected by obviously longer time to ignition, 1.5–3.0 times higher fire performance index, and greatly decreased heat releases, but also has about 10 °C higher initial decomposition temperature in both air and nitrogen atmospheres as well as about 1.2–1.3 times higher impact and flexural strengths, clearly demonstrating that ATPB is a multi-functional and green modifier for bismaleimide. The origin behind these attractive results of BDM/ATPB resins was intensively discussed.
Keywords: Green flame retardant; Bismaleimide resin; Organic boron-containing compound; Toughness; Mechanism;
Synthesis of a novel linear polyphosphazene-based epoxy resin and its application in halogen-free flame-resistant thermosetting systems by Huan Liu; Xiaodong Wang; Dezhen Wu (45-58).
The synthesis of a novel linear polyphosphazene-based epoxy resin (LPN–EP) was performed via a six-step reaction pathway, and the chemical structures of the intermediate and target products were characterized by 1H and 31P NMR spectroscopy and Fourier transform infrared spectroscopy. A series of thermosetting systems consisting of diglycidyl ether of bisphenol–A and LPN–EP were prepared, and their mechanical properties, thermal stabilities, and flame retardant properties were investigated. The resulting thermosets exhibited excellent flame resistance with the UL–94 V-0 rating but also achieved a significant improvement in impact toughness as a result of the incorporation of rubbery LPN–EP. The thermosets also showed a good thermal stability highlighted for high char yields. The mechanism study indicates that the synergistic effect from the combination of phosphorus and nitrogen in polyphosphazene segments could effectively enhance the flame retardancy by acting in both condensed and gaseous phases to promote the formation of intumescent phosphorus-rich char on the surface of the thermosets. Such a char layer plays a role of insulating protective shell to prevent the volatiles from transferring to the surface of the thermosets as well as to shield the heat and oxygen diffusion, thus resulting in a self-extinguishing flame rating.
Keywords: Linear polyphosphazene-based epoxy resin; Synthesis; Thermosetting systems; Flame retardant properties; Impact resistance;
Thermal degradation and pyrolysis behavior of aluminum alginate investigated by TG-FTIR-MS and Py-GC-MS by Yun Liu; Zhongfang Li; Junsheng Wang; Ping Zhu; Jinchao Zhao; Chuanjie Zhang; Yi Guo; Xing Jin (59-68).
The pyrolysis behavior of aluminum alginate is compared with that of alginic acid. The thermal degradation and pyrolysis behavior of aluminum alginate have been studied using a thermogravimetric analyzer coupled with Fourier transform infrared analysis and mass spectrometry (TG-FTIR-MS) and a pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), respectively. TG-FTIR-MS and Py-GC-MS results indicated that the aluminum ions influenced the devolatilization gas products upon pyrolysis process. The pyrolysis of alginic acid was found to yield much more kinds of products than aluminum alginate was. And it suggested that the aluminum ions could strongly catalyze the fragments formed in the pyrolysis process of aluminum alginate to produce the less molecular weight and more stable products, such as carbon dioxide and furfural. The results indicated that the aluminum ions had the catalysis effect on the pyrolysis process of aluminum alginate. The possible thermal degradation mechanism of aluminum alginate was proposed according to the results of Py-GC-MS of aluminum alginate. The results of our study provide useful information for understanding the flame retardant mechanism of alginates.
Keywords: Aluminum alginate; TG-FTIR-MS; Py-GC-MS; Thermal degradation; Pyrolysis;
Synthesis of polybutadiene-silica nanoparticles via differential microemulsion polymerization and their hydrogenated nanoparticles by diimide reduction by Thanyaporn Tancharernrat; Garry L. Rempel; Pattarapan Prasassarakich (69-81).
Polybutadiene (PB)–SiO2 nanoparticles were successfully synthesized via differential microemulsion polymerization. The core-shell structured PB-SiO2 nanoparticles were designed to achieve a monodispersion with reduced nanosilica aggregation. A high monomer conversion (81.5%), grafting efficiency (78.5%) and small particle size (27 nm) with narrow size distribution was obtained under optimum reaction conditions when using an extremely low surfactant concentration, 5 wt% based on monomer. The PB-SiO2 latex could be hydrogenated by diimide reduction in the presence of hydrazine and hydrogen peroxide to provide hydrogenated polybutadiene (HPB)–SiO2. A high hydrogenation degree of 98.6% was achieved at a ratio of hydrazine to hydrogen peroxide of 0.75:1, and showed a maximum degradation temperature of 469.6 °C resulting in excellent thermal stability. A new nanocomposite of PB-SiO2 and HPB-SiO2 could be used as a novel nanofiller in natural rubber. Especially, NR/HPB-SiO2 composites had improved mechanical and thermal properties, and exhibited good resistance toward ozone exposure.
Keywords: Emulsion polymerization; Diimide hydrogenation; Nano-structures; Particle-reinforcement; Mechanical properties; Thermal properties;
Organochalcogen stabilizers efficiently protect model polyolefins exposed to chlorinated media by A. Kirchhain; W. Yu; L. Engman (82-87).
The small amounts of chlorine dioxide that are routinely supplemented to drinking water as a disinfectant also cause a degradation of the polyolefin pipes that are used for distribution of the water. Commonly used phenolic antioxidants can extend the service life of the polymer but the expected lifetime is still much shorter than desired (50 years) due to depletion of the antioxidant in the surface zone exposed to the aqueous solution. In search for better stabilizers for the pipes, we have tested an organotellurium compound, 4-(N,N-dimethylamino)phenyl 3-phenoxypropyl telluride (1), as well as its corresponding selenium and sulphur analogues and a series of organotellurium compounds where the electron density at the heteroatom was varied. Stabilizers were dissolved in squalane, which is a liquid hydrocarbon that could serve as a model for a polyolefin. The oxidation induction time (OIT), determined after exposure of the squalane solution to an aqueous solution of 10 ppm of chlorine dioxide for various times was determined by DSC to indicate the loss of antioxidant protection. Whereas Irganox 1010 was only effective as a stabilizer for a few hours, many of the organochalcogen compounds were considerably more resistant (>91 h for compound 1) towards chlorine dioxide.Thermogravimetric analyses of antioxidants indicated insignificant decomposition below 200 °C and increasing stability for the lighter chalcogen compounds (telluride < selenide < sulfide). Among organotelluriums, stability increases with increasing electron density at the heteroatom. Oxidation potentials of stabilizers as determined by cyclic voltammetry correlated fairly well with their protective effect in squalane (OIT-values). We therefore hypothesize that these compounds act primarily as electron donors towards peroxyl radicals. As determined by 125Te NMR-spectroscopy, organotellurium compound 1 in the presence of an excess of chlorine dioxide failed to produce an oxidation product. This may be the clue to its long-lasting protective effect in the squalane-assay.
Keywords: Polyethylene; Chlorinated water media; Organotellurium stabilizers; Oxidation induction time;
Influence of process variables on chemical devulcanization of sulfur-cured natural rubber by Malihe Sabzekar; Mahdi Pourafshari Chenar; Seyed Mohammadmahdi Mortazavi; Majid Kariminejad; Said Asadi; Gholamhossein Zohuri (88-95).
Chemical devulcanization of sulfur cured natural rubber (NR) was investigated using benzoyl peroxide (BPO) as a devulcanizing agent. The influence of important reclaiming parameters such as reaction time, reaction temperature and concentration of the devulcanizing agent on the devulcanization process and mechanical properties of the resulting products were studied. At devulcanization reaction time of 2 h (instead of 4 h) and lower concentrations of the devulcanizing agent selective scission of sulfur crosslinks were observed, however, both longer of the reaction time and higher concentrations of the devulcanizing agent process resulted non-selective chain scission. Mechanical properties of the devulcanized and revulcanized samples using 6 phr of BPO, with different reaction times and temperatures were also investigated. Longer reaction time led to lower crosslink density which in turn caused tensile strength and elongation at break to decrease significantly. Likewise, higher reaction temperature accelerated scission of network crosslinks and resulted lower tensile properties. Blending of 40 wt% of the virgin rubber with the devulcanized one in the compound had no adverse effect on the scorch and optimum cure time and also does not extremely deteriorate the mechanical properties of the virgin rubber. This provided an effective route for chemical devulcanization of NR.
Keywords: Natural rubber; Chemical devulcanization; Crosslink density; Mechanical properties;
Degradation of a model epoxy resin by solvolysis routes by Géraldine Oliveux; Luke O. Dandy; Gary A. Leeke (96-103).
Different technologies based on hydrolysis were applied to degrade an epoxy resin model: CO2-expanded water and generally recognised as safe solvents used neat or in mixture with water. The results showed that the degradation reaction can be enhanced thanks to the injection of CO2 or the addition of a solvent generally recognised as safe, enabling supercritical fluids or enhanced fluidity liquids (resembling supercritical fluids) at lower temperature and pressure than for supercritical water.
Keywords: Recycling; Composites; Epoxy; Solvolysis;
Research on the degradation performance of the lotus nanofibers-alginate porous materials by Ying Gong; Guang Ting Han; Yuan Ming Zhang; Jin Feng Zhang; Wei Jiang; Ying Pan (104-110).
Controllable degradation of natural biomaterials for tissue engineering is a big issue that has to be solved. In this paper, sodium alginate was aldehyde-modified and the product (oxidized sodium alginate) was degraded in vitro. Then, oxidized sodium alginate was cross-linked with calcium chloride and its degradation performance was studied. Results showed that the degradation rates of porous materials increased while pH values of degradation liquid decreased, which was proportional to the degree of oxidation. Lotus fibers were carboxyl-modified with TEMPO/NaClO/NaBr system and then lotus nanofibers were obtained. It is found that the degradation rates of the oxidized sodium alginate porous materials which were added lotus nanofibers were slow. Thus, the blending porous materials are expected to be used in medical fields.
Keywords: Alginate; In vitro test; Degradation; Nanofibers; Porous material;
Thermal aging of an anhydride-cured epoxy resin by Yongming Yang; Guijun Xian; Hui Li; Lili Sui (111-119).
Fiber reinforced polymer (FRP) composites with anhydride cured epoxy resin matrices are widely used in civil engineering (e.g., pultruded FRP plates and bars), and their thermal aging behavior is a concern when they are subjected to elevated temperatures (e.g., FRP chimney). In the present article, thermal aging of an epoxy resin matrix at 130 °C–160 °C for 30 days was performed, and the effects on the flexural properties, molecular structures, free volume fraction, and mechanical properties were investigated. FTIR spectroscopy indicated that oxidation and molecular rearrangement occurred in the skin of the epoxy samples during thermal aging. Dynamic mechanical thermal analysis (DMTA) further illustrates the dominant effect of the molecular rearrangement in the sample skin with a thickness less than 100 μm, leading to a new high temperature tan δ peak. The free volume fraction of the skin and the bulk epoxy sample was characterized by positron annihilation lifetime spectroscopy (PALS). The results indicate that a noticeable reduction of the apparent free volume fraction occurred in the sample skin, while the bulk sample was only slightly affected. The flexural results indicate that thermal aging obviously reduced the break strain, while the flexural strength was only slightly affected and the modulus increased.
Keywords: Epoxy resin; Thermal aging; Chemical structure; Thermal-mechanical properties; Free volume;
Synthesis of a novel PEPA-substituted polyphosphoramide with high char residues and its performance as an intumescent flame retardant for epoxy resins by Wei Zhao; Jiping Liu; Hui Peng; Jiaying Liao; Xiaojun Wang (120-129).
A novel polymeric intumescent flame retardant, poly(4,4′-diamino diphenyl sulfone 2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-methanol (PEPA)-substituted phosphoramide) (PSA), has been synthesized through solution polycondensation. The product has been characterized by Fourier transform infrared spectroscopy (FTIR), 1H NMR, 13C NMR, 31P NMR, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). GPC and TGA suggested that PSA had sufficient molecular weight and high thermal stability, with a residual char of 66.3 wt.% at 700 °C. The performances of PSA and its mixtures with ammonium polyphosphate (APP) in enhancing the flame retardancy and thermal stability of epoxy resins have been evaluated by various methods. Differential scanning calorimetry (DSC) indicated that the incorporation of PSA and APP slightly increased the glass transition temperature of EP. The maximum LOI value of EP/PSA composites reached 32.0% and passed the UL 94 V-0 rating. An obvious synergistic effect between PSA and APP was observed by LOI, CONE tests, and TGA. Moreover, remarkable decreases in the peak heat release rate, total heat release, and total smoke release were observed when PSA was incorporated into EP. TGA data showed that the addition of PSA and APP greatly increased the amount of residual char and apparently reduced the amount of pyrolysis products during combustion. Additionally, the structure and morphology of the residual chars have been studied by FTIR, XPS, and SEM. The FTIR and XPS results illustrated that the flame retardancy of PSA and APP was mainly exerted in the condensed phase and could be attributed to the formation of residual char with aromatic structures bridged by P–O–C and P–O–P bonds.
Keywords: Polyphosphoramide; Epoxy resins; Flame retardant; Thermal stability;
Hydrolytic degradation of cellulose-graft-poly(l-lactide) copolymers by Chenghu Yan; Jin Wu; Jinming Zhang; Jiasong He; Jun Zhang (130-136).
A series of cellulose-g-poly(l-lactide) (cellulose-g-PLLA) copolymers with 30.65–85.21 % PLLA weight content and the molar substitution of PLLA (MSPLLA) from 0.99 to 12.73 were synthesized via the homogeneous graft-from reaction in 1-allyl-3-methylimidazolium chloride (AmimCl) with 4-dimethylaminopyridine (DMAP) acting as the catalyst. In common organic solvents, the solubility of obtained graft copolymers was better than cellulose and strongly depended on the MSPLLA. The hydrolytic degradation of cellulose-g-PLLA copolymers was investigated in phosphate buffered solution (PBS, pH 7.4) at 37 °C. Interestingly, it was found that, when the MSPLLA was below 8.83, the hydrolytic degradation rate of cellulose-g-PLLA copolymers was obviously faster than that of both pristine cellulose and PLLA. Moreover, as the MSPLLA decreased, the cellulose-g-PLLA copolymers showed a more rapid weight loss, due to its higher hydrophilicity. Both XPS and 1H NMR analyses demonstrated the degradation occurred mainly at PLLA segments. The morphological observations indicated that, during the hydrolytic degradation, the graft copolymers firstly experienced a surface erosion process, and then the bulk erosion happened.
Keywords: Cellulose; Poly(l-lactide); Graft copolymer; Ionic liquids; Hydrolytic degradation;
Thermomechanical behavior of a novel biobased poly(furfurylalcohol)/silica nanocomposite elaborated by smart functionalization of silica nanoparticles by Nicolas Bosq; Nathanaël Guigo; Luc Vincent; Nicolas Sbirrazzuoli (137-146).
The Polyfurfuryl Alcohol (PFA) is a biobased cross-linked polymer presenting high thermal performances. This work presents the processing of PFA/silica nanocomposite starting from pre-existing spherical silica nanoparticles obtained via the Stöber method. Prior to dispersion, silica nanoparticles were smartly decorated with furanic entities and such modification was analyzed by ThermoGravimetric Analysis (TGA), Fourier Transform InfraRed spectroscopy (FTIR) and solid state Nuclear Magnetic Resonance (NMR) spectroscopy. About 2/3 of surface Si–OH sites were grafted with furans and these modified silica nanoparticles were efficiently dispersed during polymerization of Furfuryl Alcohol (FA) as confirmed by Transmission Electronic Microscopy (TEM) observations. The thermo-mechanical performances of the PFA/silica nanocomposites were investigated by means of Dynamic Mechanical Analysis (DMA) and TGA. Unmodified nanoparticles do not change the final properties while the nanocomposite processed with functionalized nanoparticles presented improved properties. Strong interactions between cross-linked furanic matrix and the furfurylated nanoparticles resulted in a more rigid material whose thermal degradation processes were shifted to much higher temperature (+65 °C).
Keywords: Silica nanoparticles; Biobased thermoset; Poly(furfuryl alcohol); Nanocomposite; Thermal degradation; Glass transition;
Reactivity of the tin homolog of POSS, butylstannoxane dodecamer, in oxygen-induced crosslinking reactions with an organic polymer matrix: Study of long-time behavior by Krzysztof Rodzeń; Adam Strachota; François Ribot; Libor Matějka; Jana Kovářová; Miroslava Trchová; Miroslav Šlouf (147-166).
The chemical activity of the heavier POSS homolog, n-butylstannoxane dodecamer cage, in an epoxy matrix containing polopropylene oxide (PPO) chains was studied in detail, especially the long-time development of the effect and its limits in time at different concentrations. A multi-method investigation was carried out, employing spectrometric analysis of chemical composition (NMR, IR), TEM, thermogravimetry, weight loss analysis during isothermal oxidation at 180 °C, as well as dynamic-mechanical thermal analysis (DMTA) of intact and of oxidized epoxy/stannoxane hybrids. The PPO segments of the matrix were found to be preferentially degraded by oxidation or by anaerobic pyrolysis, while at the same time these segments are the sites of crosslinking reactions with stannoxane, which counteract matrix degradation. It was demonstrated, that the cages undergo repeated reactions on the Sn atoms, and remain finely dispersed and well-accessible even after long oxidation times. The repeated reactions also explain the observed very strong stabilizing effect of stannoxane at very low concentrations. Efficient stabilization against the degradation of the mechanical properties was found to require higher – but still very low – concentrations, than the stabilization against weight loss. Interestingly, certain amounts of stannoxane caused simultaneously enhanced weight losses and a mechanical reinforcement due to a higher amount of radical reactions.
Keywords: POSS; Stannoxane; Reactivity; Epoxy; Nanocomposite;
Effect and mechanism of N-alkoxy hindered amine on the flame retardancy, UV aging resistance and thermal degradation of intumescent flame retardant polypropylene by Huali Xie; Xuejun Lai; Rimin Zhou; Hongqiang Li; Yajun Zhang; Xingrong Zeng; Jianhua Guo (167-177).
A multifunctional additive N-alkoxy hindered amine (NOR116) possessed free-radical quenching capability was combined with ammonium polyphosphate/pentaerythritol (APP/PER) to flame-retard polypropylene (PP). The effects of NOR116 on the flame retardancy, ultraviolet (UV) aging resistance and thermal degradation of the PP/APP/PER mixture were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT), UV aging test and thermogravimetric analysis (TGA). It was found that NOR116 showed a synergistic effect with APP/PER in flame retardant PP. When the content of APP/PER and NOR116 were 24.5 wt% and 0.5 wt%, respectively, the LOI value of the PP/APP/PER mixture was increased from 31.0% to 35.0% and a UL-94 V-0 rating was achieved. Meanwhile, the UV aging resistance of the PP/APP/PER mixture was improved significantly. The synergistic mechanism between NOR116 and APP/PER was explored and revealed. During the combustion, NOR116 could not only block the radical chain reaction in the gas phase by quenching the active free-radicals, but also promote the formation of the thermostable intumescent char in the condensed phase.
Keywords: N-alkoxy hindered amine; Intumescent flame retardant; Polypropylene; UV aging resistance; Thermal degradation;
NMR evaluation of polystyrene nanocomposites degradated by repeated extrusion processing by Jorge P. Chimanowsky; Roberto Pinto Cucinelli Neto; Maria Inês Bruno Tavares (178-187).
Polystyrene nanocomposites with organoclay were prepared by melt extrusion in a twin screw extruder. After that, the samples were submitted to several cycles in the extruder to degrade them. The materials obtained before and after degradation cycles were analyzed by melt flow index measurements, X-ray diffraction and principally by nuclear magnetic resonance spectroscopy. The results showed the formation of nanomaterials with good dispersion and distribution containing low nanoparticle concentration and the nanostructured materials formed presented mixed morphology, composed of intercalated and exfoliated structures. The use of NMR spectroscopy allowed obtaining information on sample degradation with the increase of cycle times through the loss of structural organization and changes in the molecular dynamics of the materials through the T1H relaxation data. All the results shed light on the behavior of the degradation process in the materials formed.
Keywords: Clay; Nanocomposites; NMR; Low field; Polymer degradation; Extrusion;