How will additives shape the future of plastics?

Additives are essential components of plastic formulations providing maintenance and/or modification of polymer properties, performance and long-term use. The extension of polymer properties by additives has played a substantial role in the growth of plastics. At the beginning of the plastics age additives were used mainly to maintain polymer properties and to help plastics to survive heat treatment during transforming processes. The next generation of additives provided extension of service life as well as modification of mechanical and physical properties. These well-established additives - antioxidants, heat stabilizers, light stabilizers and others - cover the requirements of standard plastics and today's mass applications. The more recent developments of high-performance additives address more stringent or new requirements, more severe processing and use conditions and/or environmental concerns, but still with the main target of maintaining plastic properties. The future will introduce more and more new effects and functionalities through additives in plastic applications tailoring the properties of polymers and offering a vast potential of innovation in the plastics area. Recent examples of emerging technologies show that additives will not only modify the polymer itself and add new properties, but can also, when incorporated into the plastic, beneficially impact properties, which are of high value for the user. The paper shows the role of additives used in plastics from the past to the present with the focus on stabilization and performance of additives incorporated during melt processing, and outlines future trends.     

In-reactor stabilization of polypropene

Propene was polymerized with a high activity, high stereospecific supported Ziegler-Natta catalyst in presence of phenolic antioxidants (AO), phosphite processing stabilizers (PS) or sterically hindered amine stabilizers (HAS).PS and some HAS grades did not influence propene polymerization, but AO and most commercial HAS could interfere with the catalyst and reduce catalyst activity.     

Glow wire ignition temperature (GWIT) and comparative tracking index (CTI) of glass fibre filled engineering polymers, blends and flame retarded formulations

Engineering thermoplastic polymers such as polyamides, polycarbonates, semi-crystalline aromatic polyesters and their blends are widely used as insulating materials in electrical and electronic appliances. Flame retardants are often employed in the formulation of these materials, since good performance in terms of ignition and tracking resistance, evaluated by Glow Wire Tests (GWIT) and Comparative Tracking Index (CTI) are required in these applications. In this paper, a comparative evaluation of GWIT and CTI performances has been simultaneously performed for a wide set of glass fibre filled materials chosen among engineering thermoplastics and their blends. Some flame retarded formulations have been also tested, in order to screen the effects of various additives. Useful indications have been obtained on the effect of each polymer and additives on GWIT and CTI properties. In addition, interesting synergies have been observed, especially by blending polyesters and polyamides. Thermogravimetric measurements of char yields have been successfully related with CTI behaviour. The presence of additives changes the structure of the carbonaceous residue, hence the conductivity of the tracks. Neat polycarbonate passed the GWIT test but not CTI, while poly(butylene terephthalate) showed the best balance of GWIT and CTI performance among the pure resins tested. Blending polycarbonate with polyester did not improve significantly GWIT performance, but had a negative effect on tracking resistance. Polyesters/polyamide blends were dominated by polyester in GWIT, but they showed synergistic effects in CTI.     

Preparation and combustion properties of flame retarded polypropylene-polyamide-6 alloys

In this work, polypropylene (PP) and polyamide-6 (PA6) alloys were prepared by blending PP and PA6 or nano-PA6 while using a compatibiliser such as maleic anhydride-g-polypropylene (MAPP). Their physical structures were characterized by Hitachi X650 scanning electron microscope (SEM) and transmission electron microscopy (TEM). An intumescent flame retardant (IFR) was added to the PP/PA6 alloys and their flammability behaviour was evaluated using cone calorimeter and real time Fourier transform infrared (FTIR). The probable mechanisms are discussed.     

Nanocomposites: Industrial opportunity or challenge?

Polymer nanocomposites based on organically modified layered silicates are an area of substantial scientific interest and of emerging industrial practice. Despite the proven benefits of nanocomposites such as mechanical properties, barrier properties and contribution to fire retardancy, polymer nanocomposites are used today only in niche applications. The reasons for the limited growth of nanocomposites are explained through the availability of alternative solutions, processing and dispersion challenges and inferior oxidative and photooxidative stability. Recent developments show the improved dispersion of unmodified nanoclays in polyolefins with the help of selected copolymer structures. The (photo)oxidative instability of nanocomposites is compensated with adjusted stabilizer systems.     

A quantitative study of carbon monoxide and carbon dioxide evolution during thermal degradation of flame retarded epoxy resins

Thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases analysis (EGA) has been used to study the thermal degradation behaviour of epoxy resin both in air and nitrogen. The mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂), and oxygen consumption as measured using an oxygen analyser. An analytical technique has been developed to quantitatively measure the carbon monoxide and dioxide gases evolved. The effect of a range of flame retardants containing phosphorus, nitrogen and halogen elements on CO and CO₂ evolution during thermal degradation of flame retarded epoxy resins has also been observed.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

Nanomorphology and reaction to fire of polyurethane and polyamide nanocomposites containing flame retardants

The reaction to fire of polymer nanocomposites (thermoplastic polyurethane and polyamide-6) containing two different nanofillers (organoclay and carbon nanotube) has been investigated. Polymer nanocomposites exhibit significant reduction of peak of heat release rate but the nanomorphology (exfoliation, intercalation and presence of tactoids) does not play any significant role, although a reasonable level of nanodispersion is necessary to achieve good flame retardancy in specific cases (mass loss calorimetry experiment). Modelling aspects for the time to ignition are also proposed in the paper. It is shown that the approach ‘nanocomposite’ gives the best results combined with conventional flame retardants (phosphinate and phosphate) and leads to synergistic effects. The aspects of nanodispersion of the nanoparticle with the flame retardant (microfiller) are fully commented in the paper using TEM and solid state NMR. Mechanisms of action are finally proposed explaining the synergy when conventional flame retardants are combined with nanoparticles.     

Compatibilized polyamide 6/polyethylene blend-clay nanocomposites: Effect of the degradation and stabilization of the clay modifier

Blends of polyamide 6 (PA6) and high-density polyethylene (HDPE) were compatibilized using an already investigated method and a sample of Cloisite 15A, a montmorillonite modified with ammonium quaternary salts was added. The blends were prepared in a twin screw extruder and characterized from a morphological, rheological and mechanical point of view. The results indicated that, despite a good morphology achieved in the filled blends and a moderate intercalation of the clay, the mechanical properties are far from being good, especially the ultimate properties.In order to investigate the possible influence of the inhibition of the crystallization and of the degradation of the organic modifier of the clay, DSC measurements and FTIR-ATR were carried out. The results confirm that the clay causes a slight decrease of the crystallization, particularly in the HDPE phase. In addition, in the preparation conditions, the clay modifier is sensitive to thermo-oxidation. Both features can, therefore, explain the bad mechanical performance, even if the degradation effects seem to be more important. In order to prevent, or at least to reduce, the thermo-oxidation, a stabilizing system was added to the filled blends. In this case, the mechanical properties are improved for the entire compatibilized blend set.     

Ammonium sulfamate flame retarded polyamide 6: Morphology and thermal degradation

<正>The effect of ammonium sulfamate(AS) content on the flame retardancy of polyamide 6(PA6) was studied.It is found that the limiting oxygen index(LOI) of PA6 increases with the increase of AS content and the flame retardancy of PA6 is significantly improved.The morphology of the residues after combustion was examined by means of scanning electron microscopy(SEM).SEM results show that AS facilitates the formation of the intumescent char layer with honeycomb-like structure,which inhibits the transfer of heat and mass,and thus improves the flame retardancy of PA6.The thermal degradation of AS flame retarded PA6 was studied by thermogravimetric analysis(TGA).The Kissinger method was applied to estimate the activation energy(E_a) of the degradation.The activation energy of the thermal degradation of PA6 decreases by adding AS,indicating that AS can promote the degradation of PA6.     

Studies of degradation enhancement of polystyrene by flame retardant additives

Experimental methods as well as thermodynamic modeling techniques were utilized to explore potential gas and condensed-phase contributions of various flame retardant (FR) additives with polystyrene polymer. FR additives investigated include hexabromocyclododecane (HBCD), triphenyl phosphine oxide (TPPO), triphenyl phosphate (TPP), triphenyl phosphine sulfide (TPPS), and sulfur. Flame studies of fundamental FR activity were also employed using molecular beam mass spectrometry analysis of FR active species directly in a flame system. The flame studies show direct evidence for active bromine (HBr, Br) species for HBCD and active phosphorous species (HPO₂, PO, PO₂ HPO₃) species for TPPO and TPP which provide high potential for gas-phase activity for these FR additives. Various experimental measurements were also done to assess the degradation species and the degree of degradation of polystyrene by the FR additives. These studies support enhanced degradation of the base polystyrene polymer by the FR additive as a major pathway for condensed FR activity for HBCD and sulfur FR additives. Phosphorous based structures appear to show little enhancement of polystyrene degradation.     

The absence of size-dependency in flame retarded composites containing low-melting organic-inorganic glass and clay: Comparison between micro- and nanocomposites

Due to optimised processing of epoxy based composite materials containing a low-melting organic-inorganic glass together with an organo clay, the size of the glass particles could be successfully reduced. Thus truly nano-dispersed composites were obtained, with glass particles in the range of 10 nm to 200 nm. The small particle size allowed efficient interaction of glass particles and organo clay layers. The flame retardancy as well as the thermo-mechanical properties were tested, and the results showed that the low-melting glass led to a remarkable reduction of peak heat release rate by forming an enhanced barrier layer. Nevertheless no further improvement could be achieved by lowering the particle size to the nanometre region. For good flame retardancy a microdispersion of the low-melting glass was already sufficient.     

Effects of zinc-based flame retardants on the degradation behaviour of an aerospace epoxy matrix

Flame behaviour is a fundamental requirement for advanced aerospace composites. In this work, a commercial, low-viscosity epoxy system, typically used in liquid infusion composite processes, and its mixtures with three different zinc-based flame retardants (ZB, ZS, ZHS) at different weight percentages has been investigated by cone calorimetry and thermogravimetric analysis.Cone calorimetry has been performed to verify the flame retardancy effects induced by each filler composition. Nevertheless manufacturability issues require the evaluation of the rheological changes induced by filler on the unloaded matrix system. Rheological tests have been, therefore, performed to identify the maximum concentration of filler. Based on these results thermogravimetric tests have been performed to investigate thermal degradation kinetics of selected systems. The feasibility of Kissinger and Flynn-Wall-Ozawa method for the determination of characteristic degradation kinetics parameters has been evaluated and results were analysed. A simplified decomposition model was assumed to analyse epoxy degradation behaviour; it was found that this model gives appreciable matching with experimental TGA curve trend for neat epoxy whereas for the filled compounds additional stages were assume to occur.     

Investigation of melamine and DOPO-derived flame retardants for the bioplastic cellulose acetate

In order to identify suitable flame retardant additives for the eco-friendly polymer cellulose acetate (CA), high-melting derivatives of the known flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were combined with the thermoplastic CA and the combustion properties were tested. CA mixtures with bis-phosphonamidates (EDA-DOPO and PIP-DOPO) showed distinct flame retardation effects and a reduction of peak heat release rates (PHRR) by up to 18%. CA mixtures with MDOP, a melamine salt of DOPA (an oxidation product of DOPO), also showed considerable effects and a reduction of PHRR by up to 27%. While producing more smoke than pure CA and CA plus melamine, owing to its aromatic component, MDOP was superior to the CA mixtures with DOPO, EDA-DOPO and PIP-DOPO in this regard. The mixture of CA with melamine gave rise to a distinctly reduced formation of toxic CO and smoke when compared with pure CA. Thus, these additives can be considered for future applications of CA-based polymers with enhanced flame protection.     

气相色谱-质谱法测定玩具中的4种阻燃剂

建立了玩具中三(2-氯乙基)磷酸酯、磷酸三邻甲苯酯、2,2′,4,4′,5-五溴联苯醚、2,2′,3,3′,4,4′,6,6′-八溴联苯醚等4种阻燃剂的气相色谱-质谱分析方法。玩具样品以V(正己烷):V(二氯甲烷)=1:1混合溶液为提取溶剂,超声提取30min,提取液以DB-5HT石英毛细管色谱柱(15m×0.25mm×0.10μm)分离后进行选择离子监测模式下的定性及定量分析。4种阻燃剂的定量限为0.1mg/kg,在低、中、高3个添加水平范围内,4种阻燃剂的平均回收率为93.5%～97.3%,相对标准偏差在2.4%～4.1%之间。     

Influence of hydrogenated oligo(cyclopentadiene) on the structure and the thermal degradation of polypropylene-based nanocomposites

Polypropylene has been compounded with a commercial organoclay both in the absence and in the presence of hydrogenated oligo(cyclopentadiene) (HOCP) as a compatibiliser. The characteristics and the properties of the nanocomposites were evaluated and compared. HOCP favours the intercalation of the polypropylene in the organoclay galleries and enables a more homogeneous dispersion of the nanoclay throughout the polymer matrix. In the compatibilised nanocomposite, the diluent effect ascribed to the HOCP component is associated with the nucleating action of the nanoclay, resulting in the development of the β-crystalline form of the polypropylene. The presence of HOCP preserves the molecular weight of the polymer during the processing and gives good overall mechanical properties to the compatibilised nanocomposite. The thermo-oxidative degradation of the polypropylene is strongly delayed in the compatibilised nanocomposite.     

Mode-of-action of self-extinguishing polymer blends containing organoclays

We have shown that the addition of nanoclays is an effective means for enhancing the flame retardant properties of polymer blends. Polymer blends are difficult to render flame retardant even with the addition of flame retardant agents due to dispersion and phase segregation during the heating process. We show that the addition of 5% functionalized Cloisite 20A clays in combination with 15% decabromodiphenyl ether and 4% antimony trioxide to a polystyrene/poly(methyl methacrylate) blend can render the compound flame resistant within the UL-94-V0 standard. Using a variety of micro-characterization methods, we show that the clays are concentrated at the interfaces between the polymers in this blend and completely suppress phase segregation. The flame retardant (FR) is absorbed onto the clay surfaces, and the exfoliation of the clays also distributes the FR agent uniformly within the matrix. TGA of the nanocomposite indicates that prior to the addition of clay, the dissociation times of the individual components varied by more than 20 °C, which complicated the gas-phase kinetics. Addition of the clays causes all the components to have a single dissociation temperature, which enhanced the efficacy of the FR formula in the gas phase. Cone calorimetry also indicated that the clays decreased the heat release rate (HRR) and the mass loss rate (MLR), due to the formation of a robust char. In contrast, minimal charring occurred in blends containing just the FR. SEM examination of the chars showed that the clay platelets were curved and in some cases tightly folded into nanotube-like structures. These features were only apparent in blends, indicating that they might be associated with thermal gradients across the polymer phase interface.SEM and SAXS examinations of the nanocomposites after partial exposure to the flame indicated that the clays aggregated into ribbon-like structures, approximately microns in length, after the surfactant thermally decomposed. Thermal modeling indicated that these ribbons might partially explain the synergy due to better distribution of the heat and improve the mechanical properties of the melt at high temperatures, in a manner similar to the one reported for carbon nanotubes.     

Thermal stability and flame retardant effects of halloysite nanotubes on poly(propylene)

Naturally occurred halloysite nanotubes (HNTs) with hollow nanotubular structures were used as a new type filler for poly(propylene) (PP). Nanocomposites based on PP and HNTs were prepared by melt blending. Scanning electronic microscopy (SEM) results suggested HNTs were dispersed in PP matrix evenly at nanoscale after facile modification. Thermal stability of the nanocomposites was found remarkably enhanced by the incorporation of HNTs. Cone calorimetric data also showed the decrease of flammability of the nanocomposites. Entrapment mechanism of the decomposition products in HNTs was proposed to explain the enhancement of thermal stability of the nanocomposites. The barriers for heat and mass transport, the presence of iron in HNTs, are all responsible for the improvement in thermal stability and decrease in flammability. Those results suggested potential promising flame retardant application of HNTs in PP.     

Thermal degradation of polymers and flame retardants

We have carried out simultaneous Thermal Analysis/Mass Spectrometry by use of a Netzsch STA 429 Thermal Analyzer (TG-DTG-DTA) combined with a Balzers QMG 511 quadrupole Mass Spectrometer.The combined apparatus is interfaced to a Digital Equipment PDP 11/23+ microcomputer. The complete set of the TA/MS data obtained simultaneously after each run results in detailed information about the thermal degradation of a sample material in general and in addition about the structure-temperature dependent fragmentation. Experiments by use of a Perkin-Elmer DSC 7 Thermal Analysis Station leads to quantitative determination of the characteristic data.

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Zusammenfassung Es wurden simultane thermoanalytische — massenspektrometrische Untersuchungen mit Hilfe einer Gerätekombination Netzsch STA 429 (Thermowaage) und Balzers QMG 511 (Quadrupol Massenspektrometer) durchgeführt. Dieses Kopplungssystem ist mit einem Digital Equipment PDP 11/23+ Microcomputer verbunden. Der komplette Datensatz, der aus einer TA/MS Messung erhalten wird, charakterisiert in sehr detaillierter Weise das thermische Abbauverhalten von Substanzen und gibt Aufschluß über die temperatur-struktur-abhängige Fragmentierung der Verbindungen.

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Development of flame retarded self-reinforced composites from automotive shredder plastic waste

Multilayered self-reinforced composites were developed from a density-separated light fraction of automotive shredder waste of high polyolefin content, which can fulfil the current technical, safety and environmental requirements of structural materials. The significantly enhanced mechanical properties of the recycled composites were ensured by polypropylene fabric reinforcement; meanwhile, reduced flammability was obtained by modifying the matrix layers, made of secondary raw materials, with phosphorous-containing flame retardant additive. The results of the new flame retarded composite systems allowed the discussion of a novel mechanistic observation. The mechanical and flammability properties of the prepared self-reinforced composites are compared to conventional glass fabric reinforced composites and to compounds without reinforcement.