Polymer Degradation and Stability (v.75, #3)

Properties such as resistance towards heat, ozone and gamma radiation and flame resistance of aluminium powder filled natural rubber composites were studied. Aluminium powder filled natural rubber composites showed better retention of mechanical properties after thermal ageing compared to other fillers like HAF, GPF, silica and acetylene black. Tensile strength of natural rubber (NR)–aluminium powder vulcanizates increased slightly after ageing for 7 days at 70 °C due to the slow and continued crosslinking, but on prolonged ageing, chain scission predominated, which decreased the tensile strength. These composites also have better resistance towards ozone exposure. The cracks generated due to ozone exposure are small and discontinuous in aluminium powder filled vulcanizates, whereas the cracks are deeper, wider and continuous for other filler incorporated samples. Effects of various bonding agents namely hexamethylene tetramine-resorcinol system (HR), bis [3-(triethoxysilyl) propyl] tetrasulfide (Si-69), cobalt naphthenate (CoN) and toluene diisocyanate (TDI), on the ageing characteristics of natural rubber-aluminium powder composites were studied and it was found that these composites have better resistance towards heat, ozone, and gamma irradiation.
Keywords: Natural rubber; Aluminium powder; Degradation;

Glycolysis of rigid polyurethane from waste refrigerators by Chao-Hsiung Wu; Ching-Yuan Chang; Jiunn-Kuen Li (413-421).
Glycolysis of rigid polyurethane (PU) has been investigated to provide useful data for the recycling of waste refrigerators. The glycolysis experiments were performed under atmospheric pressure in a stirred flask kept at a constant temperature. Diethylene glycol (DEG) and potassium acetate (KAc) were used as the solvent and catalyst in the glycolysis system, respectively. The properties of the glycolysis products were determined by analyzing the hydroxyl value, mass mean molecular weight (M w), viscosity, and the conversion of the –NCOO– functional group in PU. The results indicate that an adequate concentration of KAc is about 2% of the weight of the PU and an adequate reaction time is about 2 h. The yields of glycolysis products are about 87–95% for our experimental conditions. Thus, the recovery of liquid products containing polyols can be achieved by the distillation of glycolysis products.
Keywords: Glycolysis; Polyurethane; Waste refrigerator;

Photostabilization of Nylon 66 in presence of acid blue dyes by P.N. Thanki; R.P. Singh (423-430).
We have examined the effect of two different classes of photostabilizers, UV absorber and hindered amine light stabilizer (HALS) on Nylon 66 to prevent the photo-oxidation of the polymer matrix and colour fading of the dye. Acid blue dyes, UV absorber and HALS were observed to impart photostability to Nylon 66. UV absorber and HALS showed photostability directly proportional to their relative concentration in the polymer whereas in case of dye, 0.2% w/w concentration was observed as the optimum concentration. Loss of UV absorber with photo-irradiation time was found to be inversely proportional to the UV absorber concentration in the polymer whereas the fading of the dye was directly proportional to its concentration in the polymer. UV absorber imparted higher lightfastness to the dye as compared to HALS. No influence of the substitution on pendant phenyl ring of anthraquinone acid blue dyes was observed for their photostabilizing efficiency.
Keywords: Acid blue dye; Degradation; Lightfastness; Nylon 66, Photostabilization; UV absorber;

Preparation and degradation of l-lactide and ε-caprolactone homo and copolymer films by Hülya Yavuz; Ceyhun Babaç; Kadriye Tuzlakoğlu; Erhan Pişkin (431-437).
l-Lactide and ε-caprolactone homo and copolymers were synthesized by ring-opening polymerization using stannous octoate, as the catalyst. The number and weight average molecular weights, and polydispersity indices were in the range of 30,000–35,000, 52,000–56,000, and 1.53–1.86, respectively. All polymers were semicrystalline, as indicated by DSC. The LLA/CL ratio in the final copolymer was 60/40, as obtained by 1H-NMR. Polymeric films (120 μm) were prepared by solvent casting, using chloroform as the solvent and drying in air. Degradation of these films was investigated in aqueous media with or without the presence of a micro-organism (Pseudomonas putida) for 60 days. We followed the degradation by measuring the changes in the molecular weights and distribution, and also changes in mechanical properties. Molecular weights decreased with time, but there was no significant changes in the molecular weight distributions. There were significant changes in the mechanical behavior of the films. They became much less flexible, even brittle and mechanically weaker in 60 days. The changes were more pronounced in the case of copolymer film. We observed almost no effect of micro-organisms on either molecular weights or mechanical properties.
Keywords: l-Lactide/ε-caprolactone homo and copolymers; Films; Degradation; Pseudomonas putida;

The effects of accelerated weathering on the brittleness of siloxane-based hardcoats coated on polycarbonate sheet were quantified using fracture energy testing and chemical composition change measurements. The hardcoat containing no ultraviolet light absorber (UVA) showed a faster decrease in the fracture energy as weathering progressed, compared to the hardcoat formulated with UVA. In addition, the rate of weathering induced chemical composition change, as measured by photoacoustic infrared spectroscopy, was greater in the UVA free hardcoat. The decrease in the fracture energy appears to be proportional to the amount of chemical composition change, regardless of whether the hardcoat contains UVA.
Keywords: Polycarbonate; Hardcoat; Weathering; Fracture;

The dependence of PVA biodegradation on polymer molecular weight, degree of hydrolysis, and content of head-to-head structural units was investigated in the presence of a PVA-degrading microbial population and of the relevant culture supernatant. Respirometric tests carried out in the presence of the selected microbial population evidenced a limited but significant delay in the mineralization profile depending upon the degree of PVA hydrolysis, whereas no remarkable effect by molecular weight was detected. Five bacterial strains were isolated from the PVA-degrading microbial population, but only the degradation of low molecular weight fractions was recorded in cultures inoculated with single bacterial strains. The exclusive attack of low molecular weight fractions is in accordance with the occurrence of an additional degradation mechanism different from that generally proposed for PVA biodegradation. Experiments carried out in the presence of the culture supernatant clearly demonstrated the presence of a PVA degrading enzymatic system in the solution. Kinetic studies carried out under the reported conditions suggested the occurrence of a random cleavage of PVA chains. No influence of both molecular weight and content of head-to-head structural units on the enzymatic degradation process was observed. Enzymatic assays excluded the presence of extracellular esterases in the culture supernatant but confirmed the presence of oxidases.
Keywords: PVA biodegradation; Mixed microbial culture; Culture filtrate; Molecular weight effect; Degree of saponification effect;

Reprocessing and restabilization of greenhouse films by N Tzankova Dintcheva; F.P La Mantia; R Scaffaro; M Paci; D Acierno; G Camino (459-464).
From the ecological and economical points of view, reprocessing of polyethylene greenhouse films is a promising solution to reduce discarded materials and to produce useful, or potentially useful, objects for service. Films exposed outdoors, however, show inferior mechanical properties and the melt processing worsens these properties. The addition of stabilizers and antioxidants to recycled plastic products prevents inherent thermal instabilities from occurring within the time frame of proper processing. In this study, we attempt to explore ways for improving product performance by the addition of four different additives when the recycled films undergo intensive shear processing. The process is evaluated by measuring the changes in chemical structure (carbonyl evolution) as well as rheological and mechanical characteristics (tensile properties). The effectiveness of the various additives was estimated and the one with the best antioxidant ability was identified. The analysis of processing conditions allowed us to find that the best results are emphasized by the continuous addition of the stabilizer at each step of reprocessing.
Keywords: Recycling; Greenhouse films; Restabilization;

The isothermal degradation of some polyetherketones: a comparative kinetic study between long-term and short-term experiments by Lorenzo Abate; Ignazio Blanco; Oriana Motta; Antonino Pollicino; Antonino Recca (465-471).
The kinetics of the isothermal degradation of three high thermally stable aromatic polyetherketones was studied by both a long-term (about 3 years) experiment at a temperature (270 °C) largely lower than the temperatures of fusion, and a set of short-term experiments at temperatures near the temperatures of fusion. An induction period was observed at 270 °C, followed by two degradation stages, the first with an exponential increase of the weight loss rate (V) as a function of heating time (t) and the final one showing constant weight loss rate. Short-term experiments showed similar behaviour, but no induction period was observed. The equations V=V o×2 αt and V=K at various temperatures were determined for the exponential and linear degradation stages, respectively. The e-folding time α increased with temperature according to Arrhenius-type equations, by which the apparent activation energy values for degradation could be determined. The results are discussed and indicate that the kinetic parameters of degradation change with temperature.
Keywords: Thermogravimetric analysis; Polyetherketones; Kinetic parameters; Thermal degradation;

Melt stabilization of wet polyamide 6 by F.P La Mantia; R Scaffaro (473-477).
Melt processing of polycondensate polymers must be carried out after careful drying in order to avoid any hydrolytic chain scission caused by the presence of water or other small molecules. In this work, the effect of two different antioxidants on the processing and flow properties of a polyamide 6 sample not dried before processing operations has been studied. One of these stabilizers seems to protect the wet polymer from hydrolytic chain scission. This action has been interpreted considering that the stabilizer hydrolyses instead of the polyamide macromolecules.
Keywords: Melt stabilization; Polyamide;

The flammability behaviour of a blend fabric cannot be predicted from the flammability characteristics of its component fibers because of the physical or chemical interaction of the thermal degradation products of the blend during heating or combustion. In order to consider the design of flame retardant fabrics from blends of cotton as a flammable fiber and aromatic polyamide fiber as a nonflammable fiber, the thermal degradation of each and blends of fiber has been studied using a conventional dynamic thermogravimetric technique in a flowing air atmosphere at several heating rates. Quantitative data are presented which pinpoint how the thermal degradation behaviour of this blend differs from that of the components. Comparison of the thermogravimetric curves and calculated kinetic parameters indicates that interactions occur faintly between the cotton and aromatic polyamide components in the blends. The thermogravimetric analysis data show three degradation stages in an air atmosphere.
Keywords: Flame retardant fiber; Thermal degradation; Thermal analysis; Aromatic polyamide fiber;

Carbon Black is recognised for its ability to stabilise polyolefins against UV degradation. Linear low density polyethylene (LLDPE) 75 μm extruded films containing a variety of carbon black with different particle size, structure and concentrations were exposed to two accelerated artificial weathering devices, a xenon arc source, e.g. Xenotest 150S, and fluorescent tube sources with UVA and UVB lamps, under controlled temperature and humidity. The changes in physicochemical properties during exposures were studied using tensile testing, Fourier transform infrared (FTIR) spectroscopic and differential scanning calorimetric (DSC) methods. Presence of each carbon black shows significant improvement in UV stabilisation compared to clear films, especially for those with small particle sizes as expected. There is no consistent effect of carbon black structure on UV stabilisation for various particle-sized carbon blacks. An increase in carbon black concentration from 1.5 to 3.5% w/w also improved UV stabilisation. For UVA and UVB sources, presence of carbon black, while increasing carbonyl group generation with respect to unit loss in tensile property with respect to unfilled LLDPE, also appears to suppress Norrish Type II scissions at photochemically generated carbonyl centers in polymer chains. This is especially the case for the smallest (20 nm) particle sizes. Thus the photostabilising efficiency of carbon black is based on both physical surface-area-dependent UV absorption and photochemical activity. Under xenon arc exposure, however, this latter is minimal.
Keywords: Polyethylene; LLDPE; Carbon Black; UV; Carbonyl; Vinyl; Photodegradation;

Thermal behaviour of some polymethacrylates with a 1,3-dioxolane ring by Zülfiye İlter; Mehmet Çoşkun; İbrahim Erol; Arzu Ünal; Misir Ahmedzade (501-508).
(2-Cyclohexylidene-1,3-dioxolane-4-yl)methyl methacrylate and (2-cyclopentylidene-1,3-dioxolane-4-yl)methyl methacrylate prepared from the reaction of glycidyl methacrylate with cyclohexanone and cyclopentanone, have been polymerised by benzoyl peroxide. Spectroscopic characterization of the monomers and their homopolymers have been done by Fourier transform infrared (FT–IR) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopies. Thermal degradation of the polymers has been studied by thermogravimetric analysis and FT–IR. Volatile products of the degradation have been investigated by FT–IR, 1H and 13C NMR and gas chromatography–mass spectrometry techniques. Total degradation of the polymers to 450 °C produces extensively the monomers, especially degradation of poly[(2-cyclohexylidene-1,3-dioxolane-4-yl)methyl methacrylate]. The degradation products and the mechanism are discussed.

Depth-profile of photo-oxidation of polyoctenamer by A Kumar; S Commereuc; L Gonon; V Verney (509-516).
The non-uniformity of photo-oxidation across polyoctenamer films has been investigated by bulk and surface analysis. Standard transmission FTIR (TIR), photoacoustic (PAS), internal reflection spectroscopy (ATR) and hydroperoxide titration give a detailed picture of the spatial distribution of photo-products to characterise the depth profile of degradation. Our finding is that the chemical oxidation profile develops from the very beginning of irradiation of polyoctenamer at λ >300 nm. We assume that the distribution of by-products is uniform in the superficial layer in the range 3–15 μm. Nevertheless a strong depth profiling of by-products is detected in bulk layers (>20 μm) and no photo-products are revealed by FTIR spectroscopy in the core of oxidised samples (>50 μm).

Waste petroleum refining catalyst from FCC unit was evaluated as a possible component in ammonium polyphosphate (APP) and pentaerythritol (PER) flame-retarding intumescent compositions for polyethylene-based polymers. The use of heating microscopy was introduced as a means of monitoring the intumescence process in situ. By the association of this technique with TG analysis, it was possible to observe that the addition of the waste material to the APP/PER formulations brought about an increase in the residual mass and helped the polymer samples to maintain their structure at temperatures higher than 600 °C.
Keywords: FCC catalyst; Waste materials; Heating microscopy; Intumescence; Flame retardancy; Ammonium polyphosphate; Pentarythritol;

Phenolic antioxidants were studied extensively in the 1960s. During that time, the action mechanism might have seemed to be clarified completely. Based on our recent study, however, there remain some unclear points on the interpretation of substituent effects. In this work, o-methoxyphenols having m-substituent have been investigated in detail to make any m-substituent effect clear. It was found that the m-substituent of an m-substituted o-methoxyphenol may behave as if it were on the p-position. This fact is explained by the suggestion that the m-substituent affects its p-substituent, which then influences its o-position by resonance. That is, an m-substituent on the phenol can affect the antioxidant activity, if the phenol also has an o-substituent. Such a substituent effect is proposed as a “secondary substituent effect”.
Keywords: Antioxidant; Phenol; o-Methoxyphenol; m-Substituent; Secondary substituent effect;

A hyperbranched polyurethane acrylate containing phosphorus was found to display flame retardance with a limiting oxygen index of 27.0 after being UV cured. The retardant mechanism was investigated by observing the site where retardance take places and the synergistic effect of phosphorus and nitrogen. It is shown that the best synergistic effect happens when the phosphorus content is around 0.7 wt.%. The thermo-degradation process was monitored by in-situ FTIR. The P–O–C bonds break more easily than C–O–C bonds, forming P–O–P bonds. The morphological characteristics of the charred crust of the product were studied by scanning electron microscopy based on comparison with that of the urethane acrylate without phosphorus. The presence of phosphorus promotes the formation of compact char, which protects the underlying polymeric materials from further attack from flame or heating.
Keywords: Halogen-free flame retardant; Mechanism; Polyurethane acrylate; UV curing;

Antioxidant activity of aromatic cyclic amine derivatives by Tomihiro Nishiyama; Tatsuya Suzuki; Yasuhiro Hashiguchi; Shingo Shiotsu; Masataka Fujioka (549-554).
The antioxidant activities of indolines, indoles, and 1,2,3,4-tetrahydroquinolines in the oxidation of tetralin at 61 °C induced by an azo-initiator were evaluated. Indoline itself and indolines with a methyl or methoxy group were strong antioxidants in this tetralin system. Although indoles and 1,2,3,4-tetrahydroquinolines did not have an antioxidant effect, 5-hydroxyindole and 6-methoxy-1,2,3,4-tetrahydroquinolines were potently antioxidant. Among the antioxidants tested, 5-hydroxyindole exhibited the highest induction period, 1.7 times that of BHT. A semiempirical MNDO-AM1 calculation was applied to study hydrogen abstractions of antioxidants in the chain process of autoxidation. These results indicated that the rates of oxidation during the induction period correlated with the dissociation energies of the N–H bond.
Keywords: Antioxidant activity; Indoline; Indole; Tetrahydroquinoline; Bond dissociation energy;

The thermal degradation behavior of polyaniline (PANI) in PANI/Na+-montmorillonite (Na+-MMT) nanocomposites prepared by in-situ intercalative polymerization of aniline into Na+-MMT has been investigated by thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The residual weight (TG curves) and its weight derivative (DTG curves) of the nanocomposites suggest that the PANI chains for PANI/Na+-MMT nanocomposites are more thermally stable than those for a simple PANI/Na+-MMT mixture. This improvement in the thermal stability for the nanocomposites is attributed to the presence of Na+-MMT nanolayers with a high aspect ratio acting as barriers, thus shielding the degradation of PANI in the nanogalleries and also hindering the diffusion of degraded PANI from the nanocomposites. The shielding effect of the nanolayers is found to be significant as the Na+-MMT content in the PANI/Na+-MMT nanocomposites is increased. The XRD patterns of the nanocomposites after TGA measurements indicate that the basal spacing (d 001) of the PANI/Na+-MMT nanocomposites is almost intact, implying that the thermal decomposition of the PANI chains is believed to occur mainly outside the silicate layers.
Keywords: Polyaniline; Na+-montmorillonite; Intercalation; Nanocomposites; Thermal stability; Thermogravimetric analysis (TGA);