Polymer Degradation and Stability (v.73, #3)
MoDeSt Special Edition by Norman Billingham (379).
Hans Zweifel (18 June 1939–19 February 2001) by B. Rotzinger; F. Gugumus (381).
The influence of bisphenol antioxidants on thermo-oxidative degradation of plasticised poly(vinyl chloride) by N Mukmeneva; E Gotlib; M Verizhnikov; G Nagumanova; L Grinberg; R Chakirov (383-386).
A number of phenolic antioxidants have been evaluated, alone and in combination with phosphites, for their ability to reduce HCl evolution from PVC formulations plasticised with a new class of plasticiser based on formals of dioxane alcohols. The results show that the effectiveness of phenols is more or less independent of the chemical structure but determined by their evaporation rates. The best formulations decrease the chloride ion concentration in the working zone air during PVC linoleum production by approximately three times.
Keywords: Plasticizer; Stabilizer; Antioxidant; Poly(vinyl chloride); 1,3 Dioxane derivatives;
Mechanism of photostabilization of perfluoropolyether coatings by hindered amine stabilisers by Maria P. Luda; Giovanni Camino; Enzo Laurenti; Sergio Novelli; Tatiana Temtchenko; Stefano Turri (387-392).
Perfluoropolyethers show promising properties for coil coating application and a suitable layer is obtained by incorporating them in a crosslinked polyurethane network. However, photo-oxidative stability of urethane linkages is intrinsically low and an appropriate stabiliser must be added to the reactants prior to curing. The N-methyl HAS bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (Tinuvin765) has been selected for this model study. The chemical structure of the network strongly depends on the curing conditions: coil coating conditions (280 °C/1 min in air) lead to a polyurethane network also containing some urea-bridges and unreacted isocyanate. HAS further modifies the network increasing the urea-bridges at the expenses of the unreacted isocyanate. This kind of network is shown to be intrinsically more resistant to the photo-oxidation than pure polyurethane. In curing conditions the N-methyl HAS is partially transformed into –NH derivatives which are still active antioxidants. During photo-oxidation HAS acts as a radical scavenger but slowly evaporates from the film.
Keywords: Perfluoropolyether derivatives; Fluorinated polyurethane; Photo-oxidation; HAS stabiliser;
Chemiluminescence from stabilised polypropylene. The effect of annealing on the induction time of oxidised polypropylene stabilised with Irganox 1010 and Irganox 1076 by Lyda Matisová-Rychlá; Jozef Rychlý (393-398).
Chemiluminescence under isothermal and non-isothermal conditions has been used for a more detailed study of the oxidation of isotactic polypropylene stabilised with Irganox 1010 and Irganox 1076. Annealing of the stabilised films of polypropylene at lower temperatures prolongs the induction time of oxidation measured at higher temperatures. Arrhenius plots of induction time over a wide temperature interval have been derived from non-isothermal chemiluminescence runs.
Keywords: Chemiluminescence; Oxidation; Polypropylene; Irganox 1010; Irganox 1076; Annealing;
Thermal ageing studies on room-temperature vulcanised polysiloxane rubbers by M. Patel; A.R. Skinner (399-402).
RTV 5370 siloxane rubbers have been thermally aged in inert gas atmospheres and in the presence of moisture at temperatures up to 190 °C. Results from a variety of analysis techniques showed that siloxane rubbers aged in a closed system softened with time. The samples aged open to air did not show this behaviour. These experiments allowed the important factors involved in reproducing the service ageing environment, in particular closed system ageing, to be identified. It was recognised that ageing under the identified conditions would lead to compression set and, as the material is used under load during service, a performance criterion could be defined. This was based on the fact that the degree of compression set should not equal or exceed the nominal compressive strain of 25%, otherwise it will no longer be under load. The compression set properties of samples aged under the identified conditions have been assessed at a number of different temperatures. The data obtained were found to be amenable to time–temperature superposition and Arrhenius treatment. The results suggest the presence of two degradation processes with activation energies of 21.82±6.85 kJ mol−1 (for temperatures below 150 °C) and 76.90±44.53 kJ mol−1 (for temperatures above 150 °C) respectively. The approach adopted predicts that the compression set in the rubber is likely to reach a value of 25% (the failure criterion) over a timescale of 18.8 (+13.3/−5.5) years. However, the apparatus used was limited in that the samples could only be tested to a maximum compressive strain of 10% and, therefore, the dependence of compression set on the degree of initial strain needs to be assessed to verify the prediction.
Keywords: Polysiloxane; Compression set; Thermal ageing;
Effect of polymer matrix on photo-stability of photo-luminescent dyes in multi-layer polymeric structures by I. Baumberg; O. Berezin; A. Drabkin; B. Gorelik; L. Kogan; M. Voskobojnik; M. Zaidman (403-410).
The present study considers the photo-stability of luminescent dyes in multi-layer coatings made of various polymers [low-density polyethylene (LDPE), poly(vinyl chloride) (PVC) and poly(vinylidene fluoride) (PVDF)] . Dye stability is shown to depend on both the chemical structure of the colourant and the photo-stability of the polymer matrix. The influence of colourant self absorption on its photo-stability is shown. This effect was used to increase dye lightfastness in multi-layer coatings. In the case of a coloured PVC intermediate layer covered by an upper PVDF layer it is possible either to decrease or to increase lightfastness depending on the presence of UV-absorbers in the upper layer and its thickness and flexibility. Use of blends of PVDF based polymers with coloured PMMA substantially improves photo-stability of dyes compared to colourants introduced into pure PVDF.
Keywords: Photo-stability; Luminescent dyes; Coatings; PVC; PVDF;
Diffusion coefficient and activation energy of Irganox 1010 in poly(propylene-co-ethylene) copolymers by Giuseppe Ferrara; Monica Bertoldo; Marco Scoponi; Francesco Ciardelli (411-416).
The diffusion of a thermal stabiliser, Irganox 1010, has been studied both in a commercially available polypropylene homopolymer (HomoQ) and in a poly(propylene-co-ethylene) copolymer (RacoS). The diffusion experiments were carried out by using the Roe method formed by a stack of several polymer films having 60–70 μm as thickness under nitrogen atmosphere. The concentration profile of stabiliser in every film has been monitored by the absorbance at 282 nm in UV spectra recorded for every film forming the stack assembly. Under our experimental conditions, the diffusion of Irganox 1010 in each film stack for both polymer materials can be correctly interpreted by using the Fick's second law. The best fit of the experimental data with this equation allows calculation of the diffusion coefficients, D, for these polymer materials at 40, 70 and 80 °C. By applying an Arrhenius equation to the calculated D coefficients, an estimation of activation energies of the diffusion process has been also achieved.
Keywords: Polypropylene; Polyolefin copolymers; Thermal stabilisation; Thermal stabilisers diffusion; Irganox 1010;
Different thermo-oxidative degradation routes in poly(vinyl chloride) by R. Benavides; B.M. Castillo; A.O. Castañeda; G.M. López; G. Arias (417-423).
PVC and mixtures with calcium stearate (CaSt2) or zinc stearate (ZnSt2) were degraded at different temperatures (160, 170, 180 and 190 °C) in order to follow their HCl evolution. The same mixtures were degraded in similar conditions but at convenient time intervals to have samples to characterise and follow such curves by many other techniques. Yellowing index (YI) and visible reflectance spectroscopy were used to study colour changes, Carbonyl index by FTIR (CI) and fluorescence spectroscopy to follow oxidation and chromophoric species and molecular weight and gel percentage to detect crosslinking and chain scission. Temperature does not affect the amount of HCl evolved, only the rate and YI does not represent the release of acid for PVC and PVC+CaSt2 only for PVC+ ZnSt2. On the other hand, visible reflectance always shows the colour trends observed by eye. Crosslinking is favoured by high temperature for the first two mixtures, but where the Zn soap is added chain scission plays an important role.
Keywords: Degradation routes; PVC; Stearates; Stabilisation;
New high performance phosphites by S Costanzi; R Farris; D Girelli (425-430).
Phosphorous based derivatives (phosphites and phosphonites) are well known to be effective as polymer stabilisers mainly during processing, acting as secondary antioxidants and are particularly effective in combination with phenols (primary antioxidants). In addition some phosphites and phosphonites can help in improving the discoloration of polymer articles when they are exposed to heat, UV light, nitrogen oxides (gas fading ) and to gamma rays. However, phosphorous based stabilisers are sensitive to heat and moisture so they can cause undesired side problems during processing and in the life time of polymer articles making useless their benefits. The aim of this study is to test a new phosphite compound more hydrolytically stable than the commercial ones and to present its outstanding performances in improving discolouration during processing as well as when polymer articles are exposed to gamma rays. The comparison has been carried out with standard available products.
Keywords: Phosphites; Antioxidants; Polymer stabilisers; Gamma ray degradation;
A comparative study on the thermo-oxidative degradation of poly(ether-esters) by Gabriela Botelho; Arlete Queirós; Pieter Gijsman (431-435).
A comparison is made between the thermo-oxidative degradation processes in two copolymers of polybutylene terephthalate, one containing polyethylene oxide (PBT/PEO) and the other polybutylene oxide (PBT/PBO), in an oxygen atmosphere at 140 °C. The degradation processes were followed by monitoring the oxygen uptake and CO/CO2 formation during degradation and characterizing the degraded samples by GC–MS, FTIR and 1H-NMR techniques. The formation of peroxides was measured titrimetrically. The presence of carboxylic acids and alcohols was detected by chemical treatment with SF4 and NO, respectively. In order to gain more insight into the mechanism of the degradation, model compounds of each of these copolymers were used, namely diethyleneglycol dibenzoate (DEGDB) and dibutyleneglycol dibenzoate (DBGDB). The results are explained in terms of the initiation of oxidation at the methylene carbon vicinal to the oxygen ether, leading to the formation of new ester linkages. Simultaneously carbon–carbon and carbon–oxygen bond cleavage occurs, leading to aliphatic and aromatic carboxylic acids, formates and alcohols.
Keywords: Thermo-oxidative degradation; Model compounds; Poly(ether-esters); Diethyleneglycol dibenzoate; Dibutyleneglycol dibenzoate;
The influence of transition metal salts on photo-oxidative degradation of poly(ethylene oxide) by Halina Kaczmarek; Alina Sionkowska; Alina Kamińska; Jolanta Kowalonek; Małgorzata Świątek; Aleksandra Szalla (437-441).
The influence of iron (III), cobalt (II) or nickel (II) chlorides on photo-oxidative degradation of poly(ethylene oxide) (PEO) has been investigated. The rates and efficiencies of photochemical reactions occurring in PEO containing small amounts (1–3%) of the transition metal chlorides were compared. The mechanism of reaction induced by UV-irradiation in doped PEO is discussed. The role of active Cl atoms and chlorine radical anion Cl2 •− (formed in the first step of metal salt photolysis) in initiation of polymer degradation is pointed out. The iron salt was found to be the most effective agent accelerating PEO photodegradation.
Keywords: Poly(ethylene oxide); Transition metal salts; Photo-oxidation; Photodegradation;
Photo-oxidation studies on polyurethane coating: effect of additives on yellowing of polyurethane by R.P. Singh; Namrata S. Tomer; S.Veera Bhadraiah (443-446).
Urethane clear coatings based on castor oil and MDI, develop extensive yellowing in the sunlight. The photo-oxidation and yellowing in the urethane coatings upon polychromatic irradiation was monitored by FT–IR spectroscopy, UV/visible spectroscopy and Colormate HDS colorimetry. Several quinoidal oxidation products have been evaluated. The photo-oxidation and yellowing have also been evaluated for coatings modified with different additives and/or their synergistic mixtures.
Keywords: Photo-oxidation; Polyurethane; Coating; Yellowing; Polychromatic-irradiation;
Thermal degradation of poly(vinyl chloride) plastisols based on low-migration polymeric plasticizers by A Jiménez; L Torre; J.M Kenny (447-453).
The analysis of the thermal degradation of poly(vinyl chloride) (PVC) plastisols formulated with low-toxicity polymeric plasticizers is reported. Dynamic and isothermal thermogravimetric analyses are applied to study the behavior of these materials at high temperatures and to evaluate their degradation kinetics. The results used for the optimization of the processing conditions, in particular the cure time and temperature, to maximize the thermal stability of the plastisol. The optimum plasticizer concentration is also determined. TGA results have been used to determine the parameters of the degradation kinetic model using Friedman and Horowitz methods. A comparison with the thermal behavior of traditional plastisols normally employed in industrial applications is reported.
Keywords: PVC; Plastisol; Degradation; Kinetics; Cure;
Using the DTG curve fitting method to determine the apparent kinetic parameters of thermal decomposition of polymers by J. Yang; R. Miranda; C. Roy (455-461).
A new method, called the DTG curve fitting method, has been used to determine the kinetic parameters of six major plastic materials found among urban refuse: high-density polyethylene, low-density polyethylene, polystyrene, polypropylene, poly(vinyl chloride), and poly(ethylene terephthalate). This method involves first measuring the weight loss behaviour by using thermogravimetry (TG) and then using the Arrhenius equation to fit the DTG curves obtained from the TG measurement. The kinetic parameter data obtained have been compared to, and agree well, with the literature data. With this method, computer software, named “DTGsim” has been developed, for use under Windows with a user friendly interface.
Keywords: TG; DTG; Curve fitting; Kinetics; Plastics; HDPE; LDPE; PS; PP; PVC; PET;
Effect of interface modification on the photo-stability of pigmented polyethylene films by P. Anna; Gy. Bertalan; Gy. Marosi; I. Ravadits; M.A. Maatoug (463-466).
The deterioration of differently stabilised and pigmented high density polyethylene films was investigated by DSC and UV spectroscopy methods in the course of accelerated photo-ageing and compared to earlier XPS and gel-content results. Unexpectedly quick destruction of phthalocyanine containing film was observed and explained by the adsorptive removal of the stabiliser from the polymer matrix. In the pigment (filler)-solvent-stabiliser model systems the high susceptibility of hindered phenol type heat-stabiliser to adsorb on talc and phthalocyanine pigment was proved by UV spectroscopic measurements. Surface coating of the talc and pigment with a reactive surfactant considerable reduced the adsorption capacity and thus improved the photo-stability of the pigmented film.
Keywords: Photo-stability of HDPE; Stabiliser adsorption; DSC; UV spectroscopy; Interface modification; Reactive surfactant;
Correlation between thermal properties and conformational changes in poly(ethylene terephthalate)/poly(ether imide) blends by Adhemar Ruvolo-Filho; Adriana de Fátima Barros (467-470).
Miscibility, crystallisation and melting behaviour in blends of virgin and recycled poly(ethylene terephthalate) (PET) with poly(ether imide) (PEI) have been examined using DSC. The blends exhibit single, composition-dependent T g's over the entire composition range and a negative value of the Flory interaction parameter, indicating miscibility of the amorphous polymers. The crystallisation of the PET/PEI blends was dramatically slowed by PEI contents higher than 20%. A linear correlation between a structure-dependent parameter R T (from FTIR measurements) and the enthalpy of fusion (from DSC measurements) for both types of PET samples used in the blends, make the determination of the degree of crystallinity of the PET in any PET/PEI blend possible. In agreement with the melting behaviour of the PET/PEI blends, the average values of the activation energy for trans- conformer formation confirm the negative effect of the PEI on the crystallisation of the PET.
Keywords: PET; PEI; Blends; Thermal properties; Conformational changes; FTIR;
Spectral profiling of radicals in polymer degradation based on electron spin resonance imaging (ESRI) by Shulamith Schlick; Krzysztof Kruczala; Mikhail V. Motyakin; John L. Gerlock (471-475).
We have developed 1D and 2D electron spin resonance imaging (ESRI) in order to deduce the spatial variation of radical properties in polymers exposed to UV radiation in the presence of oxygen, or thermally treated. The accelerated degradation of poly (acrylonitrile-butadiene-styrene) (ABS) containing Tinuvin 770 as the hindered amine stabilizer (HAS) was studied in a weathering chamber equipped with a Xe source that mimics the spectral range of sunlight. The HAS-derived nitroxides detected by ESR occupy two sites and were assigned to radicals located in domains differing in their monomer composition. The spatial distribution of the radical intensity obtained by 1D ESRI indicated that nitroxide radicals are produced initially only on the irradiated side, but the intensity of radicals on the opposite side increases with irradiation time. By contrast, the spatial distribution of nitroxides produced during thermal degradation at 600C is spatially homogeneous. Via 2D ESRI it was possible to visualize the spatial variation of the ESR spectra and to deduce the relative intensity of the nitroxides in the two distinct sites along the selected spatial coordinate. The spectral profiling made possible by ESRI provided spatial details that can be used to deduce morphology-sensitive chemical processes along the sample depth.
Keywords: Polymer degradation; Hindered amine stabilisers; Electron spin resonance (ESR); ESR imaging (ESRI);
Substituted triazines with phosphonyl group as antioxidants for elastomers and their compounds by Maria Giurginca; Aurelia Meghea; Ion Peleanu (477-480).
A number of substances with a triazinic structure provide antioxidant properties, but they have been less studied and used in elastomer processing. The presence of thiol groups also allowed the grafting of the triazinic antioxidant on the chain of the unsaturated elastomer during processing, vulcanization and/or the oxidative process. We have evaluated the protective capacity of some substituted triazines both in elastomer matrix and in vulcanizates. Two kinds of triazines, with aminophenolic and phosphonic substituents, have been evaluated for their protective action in diene elastomers as such and in simplified recipe with NR matrix. In elastomers, the triazinic component with one phosphonic group has a superior protective capacity to that of triazine substituted with two phosphonic groups.
Keywords: Triazines antioxidant; Degradation; Elastomers; Vulcanizates;
Non-conventional antioxidants with a synergistic effect for protection of some elastomers and their vulcanizates by Aurelia Meghea; Maria Giurginca (481-483).
The protection efficiency of antioxidant couples consisting of a classical compound (disubstituted p-phenylendiamines and dihydroquinoline derivatives) and compounds with a disulfide bridge resulting from diamine and phenolic structures has been tested in accelerated ageing. The antioxidant couples were tested in diene elastomers and practical recipes and reveal that antidegradants with a disulfide bridge are able to graft onto the elastomer chain during processing and curing, leading to a level of protection superior to the classical antidegradants. Antidegradants with disulfide bridge are able to cooperate by synergistic or additive interactions with IPPD, bringing about an improvement in the storage time of the elastomers.
Keywords: Antioxidants; Synergistic effect; Degradation; Elastomers; Vulcanizates;
Spectromechanical analysis of the structure and oxidation of PMR thermoset thermally-stable resins by N. Régnier; J. Berriot; E. Lafontaine; B. Mortaigne (485-490).
The long-term ageing of high temperature polyimide thermoset polymers such as the commercial PMR15 resin and model molecules which compose the PMR15 chemical structure, was studied. The amount of each oligomer directly influences the physico-chemical and mechanical properties. The aim was to understand the oxidation mechanisms of these thermoset polyimide resins and the consequences for the mechanical properties. Nuclear magnetic resonance analysis has been associated with the thermo-mechanical transitions.
Keywords: Polyimide; Thermo-oxidation; NMR spectroscopy; Thermal ageing; Thermo-mechanical transitions;
The antioxidant role of vitamin E in polymers V. Separation of stereoisomers and characterisation of other oxidation products of dl-α-tocopherol formed in polyolefins during melt processing by S Al-Malaika; S Issenhuth; D Burdick (491-503).
The nature of specific transformation products based on isolated isomeric forms of oxidative coupling products, aldehydes and a quinone, formed when the antioxidant vitamin E (dl-α-tocopherol) is incorporated in polyethylene (PE) and polypropylene (PP) during melt processing, are investigated. These products were separated and isolated by high performance liquid chromatography (HPLC) and characterised by spectroscopy. It was shown that although a large number of HPLC product peaks are formed, these corresponded to different stereoisomeric forms of only a small number of oxidative coupling products, in addition to a quinone and aldehydes. The observed sixteen HPLC peaks were shown to correspond to three main oxidative coupling products of tocopherol namely, trimers, TRI, dihydroxydimers, DHD, and spirodimers, SPD, formed in both polymers under all processing conditions. The identity of nine of these HPLC product peaks was confirmed to be the different stereoisomeric forms of the trimeric (TRIs) and dimeric (DHD's and SPD's) products of tocopherol. This confirmation was based on a comparative study of their spectral and chromatographic characteristics (FTIR, UV, NMR, MS and HPLC retention times) and authentic isomeric forms of the corresponding products which were synthesised previously in our laboratory from solution oxidation reactions of dl-α-tocopherol. Furthermore, up to five tocopherol-derived aldehydes were found to form at low concentrations under ‘normal’ processing conditions, three of which were fully characterised from extracts of PP-vitamin E stabilised samples. The changes in the concentration of individual aldehydes with processing parameters was examined in both polymers and it is shown that the initially low aldehydes concentration increases dramatically with severe processing, including multi-pass extrusions and presence of oxygen, with the 5-formyl-γ-tocopherol (ALD-1) showing the highest relative concentration (with respect to the other aldehydes) under all conditions. Tocoquinone (TQ) which was formed in both polymers was also isolated and fully characterised.
Keywords: Vitamin E; α-Tocopherol in polyolefins; Characterisation of antioxidant products;
Characterisation and oxidative degradation of a room-temperature vulcanised poly(dimethylsiloxane) rubber by A.N. Chaudhry; N.C. Billingham (505-510).
A typical room-temperature vulcanised, foamed, silica-filled siloxane rubber has been characterised using FTIR(ATR), SEM, density measurements and measurements of swelling in toluene vapour. The results show that the foamed PDMS rubber is an open-cell structure with a void fraction of 50% of the total volume. Long term stability was assessed by degrading the material at high temperatures (180–200 °C) in air. Changes in FTIR (ATR) were not noticeable, except rapid loss of peaks due to the catalyst and its solvent. The material showed a small, but statistically significant, increase in density and decrease in equilibrium swelling. The most sensitive method to measure degradation was chemiluminescence (CL), which confirms that the PDMS is extremely stable because the CL intensity is weak as compared to carbon chain polymers. Removal of oligomers and catalyst residues by toluene extraction results in the disappearance of initial decay and removal of peroxide residues by treatment with nitric oxide also confers greater oxidative stability. Ramped chemiluminescence in air shows that the PDMS residue after toluene extraction is more stable than the virgin material, indicating that degradation is due to small fragments and catalyst solvents rather than the main siloxane network.
Keywords: Polysiloxane; Degradation; Ageing; Chemiluminescence;
The action of ozone on polymers having unconjugated and cross- or linearly conjugated unsaturation: chemistry and technological aspects by Franco Cataldo (511-520).
We review the most recent work on the reaction of unsaturated polymers with ozone. Initially a series of diene polymers with unconjugated double bonds is considered and it is shown that the reaction rate with ozone (in solution) correlates with the free energy of reaction of each molozonide calculated according to MM+ and AM1 methods. The lower the free energy of reaction, the higher the reaction rate with ozone. Additionally, the reactivity of cured diene rubber with ozone in the solid state, in dry and moist ozone is discussed. A discussion is also presented about the crack growth of cured samples in the light of fracture mechanics. The reactivity and the peculiar mechanism of reaction with ozone of polymers having a long series of linearly conjugated double bonds is presented and discussed in comparison to an oligomeric model polyene compound: β-carotene. A new mechanism is proposed to explain both the cis-trans isomerization (and vice-versa) and the experimental detection of radical cation species during the ozone treatment of polyenes. The final topic covers the reactivity with ozone of a unique polymer having a three-dimensional structure and 30 cross-conjugated double bonds: C60 fullerene. The structure of the C60 molozonide is reported together with calculations according to MM+ and AM1 which suggest the possible derivatives formed from the molozonide. Among the possible derivatives considered, the epoxide, experimentally observed, is among the most favoured.
Keywords: Ozonation; Diene rubber; Polyenes; Fullerene; Mechanism; Reaction speed; Theoretical calculations;
Thermal degradation and fire resistance of epoxy–amine–phenolic blends by Debora Puglia; Liliana B. Manfredi; Analia Vazquez; José M. Kenny (521-527).
The effects of the addition of different epoxy resins on the thermal stability of phenolic resolees are reported. Blends of phenolic resins with different compositions of epoxy resins, cured with amine hardeners, were characterized by thermal gravimetric analysis and cone calorimetry to determine their thermal stability and fire resistance. The thermal degradation of phenolic resolees is characterized by a complex mechanism with at least two different processes which lead to the production of a stable and resistant char structure. On the other hand, the epoxy resins studied, either aliphatic or aromatic, degrade in a single step. The results demonstrate that the epoxy–amine content should be kept under 15 wt.% to avoid a significant reduction of the thermal stability of the blend. However, blending with epoxy–amines is a suitable route to improve the mechanical properties of phenolic resins or to reduce the cure temperature.
Keywords: Phenolic resolee; Epoxy; Blends; Thermal degradation; Fire resistance;
Environmentally friendly wood adhesive from a renewable plant polymer: characteristics and optimization by Syed H. Imam; Sherald H. Gordon; Lijun Mao; Liang Chen (529-533).
A wood adhesive was prepared from a natural renewable resource. The characteristics and optimization of starch and polyvinyl alcohol (PVOH)-based crosslinked adhesive suitable for wood-to-wood bonding in interior applications are described. The crosslinker, hexamethoxymethylmelamine (Cymel 323) produced effective crosslinking through a transetherification reaction between methoxy groups in Cymel 323 and hydroxyl groups in starch, PVOH and wood, where hydroxyl groups replaced methoxy groups forming ether bonds with the crosslinker. Optimal viscosity of the adhesive was obtained at 27% solid content. Addition of latex in the formulation increased moisture resistance. The optimum cure temperature and cure time were 175°C and 15 min. Wood samples conditioned at 93% RH for two months exhibited >95% failure in wood but little in adhesive joints. Scanning electron microscopy revealed no visible growth of fungi or other microorganisms on the adhesive after two months exposure of samples at 97% RH followed by 1 year at 50% RH.
Keywords: Plant polymer; Starch; Wood; Adhesive; Glue; Renewables;
Some preventive cellulose antioxidants studied by an aromatic hydroxylation assay by Matija Strlič; Jana Kolar; Boris Pihlar (535-539).
Since the oxidative degradation of cellulose is enhanced in the presence of ferric compounds, the N,N′-(5-nitro,1,3-phenylene)bisglutaramide hydroxylation assay was used to test the efficiency of possible preventive antioxidants: EDTA, DTPA, citrate, desferrioxamine methanesulphonate (desferal) and phytate. The corresponding rate constants and apparent activation energies for hydroxyl radical production in the aqueous systems in the pH interval 6.5–8 were obtained. The rate constants were correlated with the decrease of degree of polymerisation of artificially aged cellulose samples enriched with CaCO3 and iron in the form of the corresponding complex (R=0.9891). It is concluded that the catalytic role of iron is similar in both systems and that the hydroxylation assay may provide valuable estimations of the degradation rates of cellulosic materials in the conditions of use. The chelating compounds shown to have an antioxidant effect at 20 °C in the pH interval studied are DTPA, phytate, and desferal, in the order of increasing positive effect.
Keywords: Cellulose degradation; Autoxidation; Preventive antioxidants; Fenton reaction;
Crystallisation and morphology of neat and degraded poly(p-dioxanone) by M.A. Sabino; J.L. Feijoo; A.J. Müller (541-547).
The present work compares the morphology and crystallisation kinetics of neat and hydrolytically degraded poly(p-dioxanone), PPDX. The hydrolytic degradation was performed in a phosphate buffered saline solution (0.2 M, pH 7.4) at 37 °C. The spherulitic morphology and the isothermal spherulitic growth rate were studied by optical microscopy while the overall crystallisation rate was determined by DSC. A thermal fractionation procedure was applied to the samples using the successive self-nucleation and annealing (SSA) protocol. The results indicate that the peculiar spherulitic morphologies exhibited by neat PPDX change as a function of molecular weight loss, but this change can be qualitatively rationalised as a function of the apparent supercooling applied to the crystallising sample. A change in growth regime with supercooling (from regime II to regime III) was detected using Hoffman's kinetic crystallisation theory for neat and degraded PPDX. It was found that both the overall crystallisation rate and the spherulitic growth rate were substantially increased as the molecular weight was decreased by hydrolytic degradation. The SSA results indicate that degradation depletes the longest chains within the molecular weight distribution of neat PPDX first, a fact consistent with an initial attack of the amorphous regions of the sample.
Keywords: Poly(p-dioxanone); Spherulites; Crystallisation; SSA; DSC;
Composite films based on waste gelatin: thermal–mechanical properties and biodegradation testing by Emo Chiellini; Patrizia Cinelli; Andrea Corti; El Refaye Kenawy (549-555).
Within a research project on the utilization of waste and raw material from agricultural and industrial by-products, a thorough investigation was carried out on the propensity to biodegradation behaviour of casting films based on waste gelatin (WG). After characterization of thermal and thermomechanical behaviour of the present blends biodegradation experiments were carried out under incubation conditions aimed at simulating soil burial conditions. The results reported here evidenced the complete and very fast biodegradability of waste gelatin cast films. The effect of a crosslinker agent such as glutaraldeyde on both thermal properties than degradation rate was further investigated. Parallel biodegradation testing were carried out on composite films based on waste gelatin, poly(vinyl alcohol) (PVA) blends comprising sugar cane bagasse as filler. The possibility of modulating the durability of the films by crosslinking and blending with poly(vinyl alcohol) and/or lignocellulosic waste material was also ascertained. The films meant to be used for the preparation of self fertilizing mulches tended to be disintegrated by soaking in water at relatevely fast rate depending upon the PVA or crosslinker content. The biodegradation extent reached levels after 30–60 days of incubation in any case lower than that reached with WG films.
Keywords: Biodegradable materials; Gelatin; Poly(vinyl alcohol); Degradation; Soil burial;
Solid state production of cellulose–chitosan blends and their modification with the diglycidyl ether of oligo(ethylene oxide) by S.Z Rogovina; T.A Akopova; G.A Vikhoreva; I.N Gorbacheva (557-560).
Blends of the naturally occurring polysaccharides, cellulose and chitosan, obtained in the solid phase by the combined action of high pressure and shear deformation using various equipment, were studied. It was shown by IR-spectroscopy that the system of hydrogen bonds formed between hydroxyl and amino groups of the polysaccharides undergoes a qualitative change. This provides evidence that the blending of polysaccharides occurs at the molecular level. A mechanism of cellulose–chitosan blend formation in the presence of a diepoxide as a crosslinking agent was also studied. It was established that the crosslinking agent reacts predominantly at the amino groups of chitosan, with the formation of a three-dimensional network, cellulose macromolecules being located within and partially bound with this network by the crosslinks. It is shown that the formation of the aforementioned structures results in the insolubility of cellulose–chitosan compositions in acidic and alkaline aqueous media.
Keywords: Cellulose; Chitosan; Blends; Cross-link; Joint action of high pressure and shear deformation;
Aliphatic polyester-based biodegradable materials: new amphiphilic graft copolymers by Delphine Rutot; Emmanuel Duquesne; Isabelle Ydens; Philippe Degée; Philippe Dubois (561-566).
Biodegradable brush-like amphiphilic graft copolymers were synthesized by covalently grafting poly(ε-caprolactone) PCL sequences onto a natural and mainly linear α(1–6) exopolysaccharide backbone, i.e. dextran. A three-step procedure is proposed to control the synthesis which consists in the reversible protection of the hydroxyl groups of the polysaccharide backbone by silylation, followed by the ring-opening polymerization of ε-caprolactone initiated by the remaining free hydroxyl groups of the partially silylated dextran after adequate activation into Al alkoxide active species. The third and final step involves the deprotection of the polysaccharide hydroxyl groups under very mild conditions. The high efficiency of grafting and the control over the graft molecular weight and molecular weight distribution rely upon the well-known “living” character of the coordination-insertion mechanism of the ring-opening polymerization that is initiated by aluminum alkoxides. Poly(ε-caprolactone)-grafted dextran copolymers with precise composition and well controlled number and length of PCL grafts were incorporated into PCL/granular corn starch composites by melt kneading at 130 °C. When located at the filler/matrix interface, the copolymers proved to be very efficient compatibilizers, enhancing the interfacial adhesion, and accordingly the mechanical properties of the composite materials as evidenced by tensile testing. To ensure the migration of the amphiphilic graft copolymer at the starch/PCL interface, it is better to first precipitate it onto the filler surface or to blend it with the starch granules before melt blending with the polyester matrix.
Keywords: Poly(ε-caprolactone); Dextran; Polysaccharide; Starch; Amphiphilic copolymers; Ring-opening polymerization; Biodegradable composites; Polymeric surfactant; Graft copolymers;
Wood and Cellulosic Chemistry by E.D Suttie (567-569).
Spectroscopy of Polymers by N.C Billingham (567-569).
Polymers and the Environment by N.C Billingham (567-569).