Thermal and photo-chemical degradation of nylon 6,6 polymer: Part 1—Influence of amine-carboxyl end group balance on luminescent species

Nylon 6,6 polymers of different degrees of polymerisation have been characterised by ultra-violet (uv) absorption, fluorescence and phosphorescence emission spectroscopy, viscosity number and amine end-group balance and the data related to their subsequent thermal and photo-chemical stabilities. The latter, determined by the percentage change in viscosity number, clearly shows that in both cases polymer stability is markedly influenced by the final stages of polymerisation under both steam and nitrogen atmospheres, the latter being the most detrimental. During both of these processes the molecular weight increases, as indicated by an increase in viscosity number, as does the concentration of fluorescent and phosphorescent impurities and products absorbing uv at 294 nm. Extraction of some of these species by 2-propanol results in a marked improvement in polymer photo-stability, implicating the involvement of these chromophores in initiation of photo-oxidation. Thermal degradation at 120°C confirms the presence of two types of fluorescent species. The first is reactive, rapidly diffuses out of the polymer and is associated with cyclic α, β-unsaturated carbonyl compounds; the second is non-volatile in-chain in type, increases in concentration and is associated with α-ketoimide structures. However, whilst correlations between the presence of light absorbing/luminescent carbonyl species is evident to some extent another, more important, factor based on the concentration of amine end-groups appears to be dominant. In this case a higher concentration of amine end-groups at lower degrees of polymerisation results in an increase in polymer stability, both thermally and photo-chemically and is associated with the radical/oxygen scavenging ability of the amine end-group, not unlike that of the well-known hindered piperidine light stabilisers. This is confirmed by the observation that treatment of nylon 6,6 films with sulphur dioxide gas, which reacts with the amine groups, thus generating sulphonamides, sensitises the photo-chemical oxidation of the polymer, an effect which contrasts with that found earlier for polyolefins.     

Thermo-mechanical characterisation of in-plane properties for CSM E-glass epoxy polymer composite materials – Part 1: Thermal and chemical strain

The in-plane thermo-mechanical properties and residual stresses of a CSM E-glass/Epoxy material are characterised through the use of DSC and TMA. The measured data is used to generate material models which describe the mechanical behaviour as a function of conversion and temperature. The in-plane thermal expansion coefficient (α) of the composite material decreases above the glass transition temperature (T_g), which is compensated by a higher out of plane deformation above T_g. Comparison of α and chemical shrinkage measurements suggests that chemical bonds between the polymer matrix and the glass fibres are formed prior to shrinkage of the epoxy matrix, i.e., at an early processing stage. This suggests that production of composites with low residual stresses requires focus on reactivity between the matrix and the sizing rather than the matrix cure properties. As a consequence, residual stresses in the composite material are mainly a result of restricted cure shrinkage rather than mismatch between thermal expansion coefficients.     

Recycling of polymer waste: Part 1—Photo-oxidized polypropylene

In order to recycle photo-oxidized polypropylene, blends of this polymer waste with virgin polypropylene have been prepared with different compositions.Both rheological and mechanical properties depend on composition. Rheological properties indicate some interactions between the two polymers at low shear rates. On the other hand, at high shear rates there is evidence of incompatibility.The nominal tensile strength is almost independent of the composition, while the other mechanical properties are similar to those of the degraded material up to a virgin PP content of about 75%, after which they quickly reach the values for the virgin polypropylene.These features are correlated with the large spherulite size of these blends.     

Influence of dissolution processing of PVA blends on the characteristics of their hydrogels synthesized by radiation—Part I: Gel fraction,swelling, and mechanical properties

In this work several hydrogels were obtained with two different poly(vinyl alcohol)s/PVAs as the main polymer in aqueous solutions containing 10% of PVA, 0.6% of agar, and 0.6% of κ-carrageenan (KC), cross-linked by gamma-rays from a ⁶⁰Co irradiation source. The PVAs tested have different degrees of hydrolysis and viscosities at 4% with values closed to 30 mPa s. The aqueous polymeric solutions were prepared using two distinct processes: the simple process of heating–stirring and that of making use of an autoclave. The purpose of this study was to evaluate the influence of the dissolution process by means of both methods on the hydrogels’ properties obtained. These were investigated by means of degree of cross-linking/gel fraction, degree of swelling in water, and some mechanical properties. The results that are obtained for hydrogels synthesized from solutions of PVA, agar, KC, and blends thereof prepared by both dissolution processes showed higher degrees of swelling for hydrogels from the autoclaved polymer solutions than those from the solutions prepared by simple heating–stirring process. Furthermore, their hydrogels containing totally hydrolyzed PVA displayed higher tensile strength and lower elongation properties.     

Degradation of polymer blends—II. Oxidative radiolysis and stabilization of blends of low-density polyethylene and styrene-butadiene-styrene copolymers

The solubility, infra-red and mechanical properties have been studied for LDPE-SBS blends irradiated with γ-rays in the presence of oxygen. The results have been compared with those obtained for the oxidative radiolysis of pure LDPE and for the photo-oxidation of the same LDPE-SBS blend. The oxidative degradation mainly occurs in the polybutadiene part of the blend. Efficient stabilization by hindered amines Tinuvin 770 is reported.     

Effects of medium and chemical modification on thermal characteristics of Β-lactoglobulin

The thermal properties of -lactoglobulin (-LG) were studied by differential scanning calorimetry (DSC) under different medium conditions.pH, neutral salts, protein perturbants, and polyols all affected the DSC characteristics of -LG. Acylation with fatty acids also changed the thermal properties, particularly peak width at half-height. The results suggest that the structural stability of -LG is controlled by non-covalent forces, particularly electrostatic and hydrophobic interactions. Disulfide bonds did not contribute to the thermal response of -LG. Fatty N-acyl-amino acids caused marked increases in thermal stability and decreases in denaturation enthalpy, and additional peaks were observed in the presence of some palmitoyl derivatives.Contribution No. 2310, Centre for Food and Animal Research.We thank D. Raymond for her excellent technical assistance.     

Allylic monomers as reactive plasticizers of polyphenylene oxide. Part III – Rheological and mechanical properties

The chemorheology of blends of diallyl ortho-phthalate (DAOP) as reactive plasticizer of polyphenylene oxide (PPO) were monitored during their cure with either dicumyl peroxide (DCP) or tert-butyl hydroperoxide (TBHP), and their mechanical properties and morphology were studied. The steady shear and dynamic rheology behaviour was consistent with chemical gelation of DAOP in blends with low concentrations of PPO but the gelation behaviour at higher PPO concentrations was more complex. Dynamic mechanical thermal analysis of the blends of PPO:DAOP cured with either DCP or TBHP indicated a two phase structure. For PPO:DAOP/DCP, the lowest transition (between 150 °C and 200 °C) was attributed to a DAOP-rich phase and its T_g was higher than that for pure DAOP/DCP due to the presence of PPO in the DAOP-rich phase. The smaller damping shoulder near 250 °C was caused by a PPO-rich phase with a T_g that was lower than pristine PPO due to the presence of unpolymerized or polymerized DAOP. In contrast, the glass transition region of the PPO:DAOP/TBHP system was very broad due to an overlap of the transitions for DAOP-rich and PPO-rich phases caused by higher levels of unpolymerized DAOP. SEM observations of the blends revealed a two phase morphology with PPO-rich particles in a poly-DAOP matrix for blends with ?30 wt% PPO, a co-continuous morphology for blends with 40 wt% PPO, and a phase inverted morphology with more than 50 wt% PPO. These SEM observations agree with studies of the swelling, disintegration or dissolution of matrix of the blends in solvent.     

Effect of epoxidized palm oil on the mechanical and morphological properties of a PLA–PCL blend

In this study, the effects of epoxidized palm oil (EPO) on the mechanical and morphological properties of a blend of two types of biodegradable polymer, poly(lactic acid) (PLA) and polycaprolactone (PCL), were investigated. The solution-casting process, with chloroform as a solvent, was used to prepare samples. Addition of EPO reduced the tensile strength and modulus but increased elongation at break for the PLA–PCL blend. The highest elongation at break was observed for the blend with 10 % (w/w) EPO content. Scanning electron microscopy (SEM) indicated that the fractured surface morphology of the PLA–PCL blend became more stretched and homogeneous in PLA–PCL–EPO. Possible interactions between the PLA–PCL blend and EPO were also characterized by use of Fourier-transform infrared (FTIR) spectroscopy. Thermal stability was studied by differential scanning calorimetry and thermogravimetric analysis. The results from FTIR and SEM revealed that the miscibility of the PLA–PCL blend was improved by addition of EPO.     

Effect of TMAB concentration on structural,mechanical and corrosion properties of electrodeposited Ni–B alloys

The influence of trimethylamine borane (TMAB) concentration as a boron (B) source on the structural and corrosive properties of Ni–B alloy coatings produced by electrodeposition was investigated. The crystal structure of the Ni–B coatings is influenced by the B content in the coating, having a slight (220) preferred orientation. The B content in the coating increased from 16 to 34 at.% with the corresponding increase in the concentration of TMAB from 1 to 20 g/L, while interestingly retaining a crystal structure. The hardness of the coatings increased with increasing B content owing to the formation of smaller crystallites. An increase in B content in the alloy coatings, led to a shift in the E_corr values to more anodic potentials, indicating increase corrosion protection for the Ni–B coatings. This study achieved to reach 34 at.% B content in Ni–B alloy coatings produced by electrodeposition while preventing amorphization of the coating layer.     

The mechanism of chemical degradation of polymers: Part III—The anomaly in the hydrolysis of glycolide copolymers

The data published on the chemical and enzymatic degradation of polyesters and some other polymers is analysed. Earlier studies on copolymers have shown that chemical stability changes monotonously with change in composition if the corresponding homopolymers differ in their sensitivity to the action of a degrading agent. The present work shows that anomalous dependence of chemical stability on copolymer composition is observed for a copolymer based on the isomeric monomers, glycolide and ethylene glycol oxalate. In this case the minimum in the chemical stability versus copolymer composition curve corresponds to the minimum in the copolymer melting temperature versus copolymer composition curve. A possible interpretation of the observed phenomenon is given.     

Solution properties of octyl β-D glucoside. Part 1: Aggregate size. shape and hydration

Aqueous solutions of octyl--D-glucoside have been examined in a wide concentration range. By combining information from density, viscosity and dielectric permittivity, the transition from molecular to micellar state has been evidentiated. Classical equations for the viscosity colloidal dispersions have been reexamined and applied to get information on micelle shape. A combined analysis of dielectric and viscosity findings indicates a slight and continuous dependence of micellar shape on surfactant content. The role of hydration on micellar stability is significant.     

Thermal degradation of keto polymers: Part 1—Poly(vinylacetophenone)

The thermal degradation of poly(vinylacetophenone) (PVAP) was studied at 380°C under high vacuum. The degradation products were separated into gaseous and liquid fractions and identified (gc, nmr, ms). The principal reactions are removal and decomposition of acetyl groups, depolymerization and random chain scission, as evidenced by the pattern of number average molecular weight changes. While the basic mechanism of degradation resembles that of poly(styrene) (PS), i.e. initial random chain scission, the number of transfer reactions is considerably greater due to the presence of methyl radicals which abstract from C-atoms in the polymer chain. The resulting chain radicals undergo β-scission (the principal mode of chain scission) to yield a terminally unsaturated molecule and a macro radical. These two species further decompose to give oligomeric products and monomer. The relative abundance of oligomers to monomer is considerably greater than that observed for PS. This has been attributed to shorter zip lengths for depolymerization and to the occurrence of more transfer reactions in PVAP. Plausible mechanisms for the formation of the various reaction products are given.     

Studies on the synthesis and properties of malachite green imprinted polymer

A new molecularly imprinted polymer was synthesized with malachite green (MG) as molecular template, methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and azobisisobutyronitrile (AIBN) as initiator. Recognition properties of the MG imprinted polymer were studied by equilibrium adsorption and HPLC. The results showed that the imprinted polymer had good affinity and marked selectivity for MG, and can separate MG with its analogue commendably. The new polymer can be used for the enrichment of MG in complex sample, and can work as separation media to separate and detect MG by HPLC.     

Effect of γ-irradiation on optical and electrical properties of Se1−xTex

The effect of γ-irradiation on optical and electrical properties of amorphous and polycrystalline Se_1−xTe_x (0.211<x<0.802) thin films of thickness 180 nm were investigated. The analysis of the absorption coefficient data revealed the existence of indirect transition both before and after irradiating. It was observed that the value of the optical energy gap depends on the value of x, decreasing as x increases. It was found also that the optical energy gap decreases with an increase of γ-doses for all compositions. The obtained results for all Se_1−xTe_x, films have been interpreted in terms of density of states model of Mott and Davis. From the experiment of electrical conductivity σ at various temperatures, it was observed that Se_1−xTe_x. films exhibited ln σ versus T⁻¹ relationships at high temperatures and ln σ(T)^1/2 versus T^−1/4 hopping conductivity behaviour at low temperatures. It was found that the thermal activation energies ΔE decrease with increasing Te content and increases with decreasing γ-doses. X-ray diffraction patterns for the as-deposited Se_1−xTe_x, show that polycrystalline films start to appear for x>0.407.     

Effect of ZnO nanoparticles on kinetics of thermal degradation and final properties of ethylene–propylene–diene rubber systems

The morphology, thermal degradation behavior in addition to static and dynamic mechanical properties of various ethylene?Cpropylene?Cdiene (EPDM) rubber compounds containing nano-zinc oxide (NZnO) were investigated compared to those of EPDM with ordinary-sized ZnO (OSZnO). The field-emission scanning electron microscopy studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for NZnO filled systems. Thermogravimetric analysis (TG) revealed that the thermal degradation of EPDM system was delayed upon the inclusion of NZnO instead of OSZnO in the compound. The kinetic analysis of TG data based on Friedman and Kissinger methods showed that the nanocomposite samples exhibited higher activation energy (E _a ) and lower order of reaction (n) over the conventional system, suggesting the enhancement of thermal stability upon decreasing ZnO particle size. The results obtained from dynamic mechanical analysis and static mechanical characterizations in terms of hardness, resilience, and abrasion tests interestingly indicated that NZnO not merely could act as a thermal insulator, but also could perform as a nano-filler to improve the final performance of EPDM elastomers.     

Effect of 60Co-γ on the melting behaviour of single and poly-crystalline polyethylene

The effect of ionizing radiation on high density poly (HD) and single (SC) crystals of polyethylene samples were investigated by DSC. For HD material the heat of fusion (ΔH_f) was found to drop by only ∼ 17% at about 700 Mrad of radiation dose with no detectable corresponding change in the melting temperature T_m. In contrast approximately 67% drop in ΔH_f and 18 K in T_m was observed for SC specimen. Such drastic differences in the melting behaviour were ascribed to greater sensitivity of the SC material to irradiation as far as effecting the crystal structure is concerned. Crosslinking taking place in the fold surface of the SC specimen (amorphous region) increases the strain energy at the fold and progressively affects the nearby crystal lattices. The amorphous region in HD material is different in morphology, and crosslinking taking place in that region does not affect the crystal structure substantially.     

Effect of supercritical carbon dioxide treatment on structure and mechanical properties of β-nucleated polypropylene processed at different temperatures

Polypropylene (PP) was compounded with β-nucleating agent and injection-molded at 180 °C or 220 °C. The samples were subsequently treated by supercritical carbon dioxide (scCO₂) at different temperatures. Results show that processing temperature and scCO₂ treatment could strongly influence the tensile and impact properties of β-nucleated PP. In particular, the sample processed at 220 °C and treated at 120 °C exhibit much enhanced impact strength (4.8 times that of its untreated counterpart). FTIR, WAXD, SEM and DMA were performed to explore the effects of processing temperature and scCO₂ treatment on structure of the samples. Deformation-induced plastic flow and micro-voids were also evaluated to construct structure-property relations. It was found that the influence of processing temperature on mechanical properties is mainly associated with the β-form content and β-crystalline morphology, while the structural changes in the crystalline lamellar scale may be responsible for the toughening effect of scCO₂ treatment.     

Study on the influence of ageing on chemical and mechanical properties of N,N′-dimethyl-N,N′-diphenylcarbamide stabilized propellants

Double-base propellants undergo chemical, physical and mechanical changes upon ageing, leading to changes in ballistic performance and presenting explosive hazards. This report studies the variation of chemical and mechanical properties of aged N,N′-dimethyl-N,N′-diphenylcarbamide (methyl centralite) stabilized propellants in order to simulate and evaluate the natural ageing throughout the artificial one. Therefore, a comparative study of stabilizer depletion, plasticizers content, heat of combustion and mechanical properties such as storage modulus, loss modulus and damping of naturally and artificially aged propellants has been carried out by the following techniques: high-performance liquid chromatography (HPLC), thermogravimetric analyzer (TG), calorimeter of combustion and dynamic mechanical analyzer (DMA), respectively. The results obtained show that all properties are closely connected. In addition, the determination of stabilizer depletion, plasticizers evaporation, decrease of heat of combustion and mechanical properties are very useful for a better understanding of the decomposition and ageing behaviour of propellants. The HPLC investigation of stabilizer has shown good stability of the propellants. The results obtained for DMA have shown that some considerable changes of the mechanical and viscoelastic properties of the propellants occurred during ageing. These results confirm the results obtained by TG for the reduction of the nitroglycerine amount and the decrease of the heat of combustion.     

Impact of glycosylation on physico–chemical and biological properties of nitrification inhibitors

The lipophilic 2-mercaptobenzothiazole (MBT), known for its nitrification inhibition properties, was derivatized thanks to direct glycosylation reactions. Similar transformations were also performed starting from 2-mercaptobenzimidazole (MBI), structurally close to MBT. The resulting S-linked mono- or disaccharides derived from d-glucose or l-arabinose, and cellobiose, gentiobiose or lactose, respectively, were subsequently studied as novel nitrification inhibitors without any further formulation or physical processes, except dilution in water. Along with ecotoxicity measurements, inhibition properties of the synthesized water soluble glycoconjugates were studied in a model reactor containing nitrification bacteria. The best results were obtained for the gentiobiosyl derivatives simply dissolved in water.     

Application of potential constants: Molecular chemical potential changes on formation of heteronuclear diatomic molecules—VI

The harmonic and anharmonic potential (force) constants of heteronuclear diatomic molecules, which are usually available from normal coordinate analyses, are applied to problems of determining the molecular chemical potential changes on formation of such molecules. The approach developed here is mainly based on density—functional theory, that is, the respective atomic energies in a molecule are expanded with the numbers of electrons and the nuclear potentials. These expansions are allowable because the ground-state energy for a system of N electrons and given nuclear potential ν(r) is a functional of N and ν(r). To test the reliability of the approach, we have calculated the molecular chemical potentials of alkali halides and other heteronuclear diatomic molecules, and their results have been compared favorably with the data obtained from Sanderson's Principle and the ab initio SCF calculation. We have also estimated apparent chemical hardnesses as well as integral terms including Fukui functions that provide good measures for electron transfers between atoms on molecule formation. Brief discussions on the molecular chemical potential changes are given.