The antioxidant role of vitamin E in polyolefins

Polymers are subject to oxidation throughout their lifecycle. Antioxidants are generally incorporated in polymers to inhibit or minimise oxidative degradation. Hindered phenolic antioxidants are important stabilisers for polyolefins. However, hindered phenols undergo chemical transformations while performing their antioxidant function during processing and fabrication. In addition, antioxidants are subject to loss from polymers during processing, or subsequently in-service. Migration of antioxidants is a major concern in applications involving polymers in direct contact with food and human environment. This concern is compounded by the realisation that very little is known about the nature and the migration behaviour of antioxidant transformation products. In this work, the antioxidant role of the biological antioxidant -tocopherol (Vitamin E) , which is structurally similar to many synthetic hindered phenols, is investigated in low density polyethylene (LDPE) and polypropylene (PP). The melt stabilising effectiveness of -tocopherol (Toc) was found to be very high, higher than that of commercial hindered phenol antioxidants, such as Irganox 1076 (Irg 1076) and Irganox 1010 (Irg 1010), after multiple extrusions, especially at very low concentrations. The high antioxidant activity of Toc was shown to be due, at least in part, to the formation of transformation products during processing. The main products formed are stereoisomers of dimers and trimers, as well as aldehydes and a quinone - the relative concentration of each was shown to depend on the processing severity, the initial antioxidant concentration and oxygen availability. These transformation products are shown to impart better, similar or lower melt stability to the polymer than the parent antioxidant. The nature of the products formed from Toc during processing was compared with those formed during processing of Irg 1076 and Irg 1010 with LDPE and a mechanism for the melt stabilisation of Toc was proposed and compared with the stabilisation mechanisms of the synthetic antioxidants Irg 1076 and Irg 1010.

Compatibilisation and stabilisation of immiscible polymer blends by reactive processing

The main objectives of this research were to develop optimised chemical compositions and reactive processing conditions for grafting a functional monomer maleic anhydride (MA) in polypropylene (PP), ethylene propylene diene monomer (EPDM) and mixtures of PP-EPDM, and to optimise synthetic routes for production of PP/EPDM copolymers for the purpose of compatibilisation of PP/EPDM blends. The MA-functionalisation was achieved using an internal mixer in the presence of low concentrations (less than 0.01 molar ratio) of a free radical initiator. Various methods were used to purify MA-functionalised PP and the grafting yield was determined using either FTIR or titrametry. The grafting yield of MA alone, which due to its low free-radical reactivity towards polymer macroradicals, was accompanied by severe degradation in the case of PP and crosslinking for EPDM. In the case of MA-functionalised PP/EPDM, both degradation and crosslinking occurred though not to a great extent. The use of tri-functional coagents e.g. trimethylopropane triacrylates (TRIS) with MA, led to high improvement of the grafting yield of MA on the polymers. This is almost certainly due to high free-radical activity of TRIS leading to copolymerisation of MA and TRIS which was followed by grafting of the copolymer onto the polymer backbone. In the case of PP, the use of coagent was also found to reduce the polymer degradation. PP/EPDM copolymers with optimum tensile properties were synthesised using a 'one-step' continues reactive processing procedure. This was achieved firstly by functionalisation of a mixture of PP (higher w/w ratio) and EPDM (low w/w ratio) with MA, in the presence of the coagent TRIS and a small concentration of a free radical initiator. This was then followed by an imidisation reaction with the interlinking agent hexamethylene diamine (HEMDA). Small amount of copolymers, up to 5 phr, which were interlinked with up to 15 phr of HEMDA, were sufficient to compatibilise PP/EPDM75/25 blends resulting in excellent tensile properties compared to binary PP/EPDM 75/25 blend. Improvement in blend's compatibility and phases-stabilisation (observed through tensile and SEM analysis) was shown in all cases with significant interphases adhesion improvement between PP and EPDM, and reduction in domain size across the fractured surface indicating efficient distribution of the compatibiliser.

Flow field analysis of some mixing and conveying screw element regions, within a closely intermeshing, co-rotating twin-screw extruder.

Grafting of antioxidants and other modifiers onto polymers by reactive extrusion, has been performed successfully by the Polymer Processing and Performance Group at Aston University. Traditionally the optimum conditions for the grafting process have been established within a Brabender internal mixer. Transfer of this batch process to a continuous processor, such as an extruder, has, typically, been empirical. To have more confidence in the success of direct transfer of the process requires knowledge of, and comparison between, residence times, mixing intensities, shear rates and flow regimes in the internal mixer and in the continuous processor.The continuous processor chosen for the current work in the closely intermeshing, co-rotating twin-screw extruder (CICo-TSE). CICo-TSEs contain screw elements that convey material with a self-wiping action and are widely used for polymer compounding and blending. Of the different mixing modules contained within the CICo-TSE, the trilobal elements, which impose intensive mixing, and the mixing discs, which impose extensive mixing, are of importance when establishing the intensity of mixing. In this thesis, the flow patterns within the various regions of the single-flighted conveying screw elements and within both the trilobal element and mixing disc zones of a Betol BTS40 CICo-TSE, have been modelled using the computational fluid dynamics package Polyflow. A major obstacle encountered when solving the flow problem within all of these sets of elements, arises from both the complex geometry and the time-dependent flow boundaries as the elements rotate about their fixed axes. Simulation of the time dependent boundaries was overcome by selecting a number of sequential 2D and 3D geometries, used to represent partial mixing cycles. The flow fields were simulated using the ideal rheological properties of polypropylene and characterised in terms of velocity vectors, shear stresses generated and a parameter known as the mixing efficiency. The majority of the large 3D simulations were performed on the Cray J90 supercomputer situated at the Rutherford-Appleton laboratories, with pre- and postprocessing operations achieved via a Silicon Graphics Indy workstation. A mechanical model was constructed consisting of various CICo-TSE elements rotating within a transparent outer barrel. A technique has been developed using coloured viscous clays whereby the flow patterns and mixing characteristics within the CICo-TSE may be visualised. In order to test and verify the simulated predictions, the patterns observed within the mechanical model were compared with the flow patterns predicted by the computational model. The flow patterns within the single-flighted conveying screw elements in particular, showed good agreement between the experimental and simulated results.

The synthesis of novel biodegradable polyesters and copolyesters from anhydrosulfites

This thesis was concerned primarily with the synthesis and the ring-opening polymerisation of anhydrosulfites (1,3,2-dioxa-thiolan-4-one-2-oxides), and secondly with the copolymerisation of anhydrosulfites with -caprolactone. The polyesters and copolyesters synthesised are of considerable interest in medical applications and also for use as environmental friendly packaging. A range of anhydrosulfites were prepared according to an established method. Aliphatic anhydrosulfites were obtained with a level of purity satisfactory for polymerisation whereas aromatic anhydrosulfites decomposed during distillation and purification by chromatographic techniques. Aliphatic anhydrosulfites with a substituent, such as methyl, isopropyl, n-butyl and isobutyl were studied by NMR spectroscopy. Analysis of these spectra revealed that the five-membered anhydrosulfite ring was puckered and that when the substituent was bulky, rotations about the alkyl chains were restricted. A wide range of anionic initiators may be used to initiate anhydrosulfites. Lithium alkyls turned out to be more successful than alkali metal alkoxides and amides. The molecular weights were found to depend on the basicity of the initiator, the monomer-to-initiator ratio, the nature of the solvent and the polymerisation temperature. The molecular weight M0 of poly(L-lactic acid) ranged from (0.5 to 6)x104. Highly crystalline and purely isotactic poly(lactic acid) was synthesised from L-lactic acid anhydrosulfite (L-LAAS) whereas DL-LAAS led to an amorphous polymer with randomly distributed D-and L-lactic units. This indicated that this polymerisation was not stereoselective. However, the bulkiness of the substituent in the anhydrosulfites molecule was found to influence the stereoselectivity of the polymerisation, thus polyesters with isobutyl or n-butyl pendant group were preferentially isotactic. Block-copolymers of ε-caprolactone and several anhydrosulfites were successfully produced. Block-copolymers of LAAS with ε-caprolactone were also synthesised, but the incorporation of caprolactone units was rather small. In contrast, random copolymerisation of LAAS and ε-caprolactone led to polymers with blocky structures similar to those obtained in the block-copolymerisation of LAAS with  ε-caprolactone.

Compatibilisation of heterogeneous polymer blends by reactive processing

Functionalisation of polystyrene, PS, and ethylene-co-propylene-co-cyclopentadiene terpolymer, EPDM, with acrylic acid, AA, in a melt reactive processing procedure, in the presence of peroxide, trigonox 101, and coagents, Divinyl benzene, DVB (for PS), and trimethylolpropane triacrylate, TRIS (for EPDM), were successfully carried out. The level of grafting of the AA, as determined by infrared analysis, was significantly enhanced by the coagents. The grafting reaction of AA takes place simultaneously with homopolymerisation of the monomers, melt degradation and crosslinking reactions of the polymers. The extent of these competing reactions were inferred from measurements of melt flow index and insoluble gel content. Through a judicious use of both the peroxide and the coagent, particularly TRIS, unwanted side reactions were minimized. Five different processing methods were investigated for both functionalisation experiments; the direct addition of the pre-mixed polymer with peroxide and reactive modifiers was found to give optimum condition for grafting. The functionalised PS, F-PS, and EPDM, F-EPD, and maleinised polypropylene carrying a potential antioxidant, N-(4-anilinophenyl maleimide), F-PP were melt blended in binary mixtures of F-PS/F-EPD and F-PP/F-EPD in the presence (or absence) of organic diamines which act as an interlinking agent, e.g, Ethylene Diamine, EDA, and Hexamethylene Diamine, HEMDA. The presence of an interlinking agent, particularly HEMDA shows significant enhancement in the mechanical properties of the blend, suggesting that the copolymer formed has acted as compatibiliser to the otherwise incompatible polymer pairs. The functionalised and amidised blends, F and A-PSIEPDM (SPOI) and F and A-PPIEPDM (SPD2) were subsequently used as compatibiliser concentrates in the corresponding PSIEPDM and PPIEPDM blends containing various weight propotion of the homopolymers. The SPD1 caused general decreased in tensile strength, albeit increased in drop impact strength particularly in blend containing high PS content (80%). The SPD2 was particularly effective in enhancing impact strength in blends containing low weight ratio of PP (<70%). The SPD2 was also a good thermal antioxidant albeit less effective than commercial antioxidant. In all blends the evidence of compatibility was examined by scanning electron microscopy.

Dipole moments and Kerr effect of poly(n-vinylcarbazole) and its complexes with trinitrofluorenone

N-vinylcarbazole was polymerised using the free radical catalyst (azo-bisisobutyronitrile) and cationic catalysts (boron-trifluoride etherate and aluminium chloride). The polymers produced were characterised by molecular weight measurements and powder x-ray diffraction. The tacticity of the polymer samples was determined using proton and carbon-13 nuclear magnetic resonance spectroscopy. Measurements of their static dielectric permittivity and electro-optical birefringence (Kerr effect) in solution in 1,4-dioxane were carried out over a range of temperatures. The magnitudes of the dipole moments and Kerr constants were found to vary with changes in the tacticity of poly(N-vinylcarbazole). The results of these measurements support the view that the stereostructure of poly(N-vinylcarbazole) is sensitive to the mechanism of polymerisation. These results, together with proton and carbon-13 N.M.R. data, are discussed in terms of the possible conformations of the polymer chains and the relative orientation of the bulky carbazole side groups. The dielectric and molecular Kerr effect studies have also been carried out on complexes formed between 2,4,7-trinitro-9-fluorenone (TNF) and different stereoregular forms of poly(N-vinylcarbazole) in solution in 1,4-dioxane. The differences in the molar Kerr constants between pure (uncomplexed) and complexed poly(N-vinylcarbazole) samples were attributed to changes in optical anisotropy and dipole moments. A molecular modelling computer program Desktop Molecular Modeller was used to examine the 3/1 helical isotactic and 2/1 helical syndiotactic forms of poly(N-vinylcarbazole). These models were used to calculate the pitch distances of helices and the results were interpreted in terms of van der Waal's radii on TNF. This study indicated that the pitch distance in 3/1 isotactic helices was large enough to accommodate the bulky TNF molecules to form sandwich type charge transfer complexes whereas the pitch distance in syndiotactic poly(N-vinylcarbazole) was smaller and would not allow a similar type of complex formation.

The mechanochemical modification of polyolefins using reactive modifier systems

The principal objective of this work was to improve the mechanical properties of glass fibre reinforced polypropylene (PP) composites by the mechanochemical modification of the PP. The modification of the PP was carried out by reactive processing of the PP with a modifier in a Buss Ko-Kneader. Two main types of modifier were evaluated one type based on N-substituted maleimides the others based on 2-allylamino-4,6-dichloro-1,3,5-triazine (ACCT). The modification of the PP was carried out in two stages. Firstly the PP was reactively processed with the modifier and a free radical initiator. The objective of this stage was to bind the modifier to the PP. In the second stage the modified PP was reactively processed with the glass fibre. The objective in this stage was to form a chemical bond between the bound modifier and the silane coupling agent on the surface of the glass. Two silane coupling agents were evaluated these had a aliphatic chloro group and an aliphatic amino group respectively available for reaction with the modifier. The modifiers synthesised for this work had two main functional groups. The first was a double bond for free radical addition to the PP. The second was an organic group chosen for its potential reactivity to the silane coupling agent. A preliminary investigation was carried out using maleic anhydride (MA) as the modifier, this is reactive to the amino silane coupled glass. Studies of a commercially available system were also carried out for comparison purposes. During the work it was found that the amino silane coupled glass fibres produced, without any modification being made to the PP, mechanical properties comparable to the commercial system. Further any modification added to the amino silane system failed to improve the mechanical performance and in some cases acted in the opposite fashion. This failure was evident even when a chemical bond between glass fibre and PP could be shown. In the case of the chloro silane coupled glass fibres the mechanical properties of the composite without modification were poorer than those of the commercial system. It was found that the mechanical properties of these systems could be enhanced by the modifiers, however, no system tested significantly out performed the commercial system. Of the two modifier systems tested those based on the n-substituted maleimides were more successful at enhancing mechanical properties than those based on ACCT. This was attributed to the Poor chemical binding of the ACCT based modifiers to the PP. During the work it was found that several of the modifiers improved the properties of the PP when no glass fibres were present, particularly the % elongation and impact strength. It is possible that these modifiers could be used to improve the impact performance of PP, this may be of particular interest in recycling. These modifiers have only been tested for improving the properties of glass fibre composites. The N-substituted maleimide based modifiers could be used as compatibleisers for alloys of PP and other polymers. These could function by the formation of the bond with PP via the double bond whilst the group attached to the nitrogen atom could react with the alloying polymer.

Reactive processing of polyolefins using antioxidant systems

Various monoacrylic compounds containing a hindered phenol function (e.g.3,5-di-tert.-butyl-4-hydroxy benzyl alcohol, DBBA and vinyl-3-[3',5'-di-tert.-butyl-4-hydroxy phenyl] propionate, VDBP), and a benzophenone function (2-hydroxy-4-[beta hydroxy ethoxy] benzophenone, HAEB) were synthesised and used as reactive antioxidants (AO's) for polypropylene (PP). These compounds were reacted with PP melt in the presence of low concentration of a free radical generator such a peroxide (reactive processing) to produce bound-antioxidant concentrates. The binding reaction of these AO's onto PP was found to be low and this was shown to be mainly due to competing reactions such as homopolymerisation of the antioxidant. At high concentrations of peroxide, higher binding efficiency resulted, but, this was accompanied by melt degradation of the polymer. In a special reactive processing procedure, a di- or a trifunctional reactant (referred to as coagent), e.g.tri-methylol propane tri-acrylate, Tris, and Divinyl benzene, DVB, were used with the antioxidant and this has led to an enhanced efficiency of the grating reaction of antioxidants on the polymer in the melt. The evidence suggests that this is due to copolymerisation of the antioxidants with the coagent as well as grafting of the copolymers onto the polymer backbone. Although the 'bound' AO's containing a UV stabilising function showed lower overall stabilisation effect than the unbound analogues before extraction, they were still much more effective when subjected to exhaustive solvent extraction. Furthermore, a very effective synergistic stabilising activity when two reactive AO's containing thermal and UV stabilising functions e.g. DBBA and HAEB, were reactively processed with PP in the presence of a coagent. The stabilising effectiveness of such a synergist was much higher than that of the unbound analogues both before and after extraction. Analysis using the GPC technique of concentrates containing bound-DBBA processed in the presence of Tris coagent showed higher molecular weight (Mn), compared to that of a polymer processed without the coagent, but was still lower than that of the control processed PP with no additives. This indicates that Tris coagent may inhibit further melt degradation of the polymer. Model reactions of DBBA in liquid hydrocarbon (decalin) and analysis of the products using FTIR and NMR spectroscopy showed the formation of grafted DBBA onto decalin molecules as well as homopolymerisation of the AO. In the presence of Tris coagent, copolymerisation of DBBA with the Tris inevitably occured; which was followed by grafting of the copolymer onto the decalin, FTIR and NMR results of the polymer concentrates containing bound-DBBA processed with and without Tris, showed similar behaviour as the above model reactions. This evidence supports the effect of Tris in enhancing the efficiency of the reaction of DBBA in the polymer melt. Reactive procesing of HAEB in polymer melts exhibited crosslinking formation In the early stages of the reaction, however, in the final stage, the crosslinked structure was 'broken down' or rearranged to give an almost gel free polymer with high antioxidant binding efficiency.

Time controlled photo-oxidation of polyolefins by polymer bound additives

A variety of iron compounds containing vinyl or thiol functional groups (used as photoactivators) have been synthesised and some of these were successfully bound to both polyethylene and polypropylene backbones during processing in the presence of peroxide and interlinking agent. Concentrates (masterbatches) of the photoactivators in PP and PE were prepared and the pro-oxidant effect of the diluted masterbatches in absence and presence of an antioxidant was evaluated. An antioxidant photoactivator (FeDNC ) was found to sensitise the photoactivity of pro-oxidants (Metone A / Metone M) whereas an antioxidant (ZnDNC) was found to stabilise the polymer (PP and PE) containing both of these combinations. It was observed that the lower concentration of FeDNC sensitises the stability of the polymer containing very small concentration of NiDNC whereas higher concentration of FeDNC stabilises the polymer (LDPE) containing same amount of NiDNC compared to FeDNC alone. The photostability of unstabilised PP containing FeAc could be varied by varying the concentration of ZnDEC. Both the induction period and the UV - life time of the polymer increased by increasing concentration of ZnDEC. It is suggested that ligand exchange reaction may take place between FeAc and ZnDNC. A polymer bound UV stabiliser (HAEB) and a thermal stabiliser (DBBA) were used with a non extractable photoactivator (FeAc) in PP. Small concentrations of the stabilisers (HAEB and DBBA) in combination with the photoactivator (FeAc) sensitise the polymer. The antioxidant present in commercial polymer (LDPE and PP) was found to be of a hindered phenol type, which was found to antagonise with ZnDNC when used in combination with the photoactivators.

Functionalisation of polymers: reactive processing, structure and performance characteristics

The main aim of this work was to study the effect of two comonomers, trimethylolpropane trimethacrylate (TRIS) and divinylbenzene (DVB) on the nature and efficiency of grafting of two different monomers, glycidyl methacrylate (GMA) and maleic anhydride (MA) on polypropylene (P) and on natural rubber (NR) using reactive processing methods. Four different peroxides, benzoyl peroxide (BPO), dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis-(tert-butyl peroxy) hexane (t-101), and 1,1-di(tert-butylperoxy)-3,3,5-trimethyl cyclohexene (T-29B90) were examined as free radical initiators. An appropriate methodology was established and chemical composition and reactive processing parameters were examined and optimised. It was found that in the absence of the coagents DVB and TRIS, the grafting degree of GMA and MA increased with increasing peroxide concentration, but the level of grafting was low and the homopolymerisaton of GMA and the crosslinking of NR or chain scission of PP were identified as the main side reactions that competed with the desired grafting reaction in the polymers. At high concentrations of the peroxide T-101 (>0.02 mr) cross linking of NR and chain scission of PP became dominant and unacceptable. An attempt to add a reactive coagent, e.g. TRIS during grafting of GMA on natural rubber resulted in excessive crosslinking because of the very high reactivity of this comonomer with the C=C of the rubber. Therefore, the use of any multifunctional and highly reactive coagent such as TRIS, could not be applied in the grafting of GAM onto natural rubber. In the case of PP, however, the use of TRIS and DVB was shown to greatly enhance the grafting degree and reduce the chain scission with very little extent of monomer homopolymerisation taking place. The results showed that the grafting degree was increased with increasing GMA and MA concentrations. It was also found that T-101 was a suitable peroxide to initiate the grafting reaction of these monomers on NR and PP and the optimum temperature for this peroxide was =160°C. A very preliminary work was also conducted on the use of the functionalised-PP (f-PP) in the absence and presence of the two comonomers (f-PP-DVB or f-PP-TRIS) for the purpose of compatibilising PP-PBT blends through reactive blending. Examination of the morphology of the blends suggested that an effective compatibilisation has been achieved when using f-PP-DVB and f-PP-TRIS, however more work is required in this area.

Surface coating deterioration studies

This project is concerned with the deterioration of surface coatings as a result of weathering and exposure to a pollutant gas (in this case nitric oxide). Poly(vinyl chloride) (PVC) plastisol surface coatings have been exposed to natural and artificial weathering and a comparison of the effects of these two types of weathering has been made by use of various analytical techniques. These techniques have each been assessed as to their value in providing information regarding changes taking place in the coatings during ageing, and include, goniophotometry, micro-penetrometry, surface energy measurements, weight loss measurements, thermal analysis and scanning electron microscopy. The results of each of these studies have then been combined to show the changes undergone by PVC plastisol surface coatings during ageing and to show the effects which additives to the coatings have on their behaviour and in particular the effects of plasticiser, pigment and uv and thermal stabilisers. Finally a preliminary study of the interaction between five commercial polymers and nitric oxide has been carried out, the polymers being polypropylene, cellulose acetate butyrate, polystyrene, polyethylene terephthalate and polycarbonate. Each of the samples was examined using infra-red spectroscopy in the transmission mode.

The mechanisms of melt stabilisation of polyolefins

The effects of melt stabilisers on the oxidative degradation of polyolefins (polypropylene, low density polyethylene) have been studied under a variety of processing conditions . The changes in the both chemical and physical properties of unstabilised polymers occurring during processing were found to be strongly dependent on the amount of oxygen present in the mixer. 2 ,6 ,3' ,5' -tetra-tert-butyl-4'-phenoxy-4-methylene-2, 5-cyclohexadiene-1- one (galvinoxyl), iodine, nitroxyl radicals and cupric stearate were found to be very efficient melt stabilisers particularly when processed in a restricted amount of air. The mechanisms of their melt stabilising action have been investigated and a common cyclical regenerative mechanism involving both chain-breaking electron acceptor (CB-A) and chain-breaking electron donor (CB-D) antioxidant activity was found to be involved in each case. 2,6,3',5'-tetra-tert-butyl-4'-hydroxy phenyl-4-rrethylene-2,5-cyclohexadiene- 1-one (hydrogalvinoxy1), 4-hydroxy, 2,2,6, 6-tetra methyl-N-hydroxy piperidine and hydrogen iodide were formed together with olefinic unsaturation in the substrates during the melt processing of the polymers containing galvinoxyl, 4-hydroxy, 2,2,6, 6-tetra methyl piperidine oxyl and iodine respectively. No bonding of the melt stabilisers to the polymers was found to occur. Cupric stearate was found to undergo a similar redox reaction during its action as a melt stabiliser with the formation of unsaturation in the polymer. Evidence for the above processes is presented. The behaviours of melt stabilisers in the subsequent thermal and photooxidation of polyolefins have also been studied. Galvinoxyl which is very effective under both mild and severe processing canditions has been found to be an effective antioxidant during thermal oxidation (oven ageing) and it is also moderately good. as a photo-stabiliser. Iodine and cupric stearate acted efficiently during melt stabilisation of polymers, however they were both ineffective as thermo-oxidative antioxidants and UV stabilisers. Although the melt stabilisation effectiveness of stable nitroxyl radicals (e.g. 4-hydroxy, 2,2,6,6-tetra methyl piperidineoxyl and Bis- (2,2,6 ,6-tetra methyl-4- piperidinyl-N-oxyl) sebacate) is not as high as that of galvinoxyl during processing particularly in excess of air, they have been found to be much more efficient as UV stabilisers for polyolefins. The reasons for this are discussed.

The behaviour of antioxidants in polyolefins under conditions of U.V. exposure

The effects of antioxidants and stabilizers on the oxidative degradation of polyolefins (low density polyethylene [LDPE] and polypropylene [PPJ have been studied after subjecting to prior high temperature processing treatments. The changes in the both chemical and physical properties of unstabilized polymers occurring during processing were found to be strongly dependent on the amount of oxygen present in the mixer. Subsequent thermal and photo-oxidation showed very similar characteristics and the chromophore primarily responsible for:both thermo and photooxidative degradation of unstabilized polymers was found to be hydroperoxide formed during processing. Removal of hydroperoxide by heat treatment in an inert atmosphere although increasing ketonic carbonyl concentration, markedly decreased the rate of photo-oxidation, introducing an induction period similar to that of an unprocessed sample. It was concluded that hydroperoxides are the most important initiators in normally processed polymers during the early stages of photo-oxidation. Antioxidants such as metal dithiocarbamates which act by destroying peroxides into non-radica1 products were found to be efficient melt stabilizers for polyolefins and effective UV stabilizers during the initial photo-oxidation stage, whilst a phenolic antioxidant, n-octadecyl-3-(3',5'-di-terbutyl 4'hydroxypheny1) propionate (Irganox 1076) retarded photo-oxidation rate in the later stages. A typical 'UV absorber' 2-hydroxy-4-octyloxy-benzophenone (HOBP) has a minor thermal antioxidant action but retarded photo-oxidation at all stages. A substituated piperidine derivative, Bis [2.2.6.6-tetramethylpiperidlnyl-4] sebacate (Tinuvin 770) behaved as an pro-oxidant during thermal oxidation of polyolefins but was an effective stabilizer against UV light. The UV absorber, HOBP synergised effectively with both peroxide decomposing antioxidants (metal dithiocarbamates) and a chain-breaking antioxidant (Irganox 1076) during photo-oxidation of the poymers studed whereas the combined effect was additive during thermal oxidation. By contrast, the peroxide decornposers and chain-breaking antioxidant (Irganox 1076) which were effective synergists during thermal oxidation of LDPE· were antagonistic during photo-oxidation. The mechanisms of these processes are discussed.

A techno-economic study of the recycling of mixed plastics to useful products

The techno-economic implications of recycling the components of mixed plastics waste have been studied in a two-part investigation: (a) An economic survey of the prospects for plastics recycling, the plastics waste arisings from retailing, building, automotive, light engineering and chemical industries have been surveyed by mans of questionnaires and interviews. This was partially successful and indicated that very considerable quantities of relatively clean plastics packaging was available in major department chains and household stores. The possibility of devising collection systems for such sources, which do not lead to any extra cost, have been suggested. However, the household collection of plastics waste has been found to be uneconomic due to high cost of collection, transportation and lack of markets for the end products. (b) In a technical study of blends of PE/PP and PE/PS which are found in admixture in waste plastics, it has been shown that they exhibit poor mechanical properties due to incompatibility. Consequently reprocessing of such unsegregated blends results in products of little technological value. The inclusion of some commercial block and graft copolymers which behave as solid phase dispersants (SPES) increase the toughness of the blends (e.g. EPDM in PE/PP blend and SBS in PE/PS blend). Also, EPDM is found to be very effective for improving the toughness of single component polypropylene. However, the improved Technical properties of such blends have been accompanied by a fast rate of photo-oxidation and loss of toughness due to the presence of unsaturation in SPD's. The change in mechanical properties occurring during oven ageing and ultra-violet light accelerated weathering of these binary and ternary blends was followed by a viscoelastonetric technique (Rheovibron) over 9,, wide range of temperatures, impact resistance at room temperature (20-41'G) and changes in functional groups (i.e. carbonyl and trans-1,4-polybutadiene). Also the heat and light stability of single and mixed plastics to which thiol antioxidants were bound to SPE1 segment have been studied and compared with conventional antioxidants. The long-term performance of the mixed plastics containing SPE1 have been improved significantly by the use of conventional and bound antioxidants. It is concluded that an estimated amount of 30000 tonnes/year of plastics waste is available from department chains and household stores which can be converted to useful end products. This justifies pilot-experiments in collaboration with supermarkets, recyclers and converters by use of low cost SPD's and additives designed to make the materials more compatible.

Fundamental mechanisms affecting service performance of electroplated plastics

Ten grades of ABS and four grades of polypropylene have been plated with various copper + nickel + chromium coatings and subjected to a variety of tests. In corrosion studies the pre-electroplating sequence and plastics type have been shown to influence performance. One ABS pre-electroplating sequence was consistently associated with better corrosion performance; two factors were responsible for this, namely the more severe nature of the etch and the relatively more noble electroless nickel. Statistical analysis has indicated that order of severity of the corrosion tests was static-mobile-CASS, the latter being the least severe. In mechanical tests two properties of ABS and polypropJylene, ductility and impact strength, have been shown to be adversely affected when electrodeposited layers were applied. The cause of this is due to a complex of factors, the most important of which is the notch sensitivity of the plastics. Peel adhesion has been studied on flat panels and also on ones which had a ridge and a valley moulded into one face. High adhesion peaks occurred on the flat face at regions associated with the ridge and valley. The local moulding conditions induced by the features were responsible for this phenonemon. In the main programme the thermal cycling test was shown to be more likely than the peel adhesion test to give an indication of the service performance of electroplated plastics.