A shape memory polymer (SMP) is stimuli-responsive with the fantastic capacity to “memorize” a temporary shape under certain conditions and to recover to its permanent shape upon exposure to certain external stimulus (e.g. heat, light, electromagnetic field). In the past few decades, various SMPs have been investigated and applied in the area of aerospace, biomedicine, and textiles, etc. Recently, a special type of SMP called a ‘two-way reversible shape memory polymer’ or ‘reversible shape memory polymer’ (RSMP) capable of transitioning between two temporary shapes without the need for reprogramming after each change has attracted the attention of many researchers. In this class of polymer, the semicrystalline RSMP was studied considerably due to the various chain structures produced by relatively simple synthesis routes. The crystallization-induced elongation (CIE) and melting-induced contraction (MIC) of the oriented crystal domains has been theorized as the main mechanism of semicrystalline RSMP. However, most RSMPs are predominantly thermosets, which implies significant drawbacks regarding reprocessing and recycling. This thesis focuses on the development of RSMP based on polyolefin materials, especially novel high-performance polyolefin elastomers, due to the advantages of high crystallizability, varying chain structures, tunable and broad melting transitions, and low cost. The thesis starts off by demonstrating the reversible shape memory effect (RSME) of the thermoplastic ethylene/1-octene diblock copolymer, which contains the ethylene-rich hard segments and the 1-octene-rich soft segments. The delicately designed chain structure exhibited a broad melting transition and strong physical crosslinks, which contributed to the resulting RSME and the CIE/MIC effect at load-free conditions. Furthermore, the commercially available polyolefin elastomer blends demonstrated the RSME. The utilization of commercial products and simple processing method to achieve a thermoplastic RSMP offers easy production in large scale and low costs. The second part of the thesis developed a polyolefin-based RSMP with reconfigurable network by introducing a transesterification catalyst into a crosslinked poly(ethylene-co-vinyl acetate). The network reconfiguration achieved a dynamic covalent polymer network by breaking the ester bonds and reconnecting. The third part of the thesis explored a new RSMP foam material developed by utilizing polyolefins. The polyolefin elastomers of differing compositions were blended and foamed to fabricate the porous structure. The RSME in a load-free condition was then demonstrated successfully. This thesis represents significant progress in the development of polyolefin-based RSMPs, outlining new structural design, processability improvements, and potential applications. / Thesis / Doctor of Philosophy (PhD) / Shape memory polymer (SMP) is stimuli-responsive capable of “memorizing” a temporary shape and yet recovering to its permanent shape upon a certain external trigger. SMPs are widely studied and applied in the areas of aerospace, biomedicine, textile, etc. On the other hand, a reversible shape memory polymer (RSMP) is a new type of SMP that can shift back and forth between two different temporary shapes without the need of reprogramming between transitions, and has been applied in soft actuators, microrobotics, and artificial muscles. In this thesis, unique polyolefin-based RSMP were developed with good reprocessability and shown in new application scenarios. Firstly, a thermoplastic semicrystalline polymer was demonstrated to exhibit the reversible shape memory effect (RSME) by using a lab-designed ethylene/1-octene diblock copolymer and commercial polyolefin elastomer blends. Subsequently, the reprocessability of a crosslinked poly(ethylene-co-vinyl acetate) (PEVA) RSMP was improved by introducing a dynamic covalent polymer network. Finally, transitional changes between shapes was amplified by developing a RSMP foam by utilizing polyolefin elastomer blends. This thesis represents significant progress in the study of polyolefin-based RSMPs.

This research provides a new insight on various properties, such as rheological, mechanical, and flame-retarding properties, as well as the foaming behaviors of wood flour /plastic composites (WPCs) through the addition of a small amount of nanosized clay particles. Although WPCs have replaced natural wood in many applications, their industrial usage has been limited because of their weak modulus, low impact strength, low screwing-ability/nailing-ability, high density compared to natural wood, as well as their flammability compared to plastics. In this context, the incorporation of nanoclay and foam structure into WPC has been studied to dramatically alleviate these drawbacks. The melt blending method was used to prepare different types of clay-filled wood flour composites such as intercalated and exfoliated clay nanocomposites. The effects of key processing variables such as the mixing time, mixing temperature and screw speed on clay dispersion were investigated from the thermodynamic and kinetic point of view. Their nanostructure was determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Accordingly, effective strategies for controlling intercalation and exfoliation of polyolefin/clay nanocomposites were proposed and evaluated. Wood flour composites with high levels of clay dispersion were synthesized successfully using a general new route (i.e., maleated-polyolefin-based clay masterbatch and dilution). The effects of nanoclay particles on the rheological, thermal, and mechanical properties were identified. In addition, it was demonstrated that a small amount of well-dispersed nanoclay in WPC significantly improved flame retardancy of WPCs. The mechanism of improved flame-retarding effects on nanoparticles was elucidated as well. The relationship between the clay dispersion and the material properties were also clarified. Furthermore, the foaming behaviors of HDPE-based and PP-based wood flour/nanoclay composites were investigated using N2 as the blowing agent in an extrusion process. The cell nucleation and growth behaviors of wood flour/polyolefin/clay composite foams were elucidated while varying the temperature, pressure, wood flour content, clay content and dispersion degrees.

This research provides a new insight on various properties, such as rheological, mechanical, and flame-retarding properties, as well as the foaming behaviors of wood flour /plastic composites (WPCs) through the addition of a small amount of nanosized clay particles. Although WPCs have replaced natural wood in many applications, their industrial usage has been limited because of their weak modulus, low impact strength, low screwing-ability/nailing-ability, high density compared to natural wood, as well as their flammability compared to plastics. In this context, the incorporation of nanoclay and foam structure into WPC has been studied to dramatically alleviate these drawbacks. The melt blending method was used to prepare different types of clay-filled wood flour composites such as intercalated and exfoliated clay nanocomposites. The effects of key processing variables such as the mixing time, mixing temperature and screw speed on clay dispersion were investigated from the thermodynamic and kinetic point of view. Their nanostructure was determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Accordingly, effective strategies for controlling intercalation and exfoliation of polyolefin/clay nanocomposites were proposed and evaluated. Wood flour composites with high levels of clay dispersion were synthesized successfully using a general new route (i.e., maleated-polyolefin-based clay masterbatch and dilution). The effects of nanoclay particles on the rheological, thermal, and mechanical properties were identified. In addition, it was demonstrated that a small amount of well-dispersed nanoclay in WPC significantly improved flame retardancy of WPCs. The mechanism of improved flame-retarding effects on nanoparticles was elucidated as well. The relationship between the clay dispersion and the material properties were also clarified. Furthermore, the foaming behaviors of HDPE-based and PP-based wood flour/nanoclay composites were investigated using N2 as the blowing agent in an extrusion process. The cell nucleation and growth behaviors of wood flour/polyolefin/clay composite foams were elucidated while varying the temperature, pressure, wood flour content, clay content and dispersion degrees.

Polyolefins are the most important commodity polymers today. Their end use properties polymers depend primarily on their molecular weight (MWD) and chemical composition (CCD) distributions. Several characterization techniques are used to analyze the microstructures of the polyolefins. High-temperature gel permeation chromatography (GPC) is the most widely used technique for MWD determination. Temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) are routinely used for CCD measurement. There have been significant improvements over the last few years on CCD characterization techniques for polyolefins with the introduction of crystallization elution fractionation (CEF) and high-temperature thermal gradient interaction chromatography (HT-TGIC). The main objective of this thesis was to conduct systematic studies on HT-TGIC and CEF to provide a better understanding on the separation mechanism of these new techniques and to find out operational conditions that enhance the resolution of the measured CCDs. The effects of cooling rate, adsorption/desorption temperature range, heating rate and sample size on HT-TGIC fractionation were investigated using polyethylene and ethylene/1-octene copolymers made with metallocene catalyst. It was found out that HT-TGIC was relatively insensitive to the cooling rate within the range investigated in this study. However, the obtained profiles depended strongly on the heating rate applied during the desorption cycle. Chromatograms measured under faster heating rates were broader and had lower resolutions, supposedly due to co-desorption effects. Analysis of polyolefin blends by HT-TGIC showed that sample volume was a very important parameter affecting peak separation of the blend components; reducing the volume of the injected sample can be used to minimize the degree of co-adsorption and co-desorption effects. The effect of solvent type on HT-TGIC analysis was investigated using o-dichlorobenzene (ODCB), 1,2,4-trichlorobenzene (TCB), and chloronaphthalene (CN). Polyolefin blends were analyzed using these solvents and the best resolution was obtained iv when ODCB was used as the mobile phase. The profiles obtained using TCB and CN were similar and both were strongly affected by the co-adsorption and co-desorption phenomena. HT-TGIC profiles of ethylene homopolymers and ethylene/1-octene copolymers were also compared with the equivalent CEF profiles. Interestingly, it was found out that the differences between the profiles measured by these techniques decreased as the comonomer content increased, with CEF systematically measuring sharper profiles for samples with low 1-olefin comonomer content. A new method was also developed to quantify the degree of co-crystallization of polyolefin blends analyzed by CEF and was used to quantify operating conditions that influenced co-crystallization. The results showed that co-crystallization can be minimized using slower cooling rates, but heating rates play a less important role. A detailed study on the effect of CEF operating conditions on CCD resolution was also conducted using industrial LLDPE resins that have broad MWDs and CCDs. Cooling rate and solvent flow rate during the cooling cycle significantly affect the degree of co-crystallization of CEF profiles. However, varying the heating rate does not have a marked impact on these separations. The CEF profiles of these resins were compared with the equivalent HT-TGIC profiles, showing that CEF provided better peak separation than HT-TGIC. Finally, a new mathematical model was developed to simultaneously deconvolute the MWD and CCD of polyolefins made with multiple site-type catalysts such as Ziegler-Natta catalysts. The model was applied to several industrial linear low-density polyethylene (LLDPE) resins to estimate the minimum number of active site types, the number average molecular weight, the average comonomer mole fraction, and the mass fraction of soluble and non-soluble polymer made on each site type.

Solvent-free peroxide-initiated polymer modifications are widely used to improve the physical and/or chemical properties of commodity plastics and elastomers. Although the reactions that underlie polymer grafting are known, our understanding of H-atom transfer reactions in this context is incomplete. Fundamental questions remain unanswered, such as the difference in reactivity between different polymers (polyethylene versus polypropylene and polyisobutylene) and differences in the regiochemical outcomes of grafting reactions upon them. Herein, experimental data pertaining to the H-atom transfers involved in polyolefin graft modifications were obtained to improve our fundamental understanding of these reactions by using radical-trapping techniques and quantum chemical calculations. In this project, experimental measurements of the efficiency of H-atom abstraction by t-butoxyl radicals from polyolefins, and suitable model compounds such as pentane, 2,4-dimethylpentane and 2,2,4,4-tetramethylpentane were determined. Insight is gained from alkyl-trapping experiments to quantify the relative reactivities of the primary, secondary and tertiary positions of the model compounds. Experimental data were compared to quantum chemical calculations, which revealed that entropic effects dictate the regioselectivity and preclude abstraction at the secondary position in favour of the less enthalpically-favourable primary abstraction site. MP2 and CBS-QB3 level calculations were able to reproduce experimental trends in model compound reactivity, while the highly common B3LYP density functional, used in other investigations on the subject, could not. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-10-20 16:48:38.083

Polyolefins are the most important commodity polymers today. Their end use properties polymers depend primarily on their molecular weight (MWD) and chemical composition (CCD) distributions. Several characterization techniques are used to analyze the microstructures of the polyolefins. High-temperature gel permeation chromatography (GPC) is the most widely used technique for MWD determination. Temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) are routinely used for CCD measurement. There have been significant improvements over the last few years on CCD characterization techniques for polyolefins with the introduction of crystallization elution fractionation (CEF) and high-temperature thermal gradient interaction chromatography (HT-TGIC). The main objective of this thesis was to conduct systematic studies on HT-TGIC and CEF to provide a better understanding on the separation mechanism of these new techniques and to find out operational conditions that enhance the resolution of the measured CCDs. The effects of cooling rate, adsorption/desorption temperature range, heating rate and sample size on HT-TGIC fractionation were investigated using polyethylene and ethylene/1-octene copolymers made with metallocene catalyst. It was found out that HT-TGIC was relatively insensitive to the cooling rate within the range investigated in this study. However, the obtained profiles depended strongly on the heating rate applied during the desorption cycle. Chromatograms measured under faster heating rates were broader and had lower resolutions, supposedly due to co-desorption effects. Analysis of polyolefin blends by HT-TGIC showed that sample volume was a very important parameter affecting peak separation of the blend components; reducing the volume of the injected sample can be used to minimize the degree of co-adsorption and co-desorption effects. The effect of solvent type on HT-TGIC analysis was investigated using o-dichlorobenzene (ODCB), 1,2,4-trichlorobenzene (TCB), and chloronaphthalene (CN). Polyolefin blends were analyzed using these solvents and the best resolution was obtained iv when ODCB was used as the mobile phase. The profiles obtained using TCB and CN were similar and both were strongly affected by the co-adsorption and co-desorption phenomena. HT-TGIC profiles of ethylene homopolymers and ethylene/1-octene copolymers were also compared with the equivalent CEF profiles. Interestingly, it was found out that the differences between the profiles measured by these techniques decreased as the comonomer content increased, with CEF systematically measuring sharper profiles for samples with low 1-olefin comonomer content. A new method was also developed to quantify the degree of co-crystallization of polyolefin blends analyzed by CEF and was used to quantify operating conditions that influenced co-crystallization. The results showed that co-crystallization can be minimized using slower cooling rates, but heating rates play a less important role. A detailed study on the effect of CEF operating conditions on CCD resolution was also conducted using industrial LLDPE resins that have broad MWDs and CCDs. Cooling rate and solvent flow rate during the cooling cycle significantly affect the degree of co-crystallization of CEF profiles. However, varying the heating rate does not have a marked impact on these separations. The CEF profiles of these resins were compared with the equivalent HT-TGIC profiles, showing that CEF provided better peak separation than HT-TGIC. Finally, a new mathematical model was developed to simultaneously deconvolute the MWD and CCD of polyolefins made with multiple site-type catalysts such as Ziegler-Natta catalysts. The model was applied to several industrial linear low-density polyethylene (LLDPE) resins to estimate the minimum number of active site types, the number average molecular weight, the average comonomer mole fraction, and the mass fraction of soluble and non-soluble polymer made on each site type.

This study examined the concept of using a reactive blending process to develop new polymeric additive systems. The objective was to investigate the potential of using a reactive processing technique as a means to bond additives to functional polymers, to create “in situ” bonds between functional groups present on the polymers and those present on the additives. The work is reported in two parts; the first part studied the bonding of colorants to functional polyolefins and the second part investigated the bonding of UV stabilisers to functional polyolefins. The research was completed with the long term objective that the approach should offer alternative additives to conventional non-bonded systems for use in polypropylene. An ethylene ionomer was utilised for the bonding of dyes, this was chosen for its optical clarity and chemical functionality. Polyethylene methacrylic acid (EMAA) ionomers and methine dyes were blended in the melt phase using an internal mixer to produce bright intrinsically colored polymers. Fourier transform infrared spectroscopy (FTIR) in transmission mode was used to assess the bonding of the dye to the ionomer. Bonding resulted through electrostatic interactions between carboxylate groups on the ionomer and cations on the dye molecules. The reactive blending process also resulted in a change in the chromophoric structure of the dye. The bonded system was compared to a system whereby no bonding between the methine dye and polymer was expected. In the later system the methine dye was blended with polyethylene using an internal mixer. From FTIR results no interaction was observed between the dye and polyethylene in this system. This was supported by microscopic analysis that showed that the dye was present in the polyethylene as a dispersion. The second stage of research focussed on the UV stabilisation of polyolefins. A melt reaction was explored between polypropylene functionalised with maleic anhydride (PP-g-MA) and an alkoxyamine hindered amine light stabiliser (NOR-HALS) with hydroxyl functionality. The technology proposed is based upon the reaction between the carboxylic acid groups of maleated polypropylene and hydroxyl groups of a specific NOR-HALS (Tinuvin 152). The efficiency of the modification was assessed using FTIR to verify the esterification reaction between the NOR-HALS and the maleated polypropylene. This reaction resulted in the grafting of a pendant UV stabiliser to the polypropylene through an ester linkage. A twin-screw extruder (TSE) was used to complete this study. A larger quantity of material could be produced using a TSE compared to the colorant system where an internal mixer was used. Samples of the reactively blended materials were exposed to UV radiation for a maximum time period of three hundred hours to assess the resulting stability of the materials. Diffuse reflectance FTIR (DRIFT) spectroscopy and X-ray photoelectron spectroscopy (XPS) provided an effective means to study oxidative degradation. IR spectroscopic measurements were used to determine the effectiveness of HALS in inhibiting the photo-oxidation of maleic anhydride grafted polypropylene. The inhibition was quantified by measuring the formation of carbonyl groups, with and without HALS bonded to the polymer, at fixed exposure times of UV radiation. DRIFT and XPS analysis confirmed that stabilised samples oxidised less, as indicated by the lower carbonyl index values and O1s / C1s ratios. These findings were complemented by results from Charpy impact tests. The mechanical property results indicated that the longevity of the materials with UV stabilisers grafted to them exceeded the PPg- MA system where there was no stabiliser present. Visible spectrophotometry was used to assess the colour of the polymeric samples and change in colour following exposure to UV radiation. Samples with bonded HALS demonstrated greater colour stability than control samples. The microstructure of the polymer surfaces was viewed using scanning electron microscopy (SEM). The polymeric samples demonstrated resistance to crazing when the NOR-HALS were bonded to the polymer. For both the colorant and UV stabiliser areas of research, thermal properties of the materials were assessed using differential scanning calorimetry (DSC). It was found that increasing the additive concentration in the polymer resulted in an increase in the temperature of crystallisation (Tc). Melt flow index can indicate if any change in molar mass had occurred during processing. An increase in melt flow index values (MFI) was observed when additive loading increased which suggested that degradation of the polymer had occurred during processing. In summary, reactive processing showed considerable promise as a means to bond additives to a functional polypropylene.

This study examined the concept of using a reactive blending process to develop new polymeric additive systems. The objective was to investigate the potential of using a reactive processing technique as a means to bond additives to functional polymers, to create “in situ” bonds between functional groups present on the polymers and those present on the additives. The work is reported in two parts; the first part studied the bonding of colorants to functional polyolefins and the second part investigated the bonding of UV stabilisers to functional polyolefins. The research was completed with the long term objective that the approach should offer alternative additives to conventional non-bonded systems for use in polypropylene. An ethylene ionomer was utilised for the bonding of dyes, this was chosen for its optical clarity and chemical functionality. Polyethylene methacrylic acid (EMAA) ionomers and methine dyes were blended in the melt phase using an internal mixer to produce bright intrinsically colored polymers. Fourier transform infrared spectroscopy (FTIR) in transmission mode was used to assess the bonding of the dye to the ionomer. Bonding resulted through electrostatic interactions between carboxylate groups on the ionomer and cations on the dye molecules. The reactive blending process also resulted in a change in the chromophoric structure of the dye. The bonded system was compared to a system whereby no bonding between the methine dye and polymer was expected. In the later system the methine dye was blended with polyethylene using an internal mixer. From FTIR results no interaction was observed between the dye and polyethylene in this system. This was supported by microscopic analysis that showed that the dye was present in the polyethylene as a dispersion. The second stage of research focussed on the UV stabilisation of polyolefins. A melt reaction was explored between polypropylene functionalised with maleic anhydride (PP-g-MA) and an alkoxyamine hindered amine light stabiliser (NOR-HALS) with hydroxyl functionality. The technology proposed is based upon the reaction between the carboxylic acid groups of maleated polypropylene and hydroxyl groups of a specific NOR-HALS (Tinuvin 152). The efficiency of the modification was assessed using FTIR to verify the esterification reaction between the NOR-HALS and the maleated polypropylene. This reaction resulted in the grafting of a pendant UV stabiliser to the polypropylene through an ester linkage. A twin-screw extruder (TSE) was used to complete this study. A larger quantity of material could be produced using a TSE compared to the colorant system where an internal mixer was used. Samples of the reactively blended materials were exposed to UV radiation for a maximum time period of three hundred hours to assess the resulting stability of the materials. Diffuse reflectance FTIR (DRIFT) spectroscopy and X-ray photoelectron spectroscopy (XPS) provided an effective means to study oxidative degradation. IR spectroscopic measurements were used to determine the effectiveness of HALS in inhibiting the photo-oxidation of maleic anhydride grafted polypropylene. The inhibition was quantified by measuring the formation of carbonyl groups, with and without HALS bonded to the polymer, at fixed exposure times of UV radiation. DRIFT and XPS analysis confirmed that stabilised samples oxidised less, as indicated by the lower carbonyl index values and O1s / C1s ratios. These findings were complemented by results from Charpy impact tests. The mechanical property results indicated that the longevity of the materials with UV stabilisers grafted to them exceeded the PPg- MA system where there was no stabiliser present. Visible spectrophotometry was used to assess the colour of the polymeric samples and change in colour following exposure to UV radiation. Samples with bonded HALS demonstrated greater colour stability than control samples. The microstructure of the polymer surfaces was viewed using scanning electron microscopy (SEM). The polymeric samples demonstrated resistance to crazing when the NOR-HALS were bonded to the polymer. For both the colorant and UV stabiliser areas of research, thermal properties of the materials were assessed using differential scanning calorimetry (DSC). It was found that increasing the additive concentration in the polymer resulted in an increase in the temperature of crystallisation (Tc). Melt flow index can indicate if any change in molar mass had occurred during processing. An increase in melt flow index values (MFI) was observed when additive loading increased which suggested that degradation of the polymer had occurred during processing. In summary, reactive processing showed considerable promise as a means to bond additives to a functional polypropylene.

This study examined the concept of using a reactive blending process to develop new polymeric additive systems. The objective was to investigate the potential of using a reactive processing technique as a means to bond additives to functional polymers, to create “in situ” bonds between functional groups present on the polymers and those present on the additives. The work is reported in two parts; the first part studied the bonding of colorants to functional polyolefins and the second part investigated the bonding of UV stabilisers to functional polyolefins. The research was completed with the long term objective that the approach should offer alternative additives to conventional non-bonded systems for use in polypropylene. An ethylene ionomer was utilised for the bonding of dyes, this was chosen for its optical clarity and chemical functionality. Polyethylene methacrylic acid (EMAA) ionomers and methine dyes were blended in the melt phase using an internal mixer to produce bright intrinsically colored polymers. Fourier transform infrared spectroscopy (FTIR) in transmission mode was used to assess the bonding of the dye to the ionomer. Bonding resulted through electrostatic interactions between carboxylate groups on the ionomer and cations on the dye molecules. The reactive blending process also resulted in a change in the chromophoric structure of the dye. The bonded system was compared to a system whereby no bonding between the methine dye and polymer was expected. In the later system the methine dye was blended with polyethylene using an internal mixer. From FTIR results no interaction was observed between the dye and polyethylene in this system. This was supported by microscopic analysis that showed that the dye was present in the polyethylene as a dispersion. The second stage of research focussed on the UV stabilisation of polyolefins. A melt reaction was explored between polypropylene functionalised with maleic anhydride (PP-g-MA) and an alkoxyamine hindered amine light stabiliser (NOR-HALS) with hydroxyl functionality. The technology proposed is based upon the reaction between the carboxylic acid groups of maleated polypropylene and hydroxyl groups of a specific NOR-HALS (Tinuvin 152). The efficiency of the modification was assessed using FTIR to verify the esterification reaction between the NOR-HALS and the maleated polypropylene. This reaction resulted in the grafting of a pendant UV stabiliser to the polypropylene through an ester linkage. A twin-screw extruder (TSE) was used to complete this study. A larger quantity of material could be produced using a TSE compared to the colorant system where an internal mixer was used. Samples of the reactively blended materials were exposed to UV radiation for a maximum time period of three hundred hours to assess the resulting stability of the materials. Diffuse reflectance FTIR (DRIFT) spectroscopy and X-ray photoelectron spectroscopy (XPS) provided an effective means to study oxidative degradation. IR spectroscopic measurements were used to determine the effectiveness of HALS in inhibiting the photo-oxidation of maleic anhydride grafted polypropylene. The inhibition was quantified by measuring the formation of carbonyl groups, with and without HALS bonded to the polymer, at fixed exposure times of UV radiation. DRIFT and XPS analysis confirmed that stabilised samples oxidised less, as indicated by the lower carbonyl index values and O1s / C1s ratios. These findings were complemented by results from Charpy impact tests. The mechanical property results indicated that the longevity of the materials with UV stabilisers grafted to them exceeded the PPg- MA system where there was no stabiliser present. Visible spectrophotometry was used to assess the colour of the polymeric samples and change in colour following exposure to UV radiation. Samples with bonded HALS demonstrated greater colour stability than control samples. The microstructure of the polymer surfaces was viewed using scanning electron microscopy (SEM). The polymeric samples demonstrated resistance to crazing when the NOR-HALS were bonded to the polymer. For both the colorant and UV stabiliser areas of research, thermal properties of the materials were assessed using differential scanning calorimetry (DSC). It was found that increasing the additive concentration in the polymer resulted in an increase in the temperature of crystallisation (Tc). Melt flow index can indicate if any change in molar mass had occurred during processing. An increase in melt flow index values (MFI) was observed when additive loading increased which suggested that degradation of the polymer had occurred during processing. In summary, reactive processing showed considerable promise as a means to bond additives to a functional polypropylene.

This study examined the concept of using a reactive blending process to develop new polymeric additive systems. The objective was to investigate the potential of using a reactive processing technique as a means to bond additives to functional polymers, to create “in situ” bonds between functional groups present on the polymers and those present on the additives. The work is reported in two parts; the first part studied the bonding of colorants to functional polyolefins and the second part investigated the bonding of UV stabilisers to functional polyolefins. The research was completed with the long term objective that the approach should offer alternative additives to conventional non-bonded systems for use in polypropylene. An ethylene ionomer was utilised for the bonding of dyes, this was chosen for its optical clarity and chemical functionality. Polyethylene methacrylic acid (EMAA) ionomers and methine dyes were blended in the melt phase using an internal mixer to produce bright intrinsically colored polymers. Fourier transform infrared spectroscopy (FTIR) in transmission mode was used to assess the bonding of the dye to the ionomer. Bonding resulted through electrostatic interactions between carboxylate groups on the ionomer and cations on the dye molecules. The reactive blending process also resulted in a change in the chromophoric structure of the dye. The bonded system was compared to a system whereby no bonding between the methine dye and polymer was expected. In the later system the methine dye was blended with polyethylene using an internal mixer. From FTIR results no interaction was observed between the dye and polyethylene in this system. This was supported by microscopic analysis that showed that the dye was present in the polyethylene as a dispersion. The second stage of research focussed on the UV stabilisation of polyolefins. A melt reaction was explored between polypropylene functionalised with maleic anhydride (PP-g-MA) and an alkoxyamine hindered amine light stabiliser (NOR-HALS) with hydroxyl functionality. The technology proposed is based upon the reaction between the carboxylic acid groups of maleated polypropylene and hydroxyl groups of a specific NOR-HALS (Tinuvin 152). The efficiency of the modification was assessed using FTIR to verify the esterification reaction between the NOR-HALS and the maleated polypropylene. This reaction resulted in the grafting of a pendant UV stabiliser to the polypropylene through an ester linkage. A twin-screw extruder (TSE) was used to complete this study. A larger quantity of material could be produced using a TSE compared to the colorant system where an internal mixer was used. Samples of the reactively blended materials were exposed to UV radiation for a maximum time period of three hundred hours to assess the resulting stability of the materials. Diffuse reflectance FTIR (DRIFT) spectroscopy and X-ray photoelectron spectroscopy (XPS) provided an effective means to study oxidative degradation. IR spectroscopic measurements were used to determine the effectiveness of HALS in inhibiting the photo-oxidation of maleic anhydride grafted polypropylene. The inhibition was quantified by measuring the formation of carbonyl groups, with and without HALS bonded to the polymer, at fixed exposure times of UV radiation. DRIFT and XPS analysis confirmed that stabilised samples oxidised less, as indicated by the lower carbonyl index values and O1s / C1s ratios. These findings were complemented by results from Charpy impact tests. The mechanical property results indicated that the longevity of the materials with UV stabilisers grafted to them exceeded the PPg- MA system where there was no stabiliser present. Visible spectrophotometry was used to assess the colour of the polymeric samples and change in colour following exposure to UV radiation. Samples with bonded HALS demonstrated greater colour stability than control samples. The microstructure of the polymer surfaces was viewed using scanning electron microscopy (SEM). The polymeric samples demonstrated resistance to crazing when the NOR-HALS were bonded to the polymer. For both the colorant and UV stabiliser areas of research, thermal properties of the materials were assessed using differential scanning calorimetry (DSC). It was found that increasing the additive concentration in the polymer resulted in an increase in the temperature of crystallisation (Tc). Melt flow index can indicate if any change in molar mass had occurred during processing. An increase in melt flow index values (MFI) was observed when additive loading increased which suggested that degradation of the polymer had occurred during processing. In summary, reactive processing showed considerable promise as a means to bond additives to a functional polypropylene.