In this work sisal nanowhiskers (SNW) extracted from sisal fibres were used to reinforce polyethylene matrices, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). The nanocomposites were prepared by solution casting from toluene and meltmixing, both followed by melt pressing. In the case of melt mixing, the surfaces of the SNW were also chemically modified with 1 phr of triethoxy vinyl silane (VTES) to improve their dispersibility and compatibility with the matrices. The nanocomposites and sisal nanowhiskers were characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and X-ray diffractometry (XRD). The sisal nanowhiskers, obtained through sulphuric acid hydrolysis treatment, had average lengths of 197 ± 75 nm and diameters of 12.2 ± 3.7 nm, and a crystallinity index of 89%. FTIR confirmed the surface chemical modification of the sisal nanowhiskers. The microscopic techniques demonstrated a fairly good dispersion of the whiskers in the matrices, regardless of the treatment or the preparation method. The storage modulus for the solution mixed nanocomposites was better than the untreated melt mixed nanocomposites. This behaviour was ascribed to the formation of a rigid cellulosic network during processing. For the treated melt mixed samples, the reinforcing effect was worse, suggesting the absence of a strong mechanical network because of the good interaction between the whiskers and the host polymer matrix. TGA revealed that there was no significant influence on the degradation behaviour of both polymers. The crystallization behaviour of the polymers was found to strongly depend on their morphologies. The melting and crystallization behaviour of the LDPE nanocomposites were almost unchanged, while an increase in crystallinity was observed for all the HDPE nanocomposites. The tensile properties depended on the type of polymer, the treatment, and the preparation method. Generally there was an improvement in tensile modulus, and a decrease in elongation at break, but the stress at break only improved for the HDPE nanocomposites.

The present study covers the preparation and the characterisation of ï¢-nucleated impact polypropylene copolymer (NA-IPC), and its fractions prepared through temperature rising elution fractionation (TREF). Calcium stearate (CaSt), as well as pimelic (Pim) and adipic (Adi) acids, were doped into IPC as a mono- or bi-component nucleating agents (NAs) at varying mass ratios. The non-isothermal crystallisation kinetics, and the effect of the NAs on the morphology, thermal and mechanical properties were investigated. However, only thermal properties of the fractions were investigated on. DSC and XRD results revealed that IPC nucleated with Pim and Pim-CaSt nucleants induced up to 90% β-crystals, while Adi and Adi-CaSt formed only about 17% β-crystals. This was associated with the strong nucleation efficiency (NE) of Pim. The 110C and 120C fractions treated with Pim-based NAs were the only fractions that formed β-crystals, probably due to their higher isotacticity. The nonisothermal crystallisation kinetics showed that the crystallization of IPC and NA-IPC followed a three-dimensional growth with athermal nucleation mechanism. The SEM images showed no changes in the distribution and size of the rubber phase after treatment with NAs. FTIR showed that none of the NAs chemically reacted with IPC, and the chemical structure of the polymer was thus intact during the treatment. Formation of β-crystals in the samples with Pim and Pim-CaSt improved the impact strength by more than 50%. However, incorporation of Adi, CaSt, and Adi-CaSt nucleants had little effect on the impact resistance of IPC. The tensile properties such as Youngâs modulus, yield stress and stress at break changed very little for the nucleated samples. On the other hand, the elongation at yield and at break increased. This is an indication of the strong ductility of IPC caused by the formation of β-crystals. The glass transition temperatures shifted slightly to higher temperatures with increasing β-crystal contents, due to the immobilization of the chains in the amorphous phase in the vicinity of the β-lamellae.

The effects of dicumyl peroxide/vinyltriethoxysilane (DCP/VTES) treatment, nanoclay content and the nature of the nanoclay were investigated for low-density polyethylene (LDPE)/clay and high-density polyethylene (HDPE)/clay nanocomposites. LDPE was treated with 0.1 phr of DCP with respectively 1 phr and 3 phr VTES (System A), and with 0.2 phr of DCP with the same amounts of VTES, and then mixed with different contents (1, 3, and 5 wt. %) of modified (Cloisite 15A) and unmodified (calcium montmorillonite) clay. The HDPE nanocomposites were prepared according to System A, using Cloisite 15A. The polymer-clay nanocomposites were prepared through melt mixing in a Brabender Plastograph internal mixer, and were characterized for their morphology, thermal properties, mechanical properties, thermomechanical properties and the extent of grafting/crosslinking. FTIR analysis clearly showed that grafting in System A was not very effective, and that the âgraftedâ LDPE contained an appreciable amount of ungrafted (pure or hydrolysed) VTES. However, sufficient grafting was achieved in System B, but there was also a higher extent of crosslinking. The XRD and TEM results showed that C15A was more intercalated than Ca2+MMT showed, and also slightly exfoliated. Nanocomposites prepared according to System A showed intercalated structures, while those prepared according to System B showed partially exfoliated structures. The DSC results showed that the presence of DCP/VTES decreased the melting temperature and crystallinity of both the polymer matrices due to a decrease in lamellar thickness as a result of crosslinking between the polymer chains, in addition to VTES grafting. The addition of clay and its nature had no significant influence on the melting temperature and crystallinity of both polymers. The TGA results showed an improvement in the thermal stability of all the nanocomposites, but the silane treated C15A nanocomposites showed a higher degradation rate at higher clay contents. The mechanical and thermomechanical properties of the untreated nanocomposites were better than those of the treated nanocomposites at the same clay loading.

Since the introduction of synthetic analogues in both the health-related and cosmetic industry, a new generation has emerged in search of beneficial bioactivity compounds. This generation of ânatural and greenâ focuses mainly on natural compounds and their health relating application. This research project focused on the natural polyphenolic compounds, Flavonoids. Flavonoids are known to be strong antioxidants, these are molecules that quenches reactive oxygen species (ROS). This generation of free radicals in the stratum corneum is the main factor in the development of skin damage and premature ageing. The two main sources of antioxidants are our bodyâs own in-house antioxidants or dietary antioxidants. Vitamins E and C were briefly discussed as antioxidants, but the main focus was the antioxidant activity of flavonoids. Through this study were unraveled the reaction pathways of natural antioxidants and their synthetic analogues, in chemical and biological systems. Emphasis was placed on their structure-activity relationship and correlated to their chemical and biological activities. Rooibos extract, known locally and overseas, was pursued not only for its bioactivity but rather its strong radical scavenging abilities. It is known that rooibos is not only unique to South Africa, but is hitherto the only natural source of the dihydrochalcone aspalathin (proven to be a very strong antioxidant). The uniqueness of this dihydrochalcone prompted the establishment of a viable synthetic route towards the construction of those crucial bonds in this target molecule, aspalathin. The first step would be the construction of the dihydrochalcone, 3,4,2â,4â,6â- pentahydroxy dihydrochalcone, which proved to be a challenging array of chemical reactivity. With acylations like Friedel-Craft and Fries, that is known to be very successful, it was decided to commence with the construction of the dihydrochalcone via an appropriate acylation step. Acylation of phenols can either occur via Cacylation (Friedel-Crafts reaction) or O-acylation (esterfication). This regioselectivity is governed by a set of principles incorporated in a theoretical premise, conveniently named as hard and soft acids and bases (HSAB). A new group of water tolerant Lewis acids, namely the lanthanide triflates have been introduced, and also the use of BF3·(C2H5)2O has proven success as catalyst in C-acylation. Simple phenolic substrates were used in the acylation process to assist the eventual establishment of a viable protocol. With these we were able to synthesize 1-hydroxy- 2-acetonaphthone and 3-(3,4-dihydroxy-phenyl)-1-(1-hydroxy-naphthalen-2-yl)- propan-1-one successfully, but in unsatisfactory yields (36 %). Despite many experiments under different conditions, starting with different model compounds, we were unable to improve the reaction yields. Within these reactions resorcinol produced the O-acylation product, 3â-O-hydroxy-phenyl 3-phenyl-propanoate and the C-acylation product, 2â,4â-dihydroxydihydrochalcone, whereas phloroglucinol only produced the O-acylated product, 3â,5â-dihydroxy-phenyl 3-phenyl-propanoate. From this analysis the conclusion can be made that, first occurring is the O-acylation followed by a Fries rearrangement in some cases. The neighboring hydroxy functionalities of phloroglucinol for example, posed a significant steric challenge for incoming electrophiles From the commencement of the project, replacement of the carboxylic acid group with the related, but with different chemical characteristics, nitrile groups was a necessary alternative. The Hoesch reaction was a good example of the HSAB principle, where in acid medium the nitrogen of the cyano group is protonated to afford the reactive electrophilic intermediate, the carbon of which is clearly a âsofterâ acidic site according to the HSAB theory. The C-acylated product, 2â,4â,6â- trihydroxy dihydrochalcone was produced in an impressive yield (73 %). During this reaction, an interesting result was also obtained, where the phenolic oxygen (âhardâ base) as well as the aromatic ring (âsoftâ base) reacted with the nitrile to produce the product, 3â,5â-dihydroxy-4â-phenyl-propionic acid 1â-3-phenyl-propanoate. It is noteworthy to mention the fact that phloroglucinol was by far the most potent Cand O-nucleophile in a ânormalâ series of model phenolic entries (phenol, resorcinol, catechol etc.) and resulted in the formation of the biphenyl, 3,5-dihydroxy-phenyl- 2â,4â,6â-trihydroxy-phenylether. Since the formation of a biphenyl ether is a rare occurrence, extensive methylation was employed to confirm the structure. Another part of this study includes the investigation and comparison of similar reactions under the influence of microwaves. Microwave reactions are known for their very short reaction times, higher product yields, less solvent utilized and more cost-effective energy consumption, but it was proved that selectivity was not increased. BF3·(C2H5)2O was the catalyst of choice for the selective C-acylation of phloroglucinol, rather than the water soluble Hf(OTf)4 Lewis acid. Different carboxylic acids were reacted with resorcinol and phloroglucinol with both Lewis acids as catalyst. In the one reaction between resorcinol and 3-phenylpropanoic acid with Hf(OTf)4 as catalyst, a reaction mixture was produced. The reaction mixture was acetylated to give both the O- and C-acetylated products, and from this result it was indicated that Hf(OTf)4 can act as both a Brønsted and Lewis acid in a catalytic cycle. The use of protecting groups was not only to optimize the yields obtained but also to understand BF3·(C2H5)2O and Hf(OTf)4 as catalysts. The low yields for the synthesis of the unprotected dihydrochalcones can be ascribed to: the formation of 3,5- dihydroxy-phenyl-2â,4â,6â-trihydroxy-phenylether, and the formation of 6,7- dimethoxy-indan-1-one and 5,6-dihydroxy-indan-1-one (intramolecular cyclization). At last the C-glycosylated flavonoid, aspalathin was synthesized. The best reaction result of phloroglucinol and 3,4-dihydroxyhydrocinnamic acid was catalyzed by BF3·(C2H5)2O to produce 3,4,2â,4â,6â-pentahydroxy dihydrochalcone, which resulted in a 20 % yield. A reliable method for the direct C-glycosylation of 3,4,2â,4â,6â- pentahydroxy dihydrochalcone with an unprotected sugar, D-glucose in aqueous media was used and yielded synthetic aspalathin (10.7%). Not only was this reported as the first 2 step synthesis of aspalathin, but was distinguished as the first complete free phenolic synthesis of a C-glycosylated flavonoid being reported. Combining this unique synthesis with a global industry such as cosmetics was possible. A study was conducted by Miao-Juei Huang and according to their results it was confirmed that aspalathin would be ideal for the use in topically applied cosmetic products, due to the accumulation of aspalathin in the stratum corneum. This causes a barrier on the skin with strong antioxidant properties, which protects the skin from harmful UV rays, reduce reactive oxygen species and slow down the aging process. Finally the potential of the desired compound to act as an active ingredient in commercial products was confirmed.

In this study, three types of polyethylene, low-density (LDPE), linear low-density (LLDPE), and high-density (HDPE) polyethylene, were used as polymer matrices to prepare sisal fibre reinforced polyethylene composites containing 10-30 wt% fibre. The untreated and the dicumyl peroxide (DCP) treated composites were prepared by melt mixing, followed by hot melt pressing. The influence of the DCP treatment, the polyethylene molecular characteristics, and the sisal fibre loadings on the morphology and on the thermal, mechanical, and dynamic mechanical properties of the composites was investigated. The gel contents of the composites varied significantly depending on the polyethylene molecular characteristics. The LLDPE composites had the highest gel content values followed by LDPE and then HDPE, for which the gel content did not change significantly. These results strongly suggested the presence of grafting of the polyethylene chains onto the sisal fibre surfaces combined with crosslinking between the polymer chains. The morphologies of the cryofractured surfaces and the xylene-extracted samples further confirmed the presence of the grafting, particularly in the case of the treated LLDPE and LDPE composites. The SEM micrographs of the treated LLDPE and LDPE composites showed better interfacial adhesion between the polymers and the sisal fibres. For HDPE composites, however, such interfacial bonding was not observed from the SEM micrographs. The SEM images of all the untreated polyethylene composites showed poor interfacial interactions. TGA analyses showed that the treatment did significantly affect the thermal stabilities of the composites, and all the untreated and the treated samples were thermally less stable than the neat polymer matrices. The DSC results demonstrated that the crystallization and melting behaviour of all the untreated polyethylene composites remained unaffected. However, both the DCP treatment and the sisal fibre loadings to some extent influenced the crystallization and melting behaviour of the LLDPE composites, whereas those of the LDPE composites were only slightly affected. The treated HDPE composites, however, did not show significant changes in their crystallization and melting behaviour. The elongation at break for all the treated and the untreated polyethylene composites showed similar trends and the treatment did not bring about any differences. Compared to the untreated composites, the tensile strength and the Youngâs modulus of the treated LLDPE and LDPE composites were remarkably higher, whereas the Youngâs modulus of the treated HDPE composites was observably lower and no significant effect on the tensile strength was noticed. The storage modulus of the LLDPE and LDPE composites showed good correlation with the tensile testing results. The tan δ curves showed a slight increase in the glass transition temperatures for the treated composites. The storage modulus of the treated HDPE composites remarkably decreased, and the tan δ curves did not show the β-relaxation as in the case of the other two polymers. The effect of the incorporation of sisal whickers on the properties of poly(lactic acid) was also investigated in this study. Untreated and the MA/DCP and DCP treated PLA nanocomposites, with sisal whiskers loadings of 2 and 6 wt%, were prepared by melt mixing and hot melt pressing. The dispersion of the whiskers in the PLA matrix as well as the thermal and viscoelastic properties of the nanocomposites were determined using TEM, DSC, TGA, and DMA. The dispersion of the whiskers was found to be similar, whether the samples were treated or not. The presence and the amount of whiskers in the untreated nanocomposites slightly decreased the calculated percent crystallinity, but the Tm, Tc and Tg remained fairly constant compared to neat PLA. The type of treatment was also found to influence the crystallization and melting behaviour of the nanocomposites. The TGA results showed that neither the sisal whiskers loading nor the treatment had a significant effect on the thermal stabilities of the nanocomposites. The incorporation of the whiskers remarkably reduced the intensity of the glass transition in the tan δ curve, and all the nanocomposites showed higher storage modulus values compared to the neat PLA. The type of treatment did not really influence the stiffness of the samples. Entirely bio-based nanocomposites of PFA and sisal whiskers were prepared by an in situ polymerization method. The effect of increased sisal whiskers loadings (1 and 2 wt%) on the thermal and the dynamic mechanical properties of the nanocomposites were studied. No significant changes in the thermal stabilities of the nanocomposites could be seen. The storage moduli of the nanocomposites were significantly increased by the presence and the amount of sisal whiskers, and the intensity of the glass transition relaxation in the tan δ curve observably decreased and slightly shifted to lower temperatures.

Vanadium is an early first-row transition metal that is known for the beautiful coloured compounds that it forms in a wide range of oxidation states. In high oxidation states, vanadium is very oxophilic whilst at low oxidation states, Ï-donating ligands are preferred. It is the only element in the periodic table to be named after a goddess (the Nordic goddess Vanadis), and perhaps with this legacy in mind some unpredictable and surprising chemistry might be expected. This research study focussed on the rich and diverse coordination chemistry of vanadium. Various vanadium(IV) and vanadium(V) compounds were successfully synthesized with O,O and N,O-Bid ligand systems (Bid= five or six membered chelating ligand via O,Oâ or N,O-donor atoms). These ligands were chosen for their wide application in terms of industrial use in the development of catalysts as well as their biological activity for pharmacological application. To achieve the above mentioned aim various characterization techniques were mastered such as IR, UV/Vis, NMR and single crystal X-ray diffraction. To this regard four vanadium complexes were successfully characterized by XRD namely [VO(dbm)2], [VO(dbm)2(MeOH)]â¢2MeOH, [VO(dbm)2py] and (C9H17O2)[VO2(cupf)2]. The three diketonato containing complexes provided unique stereo-electronic changes in each case and the effect upon distortion of the vanadium centre as well as the trans effect of the oxido bond could be evaluated. The last mentioned compound was of special interest as the novel 2,2,6,6- tetramethyldihydropyran-4-onium that acts as cation for the anionic vanadium complex was speculated to have formed either by cyclization of acetone during the reaction or by action of the vanadium present. In addition to the synthesis component of the research a kinetic substitution study was instigated. The complex solution chemistry of vanadium resulted in a wide array of experiments to evaluate the effects of not only ligand concentration on reaction rates but also pH dependence of certain species in solution. This culminated in a proposed reaction mechanism and rate law that accounts for various pH, pKa and concentration effects. As vanadium is known for its biological activity, selected complexes synthesized from this study was investigated for in vitro cancer screening. These results were concluded as not being positive but provided valuable insight for future ligand and complex design. 51V NMR was effectively used in this study both in the synthesis component as well as the kinetic study conducted. Valuable insight into the electronic environment experienced by the vanadium centre was obtained and correlations could be established between steric strain within a complex and the amount of shielding experienced by the vanadium centre. Additionally, experiments such as in the kinetic study could be followed over time on 51V NMR and revealed important information regarding product formation and the identification of an intermediate [VO(O2)(2,3-dipic)]2- in the reaction which was vital in construction of the reaction mechanism.

The study deals with the preparation and characterization of polystyrene (PS) capsules containing M3 paraffin wax as phase change material for thermal energy storage embedded in a polypropylene (PP) matrix. Blends of PP/PS:wax and PP/PS were prepared without and with SEBS as a modifier. The influence of PS and PS:wax microcapsules on the morphology and thermal, mechanical and conductivity properties of the PP was investigated. The SEM images of the microencapsulated PCM show that the capsules were grouped in irregular spherical agglomerates of size 16-24 μm. However, after melt-blending with PP the much smaller, perfectly spherical microcapsules were well dispersed in the PP matrix. The results also show fairly good interaction between the microcapsules and the matrix, even in the absence of SEBS modification. The FT-IR spectrum of the microcapsules is almost exactly the same as that of polystyrene, which indicates that the microcapsules were mostly intact and that the FTIR only detected the polystyrene shell. The amount of wax in the PS:wax microcapsules was determined as 20-30% from the DSC and TGA curves. An increase in PS:wax content resulted in a decrease in the melting peak temperatures of PP for both the modified and the unmodified blends due to the plasticizing effect of the microcapsules. The thermogravimetric analysis results show that the thermal stability of the blends decreased with an increase in PS:wax microcapsules content as a consequence of lower thermal stability of both the wax and PS. The DMA results show a drop in storage modulus with increasing PS:wax microcapsules content. The microcapsules acted as a plasticizer and thus enhanced the mobility of the polymer chains. Generally the thermal conductivity of the unmodified and modified blends decreased with increasing PS:wax microcapsule content when compared to PP. The polystyrene shell has a lower conductivity than the PP matrix, which explains the lower thermal conductivities of the blends with increasing PS content.

The effect of degraded LDPE (dLDPE) as compatibilizer on the morphology, as well as thermal, mechanical, and thermo-mechanical properties, of LDPE/wood flour (WF) composites was investigated in this study. The composites were prepared through melt mixing in a Brabender Plastograph internal mixer, while the LDPE was thermally degraded in an air oven at 80 ï°C for different periods of time. The formation of functional groups on the polyethylene chains during the degradation enables the dLDPE to be used as a compatibilizer. Composites with different amounts of WF, compatibilized with dLDPEs having different carbonyl indices, were characterized with scanning electron microscopy (SEM), Fouriertransform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), as well as tensile, impact and hardness testing. Addition of dLDPE as compatibilizer generally enhanced the mechanical properties of the composites. The SEM images show smooth surfaces with fewer voids and fibre pullout for the dLDPE modified composites. The FTIR results show an increase in carbonyl index up to 7 weeks degradation, and the GPC results show that the molecular weight decreased significantly with increasing degradation time. The DSC results show that the presence of WF particles, and increasing filler loading, had very little influence on the melting and crystallization behaviour of the untreated LDPE/WF composites. However, in the dLDPE treated composites a nucleating effect of the fibres gave rise to increased LDPE melting and crystallization enthalpies. There was no significant improvement in the thermal stability of the dLDPE treated composites. The DMA results show that the presence of dLDPE (especially the 7 weeks dLDPE with a carbonyl index of 0.90) observably influenced the viscoelastic properties of the composites. In summary, it was found that the higher carbonyl index dLDPEs are more efficient compatibilizers in LDPE/WF composites, despite their significantly reduced molecular weights.

<p>Organic pi-conjugated materials are emerging as commercially relevant components in electronic applications that include transistors, light-emitting diodes, and solar cells. One requirement common to all of these functions is an aptitude for accepting and transmitting charges. It is generally agreed that the development of organic semiconductors that favor electrons as the majority carriers (n-type) lags behind the advances in hole transporting (p-type) materials. This shortcoming suggests that the design space for n-type materials is not yet well explored, presenting researchers with the opportunity to develop unconventional architectures. In this regard, it is worth noting that discrete molecular materials are demonstrating the potential to usurp the preeminent positions that &#960;-conjugated polymers have held in these areas of organic electronics research. </p><p>This dissertation describes how an extraordinary class of molecules, meso-to-meso ethyne-bridged porphyrin arrays, has been bent to these new uses. Chapter one describes vis-NIR spectroscopic and magnetic resonance measurements revealing that these porphyrin arrays possess a remarkable aptitude for the delocalization of negative charge. In fact, the miniscule electron-lattice interactions exhibited in these rigid molecules allow them to host the most vast electron-polarons ever observed in a pi-conjugated material. Chapter two describes the development of an ethyne-bridged porphyrin-isoindigo hybrid chromophore that can take the place of fullerene derivatives in the conventional thin film solar cell architecture. Particularly noteworthy is the key role played by the 5,15-bis(heptafluoropropyl)porphyrin building block in the engineering of a chromophore that, gram for gram, is twice as absorptive as poly(3-hexyl)thiophene, exhibits a lower energy absorption onset than this polymer, and yet possesses a photoexcited singlet state sufficiently energetic to transfer a hole to this polymer. Chapter three describes synthetic efforts that expand the repertoire of readily available meso-heptafluoropropyl porphyrin building blocks. The findings suggest that the remaining challenges to the exploitation of these pigments will be overcome by a sufficiently firm grasp of their subtle electronic structures, and a willingness to eschew the customary strategies of chromophore assembly.</p> / Dissertation

The work presented here is the first of its kind where nanocrystal-based photovoltaics are characterized by directly imaging the electronic properties and correlating them to the structure of the sample. Through electron beam-induced current (EBIC), a finite beam of high energy electrons mimics photons to generate a photoresponse in the device, thus enabling the measurement of the current being generated in a precise region of the specimen. Two different nanocrystal-based architectures were studied in this manner: (1) a hybrid bulk heterojunction composed of CdSe nanorods dispersed in a conductive polymer matrix and (2) a PbS quantum dot depleted-heterojunction device. Both yielded significant results, such as high hole mobility in the case of (1), and changes in the EBIC signature as a result of defects in (2); the electronic shortcomings of the devices believed prior to this work were also confirmed. Another PbS quantum dot-based device was characterized using high resolution elemental mapping; this architecture comprised of titania nanotubes rather than nanoparticles as used in the photovoltaic described in (2). Preliminary work on CdTe thin film solar cells was also conducted as a test bed for higher resolution EBIC. With EBIC, maps of nanocrystal-based, solid state photovoltaics were collected and analyzed to reveal important information regarding the electronic properties of the devices as well as areas of improvement. As a result of the latter, more efficient solar cell technology can be developed to help meet the energy demands of the global population.