This review article covers the synthesis and design of conjugated polymers for carefully adjusting energy levels and energy band gap (EBG) to achieve the desired photovoltaic performance. The formation of bonds and the delocalization of electrons over conjugated chains are both explained by the molecular orbital theory (MOT). The intrinsic characteristics that classify conjugated polymers as semiconducting materials come from the EBG of organic molecules. A quinoid mesomeric structure (D-A ↔ D⁺ = A⁻) forms across the major backbones of the polymer as a result of alternating donor–acceptor segments contributing to the pull–push driving force between neighboring units, resulting in a smaller optical EBG. Furthermore, one of the most crucial factors in achieving excellent performance of the polymer is improving the morphology of the active layer. In order to improve exciton diffusion, dissociation, and charge transport, the nanoscale morphology ensures nanometer phase separation between donor and acceptor components in the active layer. It was demonstrated that because of the exciton’s short lifetime, only small diffusion distances (10–20 nm) are needed for all photo-generated excitons to reach the interfacial region where they can separate into free charge carriers. There is a comprehensive explanation of the architecture of organic solar cells using single layer, bilayer, and bulk heterojunction (BHJ) devices. The short circuit current density (J_sc), open circuit voltage (V_oc), and fill factor (FF) all have a significant impact on the performance of organic solar cells (OSCs). Since the BHJ concept was first proposed, significant advancement and quick configuration development of these devices have been accomplished. Due to their ability to combine great optical and electronic properties with strong thermal and chemical stability, conjugated polymers are unique semiconducting materials that are used in a wide range of applications. According to the fundamental operating theories of OSCs, unlike inorganic semiconductors such as silicon solar cells, organic photovoltaic devices are unable to produce free carrier charges (holes and electrons). To overcome the Coulombic attraction and separate the excitons into free charges in the interfacial region, organic semiconductors require an additional thermodynamic driving force. From the molecular engineering of conjugated polymers, it was discovered that the most crucial obstacles to achieving the most desirable properties are the design and synthesis of conjugated polymers toward optimal p-type materials. Along with plastic solar cells (PSCs), these materials have extended to a number of different applications such as light-emitting diodes (LEDs) and field-effect transistors (FETs). Additionally, the topics of fluorene and carbazole as donor units in conjugated polymers are covered. The Stille, Suzuki, and Sonogashira coupling reactions widely used to synthesize alternating D–A copolymers are also presented. Moreover, conjugated polymers based on anthracene that can be used in solar cells are covered.

The effect of ethynylene or ethynylene–thiophene spacers on the band gap of alternating polymers, containing 4,9-naphthothiadiazole units as an acceptor and 2,7-linked fluorene repeat units as a donor, were investigated. The Sonogashira coupling reaction was employed to prepare the two novel copolymers, namely ((9,9-dioctyl-fluorene)-2,7-diethynylene-alt-4,9-2,1,3-naphthothiadiazole (PFDENT) and poly(5,5’-(9,9-dioctyl-fluorene-2,7-diyl)bis(ethynyl-2-thienyl)-alt-4,9-(2,1,3-naphthothiadiazole) (PFDTENT). The optical, electrochemical and thermal properties of the two obtained polymers were widely investigated and compared. Both resulting polymers showed low solubility in common organic solvents and moderate molecular weights. It is believed that the introduction of acetylene linkers rather than acetylene–thiophene spacers on the polymer chains reduces the steric hindrance between the donor and acceptor units which leads to the adoption of more planar structures of polymeric chains, resulting in decreased molecular weights of the resulting conjugated polymers. Thus, both ethynylene-based polymers and ethynylene–thiophene-based polymers showed red-shifted absorption maxima compared to their counterpart (thiophene-based polymer), owing to the adoption of more planar structures. Optical studies revealed that the new ethynylene and ethynylene–thiophene-based polymers displayed low band gaps compared to their thiophene analogue polymer PFDTNT. Both resulting polymers showed good thermal stability. X-ray diffraction (XRD) patterns of both polymers revealed that PFDENT and PFDTENT possessed an amorphous nature in solid state.

This research work has evaluated the modification effects of adding the reactive polymer (poly methyl methacrylate - (PMMA)) at different contents with Iraqi asphalt in the presence of poly phosphoric acid (PPA) at constant ratio as cross-linking agent on the thermal and rheological behavior of asphalt material with penetration grade 40/50. Moreover, the chemical structure of Iraqi asphalt and its fractions (asphaltene and maltene) was analysed using FTIR analysis. Combination of PMMA/PPA with asphalt has been presented as a new alternative approach to modify the rheological and thermal behavior of modified asphalt binders via forming chemical bonds and the changing in rheological and thermal characteristics of blended materials. Ten different PMMA percentages ranging from 0.5% to 5% by weight with 0.2% PPA for each sample were blended with 40/50 asphalt binder, the rheological properties of modified asphalt samples at different contents were examined by standard testing including ductility, penetration, softening point and penetration index. It was noted that due the addition of high loadings of PMMA into asphalt, the softening point value increased from 51 ˚C to 66 ˚C, whereas the ductility and penetration values decreased from 150 cm and 41 mm to 33 cm and 12 mm respectively. The result obtained revealed that the incorporation of PMMA/PPA with asphalt at specific level significantly improved elasticity and strengthens of asphalt mixture, which finally enhances the cracking and rutting resistance performance as well as temperature susceptibility of asphalt pavement. The thermo gravimetric analysis (TGA) indicated that the modified asphalt samples had less evaporation and higher thermal stability compared to virgin asphalt, this means that the thermal attitude of modified asphalt was improved. X-ray diffraction (XRD) patterns were performed to study the morphological properties of asphalt and modified one, these results showed that modified asphalt sample possessed homogeneous surface as a result of uniform dispersion of polymers into asphalt morphology due to chemical interaction between polymers and asphalt.

The present study employed cardboard waste as feedstock for bioethanol production. Physicochemical and biological treatments were utilized to enhance the free sugar level from cardboard waste converted to bioethanol through metabolic pathways using yeast. The minimum production of sugar was 16.2 mg/mL when the cardboard waste was pre-treated with dilute sulfuric acid (1%) at an acid/waste ratio of 10 mL: 1 g, which produced the highest bioethanol yield after fermentation. To concentrate the bioethanol obtained, distillation and dry agent were used respectively to afford high-purity bioethanol with yield of 29.0%. The bioethanol produced was characterized through NMR and FTIR spectroscopy techniques. Furthermore, bioethanol and traditional gasoline were blended at different ratios to produce blends E0, E6, E8, E10, and E12. The binary mixtures were evaluated experimentally using American Standard for Testing and Materials (ASTM) methods, including Reid vapor pressure (RVP), density, water content, and, research octane number (RON). The fuel blend densities increased linearly with an increasing ratio of ethanol content in the binary mixture, while RVP values decreased. RON and water content of bioethanol-gasoline blended fuel steadily increased with the addition of bioethanol. KEY WORDS: Acid pre-treatment, Bioethanol-gasoline blends, Lignocellulosic wastes, S. cerevisiae Bull. Chem. Soc. Ethiop. 2025, 39(8), 1621-1637. DOI: https://dx.doi.org/10.4314/bcse.v39i8.13

The objective of this study was to evaluate the rheological performance of rubberised asphalt binder with varying dosages of crumb rubber (CR), and compare these modified materials with unmodified asphalt binder. It is very important to investigate the characterization of chemical structures of the asphalt binder from a closer view for useful modifications of the virgin binder by polymer waste as modifiers. The current research employed a thin layer chromatography technique (TLC) to separate and determine the different fractions in asphalt. Nuclear Magnetic Resonance (NMR) spectroscopy was also used to characterize and confirm the chemical compositions of asphalt and its fractions. Despite of NMR spectra of asphalt is difficult to be interpreted via its structural complexity, but this technique is still able to provide useful data especially with regard to asphaltene fraction. Crumb rubber is a polymer waste which used as modifier of asphalt binder via the economic benefits and improving the rheological properties of modified asphalt binder. The rubberised asphalt binders were produced by blending the virgin asphalt with CR at various contents (3%, 5%, 10%, 15% and 20%). The effects of CR contents on the rheological behaviors of modified asphalt binder have been investigated including: penetration, softening point, ductility. Furthermore, morphological analysis of rubberised asphalt was conducted via scanning electron microscopy (SEM) to assess the effect of CR on the binder morphological structure. Based on results obtained, binder with highest CR content showed improvement in rheological properties of the modified binders in terms of decreasing in penetration, increasing in softening point values and keeping the ductility higher, unlike other CR contents which exhibited poor performance of modified asphalt.