Formulation and Characterization of Wood Polymer Composites from Ethiopian Lowland Bamboo Fibrous particles and Recycled Thermoplastic Polyblends
No Thumbnail Available
Date
2025-09
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Increasing global concerns over environmental sustainability and the responsible use of natural resources have increased efforts to develop eco-friendly materials derived exclusively or partly from renewable sources. One of these efforts aim to mitigate the environmental degradation and resource depletion caused by the widespread use and poor end-of-life management of petroleum-based synthetic polymers, which are non-biodegradable and accumulate in large volumes. Within this context, the valorization of thermoplastic waste through innovative recycling and repurposing strategies has emerged as a key solution under the circular economy framework. Concurrently, increasing urbanization and population growth, along with the environmental drawbacks of conventional construction materials, highlight the urgent demand for more sustainable alternatives. One promising alternative is the formulation of Wood Polymer Composites (WPCs), which effectively combine thermoplastic wastes as matrices with bio-based fibrous fillers, providing a sustainable pathway toward affordable building components and environmentally friendly construction materials.
In this doctoral study, a wide range of WPC formulations was developed using six recyclable thermoplastics sourced from post-consumer and electronic waste as matrices and fibrous particles from Ethiopian indigenous lowland bamboo (Oxytenanthera abyssinica, LLB) as a novel reinforcement. Key formulation variables—including reinforcement content, matrix composition, polymer blending, particle size, and interfacial modifications through coupling and crosslinking agents—were systematically investigated to evaluate multiscale reinforcement mechanisms and synergistic interactions within multipurpose thermoplastic matrices. Composite prototypes were prepared by compounding in an internal Haake mixer configured with a counter-rotating twin-screw, followed by compression molding into board panels. Their performance was comprehensively assessed through fundamental mechanical testing, thermal stability and dynamic mechanical analysis, water absorption, dimensional stability, and interfacial characterization. All formulations were benchmarked against commercial polyolefin-based WPCs to assess their viability as sustainable alternatives within the four main sub-studies outlined below.
The first sub-study investigated recycled polyethylene polyblends—comprising linear low-density (rLLDPE), medium-density (rMDPE), and high-density (rHDPE)—sourced from municipal waste as matrix materials. Their chemical composition, heavy metal and polycyclic aromatic hydrocarbons (PAHs) content, and thermal degradability behavior were characterized including the compositions of LLB biomass. The ultimate tensile strength (TS) and flexural strength (FS) decreased as the LLB content increased from 40% to 60%; however, the best mechanical performance was achieved at 40% loading, primarily due to improved melt flow and better matrix encapsulation of the bamboo particles. Nevertheless, even at the higher LLB content (60%), the incorporation of MAPP effectively preserved substantial mechanical integrity by enhancing interfacial adhesion between the matrix and the reinforcement. In contrast, both Flexural modulus (FM) and tensile modulus (TM) show an increasing trend with increased with higher LLB loadings in all formulations, while the influence of MAPP on these properties was minimal. Equal-phase melt blends demonstrated distinct improvements over separate-phase blends, likely due to thermally induced crosslinking and enhanced compatibility despite inherent immiscibility. Furthermore, in situ compatibilization with maleic anhydride grafted polypropylene (MAPP), combined with balanced blending of rLLDPE, rMDPE, and rHDPE, yielded significant property enhancements while retaining desirable characteristics of the constituent polymers.
Next, WPCs were developed using an equal blend of recycled polystyrene (rPS) from electronic waste and rHDPE from post-consumer packaging based on the inherent properties of the polymers before blending. rHDPE may provide ductility and toughness, while rPS may contribute to rigidity, hardness, and dimensional stability. The LLB-reinforced blend composites were processed by incorporating both MAPP and dicumyl peroxide (DCP) to promote chemical level interaction. The study assessed the comparative effects of LLB particle size, equal polymer blend composition, and LLB content. Results demonstrated that reactive blending with MAPP and DCP substantially enhanced mechanical and thermal properties compared to uncoupled blends. Particularly, formulations containing LLB particles below 500 μm synergistically improved stiffness, toughness, and rupture properties, highlighting application of new insight to WPC formulations.
Subsequently, further investigations were conducted on a 50/50 blend of rHDPE and rPS reinforced with LLB particles below 500 μm, compatibilized using either MAPP or SEBS-g-MA (triblock copolymer of styrene–ethylene–butylene–styrene block copolymer (SEBS) grafted with a maleic anhydride) in combination with 1% DCP for crosslinking. The study evaluated various compatibilizer loadings (3%, 5%, 7%, and 10%) to assess their effects on composite performance. Results demonstrated that SEBS-g-MA markedly enhanced water resistance, dimensional stability, and thermal degradation behavior, with impact strength and interfacial compatibility improving linearly across all loading levels. In contrast, MAPP combined with DCP contributed primarily to improvements in tensile and flexural properties as well as dynamic mechanical performance. Optimal composite performance was achieved at 5% MAPP or 3% SEBS-g-MA in combination with 1% DCP, yielding the highest overall strength while the remaining property remained significantly at all loading.
Finally, high-performance WPCs were developed using recycled acrylonitrile butadiene styrene (rABS) and high-impact polystyrene (rHIPS) matrices reinforced with 50% LLB particles. Ethylene propylene diene monomer (EPDM) and methyl methacrylate-butadiene-styrene (MMBS) were applied synergistically with maleic anhydride (MA) and DCP to enhance multipurpose toughening and interfacial compatibility. EPDM and MMBS contents (5–15%) were varied to optimize mechanical performance, while MA and DCP were fixed at 1% and 0.5%, respectively. Comprehensive evaluations showed that MMBS-modified rABS and rHIPS composites (10% MMBS, 1% MA, 0.5% DCP) achieved superior flexural strength (74.5 MPa), modulus of rupture (6.09 GPa), and dimensional stability (+65.65%) compared to uncoupled and unmodified composites. EPDM enhanced thermal stability and reduced water uptake in both systems, though excessive amounts slightly reduced stiffness and strength, while still outperforming unmodified matrices.
In conclusion, the formulated WPCs offer lightweight, eco-efficient, low-carbon, and sustainable construction materials that support circular resource utilization by valorizing waste thermoplastics and utilizing the untapped potential of indigenous Ethiopian LLB particles. These composites achieved performance comparable to or exceeding that of commercial polyolefin-based WPCs, without the need for fiber extraction or energy-intensive nonreinforcement processes.
Description
Keywords
Wood plastic composite, Interfacial compatibility, Bamboo fibrous particles, cascading thermoplastic waste, Sustainable building materials, Postconsumer thermoplastic valorization, polyblend polymeric matrices