| dc.description.abstract | Production activities in the horticulture industry mainly rely on petroleum-based plastic containers for cultivating and propagating plants because they are low-cost, absorb little water, and are structurally durable. However, the extensive use of plastic creates environmental problems that cannot be ignored. This has led to increased research into bio-based alternatives. Yet, many of these options have limitations due to their inherent properties. This study aims to explore the potential of bio-based containers and bio-composites as substitutes for commonly used synthetic containers, examining how the inclusion levels of constituent materials affect container performance. The specific objectives of this research include assessing commercially available bio-based containers (such as Asili pot and BioPax) and prototype containers made from biopolymers, including wood fibers (WF), polybutylene succinate (PBS), blends of polylactic acid (PLA) and polyhydroxyalkanoates (PHA), with and without biochar incorporation, in comparison to synthetic polypropylene (PP) containers (Chapters 2 and 3). The next objective investigates the development and performance of bio-composites made with lignocellulosic fibers (LCF), microfibrillated LCF (LCMF), and biochar, using polyvinyl alcohol (PVA) as a binder, for horticulture container applications (Chapter 4). The third objective assesses how the wet strength additive, polyamideamine-epichlorohydrin (PAE), affects the performance of the bio-composites (Chapter 5). The series of assessments carried out for the first objective involved an eight-week greenhouse study, which showed that bio-based containers performed similarly to, and in certain cases, better than synthetic PP containers. Plant performance metrics, such as the plant growth index, showed no statistically significant difference among container types. The plant dry weights for bio-based containers were comparable to those in synthetic containers, except for WF containers, which had a significantly lower dry weight of 2.18 g (p = 0.03, α = 0.05). Results also revealed that bio-based containers had comparable and higher mechanical properties than PP containers, in terms of the tensile strength and elongation at break (up to 61.3% and 75.9% higher, respectively, for thermoformed blends of PLA and PHA), modulus of elasticity (up to 46% higher for white-colored Asili pots) and force at maximum load (up to 64.2% higher for BioPax). Water absorption assessment showed that bio-based containers generally retained water well, except for WF containers, which lost water faster and had the lowest retention. In addition, the rate of mass loss over the greenhouse study was highest in WF, BioPax, and PBS containers, approximately 2.66%, 9.56%, and 9.43%, respectively, likely due to surface erosion from microbial activity, enzymatic hydrolysis, and/or environmental factors. For the second and third objectives, investigations into the development and performance of biochar-/lignin-containing microfibrillated cellulose fiber bio-composites showed that polyvinyl alcohol (PVA) as a binder at 20% provided considerable interfacial interaction with the other constituents, improving the dry tensile strength (16.7 ± 0.14 MPa) and force at maximum load (240 ± 4.71 N), although it increased brittleness. Water absorption of the bio-composite decreased with increasing PVA content up to 20% inclusion, though the water absorption remained above 100% due to the fibers' inherent hydrophilic nature. It was also found that the individual constituents affected the performance of the bio-composites in line with their properties. At higher loadings, LCF improved tensile strength by allowing better stress distribution; LCMF and biochar increased stiffness and brittleness, with biochar also reducing water absorption and boosting thermal stability due to its hydrophobic and thermally stable nature. However, performance declined in wet conditions, necessitating the use of the wet strength additive, PAE. Results showed that the inclusion of PAE at 1% maintained the bio-composites' wet strength by forming covalent ester bonds between the azetidinium groups of the PAE and the carbonyl groups of LCF and LCMF, in addition to other interactions. Under wet conditions, the force at maximum load for bio-composites with 1% PAE was approximately 15.4
± 1.43 N, approaching the suggested threshold of 19.6 N considered sufficient for handling horticultural containers without falling apart. This research demonstrates the potential of bio-based containers as functional alternatives to synthetic options. It also adds to the body of knowledge on tuning the performance of bio-based containers by leveraging their constituents’ inherent properties and inclusion levels, and by incorporating additives to suit horticulture container applications. | en_US |
