Browsing by Author "Mdungazi, Sean"

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    Cellulose nanoparticles as reinforcement and fillers in LDPE nanocomposites for production of low density packaging material
    (Stellenbosch : Stellenbosch University, 2022-12) Mdungazi, Sean; Chimphango, Annie Fabian Abel; Greyling, Guilaume; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Cellulose nanocrystals (CNC) have the potential to be used as reinforcement in petroleum-based polymers such as low-density polyethylene (LDPE) in the synthesis of LDPE nanocomposites. One of the challenges is the addition of the CNC in the LDPE form agglomerates. Therefore, surface modifications of the CNC such as acetylation and polyethylene adsorption may be utilized to reduce the agglomeration. However, these modifications have the potential to impact the cumulative energy demand (CED) and global warming potential (GWP) of the overall synthesis process. The study aimed to investigate the effect of acetylation and polyethylene adsorption of the CNC on the dispersion in LDPE, and on Young’s modulus, tensile strength, stress at break, water contact angle (WCA), moisture absorption, CED and GWP of the LDPE nanocomposites. The LDPE nanocomposites reinforced with acetylated cellulose nanocrystals (ACNC) were prepared by mixing LDPE with ACNC. The degree of substitution (DS) of the ACNC was varied (DS 1.19, 1.62, and 1.94) with CNC loading (1, 3, and 5 wt. %). Subsequently, the LDPE nanocomposites reinforced with polyethylene oxide (PEO) adsorbed cellulose nanocrystals (PEO-CNC) were developed by mixing the LDPE with PEO-CNC. The PEO:CNC dosage was varied (0.5:1, 1.5:1, and 2.5:1) with CNC loading (1, 3, and 5 wt. %). The nanocomposites were solvent cast (140 °C) and injection moulded (130 °C, 350 bar). The dispersion was described using Free-path spacing and characterization was done using field emission scanning electron microscopy (FE – SEM). The functional (mechanical and physical) properties were investigated using stress-strain curves, the sessile drop method, and a precision balance. The CED and GWP were estimated using a life cycle assessment conducted using OpenLCA software. The results showed that only CNC loading had a significant effect (p<0.05) on the dispersion (D0.1 %) of the LDPE nanocomposites reinforced with ACNC and PEO-CNC. The dispersion (D0.1 %) of the ACNC and PEO-CNC decreased from 8.81 - 4.19 % and from 7.97 – 6.96 % respectively with an increase in CNC loading (1 – 5 wt. %). DS had a significant effect (p<0.05) on Young’s modulus of the LDPE nanocomposites reinforced with ACNC. Young’s modulus increased from 181.95 – 217.2 MPa with an increase in DS (DS 1.19 – 1.94). The CNC loading had a significant effect (p<0.05) on the tensile strength of both nanocomposites. The tensile strength decreased from 26.2 – 25.9 MPa and 32.98 – 9.11 MPa with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The stress at break decreased from 50 - 14.75 % with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with PEO-CNC. The DS, PEO dosage, and CNC loading had no significant effect (p>0.05) on the WCA. The WCA decreased numerically from 89.7 – 88.5° and 76.3 – 71.5 ° with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The PEO dosage, DS, and CNC loading had no significant effect on moisture absorption (p>0.05). The moisture absorption increased numerically from 1.10 – 8.83 % and from 3.29 – 6.93 % with an increase in CNC loading (1- 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The PEO dosage, DS, and CNC loading had no significant effect (p>0.05) on the CED and the GWP. The cumulative energy demand (CED) increased numerically from 3119 - 4032 MJ and 3040 - 4304 MJ with an increase in CNC loading (1 – 5 wt. %) for LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The GWP increased numerically from 331 - 482 kg·CO2 and from 328 - 470 kg·CO2 with an increase in CNC loading (1 – 5 wt. %) for LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The findings of the study show that acetylation increased Young’s modulus of the LDPE nanocomposites while PEO adsorption decreased the functional properties of the LDPE nanocomposites. Both acetylation and PEO adsorption had no impact on the environmental impact of the LDPE nanocomposites. The functional properties and environmental impact were mainly dependent on the CNC loading.