An examination into the influence of isovanillin on carrageenan biocomposite using experimental and molecular interaction study / Mohd Aiman Hamdan

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2022

Includes bibliographical references

Plant based hard capsule is highly demanded in global market to replace the animal-based capsule products. Plant-based hard capsule from semi-refined carrageenan demonstrated that the structure of carrageenan based hard capsule is brittle and a rough surface film was produced. The property of the hard capsule failed during capsule filling process due to the weakness. Agglomeration of carrageenan particle during the solution formulation reduced the mechanical strength of the hard capsule. This work aims to investigate the effect of pre-treatment process of ultrasonication on refined carrageenan and ball milling on isovanillin; correlate and characterise the effect of ultrasonication intensity of refined carrageenan and isovanillin crosslinker concentration; simulate the molecular interaction of the crosslinked kappa-carrageenan biocomposite structure using molecular modelling software, Gaussian 09W; and elucidate the molecular interaction of the kappa-carrageenan incorporation with isovanillin using experimental approach. Isovanillin crosslinker was ball milled to reduce the solid crystal size and improve the physical crosslinking ability for hydrogen bonding network formation. The crosslinker concentration was varied at 0 to 5 wt.%. to determine best formulation that produce the highest mechanical and physicochemical properties of the refined carrageenan biocomposite film. Refined carrageenan was ultrasonicated in deionized water at 0 to 60% to determine the best ultrasonication parameter to produce a thin and smooth biocomposite film. This work also simulated the molecular interaction through H-bond between κ-carrageenan, isovanillin, and cellulose using density functional theory (DFT) software, Gaussian 09w. The physical crosslinking of H-bond interaction of the κ-carrageenan biocomposite was analyzed using nuclear magnetic resonance (NMR), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). Upon ultrasonication of refined carrageenan solution at 40%, ultrasonication transformed the helices structure of carrageenan due to a very strong mechanical oscillating power. It produced the highest tensile strength 61.04 Pa of refined carrageenan biocomposite film. Ball-milling reduced the size of isovanillin particle from 440.35 to 30.22 mm. Smaller size of isovanillin increased the interfacial area for solubility and increased the probability of physical crosslinking for H-bonding formation. The result was proven by the increased in the biocomposite film tensile strength to 44.67 MPa. Based on the physicochemical analysis, incorporation of 3% isovanillin proved the best properties among other samples. Atomic force microscopy (AFM) topography result showed that incorporation of 3% isovanillin in biocomposite film formulation had the lowest average roughness (39.21 nm), peak-to-valley ratio (195.16 nm) and root-mean-square roughness (46.09 nm) in comparison to control and 4% isovanillin samples. Intermolecular interaction via H-bond between κ-carrageenan, isovanillin, and cellulose improved the biocomposite chemical and mechanical properties. DFT simulation suggested that H-bond interaction networking occurred between κ-carrageenan-isovanillin-cellulose conjugate at O133---H101, O25---H96, O26---H116, O22---H143, and O27---H130 with bond length of 1.639 Å, 1.708 Å, 1.785 Å, 2.126 Å, and 2.232 Å, respectively. Surface analysis of refined carrageenan biocomposite film showed an increment of oxygen concentration by 16.4% which could probably suggest the development of H-bond crosslinking between κ-carrageenan, crosslinker, and cellulose nanocrystals (CNC). Role of H-bond networking in the development of refined carrageenan biocomposite hard capsule is important to improve the material property. Thus, it will be suitable for hard capsule application with a great potential for drug delivery industry.