Production and Characterization of Electrospun Cellulose Acetate/zinc Oxide (ca/zno) Nanocomposite

This career episode presents my unpublished undergraduate thesis conducted individually during my final year under the supervision of my major adviser. I fulfilled this as a final project in completion for the degree of Bachelor of Science in Chemical Engineering Major in Pulp and Paper Technology. The duration of the study was three (3) semesters from 1st semester academic year 2014-2015 to 1st semester academic year 2015-2016. I conducted and submitted the study at the Department of Forest Products and Paper Science, College of Forestry and Natural Resources (CFNR) and the Department of Chemical Engineering, College of Engineering and Agro-Industrial Technology (CEAT), University of the Philippines Los Baños (UPLB). I borrowed the portion of the electrospinning set-up from the Fiber Utilization and Technology Division of the Philippine Fiber Industry Development Authority (PhilFIDA), Diliman, Quezon City, Metro Manila, Philippines. I did the Fourier transform infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM) tests at the Chemistry Instrumentation Room II, Chemistry Department and the Surface Physics Laboratory, Physics Department, respectively of De La Salle State University (DLSU). I performed the antimicrobial tests at Microbiology Laboratory of the Institute of Biological Sciences (IBS), UPLB. B. Background (CE 1.2.) Nowadays, reported cases of microbial contamination in different areas in the Philippines are common in drinking water. The presence of microorganisms on water surfaces causes risk to human health. The development of alternative antimicrobial materials was emphasized as they can find the key to the inadequacy treatment of wastewater from different sources. Generally, I applied my knowledge as a chemical engineering student using nanotechnology, electrospinning and membrane filtration to introduce a more efficient, stable and durable process to resolve the problem on water pollution.

Thus, I focused on the study of electrospun cellulose acetate membrane embedded with zinc oxide nanoparticles for membrane filtration application. (CE 1.3.) Zinc oxide nanoparticles are known for their antibacterial activity. On the other hand, electrospun fibers have high filtration efficiency. Microbial contaminated effluents can be treated using the antibacterial electrospun nanofibers. Removing this microorganisms reduces the health risks. In detail, my specific objectives for the study are: 1. to develop a suitable process for the production of cellulose acetate nanofibers embedded with zinc oxide nanoparticles using electrospinning; 2. to determine the functional groups and compounds that can be observed with the nanofibers upon embedding zinc oxide nanoparticles; 3. to characterize the effects of embedding zinc oxide nanoparticles on the fiber morphology of the electrospun cellulose acetate nanofibers; 4. to compare the method of introducing zinc oxide nanoparticles in nanofibers using commercial zinc oxide and precursor; and 5. to test the viability of the electrospun membranes for antibacterial applications using the zone of inhibition method. C. Professional Engineering Activity (CE 1.4) On my case, I enrolled the thesis course (PPT 200 total credit units of six (6)) into three (3) terms (two (2) units per term). At first, I consulted my adviser on what topic to work on and noted his suggestions. There were other independent studies in the university that worked on the application of cellulose acetate on the various fields of engineering. I conducted initial researches on cellulose acetate fibers and chose its application on waste water treatment through membrane filtration. By reviewing related references, I came up with the preliminary study to present to the panel consisting of one (1) adviser and two (2) engineering professors. I prepared the topic presentation using Microsoft PowerPoint.

The panel discussion identified the scope, limitation and possible problems that I could encounter prior to working on the project. (CE 1.5) After the topic proposal, I further investigated relevant literatures on my study through accessing our university library for online published journals, previous undergraduate theses and other engineering reading materials. Based from these recent researches, I outlined and performed the preliminary methods to determine the optimum experimental conditions for the fabrication of electrospun nanofibers. The identified critical parameters were solution properties, processing parameters and ambient parameters. I found out that the solution concentration and feed flow rate greatly affect the fiber formation. I emphasized on these variables by setting different concentration and flow rate to achieve stability. Fiber morphology is very important for membrane formation as it determines the membrane’s porosity and surface area efficiency for waste water filtration. Before continuing the study, I showed my panel the outcomes I got from the initial experiment and raised the problems encountered. In finalizing, I revised some procedures to settle on my final objectives and methodology. (CE 1.6) In gathering the materials to be used, the reagents such as cellulose acetate, dimethylformamide (DMF) and acetone were purchased commercially.

All other needed reagents and apparatus were available in the Wood Chemistry laboratory. Prior to the experiment, I presented a Ghant chart to my adviser to be able to meet the project deadline. Likewise, before I performed the experiment, I coordinated to the laboratory manager and technicians with regards the use of the laboratory. In addition with existing laboratory safety procedures, I developed safety procedures for chemical handling, hazardous chemicals disposal and electrical safety. I read the material safety data sheet of the chemicals I used, specially the regulated solvents, to understand the potential hazard and their proper disposal. I labelled properly all the samples and reagents used to avoid mix ups and worked under the fumehood for strong acids, bases and solutions.

Due to lack of resources, the electrospinning set up I used was devised laboratory-scale, it was assembled using the available equipment we have in laboratory and some parts were borrowed from PhilFIDA. Hence, I designed the standard operating procedure for this experiment to be followed all throughout the study including safety precautions. I identified the risk of the apparatus which were the high voltage requirement (20kV) and solvent vapour exhaustion. I placed the apparatus in an isolated empty classroom, with no sources of electro-static attraction, proper ventilation, and maintained safe working distance. It was also noted that the working space can only be accessible by authorized personnel. As the user, I equipped myself with proper personal protective equipment such as insulated footwear, face mask and safety goggles to minimize static discharge and exposure to solvent. (CE 1.7)

I noted from my initial literature reviews the key points of the electrospinning process. I learned the suitability of electrospinning process in producing polymeric nanofibers and the appropriate properties for the electrospun fibrous membrane such as high surface to volume ratio, high chemical resistance and high tensile to make it a good material for filtration. I produced the CA/ZnO nanocomposite membrane through the electrospinning process in laboratory scale using zinc acetate precursor. I set the concentration of CA to 15 % (w/v) with varying the concentration of zinc acetate (0, 0.5, 1.0 and 2.0 % w/w). For data accuracy and precision, I made two (2) trials per test run which summed up to 8 nanocomposite samples. All procedures were carried out at controlled room conditions. I used the thermohygrometer to monitor and record the relative humidity and temperature inside the room for every experimental run. However, during electrospinning I encountered fluctuations on the ambient condition readings, I identified this as a problem as this could affect the samples on my further analysis. Immediately, I collected the composite membranes and dried them inside the oven set at 80 oC for 6 hours. (CE 1.8)

I subjected the electrospun CA/ZnO nanocomposite membranes to FTIR spectroscopy to determine the functional groups and compounds that can be found in the electrospun nanofibers. I prepared the samples quantitatively using the anhydrous potassium bromide (KBr) pellet method then examined using Thermo Scientific Nicolet 6700 FTIR. The spectra were recorded in the absorbance and transmittance band mode in the range of 4000 to 400 cm-1. The functional groups of most organic compounds were revealed in the infrared spectrum. I analyzed the stack spectra of the samples and observed the highest peak occurred at lower wave number. I validated this conclusion from reliable organic chemistry references, that it was the presence of Zn-O bending considering the compound to be inorganic. The occurrence of strong ionic bond of the metal ion broadened the peaks as this accounted the weak stretching vibrations. Moreover, I also generalized that the characteristic peak of ZnO in the spectrum took place at the highest concentration (2.0 %) of Zn compounds in the nanocomposite. I correlated this with the height of the spectrum is proportional to the magnitude of the concentration. (CE 1.9)

I used SEM to characterize the morphology of the nanocomposite samples. The samples were coated and subjected to JEOL 5310 scanning electron microscope. I measured the fiber diameter and bead area each micrographs using the ImageJ® version 1.49 then recorded the measurements on Microsoft Excel for tabulation and mathematical computations. I calculated the average fiber diameters, average number of beads and average bead area of the electrospun nanocomposites. I plotted the average fiber diameter profile of electrospun nanocomposites at different concentration for graphical representation. Using background of my waste water engineering courses, for filtration application to have enhanced efficiency, the acceptable diameter should not be more than 500 nm. I was able to identify that fiber diameters of samples control and 2.0 % met the requirement for nanofilter media. Applying engineering analysis, I generated the trends and correlations of my data for accuracy and reliability.

I verified the effects of zinc acetate concentration on the fiber morphology using Minitab 17. I analysed using Tukey Simultaneous Comparison test (difference of means) and One-Way ANOVA. At 95 % confidence level with p-level < 0.05, I found out the significant difference on concentration. In this case, I concluded that the precursor concentration is an important electrospinning parameter in optimizing the fabrication of electrospun CA/ZnO nanocomposite. At high zinc acetate concentrations, the preservation of fibrous structure arose. Yet, there were still presence of crystalline Zn particles. Furthermore, increasing the precursor concentration in the solution results in uniform bead-free fibers. (CE 1.10)

With the assistance of my Microbiology professor, I carried out the antimicrobial test of electrospun nanocomposites using pure CA as control on Gram positive bacteria S. aureus and Gram negative bacteria E. coli using the zone of inhibition method under normal lighting condition. MacFarland standards was used with known population of bacteria swabbed in each plate (3 replications). After few days allowing the bacterial inhibition, I faced the most challenging part of the project. I observed that no antimicrobial activity against S. aureus and E. coli for all the precursor concentrations of the sample tested. This is contradicting with my hypothesis. I reviewed my record book, and I was able to recall the fluctuations on the relative humidity during production of the membranes. Since I recreated the electrospinning room, the ambient parameters were uncontrollable. I classified this factor as extraneous as it greatly affected the results of my study. By further investigation, I accounted the negative activity of the electrospun nanocomposite to the unsuccessful thermal decomposition of zinc acetate to zinc oxide. Instead of zinc oxidation, Zn2+ ions reacted to the water on the surroundings forming a complex chelate.

I represented series of chemical equations to illustrate the reaction. I reported and consulted the result instantly to my adviser for appropriate corrective action. After the meeting, I decided to repeat all the procedure utilizing commercial ZnO at the optimum concentration of 2 % (w/w). Still, I followed the same parameters and conditions as CA-zinc acetate nanocomposite for the preparation, fabrication and characterization. I was able to obtain different results on the characteristics compared using the precursor. Similarly, there was no zone of inhibition for antimicrobial activity. However, the sample had positive result on the activity of minimum inhibitory bacterial concentration. I added this on my objectives as well as included it on my data interpretation and discussion. I recorded all the difficulties encountered throughout this study and listed recommendations for future researches. (CE 1.11)

I consolidated all the data from the computer softwares and record book I used together with my engineering analyses, methods, results, conclusions and references to be documented in my thesis paper draft. I asked my adviser for appointments to have informal discussions on the findings of my study before proceeding to the final defence and thesis writing. With his guidance, I accomplished my presentation created through Microsoft PowerPoint. At the time I presented my final project to the panel, I highlighted the optimum parameters on producing electrospun CA/ZnO nancomposite membrane for filtration application. Another key point is the embedment of ZnO and Zn2+ occurred at the highest concentration. Additionally, I explained that no inhibitory activity observed from the nanocomposites. I supported this finding using the concepts on my chemistry courses. (CE 1.12) On my final thesis writing, I followed the CEAT thesis format guidelines 3rd edition revised May 2015. To avoid plagiarism and other forms of academic dishonesty, I made sure that all the references I used were cited. The required bibliographic formats were modified American Psychological Association (APA) style. With the approval of my thesis panel and respective faculty in charge, I successfully completed my final project. D. Summary (CE 1.13) Upon finishing my undergraduate thesis, I developed my interest in the wastewater and environmental aspect of chemical engineering.

I was able to identify my forte on relating scientific research to higher chemistry concepts, unit operations, unit processes, process safety and engineering analysis as well as overcame my weaknesses. Likewise, the study I did was another accomplishment on the department’s continuing research on nanotechnology and its application. It can be continued in the future for my master’s degree. During the process, I developed good habits on communicating and updating my adviser every phase that is done to meet the objectives. I also asked questions to my adviser and panel whenever the situation is unclear. My consultation with them led me to further study the appropriate engineering and statistical software to use on data interpretation and analysis. I coordinated properly with different personnel to finish my thesis productively within the given time frame.