Dissertation for M.Sc degree
Department of Wood and Paper Engineering
October 2013
Abstract:
In this research, the physical and mechanical properties of nanocomposites obtained from cellulose nanofibers and polyvinyl alcohol polymer were investigated. Nanocomposites were prepared by mixing polyvinyl alcohol polymer as degradable matrix and nanofibrocellulose suspension as natural degradable reinforcing phase. Cellulose nanofibers were prepared by super grinding method from Bergan needle mixture. Cellulose fibers were evaluated using AFM atomic force microscope and their diameter was measured to be 10+32 nm. Polyvinyl alcohol polymers in order to prepare polymer solution in water. The distillate was dissolved. Nanocomposites were prepared by solution molding method after mixing polymer solution with cellulose nanofiber suspension. Mechanical properties were measured at 55% humidity and a significant increase in mechanical resistance was observed with increasing nano percentage. The results of mechanical properties showed that Young's modulus and tensile strength were 97 and respectively. has increased by 80%. Morphological examination of the produced films by means of field emission electron microscope FE-SEM showed that the compatibility and proper interface between the polymer and cellulose nanofibers has been achieved. Also, there was a suitable distribution of cellulose nanostructures in the polymer. In examining the contact angle properties of the produced films, no significant increase was observed and no significant difference was observed based on Duncan's grouping.
Key words: nanocomposite, cellulose nanofiber, polyvinyl alcohol, mechanical properties
Chapter 1
Introduction and General
1-Introduction
Environmental pollution and the ways to deal with it is one of the issues that has attracted the attention of many researchers, and the trend towards nature can be seen in most of the advanced and industrialized countries today. Although nature has the ability to self-purify the climate, but with the increase in population, rising living standards, and the growth of industries, the speed of pollution is often higher than nature's self-purification. (Noshirvani 1389)
Until 1960, industrialized countries did not pay much attention to environmental pollution. In 1960, the first air pollution alarm was sounded in Los Angeles, USA. Photochemical smog in these areas caused watery eyes, throat irritation and suffocation. Since then, by examining the changes that have occurred in the composition of the atmosphere and issues such as; Destruction of the ozone layer, acid rain, photochemical solution and greenhouse effect, many efforts were made to better understand the chemistry of the environment, and little by little, the urgent need to control environmental pollution was felt to maintain a sustainable development in the world. (Almasi 1388)
Plastics used are one of the polluting factors of the living environment. Due to their non-biodegradable nature, these compounds remain in the environment and cause environmental pollution.
Since 1970 and with the worsening of the problem of landfilling worldwide, the use of biodegradable polymers has been raised, and the first issue was regarding garbage bags and disposable materials, so that 30% of the plastics produced are for one-time use and only 2% of it is recovered. Therefore, biodegradable polymers were proposed as a suitable alternative to common plastics. (Noshirvani 2019)
To solve this problem, researchers have thought of using biodegradable compounds. Compounds that are easily destroyed in the environment and enter the carbon cycle. Biopolymers are a suitable alternative to synthetic compounds, they are obtained from renewable sources and are found abundantly in nature.
(images and tables can be seen in the main file)
1-1 Polymers and their types
Polymers are large molecules that are composed of a large number of repeating identical units called monomers. have been Polymers generally have a molecular weight greater than 5000. Polymers have been very effective in human life for a long time, and today they have become the most important subject of research.Synthetic polymers are mainly prepared from petroleum sources. Production and consumption of petroleum polymers approximately since the middle of the 20th century. It has started and progressed increasingly. In Figure 1-1, the trend of increasing consumption of this type Polymers have been shown during different decades (David teegarden, 2004).
(Images and tables can be seen in the main file)
This increase in the consumption of synthetic polymers (oil-based) due to limited oil resources, non-degradability in the environment and its pollution has caused many concerns and attracted the attention of scientists. It is directed towards investigating natural polymers (biodegradable).
Natural polymers are produced in nature by the activity of a wide range of living organisms such as plants, animals and bacteria. These materials are simply broken down into their components by the activity of living organisms and do not remain in the environment. The production and use of these polymers in the industry for this purpose and with the aim of having an industry in the service of sustainable development and preservation of natural ecosystems is on the agenda of many advanced countries. Some major types of natural polymers you can see in the table below (David teegarden, 2004).
Biodegradable polymers are divided into natural and unnatural categories based on their constituents in terms of origin.
1-1-1-Biodegradable polymers with natural origin
Biodegradable polymers with natural origin are divided into six groups; Polysaccharides, such as: cellulose starch and proteins, polyethers produced from microorganisms or plants, such as: polyhydroxyalkanoates or polyhydroxybutyrate, polyesters made based on natural monomers such as polylactic acid. 1-1-2-biodegradable polymers Synthesis
There are many biodegradable polymers that are produced from petrochemical raw materials, including the following aliphatic polyesters:
polyglycolic acid
aromatic polyesters or combinations with aliphatic polyesters
Polyvinylalcohols
Modified polyolefins
-1-3- Polyvinyl alcohol
Poly(vinyl alcohol) is the largest polar synthetic polymer produced in the world in terms of abundance, and its biodegradability in the environment is its most important feature. Poly(vinyl alcohol) is a semi-crystalline and water-soluble polymer with special physical and chemical properties. Due to the instability of vinyl alcohol monomer and its unwanted transformation into aldehyde, this monomer cannot be polymerized and transformed into poly(vinyl alcohol). Therefore, this polymer is usually obtained from the saponification reaction of polyvinyl acetate. (Kokabi et al., 2007). Due to its special properties, such as compatibility with the environment, solubility in water, high tensile strength, high resistance to corrosion in alkaline environments, low gas permeability, and favorable optical properties, poly(vinyl alcohol) has wide applications in the textile, papermaking, packaging, and medical industries (Lyoo et al., 2000). Its molecular weight is very important in many applications of poly (vinyl alcohol), including in the production of synthetic fibers and also as a coating for paper industry. In other applications, molecular weight is taken into consideration due to its direct effect on the physical and mechanical properties of the polymer. (Navarchian and Mousazadeh, 2010)
The chemical properties of these polymers, that is, the reactivity of their abundant hydroxyl groups, strongly depends on the amount
of the remaining acetyl groups or their degree of hydrolysis. Theoretically, partially hydrolyzed grades can be considered as a mixture of vinyl alcohol and vinyl acetate polymers. The relationship between the degree of hydrolysis and polymer properties leads to the production of different types (grades) of poly(vinyl alcohol) with diverse properties. This variety in the properties of poly(vinyl alcohol) makes it possible to use different applications. One of the most important applications of these polymers is to use them as a matrix in biodegradable nanocomposites. 1-2-nanocomposite is a multi-phase solid, one or more of which has dimensions of nanometers. has This causes It leads to unique properties compared to conventional composites.