ABSTRACT
Bacterial and fungal growth in paints were studied .Bacteria isolated from used and unused B-lux (emulsion and gloss/oil) and Saclux (emulsion and gloss /oil) were: Bacillus sp, Pseudomonas sp, Micrococcus sp and Serratia sp. Fungi isolated from used and unused B-lux (emulsion and gloss/oil) and Saclux (emulsion and gloss/oil) were: Aspergillus niger, Aspergillus fumigatus, Rhodotorula sp and Aspergillus flavus. Average count for total viable microorganisms in used paints ranged from 2.0×104 to 4.3×104cfuml-1 Its average optical density ranged from 0.39 to 0.41, its average pH ranged from 5.7 to 7.6 while for the unused paints, average counts of total viable microorganisms ranged from 1.6×104to 4.4×104 cfuml-1, its average counts for Optical Density ranged from 0.18 to 0.44, its average pH ranged from 5.7 to 7.6. Statistical analysis indicated that there was significant difference (p˂0.05) in the growth of microorganisms between used and unused paints. The use of potent biocides and reduction of contamination by microorganisms during production of paints by paint companies should not be optional but compulsory and should be enforced by the regulatory agencies to ensure the safety of these paints from microbial attack.
TABLE OF CONTENTS
Certification i
Dedication ii
Acknowledgements iii
Table
of contents iv
List
of tables and figures vii
Abstract ix
CHAPTER ONE
1.0 INTRODUCTION 1
1.1 Definition of Paints 1
1.2 History of Paint 1
1.2.1 Painting in Nigeria 3
1.3 Uses and Importance of Paints 6
1.4 Reasons for Painting 8
1.5 Categories of Paints 8
1.5.1 Industrial Paints 8
1.5.2 Decorative Paints 9
1.6 Types of Paints 9
1.6.1 Solvent Based Paints 9
1.6.2 Water Based Paints 10
1.7 Composition of Paints 11
1.8 Properties of Paints 14
1.9 Factors Influencing Growth of Microorganisms
in Paints 14
1.10 Biodeterioration and Biodeterioration of
Paints 14
1.11 Control of Microorganisms in Paints 15
1.12 How to Identify Deteriorated Paints 15
CHAPTER TWO
2.0 LITERATURE
REVIEW 16
2.1 Environmental
Factors That Promote the Growth of Microorganisms in Paints 16
2.2 Researches Made By Researchers on Paints 17
2.3 Microorganisms
in Paints 19
2.4 Aim
and Objectives 20
CHAPTER THREE
3.0 MATERIALS AND METHODS 21
3.1 Study Location 21
3.1.2 Laboratory Location 21
3.1.3 Sources of Paints 21
3.2 Materials 22
3.2.1 Instruments 22
3.2.2 Reagents Used 22
3.2.3 Microbiological Media Used 22
3.3 Collection
of Samples 22
3.3.1 Collection of Unused Samples 22
3.3.2 Collection of Used Samples 22
3.4 Laboratory
Analysis 23
3.4.1 Analysis of Used Samples 23
3.4.2 Analysis of Unused Samples 23
3.5 Isolate
Purification 23
3.6 Characterization and Identification of
Paint Utilizing Bacterial Isolates 24
3.6.1 Gram Staining 24
3.6.2 Oxidase Test 24
3.6.3 Catalase Test 24
3.6.4 Citrate Test 25
3.6.5 Indole Production Test 25
3.6.6 Methyl Red-VogesPraskeur’s Test 25
3.7 Screen Test for the Utilization of the
Paints by the Bacterial and Fungal Isolates
26
3.7.1 Monitoring the Growth Profile of Bacterial
and Fungal Isolates in Paints 27
3.8 Statistical Analysis 27
CHAPTER
FOUR
4.0 RESULTS 28
CHAPTER FIVE
5.0 DISCUSSION, CONCLUSION AND RECOMMENDATION 46
5.1 Discussion 46
5.2 Conclusion 49
5.3 Recommendation 50
REFERENCES 51
APPENDIX
LIST
OF TABLES
|
|
|
Page No.
|
|
Table1
|
Morphological, microscopic
and Biochemical profile of Bacteria isolated from both used and unused paints
|
31
|
|
Table2
|
Morphological and
microscopic characteristics of fungi isolated from both used and unused
paints
|
32
|
|
Table3
|
Percentage of occurrences for bacterial isolates
|
33
|
|
Table4
|
Result after the Screen test
|
34
|
|
Table5
|
Microbial growth at different temperatures at 48
hours interval
|
35
|
|
Table6
|
Enumeration count for used and unused paints
|
36
|
|
Table7
|
Statistical analysis for dilution factors ×105and
×106 (fifth and sixth fold dilution factors)
|
37
|
LIST
OF FIGURES
|
S/N
|
Title
|
Page No.
|
|
Fig.1
|
Graph showing the pH, Optical Density and Total
viable count of mixed fungal culture for used B-lux oil at days interval
|
38
|
|
Fig.2
|
Graph showing the pH, Optical Density and Total
viable count of mixed fungal culture for used Saclux emulsion at days
interval
|
39
|
|
Fig.3
|
Graph showing the pH, Optical Density and Total
viable count of mixed bacterial culture for used Saclux emulsion at days
interval
|
40
|
|
Fig.4
|
Graph showing the pH, Optical Density and Total
viable count of mixed bacterial culture for used B-lux oil at days interval
|
41
|
|
Fig.5
|
Graph showing the pH, Optical Density and Total
viable count of mixed bacterial culture for unused B-lux emulsion at days
interval
|
42
|
|
Fig.6
|
Graph showing the pH, Optical Density and Total
viable count of mixed fungal culture for unused B-lux emulsion at days
interval
|
43
|
|
Fig.7
|
Graph showing the pH, Optical Density and Total
viable count of mixed bacterial culture for unused Saclux oil at day’s
interval
|
44
|
|
Fig.8
|
Graph showing the pH, Optical Density and Total
viable count of mixed fungal culture for unused Saclux oil at day’s interval
|
45
|
|
|
|
|
CHAPTER ONE
1.0 INTRODUCTION
1.1
Definition of Paints
Paint is a mixture of liquid and
powder; the powder is the pigment that gives colour to the paint and the liquid
(binder) binds it and allows it to spread. In paints, the combination of the
binder and solvent is referred to as the “vehicle” which is essentially
composed of volatile organic compounds (VOCs). Pigments and additives are
dispersed within the vehicle. The amount of each constituent varies with the
particular paint. Typically solvents include toluene, xylene, methyl ethyl
ketone (MEK) and methyl isobutyl ketone (MIBK). The solvent (thinner) is also
used to make the paint easier to spread (Johnson et al, 2009).
Paint is one of the oldest
synthetic substances known to mankind, with a history stretching back into
pre-historic times (Ravikumar et al.,2012). Paints are stable
mechanical mixtures of one or more pigments and various chemical components
(Odokuma et al.,2013; Sharma 2006). The paints consist of: (a)
binder/additive, which adhere paints to the surface, (b) pigments, which give
the paint a color and prevent corrosion, and (c) solvents to make the paint spreadable
(Ravikumar et al.,2012).
1.2
History of Paint
The oldest evidence of painting was
left by primitive peoples. Cave dwellers and hunters left paintings of the
animals that they hunted. Paintings in caves have survived because of their
protected locations. Most cave paintings used the colors black, red, and
yellow. Chemical analysis of these early paintings has shown that the main
pigments used were iron and manganese oxides. To form applicable paints, the
pigments were possibly mixed with egg white, animal fats, plant sap, or water.
The resulting mixture of binder-containing pigments could then be applied to
cave walls (Lambourne et al., 1987).
During the period 3000-600 BC, many
paint-making advances were made by the Egyptians. They not only developed
pigments with a wider range of colours but are also credited with producing the
first synthetic pigment (Egyptian Blue) and developing the first lake pigments.
Preservative paints and varnishes were also used during this time (Reisch,
1995).
Drying oils as part of varnishes
were used during the period 600 BC-400 AD by the Greeks and Romans. In the
tenth century AD, Theophilus describes a varnish made by heating amber resin
with linseed oil. Varnish was used to protect painting on wood during the middle
Ages. Pigments were suspended in a varnish like the one described by Theophilus
in order to make a more durable paint (Reisch, 1995).
For hundreds of years, paint
formulations were handed down from one generation to the next and were often
carefully guarded. Paints were produced in small batches, with the procedure
being a relatively expensive one and the product not affordable to many.
However, the demand for paint and coatings became great enough that by the late
eighteenth and early nineteenth century it became profitable to make paint for
wider consumption (Reisch, 1995).
The first paint and varnish
factories were established during the nineteenth century. The industrial
revolution and the mass production of the automobile strongly influenced the
growth of the paint and coatings industry. The need for anti-corrosive coatings
as well as other special-purpose coatings helped to accelerate the rate of
scientific discovery. Titanium dioxide, the white pigment that would replace
white lead, was introduced in 1918. After the middle of the twentieth century,
the natural oils that had been used in paint formulations were replaced by
synthetic resins. Today’s coatings manufacturers offer a wide variety of products
to protect, decorate, and perform special functions on the surfaces of products
ranging from children’s toys to spacecraft (Lambourne et al., 1987).
In the later part of the twentieth
century, society’s growing environmental awareness has presented a new
challenge to the paint and coatings industry, to produce coating products that
meet the demands of manufacturers and consumers and at the same time comply
with the government environmental constraints. Certain chemicals have been
shown to be toxic and hazardous to humans and/or their environment. Regulatory
agencies are setting strict standards with which coatings manufacturers need to
comply. This has led to a greater interest in developing coatings such as those
that use water instead of volatile organic compounds in their formulation and
powdered coatings that are absolutely solvent-free (Reisch 1995).
1.2.1 Painting in Nigeria
Painting in Nigeria has its roots
in the ancient painting traditions ofNigerian societieswhich are the
Hausa/Fulanis, Igbos, Yorubas, Benin, Efiketc. Abodunrin and Oladiti (2015)
states that body painting, a style of painting, is as old as tradition of the
cultures of the Nigerian people and remains the mostpopular form and
conspicuous forms of painting found among women during ceremonial occasions
like wedding and religious festivities especially in the Yoruba, Hausa, Fulani,
Kanuri and Igbo cultures. Its main objective is to enhance beauty.
In pre-colonial societies in
Nigeria, Campbell (2007) observes that shrine painting is also an observable
feature of painting practice in Yoruba religious activities, stating that the
surface used for this kind of painting is the wall. It gives an elaborate
expression on the symbols and meaning of religious images as exemplified in the
cultural beliefs of the tradition of the people. In essence these paintings
were graphic explanations of the phenomena the represented. It is instructive
to note that in traditional Nigerian societies, all art was considered communal
property; hence, the origination of these paintings could not be attributed to
any individual. Abodunrin and Oladiti (2015) reinforce this view when they
state that the names and pioneers of the various forms of painting in the
precolonial Nigerian society were unknown. Perhaps, this is because their works
and memories of their painting were not documented by modern African Art
Historians. However, it is generally believed that the practice of painting is
generally domiciled in the vocation of the craftsmen among the Yoruba.
Nigeria’s interface with Western
(European) civilization and culture from the 15th century brought
about a gradual influence of the latter on the former, an influence that would
eventually give rise to new forms of Nigerian arts in the period of
colonialism: mid-19th to mid-20th centuries. The impact of
colonialism on painting in Nigeria is captured thus by Abodunrin and Oladiti
(2015): The development of painting in colonial Nigeria is a turning point in
the history of art in Nigeria. This period marked a shift in the cultural
techniques of painting from religious and decorative purpose to new forms in
techniques, materials and style of painting. Unlike the pre-colonial forms of
painting that is applied on wall surface and the human body. The colonial
period witnessed the application of synthetic substances to create a representational,
abstract picture or design on surfaces such as canvas, board, paper, wall and
host of others. Synthetics colours were also used which often time are
imported. The artistic development during this period was bold and tedious but
steady in the face of numerous constraints created by colonial influence with
European contact with Nigeria.
The contact with British colonial
authorities greatly influenced the art of painting in pre- colonial Nigeria.
Irivwieri (2010) specifically refers to the period between 1900 and 1938 as the
Period of Sowing the Seed of Formal Art Training in Nigeria. This manifests
with the introduction of formal and non-formal art training with the effort of
Aina Onabolu who initiated this transition into the practice of painting. Aina
Onabolu was one of theforemost Nigerian artists that recognize the importance
of teaching the society through arts. Despite British colonial indifference to
the development of arts, he openly lobbied the colonial authorities for the
establishment of schools in Lagos. Although the arts and culture in Nigeria
during this period did not assume the proportion of the Renaissance that swept
through 14th- 17thcentury Europe, it was still an awakening in Nigerian
context.
Another major contributor to the
development of painting in colonial Nigeria was Kenneth Murray, a British
national who was invited by the colonial government to modify the art
curriculum in the newly established Nigerian Art School. Murray stimulated the
appetite for traditionalism in art as opposed to Western influence or
convention, believing that the forms of representation of art generally and
painting in particular should be more of African than European orientation. To
this end, he encouraged the adaptation of indigenous elements and forms which
tremendously influenced the style of painting in Nigeria. For these efforts,
Murray is described by Art historians as the pioneer of modernist movement of
Art in Nigeria (Oloidi, 2008).
Abodunrin and Oladiti (2015) wrote
that: “By 1950’s, Nigeria had developed two different and divergent styles been
championed by the pioneer Aina Onabolu, the other by Kenneth Murray. Onabolu’s
style of painting is credited for his philosophical belief that painting should
be a universal language of expression which can be seen in his realistic and
naturalistic tendency. Kenneth Murray’s style of painting is more of cultural
forms and adaptations of African elements which metamorphose into individual identity.”
Other painters who followed Onabolu’s footsteps include AkinolaLasekan
(1916-1972), Eke Okebolu (1916-1958) and J.D. Akeredolu, among others. On the
hand, the likes ofBen Enwonwu (1921-1994), P.L.K Nnachi, Uthman Ibrahim, C.C.
Ibeto and A.E Umana got their formal training in painting through the effort of
Kenneth Murray.
The 1960 independence of Nigeria
marked the beginning of the development of painting in Post- colonial Nigeria.
It saw the establishment of art Schools such as the new art departments at the
University of Ife (now Obafemi Awolowo University) and University of Nigeria,
Nsukka.
These were in addition to the
already existing art department in the University of Ibadan and the Osogbo
School which was established through the efforts ofthree expatriate:
GiorginaBeir, UlliBeier and Suzanne Wenger (Oloidi, 1995).
With political independence came
agitations for freedom in virtually all facets of life which include the
expression in art practices. Arts and paintings produced during this period
appeared to be characterized by individualism of style. Abodunrin and Oladiti
(2015) wrote that after 1960, painters like Uche Okeke, Demas Nwoko and
JimohAkolo also produced abstracted forms; however, the works of artists like
Yusuf Grillo were more of stylization, abstraction and naturalism were
therefore unique with a pattern of elongation of form which brings the work
clearer to the audience. Other major players in the 1960s include
ErhaborEmakpae, Abayomi Barber, among others.
Following the generation of the
1960s is the generation of KoladeOshinowo, Sina Yusuf, Dele Jegede and
GaniOdutokun. Most of the painters in this group also paint naturalistic images
but occasionally oscillate between abstraction and naturalism. The 1960’s and
the succeeding decade represented a sober reflection when Nigerian painters
began to question themselves on the role they ought to be playing in modern
Nigeria.This temperament has continued to dominate the painting landscape in
Nigeria, even till date. This is however, not implying that there is a total
absence of the disciples of the “Art for Art sake” school. The point being made
is that painting is still largely utilitarian in the contemporary Nigerian
society. One of the leading lights of painting in contemporary Nigeria is Bruce
Onobakpreya, a pioneer member of the Zaria Art Society that produced works that
were characterized to a large extent by individualism in various styles and
techniques.
1.3 Uses
and Importance of Paints
(a)Protection
Paint is used to protect all sorts
of buildings and structures from the effects of water and sun. Wooden buildings
such as houses are usually painted because a coat of paint prevents water
seeping into the wood and making it rot. The paint also helps to prevent the
wood from drying out in the hot sun.
Metal structures and objects of
all sorts are painted to stop them from rusting. A very large steel structure
such as a bridge must have a team of painters who keep the paint in good
condition all the time.
(b) Decoration
Paint is used to decorate all
sorts of objects. Since pre-historic times, people have painted the inside
walls of their houses to make them look attractive. Painting and decorating the
exterior (outside) and interior (inside) of houses is an important industry in
many countries. There are many types and colours of paint to choose from.
All sorts of other objects are painted to make
them attractive. This includes furniture, toys, tools and utensils, and street
fittings. Sometimes things made of wood such as furniture are painted in
decorative patterns. In some countries, many people enjoy decorating furniture
and other small things like trays and boxes. This is one form of what is often
called Folk Art. In other countries such as Japan, painting furniture is a very
skilled profession and an antique piece of decorated furniture is very
valuable. Other people enjoy the hobby of painting small objects such as model
planes or soldiers.
(c) Information
Paint is a very good way to give important information to people, using
painted signs. Painted signs include lane markings on the road, street signs of
all sorts, advertising signs and warning signs. Paint has become the most essential item in modern times, whether it is
meant for residential purposes, or industrial applications. Decoration and
protection are two main purposes of all paints. Therefore, it is obviously
thought that paint-life, as dry film, has to be as long as possible. The
technology has advanced many folds in recent years to achieve this aim, with
many new advances in binder systems available for formulating paints, newer and
safer pigments, and innovative formulation as also application technology of
paints for their usage (Johnson et al,
2009). These efforts are oriented to achieve better chemical properties of
formulated paints, so that paint films would give extended life to the
satisfaction of the ultimate customers. A new parameter added to these
technical developments, is to probe the microbial stability of paints, since
any such growth on painted surface is known to deteriorate the functional usage
of paints. This property has assumed prime importance in modern times, last two
decades, in paints used in homes (Johnson et
al, 2009).
1.4
REASONS FOR PAINTING
By careful selection and mixing of the
film-former, pigments and thinners available, the paint manufacturer can
provide materials that under most known conditions will satisfy the
requirements for reasons of painting as follows:-
(a) To
protect the surface;
(b) To
make the surface washable
(c) To
decorate the surface
(d) To
identify the surface
(e) For
emotions and warmth.
1.5 Categories of Paint
There
are two main categories of paints, industrial paints and decorative paints.
1.5.1 Industrial
paints
Industrial paints are mainly used
for high performance purposes like in automobile coatings, steel structures and
marine coatings. It also functions as intumescent coatings for fire resistance.
The common polymers used in its manufacture are polyurethane, epoxy, fluoro polymer
and moisture-cure urethane. Industrial paints can be grouped into; inorganic
zinc, phosphate, xylan and physical vapour deposition (PVD) (Seidal et al., 1993).
1.5.2 Decorative paints
Decorative paints are further
classified on the basis of solvents used as water based (plastic or latex) or
oil based (enamel) paints and are purposely for interior or exterior
decorations of buildings. Linseed oil is the most commonly used binder in
oil-based paints and consists of triesters of glycerol with unsaturated fatty
acids. Pigments in powders are evenly dispersed in the binder to form a
colloidal suspension. The pigments provide colour and hiding power, improve
strength and adhesion of the paint film and can change gloss. The oil-base
binders react with oxygen from air and harden as they dry. The drying process
is accelerated by the action of driers like cobalt octanoate, Co[O2C(CH2)2CH3]2
which catalyses both the uptake of oxygen and decomposition of peroxides as
free radicals resulting in the hardened cross-link that bind the pigment to the
substrate (Seidal et al., 1993).
1.6Types
of Paints
The modern paints fall into two
broad types:
1.6.1
solvent-based paints
The oil-based or solvent-based
paints, thinned with mineral turpentine or other organic solvents (Odokumaet al.,2013).paints under this category include:
A. Semi-Gloss Finish: typically is used on trim to emphasise detail and elegance, and to show
off woodwork, such as on doors and furniture. It provides a shiny surface and
provides good protection from moisture and stains on walls. Its gloss does
however emphasise imperfections on the walls and similar surfaces. It is
popular in schools and factories where washability and durability are the main
considerations (Paint Finish
and Sheen Information, 2011)
B.
Flat Finish:
This paint is generally used on ceilings or walls that are
in bad shape. This finish is useful for hiding imperfections in walls and it is
economical in effectively covering relatively great areas. However this finish
is not easily washable and is subject to staining (Odokumaet al.,2013;
Gaylerde and Morton, 2001).
C.
Eggshell
Finish: This paint
has some sheen, supposedly like that
of the shell on an egg. This finish provides great washability, but is not very
effective at hiding imperfections on walls and similar surfaces. Eggshell
finish is valued for bathrooms because it is washable and water repellent, so
that it tends not to peel in a wet environment(Odokumaet al.,2013).
D.
Lacquer: is a solvent-based paint or varnish that produces an especially hard,
durable finish. Usually it is a rapidly drying formulation. (Sharma, 2006).
E. Enamel paint: Thistype of paint is formulated to give an especially
hard, usually glossy, finish. Some enamel paints contain fine glass powder or
metal flake instead of the colour pigments in standard oil-based paints. Enamel
paint sometimes is mixed with varnish or urethane to improve its shine and
hardness(Odokumaet al.,2013; Ravikumar et al., 2012).
F.
A roof coating is a fluid
that sets as an elastic membrane that can stretch without harm. It provides
Ultra Violet(UV) protection to polyurethane foam and is widely used in roof
restoration(Mitchell
and Ji-Dong, 2000).
1.6.2
Water based paints
‘Water based paints’, the
water-based vinyl or acrylic paints that may be thinned with water (Odokuma et
al. 2013). Water based are
primarily used for the interior or exterior decoration of buildings, offices
and homes.
A. Emulsion paints are
water-based paints in which the paint material is dispersed in a liquid that
consists mainly of water. For suitable purposes this has advantages in fast
drying, low toxicity, low cost, easier application, and easier cleaning of
equipment, among other factors (Odokuma
et al.,2013; Ravikumar et al., 2012).
B. Inks are similar to paints, except that they are typically
made using finely ground pigments or dyes, and are not designed to leave a
thick film of binder. They are used largely for writing or calligraphy
(Odokuma et al.,2013).
C. Finger paints are formulations
suitable for application with the fingers; they are popular for use by children
in primary school activities (Gaylerde
and Morton, 2001).
1.7 COMPOSITION OF
PAINTS
All surface coatings including
paints have principal components, these are discussed below: -A. FILM-FORMER
This is also known as the medium,
vehicle or binder whose purpose is as follows:
(a)
To
convert from the liquid coating to a solid dry film
(b)
To
bind the pigment particles together
(c)
To
provide gloss to the coating
(d)
To
make the coat adhere to the surface
(e)
To
provide resistance to water, chemicals and abrasives
(f)
To
hold the pigment in suspension
The film-formers commonly used are
Drying oils, Resins, and Oil-modified resins. Examples of Drying oils are
Linseed oil; Soya bean oil; Tung or Chinese wood oil; and dehydrated castor
oil; Examples of Resins are copal, rubber, lac, alkyd, coumarone, phenolic,
epoxy, polyurethane, polyvinyl acetate (PVA), acrylic silicon. While examples
of oil-modified resins are coumarone resin/tung oil, alkyd resin/linseed oil
(Isirima and Joshua, 2004).
B.
THINNER OR SOLVENT
This is sometimes called a diluent,
whose purpose is to make the coating liquid enough to be easily and evenly
applied by any method. It evaporates completely once the coating has been
applied. The thinner commonly used are water, white spirit, solvent naphtha,
xylol, methylated spirit and mixtures of special solvents.
The combination of a film-former
and a thinner produces a transparent coating which may be called a varnish
lacquer or clear finish. This type of coating has a limited use.
The most common type of coating in
use is paint, which is an opaque colour material. This quality is provided by a
third component called pigment (Isirima& Joshua,2004).
C.
PIGMENT:
There are different types of pigment;
they perform one ormore of the following functions:
(a) To provide opacity or
covering-power to the paint;
(b) To provide colour
(c) To aid the film-former in
protecting the surface.
The most commonly used pigment is
titanium white together with a wide range of coloured pigments and dyestuffs.
Titanium has a specific gravity of 4.2.Thereare also many other types of
pigments. Modern surface coating are complex materials, which contain also one
or more of the following components, depending upon the type of film-former
used or the use to which the coating is put(Isirima&
Joshua, 2004).
D.
DRIER, HARDENER OR CATALYST
These are substances, which ensure
that the coating is converted from liquid to the solid state; driers are added
to paints containing dry oils to speed up the drying process; curing agents,
catalysts or hardeners are used to convert epoxy and polyurethane resins into
hard films (Isirimaand Joshua, 2004).
E. PLASTICISERS
This is required by some coating to
prevent the film being too brittle.A plasticiser is a substance which when added to a material, usually
a plastic, makes it flexible, resilient and easier to handle. Early examples of
plasticisers include water to
soften clay and oils to plasticise pitch for waterproofing ancient boats.www.pvc.org,
(2015).
F. STABILIZER
This is required by some coating to
ensure that the complex film-former remains intact. The aim of stabilization is
to keep the pigment particles separated, and to control the degree of pigment
particle size through the let-down and filling phase, storage and later in
coating films during film formation(Isirima and Joshua, 2004).
G. ANTI-SKINNING
AGENTS
These are added to some oil-based
paints to prevent skinning in the tin. It is also a set of additives which are
used to prevent the forming of a skin on top of the oil based paints which
sometimes occurs whilst it is in the container (Nagode, 2017).
H. EXTENDERS
These s have various uses in most
paints, these include the following:
(a) They
add to the bulk of the paint;
(b) They
provide a key in undercoat films for finishingpaints to grip;
(c) They
prevent pigment setting to the bottom of thepaint;
(d) They
make some paints easier to apply;
(e) They
lower cost.
I. THIXOTROPIC AGENT
These agents give a jelly-like
structure to the paint, providing anti-sag and high build properties.
Thixotropic agents (thickeners) such as polyamides are added to oil-based
paints, whereas cellulose derivatives are used for the same purpose in water-
based latex paints (Fischer 1990). Plasticisers are added to paints to increase
the flexibility of the resinous film. They include dibutyl and dioctyl
phthalates, adipic and sebacic acids and their esters, polyester resins and
castor oil. (Fulcher 1989).
1.8
PROPERTIES OF PAINTS
Paints must have certain basic
qualities to ensure that:
(i)
It
is applicable,
(ii)
It
will dry in a reasonable length of time,
(iii)
It
can adapt to the physical changes of the surface;
(iv)
It
will maintain its function for an acceptable period (Fulcher 1989).
1.9FACTORS
INFLUENCING GROWTH OF MICROORGANISMS IN PAINTS
Factors influencing the
growth of microorganisms include
(a) Climate
(b) Air quality
(c) Temperature
(d) Availability of nutrients found in
the paints
1.10
BIODETERIORATION AND BIODETERIORATION OF PAINTS
Microorganisms have a simple approach
to life; they use whatever is available as a food source, attach themselves to practically
all surfaces, multiply and build biomass (Allsopp et al.,2003).The natural decay and recycling of materials by a wide
range of life forms including microorganisms is termed biodegradation and is perceived
as a beneficial process but, biodeterioration may be defined as the deterioration
of materials of economic importance by microorganisms; it is perceived as a deleterious
process (Allsopp et al.,2003).
Microorganisms have the potential
to grow in liquid paint before it is applied and also on paint films after
application (EA-UK, 2002). Fungi and bacteria both require water and
consequently, neither can grow in solvent based coatings. Water borne coatings
however, are potentially prone to in-can attack by both bacteria and fungi
(Ross, 1980). Fungi, algae and bacteria can all grow on applied paint films and
solvent based and water based coatings are susceptible. The effect of each
class of organisms depends on the environment. Films of oil and water based
paints are colonized by microorganisms on the outside and inside of buildings.
This aspect of biodeterioration can both be unsightly and hazardous to health
(Gaylarde and Morton, 2001).
1.11.
CONTROL OF MICROORGANISMS IN PAINTS
Use of effective biocides during manufacturing
process is needed. To control these troublesome organisms, coatings formulators
use microbiocides, or paint preservatives, that fall primarily into categories:
bactericides, fungicides and algaecides. Bactericides come under the general identification
of in-can preservatives and are designed to prevent microbial deterioration that
results in spoilage of water borne paint. Fungicides and algaecides are to be predominantly
included in a formulation to inhibit the growth of fungi and algae on the dry film
of both water and solvent borne paint. (Melzer, 2016).
1.12
HOW TO IDENTIFY DETERIORATED PAINTS
Deteriorated paints can be
identified commonly by the following physical and chemical changes:
·
Viscosity
Loss,
·
Maladour,
·
Discoloration,
·
Gassing,
·
Frothing,
·
Sedimentation
and
·
pH
change.
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