ABSTRACT

Cxygen-induced polymerization of blends of the
following f a t t y acids: rubberseed (RsA), linseed (LSA),
soyabean (SW) and melonseed (MSA) were done at room
temperature with a view to optimising the drying
performance of the semidrying ones f o r development of
alkyd resin paint binders. Oxygen absorption was
monitored by means of a manometer, and moles of oxygen
#
absorbed were calculated from the pressure of unreacted
oxygen using the ideal gas law.
Results obtained show two types of behaviour i n oxygen
absorption: a l i n e a r response by LSA/RSA and sBA/RSA blends
i n which oxygen absorbed increased d i r e c t l y with the amount
of the more drying f a t t y acid; and a synergistic response
MSA/RSA and MSA/SBA
by MsA/LSAB~ which oxygen absorption showed optimum values
between 40 – 50 w t 96 of MSA. T h i s behaviour by MSA holds
good promise for development of alkyd resins.
Effort t o cause autoxidised f a t t y acid, blends t o dry
by means of o i l – d r i e r mixture proved u n s u ~ c e s 8 f us~h owing
the adverse e f f e c t of free f a t t y acids on the drying
phenomenon.

 

 

TABLE OF CONTENTS

CHAPTER
T i t l e .. .
C e r t i f i c a t i o n .
Dedication . ..
Acknowledgemmt ..
Abstract . . . .
Table of Contents
L i s t of Tables *.
L i s t of Figures ..
INTRODUCTION 0.
Composition of a Paint
The Chemical Nature of
General Definition
Vegetable . . . .
Structure of Vegetable O i l s . .
composition of Vegetable O i l s . .
The Nature of the Fatty Acids Present
Vegetable O i l s .. . . . . . .
Some Commercially Important Chemical
Reactions of Fatty Acids . . . . . .
The Nature of Alkyd Resins . w . .
General Definition . . . . . . .
Raw ~atefiials .. . . . . . . .
Manufacturing Methods . . . . . .
The Effect of Monobasic Fatty Acids i n
Alkyds . . . . . w .
The Oxidat ive Polymer izat ion ( ~ryin~of)
Fatty Acids . . . . . . . . . . . .
The Mechani ma of Oxidative Polymerization
(~r~ingof) F a t t y Acids .. .. .. ..
Mechanism of Drier Action i n t h e Drying
Process .. . . . . . . . . . . . .

HI STORIC AL REVI E’W . . .
Develo~ment of Mechanism of Oxidative
~ol~mTechniques f o r Measuring Drying and
Drying Time .. . . . . . . . .
Dryinq C h a r a c t e r i s t i c s of Blends of
Some Drying Oils . . . . . . . .
Thesis Objective . . . . . . . .
Materials . . . . . . . . . .
Equipment . . . . . . . . .
Extraction of Rubberseed O i l .. . .
C haracteri sation of the O i l s . . . .
Specific Gravity Determination . .
Refractive Index Determination . .
Acid N u m b e r Determination . . . .
Alkali Refining of O i l s . . . . .
Procedure f o r BLeact-Ling of Rubberseed O i l
Preparation o f Fatty Acids . . . . . .
Oxygen Absorption Measurements on Blends
of Fatty Acids. Pure Fatty Acids and
the O i l s .. . . . . . . . . . . . .
Preparation of Samples .. . . . . . .
Procedure f o r Measuring Rate of Oxygen
.4 bsorption . . . . . . . . . . . .
Curing of Autoxidized Fatty Acids with
Oil-Drier Mixtures to Establish the
Effect of Free Fatty Acids on O i l Drying
C HAPTER PAGE
4.0 RESULTS AND D1,;CUSSION . . . . . . . . 76
4.1 C h a r a c t e r i s t i c s of the O i l s and Fatty Acids 76
4.2 Oxygen Absorption of the O i l s . . . . 77
4.3 ,Oxygen Absorption of Fatty Acids .. . . 81
4.4 Oxygen Absorption of the Fatty Acid mends 86
4.5 Curing of Autoxidi sed Fatty Acid EIL ends
Using O i l Drier Flixtures . . . . .. 101
REFERENCES . . o. o. ‘t

 

 

CHAPTER ONE

INTRODUCTION
1 COMPOSITION OF A PAINT
A paint can be defined a s l a r g e l y organic coating
applied t o surfaces t o provide both p r o t e c t i v e and
decorative functions.’ It is usually a suspension of a
s o l i d o r s o l i d s in a l i q u i d which is applied wet t o a
surface but, eventually, it d r i e s t o a more or l e s s
opaque adhering s o l i d film. 2
The basic components of a paint are:
( i ) binders – these are resins, drying (highly 1
unsaturated) o i l s , o r r e s i n s modified by such o i l s .
Originally l i q u i d s o r semi-solids i n nature, the binders
convert t o s o l i d s through the p a i n t ‘ s drying process and
thereby provide t h e surface films with the necessary
a t t r i b u t e s of adhesion, f l e x i b i l i t y , toughness and
d u r a b i l i t y . In the transformation process, binders bind
up together the other i n g r e d i e n t s , with the exception of
the v o l a t i l e components, of the paint,
( i i ) pigments – these a r e f i n e l y dispersed s o l i d
materials t h a t determine the colour and opacity of the
p a i n t f i l m , and hence of t h e surface t o which it is
applied. C e r t a i n t y p e s of pigments s p e c i f i c a l l y a c t by
improving film d u r a b i l i t y o r providing corrosion r e s i s t a n c e
f o r metal substrates.
( i i i ) v o l a t i l e solvents – these enable the application
of the paint. Being v o l a t i l e , these evaporate a f t e r a
l i q u i d f i l m is deposited, and t h e evaporation causes
s o l i d i f i c a t i o n of t h e film,
( i v ) other components, which may be termed a n c i l l i a r y
t o both binders and pigments, include extenders, d r i e r s
and fungicides etc. M e n d e r s a r e cost-reducing
ingredients t h a t help to control gloss, t e x t u r e ,
suspension, v i s c o s i t y , e t c . Fungicides i n h i b i t mo$d
growth on the film’s surface during service exposure.
Driers, as the name suggests, control the drying o r
curing process of the liquid paint.
1.2 THE CHEMICAL NATURE OF VEGETABLE OILS
1.2.1 General Definition 394
Vegetable o i l s are water-insoluble substances of
p l a n t o r i g i n which c o n s i s t predominantly of glyceryl
e s t e r s of long-chain f a t t y acids. They are most commonly
c a l l e d trielycerides. Common usage considers as o i l s
t r i g l y c e r i d e s t h a t a r e l i q u i d a t room temperature and
a s ‘fats1 those t h a t are solid o r semi-solid under t h e
same conditions. This difference i n t h e i r physical
s t a t e a r i s e s from their chemical composition:
Fats are composed of high-melting f a t t y a c i d s (mostly
saturated) while o i l s are formed from low-melting f a t t y
~id(smo st ly uns a tur a t ed) . At hi pher temp~ratures,
however, t h i s difference disappears because the f a t s
nelt t o become liquid. For this reason, the word I’oll”
in t h e expression ”fats and o i l s ” i s understood t o mean
the same kind of material as f a t .
The chief importance of vegetable o i l s l i e s i n t h e i r
food value. They arc v i t a l ingredients of a balanced
d i e t ; they can y i e l d approximately k~o/f ~b i o l o g i c a l
1
energy compared wi th 77’~ JfJo r~ car bohydrate and
protein. Pesides t h e i r use as foods, vegetable o i l s are
raw materials f o r making soaps and detergents, paints,
varnishes, l u b r i c a n t s and p l a s t i c s .
1.2.2 Structure of Vegetable C i l s 4-8
A vegetable o i l molecule a s a t r i g l y c e r i d e may be
considered a s r e s u l t i n g from the reaction of a molecule
of glycerol with three molecules of f a t t y acids whereby
three molecules of water are l i b e r a t e d a s by-products.
The f a t t y acids have the geceral formula CnH2n02 or
C n-1 H2n-l COOH (where n is an even number varying
between 4 and 24). Glycerol is a t r i h y d r i c alcohol
having t h e s t r u c t u r a l formula (1).
1
H – C -OH
The formation of a t r i g l y c e r i d c is represented by
the general equation:
CHO iH + HO~OCR~ -) B CHOOCR2 + 3H20 1
! ! 1
R1, R2 and R3 stand f o r hydrocarton chains of f a t t y acids.
They a r e designated by d i f f e r e n t numbers t o i n d i c a t e t h a t
usually there is more than one kind of f a t t y acid chain
i n an o i l molecule. A t r i g l y c e r i d e is known a s simple
t r i g l y c e r i d e i f a l l the f a t t y acids are i d e n t i c a l cog.
t r i s t e a r i n (2) and as mixed t r i g l y c e r i d t a s i n
distearin (3).
Generally, n a t u r a l l y occuring t r i g l y c e r i d e s are mixed and
contain only small percentage of simple triglycerid es.
It i s believed t h a t the f a t t y acids are d i s t r i b u t e d among
t h e d i f f e r e n t glyceride molecules i n accordance with the
p r i n c i p l e of even d i s t r i b u t i o n which requires t h a t each
f a t t y acid should be d i s t r i b u t e d i n a s many t r i g l y c e r i d e s
a s possible. For example, i f an o i l contains one-third
oleic and two-third s t e a r i c acid the o i l molecule may
have the s t r u c t u r e (3). A glyceride molecule such a s (3)
1
in which only the p o r second f a t t y acid r a d i c a l is
d i f f e r e n t is regarded a s symmetrical. If a l l the f a t t y
acid r a d i c a l s are d i f f e r e n t , t h e glyceride i s said t o be
assymetrical.
In r e a l i t y t h e s t r u c t u r a l representation of a
t r i g l y c e r i d e molecule as given above is impossible
because it implies t h a t the e n t i r e molecule is i n the plme
of the paper. I f t h a t i s t h e c a s e a considerable s t r a i n
would r e s u l t in the o i l molecule. Instead a t r i g l y c e r i d e
molecule has a three-dimensional (or t h r e e d i r e c t i o n a l )
the
s t r u c t u r e due to&ossibility of f r e e r o t a t i o n along the
carbon axis of the glycerol residue. Furthermore the
f a t t y acids are thought to be highly zig-zag chains (4)
with the carbon-carbon bond forming a 109′ bond angle.
The s t r a i g h t l i n e s represent the glycerol group.
Since there are three o r more fatty-acid r a d i c a l s
occuring i n a p a r t i c u l a r f a t o r o i l , the p o s s i b i l i t i e s
of isomerism are numerous. The number of possible
t r i g l y c e r i d e s , N, which can be formed from X d i f f e r e n t
f a t t y acids i s given by equation 1.2. 4
1.3 COMPCSITIQN OF VZGTTAl3,E OILS 5.7-15
Although f a t s and o i l s are predominantly triglycerides
(which c o n s t i t u t e 95 t o 9%), t h e r e a r e a number of minor
components which a r e present i n the n a t u r a l l y occuring
f a t s and o i l s . These include phospholipids (or
phosphatides) (1 t o yh), s t e r o l s , antioxidants, vitamins,
pigments, f r e e f a t t y acids and some impurities. These
components a f f e c t t h e colour, odour, and other q u a l i t i e s
of the o i l .
1 . 3 The Phospholipids (or ~hosphatides)
Phospholipids also hown as “gums” are f a t t y
substances in o i l s containing phosphorus. There are two
types:
(a) qly~erophospho1ipids:- these are compounds which
are derived from triglycerides in which one f a t t y acid
has been replaced by a phosphoric acid or phosphoric acid
derivative. Examples are l e c i t h i n (4) and cephalin ( 5 ) .
I n l e c i t h i n s , t h e base i s c h o l i n e (HOCH~CaHnd~ f~o r~ ~)
cep h a l i n s , ethanolamine (HOCH~CH~NHCr~ud)e. soyabcan
o i l contains 2 t o 3% l e c i t h i n s . Lecithin and cephalin
are frequently associated with membranes.
( b) sphingomyelins: – these are phospholipids which are
derived from an alcohol other than glycerol, c a l l e d
sphingenine (formerly sphingosine) whose s t r u c t u r e is
shown (6). This alcohol contains nitrogen and forms
bonds with other compounds which are unlike those formed
between glycerol and the fatty acids. Sphingenine can be
bound to:
– a f a t t y acid and phosphoric acid which is i n turn
combined with choline t o form sphingomyelin (7).
– a f a t t y acid (usually a very long one, 24 carbon atoms)
and one carbohydrate molecule such as galactose, glucose
or amino sugar, to form cerebroside (8). The cerebrosides
can be e s t e r i f i e d with sulphuric acid t o form sulphatides.
Phospholipids have been termed amphipathic compounds since
they possess both polar and nonpolar functions.
RCONHCH
It +
H~C-O-P-OCH~CH~N(HC ~)
t
1.3.2 The Sterols ( Steroid alcohols) 1
These are colourless, odourless and generally i n e r t
substances found in vegetable o i l s and f a t s . They are
c r y s t a l l i n e alcohols possessing 26 – 30 carbon atoms.
They are based on phenanthrene s t r u c t u r e (9).
The s t e r o l s account for 0.5 – 1.5% nonsaponifiable
materials in both vegetable and animal f a t s . An example
of s t e r o l which occurs in vegetable o i l is stigmasterol (10)
which d i f f e r s from c h o l e s t e r o l (which occurs i n a l l
animal t i s s u e s ) only i n having a double bond
between carbons 22 and 23,
1
I , 3, 3 Antioxidants
Most vegetable o i l s contain minor prnportions
(0.05 – [email protected]&) of antioxidants which serve t o i n h i b i t o r
delay atmospheric oxidation a s well a s peroxide formation
which causes r a n c i d i t y i n f a t s , Rancidity is marked by
presence of v o l a t i l e , bad-smellinp acids and aldehydes i n
t h e o i l . The antioxidants i n vegetable o i l s have been
i d e n t i f i e d mostly as tocopherols (1 1 ).
1.3.4 Vitamins
A number of vitamins, namely vitamins A, K, D and E
a r e f a t soluble and because some of them a r e found i n
f a t s and o i l s , they a r e included i n t h e l i p i d c l a s s of
macromole~ules. The vitamin E owes its a c t i v i t y t o i t s
tocopherol c o n t e n t . Vitamin 11 ( 12) is produced by t h e
a c t i o n of water on t h e c a r o t e n e s ( t h e p r e c u r s o r s of
vitamin A) which occur i n unbleached palm o i l and i n
t r a c e s i n o t h e r o i l s . It i s l o s t i n t h e r e f i n e d cooking
1
o i l due t o bleaching.
1.3.5 Pigments
These substances a r e r e s p o n s i b l e f o r t h e
c h a r a c t e r i s t i c c o l o u r s of o i l s . The deep red colqur of
palm o i l is due t o presence of 0.1 t o 0.2% of g-carotene
(13). The c a r o t e n e s a r e highly unsaturated and owe t h e i r
colour t o a long conjugated system of double bmds.
Olive o i l and soyabean o i l may c o n t a i n s u f f i c i e n t
chlorophyll or r e l a t e d compounds t o produce a greenish
tinge.
I. 3.6 Free Fatty Acids
The f r e e f a t t y acid content of a crude o i l is
lsually dependent upon the degree t o which t h e o i l has
Deen subjected t o enzymatic hydrolysis i n t h e parent o i l –
~earings eed be for e e x t r a c t i o n . Rubberseed o i l i s high’
In f r e e f a t t y acids. This has been r e l a t e d to the action
)f t h e lipolytic enzyme present i n the seeds.
1.4 THE NATURE OF THZ FATTY ACIDS PRESENT I N VEGETAELE
-01~ p9 s,I~1
With only a few exceptions, the f a t t y acids a r e a l l
straight-chain compounds, ranging from three t o eichteen
carbons and except f o r the C? and Cg compounds, only acids
containing an even number of carbons a r e present i n
s u b s t a n t i a l amounts, Those with sixteen and eighteen
carbon atoms a r e the most abundant. In addition t o
v a r i a t i o n i n chain length the f a t t y acids present i n
vegetable o i l s can vary i n the number of C=C double bonds
i f any (degree of unsaturation), t h e r e l a t i v e position
of the double bonds (degree of con jugation) and the
presence of polar groups such as hydroxyl o r keto group
a s well as methyl-group branches on the carbon backbone.
I n general, unsaturated f a t t y acids (the ones which
contain the C=C double bonds) are twice as abundant a s
saturated f a t t y acids i n f a t s arid o i l s from both p l a n t s
and animals.
The properties of a p a r t i c u l a r o i l can be d i r e c t l y
related to the f a t t y acid composition and t o a l e s s e r
extent properties depend upor. the M, g or V position of
1
the attachment. Since the amount of glycerol is the same
in a l l vegetable o i l s , it follows t h a t the differences in
properties encountered w i t h the d i f f e r e n t o i l s a r e l a r g e l y
determined by the variations i n the f a t t y acid structure.
The structure and physic21 p r o p e r t i e s of some of the more
important f a t t y acids present i n vegetable o i l s are given
i n Tables 1.1 and 7.2 respectively.
‘able 1.1 Structures of Some Fatty Acids Found in
Vegetable ~ils~~~~-~~
Double
EiF
,auric acid 0
lyri s t i c acid 0
‘almitic acid 0
Xearic acid 0
Jnsaturated
Xeic
Jnoleic
>inolenic
iicinoleic
Licanic
I samic
Structure
3 C 11 -C li -C H=C H-C H -C H=C H-C H2-C H=C 11-
3 2 2
3 CI-! 3 -(CH ) -CH=CH-CH-CH-CH=CH- 2 3
(cH~)?- CCOH
3 CH 3 -(CH ) -CH=CH-CH=CH-CH=CH-(CH~)~- 2 3
CO-(CH~)~-COOH
1 CH2=CH(C~2)4C~C-C~C2( )C f~ OOH
Table 1.2 Physical P r o p e r t i e s of Some Pure Fatty Acids 3 —
Molecular Nolecular Iodine
Acid formula weight 2:;?T0C ) value
Lauric I 2H2402 200.3 44.2 0
Palmitic I 6H3202 256.4 67.1 0
S t e a r i c C18H3602 284.5 69.6 0
Oleic 18~34’2 282.5 16.0 89.9
Linoleic
Linolenic 1 8H3002 278.4 -11.3 273.5
Ricinoleic 1 6H3402 298.5 5.0 85.0
obEleostearic 1 8H3002 278.4 49 273.5
The p o s i t i o n of double bonds and s u b s t i t u e n t s i n a
f a t t y acid chain i s defined by numbering t h e chain from
t h e carbonyl carbon. I n most of the unsaturated f a t t y
a c i d s t h e r e i s a d o u b l e bond ( d e s i g n a t e d A 9 ) between
carbon atoms 9 and 10. I f t h e r e a r e a d d i t i o n a l double bonds,
they usually occur between a9 double bond and t h e methylterminal
end of t h e chain, The double bonds of n e a r l y a l l
t h e n a t u r a l l y occuring unsaturated f a t t y a c i d s a r e i n t h e
c i s geometrical c o n f i g u r a t i o n , which produces a r i g i d bend
i n the a l i p h a t i c chain. By c i s configuration it is
meant t h a t the two hydrogen atoms adjacent t o t h e bond l i e
on the same side (14). The unusual trans-acids have t h e
opposite configuration (15) :
1
Cleic acid is t h e most widespread and abundant of a l l
f a t t y acids accounting f o r some 40% of the t o t a l
accumulation i n a l l n a t u r a l f a t s . It i s a cis-monounsaturated
CIR acid w i t h the double bond i n the mid
(9, 70) position. Linolenic and elensteari c acids contain
the same number of double bonds, but those of e l e o s t e a r i c
acid are i n the con jugsted position and are much more
reactive. Both oleic and r i c i n o l e i c acids contain a
single double bond each but t h e l a t t e r has a hydroxy
group, a s a r e s u l t of whick it can under c e r t a i n
conditions undergo dehydration ( t h e removal of OH and an
adjacent H) giving approximately 25% conjugated and 75%
noncon jugated double bonds. Licanic a c i d has a keto
Rroup in the chain but is otherwise the same as
e l e o s t e a r i c acid i n t h a t it contai.ns three conjugated
louble bonds. Isamic acid is an example of f a t t y acid of
musual structure: it contains conjugated t r i p l e bonds.
The melting point of a p a r t i c u l a r f a t t y acid is
lependent upon i t s molecular weight a s well as number and
:onfiguration of the double bonds: stearic acid (mol. wt.,
284.5) has a higher melting point than palmitic acid
:mole w t . , 256.4) but the l a t t e r has a higher melting
~ointth an o l e i c (mol. w t . , 282.5).
Aspreviously s t a t e d , t h e c h a r a c t e r i s t i c s o f a ,
)articular o i l or f a t w i l l depend on the amount of each
3f the acids present. Typical f a t t y acid compositions of
some important vegetable o i l s and the e f f e c t s of t h e i r
>omposition and dryin? characteri stics are l i s t e d in
Table 1.3. The c l a s s i f i c a t i o n of the o i l s as drying,
semi-drying or nondrying i s dependent on the percentage
of unsaturated f a t t y acids in the respective o i l . The
r a t e a t which drying occurs tends t o increase as degree
of unsaturation increases, Hence, o i l s of mainly linolenic
acid dry f a s t e r than those of l i n o l e i c .acid. However,
the geometry of unsaturation as determined by ccrn jugation
or non-con jugation of the carbon-carbon double bonds also
contributes t o the drying c h a r a c t e r i s t i c s of an o i l .
Consequently, tung o i l containing mainly e l e o s t e a r i c acid
d r i e s f a s t e r than linseed o i l in which linnlenic acid
predominates, It w i l l be noted from Table 1.3 t h a t
c a s t o r o i l c o n s i s t s l a r g e l y of r i c i n o l e i c acid, It is
thus one of the few f a t t y o i l s approaching a pure
compound i n character. Dehydrated c a s t o r o i l , i n
c o n t r a s t t o c a s t o r o i l , i s a valuable drying o i l ,
o i l s
The dryingLare so called because when t h i n f i l m s a r e
exposed t o a i r , as in painting, they undergo autoxidation
followed by polymerization to a hard, resinous coating.
Table 1.3 Fatty Acid Composition of Some Vegetable O i l s

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