Dissertation Report on

Finishing studies on Poly urathene (PU) and

Shellac coats on Teak (Tectona grandis) and

Deodar (Cedrus deodara) surfaces

Submitted by

ANIL MUNDOTIYA

In partial fulfilment of the requirements for the award of degree of

M.Sc. (Wood Science and Technology)

(2013-2015)

Under the supervision of

Dr. Kishan Kumar V. S.

Scientist-F

Wood Working and Finishing discipline,

Forest product division

FOREST RESEARCH INSTITUTE (Deemed) UNIVERSITY

(INDIAN COUNCIL OF FORESTRY RESEARCH AND EDUCATION) P.O. IPE, KAULAGARH ROAD, DEHRADUN – 248006

May, 2015

Finishing studies on Poly urathene (PU) and

Shellac coats on Teak (Tectona grandis) and

Deodar (Cedrus deodara) surfaces

A Dissertation report submitted in partial fulfilment of the requirement for

the degree of Master of Science in Wood Science and Technology at Forest

Research Institute (Deemed) University, Dehradun

By

ANIL MUNDOTIYA

Forest Research Institute, Dehradun

May, 2015

DECLARATION

I hereby declare that the Dissertation Report on

“Finishing studies on Poly urathene (PU) and Shellac coats

on Teak (Tectona grandis) and Deodar (Cedrus deodara)

surfaces” submitted in requirement of partial fulfillment for

the award of the degree M.Sc. Wood Science and Technology of

Forest Research Institute (Deemed) University, Dehradun,

work carried by me under the guidance of Dr. Kishan Kumar

V.S. Scientist-F, Wood working and Finishing Disciplin,

Forest Products Division, Forest Research Institute Dehradun

and that no part of this Dissertation Report has been

submitted for any other degree or diploma.

PLACE: FRI, DEHRADUN (UK) ANIL MUNDOTIYA

M.Sc. Wood Science &

Technology (2013-2015)

ACKNOWLEDGEMENT I am extremely grateful to Director/Vice chancellor of Forest

Research Institute Deemed University, Dehradun (Uttarakhand) for

providing me facilities and continuous encouragement.

I am grateful to Dr. Neelu Gera, IFS Dean, (Academic) FRI Deemed

University, Dehradun and course coordinator Dr. Pratima Patel for

providing me an opportunity to work on this aspect.

I have profound privilege of expressing my deep sense of gratitude

and indebtedness to esteemed Advisor Dr. Kishan Kumar V. S.

(scientist F) Wood working and Finishing Discipline, Forest Product

division, Forest Research Institute, Dehradun whose inspiration,

worthy guidance, constructive suggestions and criticism

throughout the making of this Dissertation Report and constant

encouragement without which this work would never be possible.

I would like to extend my thanks to Dr. Sachin Gupta, Mr. C. M. Sharma and all staff members for their support and help during the dissertation work,

I am pleased to avail this rare opportunity to express my sincere regards to my friends (Ranjeeta, Sanjay, Ajit Mishra, Sonia and Sandeep), my seniors (Mr. Shikhar Shukla, PhD Scholar) and juniors who helped me out and motivated me.

Last but not the least, I express my grateful acknowledgement to my parents (Mr. Kailash Chandra & Mrs. Lakshmi Devi) and my brother (Mr. Brij Mohan) whose blessings are constantly with me and my studies for my whole life.

Anil Mundotiya

Contents CHAPTER 1...................................................................................................................................... 1

INTRODUCTION ........................................................................................................................ 1

CHAPTER 2 ..................................................................................................................................... 4

REVIEW OF LITERATURE .................................................................................................... 4

WOOD AS A MATERIAL: .................................................................................................... 4

FINISHING AND WOOD FINISHES: ............................................................................... 4

HARDWOOD AND SOFTWOOD ANATOMY: A COMPARISON ............................. 7

MOISTURE CONTENT IN WOOD .................................................................................... 8

SHELLAC: ................................................................................................................................ 9

POLYURERTHANE: ............................................................................................................ 10

DESCRIPTION OF WORKABILITY OF THE SPECIES: ........................................ 11

CHAPTER 3 ................................................................................................................................... 13

MATERIALS AND METHOD: .............................................................................................. 13

CHAPTER 4 ................................................................................................................................... 15

Results & discussions: ......................................................................................................... 15

CHAPTER 5 ................................................................................................................................... 26

Conclusions: ............................................................................................................................. 26

REFERENCES .............................................................................................................................. 27

CHAPTER 1

INTRODUCTION

In recent years there is considerable awareness due to urbanization and

improvement in standard of living. The craze for certain woods like Deodar

(a softwood) and Teak has not diminished and both the species are quite

expensive in their prices. Those who are affording such species have an in-

built desire to get best coated-finished surface. Whereas, other timbers in

house construction are painted thereby hiding the inherent colour, texture

and grain of the species which appears to be normal with secondary species.

However, Teak and Deodar wood is well known for its grain, golden brown

colour even-texture or its fine-grain. Such species are preferred to be coated

with transparent to translucent finishes, clear lacquers and polishes. In

recent years there is a growing trend to use PU finishes for wood surfaces

after achieving tremendous success in the field of metals. The conventional

spirit shellac polish popularly known as French polish (IS: 2338, Part I,

1967) finding its use dating back to 16th century is still extensively

practiced in view of its simplicity and wider acceptability. The spirit shellac

polish can be reapplied after a period of time (refinishing) without much

efforts as pigment binder interphase quite common in paints appears to be

non-existent. It was therefore, considered desirable to take the aspect of

surface finishing on these two species and study them with regard to coating

thickness, gloss and moisture uptake. As these are important components

in the field of wood finishing.

There are two principal aspects that make it necessary to apply a

suitable finish to wood – dimensional stability and aesthetics. Wood needs

to be sheltered from changes in atmospheric humidity, microorganisms,

insects, dirt and surface wear, and from mechanical damage of its surface.

The functional aspect of finishing therefore should take into account all

these factors in the service life of a product and choose coatings

appropriately. Aesthetics is the other aspect of finishing. Wood in its

naturally occurring form and colour often needs to be decorated, tainted for

a more appealing look. Sometimes a suitable finish may improve the surface

look manifolds. Defects have to be covered for better look and inferior grade

timbers can be correctly processed to look like superior grade timber.

Wood properties such as density (specific gravity), growth rate,

hardwood-softwood, heartwood–sapwood, earlywood–latewood, grain angle,

vessels, and texture vary within and across wood species. However, if one

understands how wood properties, finish, and environmental conditions

interact, it should be possible to estimate finish performance for most wood

species.

Amongst all other factors that affect the finishing in wood, the

difference of softwood and hardwood is of major importance. Softwoods are

composed of only a few significant cell types. Many Hardwoods are composed

of at least four major kinds of cells. Only hardwoods contain vessels of which

softwoods are devoid of. The difference in the constitution of cell types in

both definitely affects the process of finishing and the nature of the coat

applied.

Similarly no coating is entirely moisture proof. As there is no way of

completely keeping moisture out of wood that is exposed to prolonged

periods of high RH. At this point, the type of substrate on which the finish

coat has been applied also affects the finish performance significantly. As

wood is exposed to varying RH conditions, it absorbs or desorbs moisture

depending on the RH. A coating that is effective at excluding moisture merely

slows absorption or desorption of moisture.

Irrespective of whether finishing is done by hand or mechanically, the

diversity and complication of the finishing materials available today make it

crucial that it has to be a well-planned partnership of the finish

manufacturer, the machine manufacturer and the end user.

Stain, Paint, and Finish are the three principal classifications for ordinary

wood treatments. Stains hold pigments and are used to shade the wood.

Paints have tinted pigments and sit on the wood to form a defensive coating.

Some finishes are purely paint without the pigment that lay down a clear

protective coating. There are five universal types of finishes in the market.

They are:

Oil

Varnish and Polyurethane

Shellac

Lacquer

Water-based Finishes

Applying finishes is lone part of wood working that doesn’t involve lots of

tools. There are mainly three key tools used to apply all of the finishes; rags,

brushes, and a spray gun. Many professionals will use a spray gun for

smooth even coats.

GLOSS:

A measurement proportional to the amount of light reflected from a surface

is gloss. Many people consider gloss to be an important factor while choosing paints,

lacquers and polishing formulations for their interior and exterior uses. The contractors

tend to prefer low gloss paint because touch-ups are easier and imperfections in the

finish are less apparent. Gloss is basically the specular reflection of light from the

finished wood surface. Gloss of the surface is measured by gloss meter defining gloss

level using 600 gloss head angle. Gloss of the surface depends on the use for which it

is to be prepared, for instance, the gloss of the surface in a well lit room should be kept

low in contrary to the dim lit room where furniture and panels are coated with high

gloss polishes.

Geometry: For best results the correct measurement geometry should be

chosen based on the reflectance of the material:

Matt Finish 85°, Mid Gloss 60°, High Gloss and Metallic 20°.

Measurement Unit: GU

CHAPTER 2

REVIEW OF LITERATURE

WOOD AS A MATERIAL: Fiest (1982) considers wood to be a naturally durable material that is

versatile in nature. Usually there lies a misconception that wood, in duration

of few years gets degraded but there are many examples that prove this

concept wrong. Like the tomb of the Egyptain pharaoh Tutankhamen, who

ruled in the14th century B. C., contained wood objects that were in perfect

condition when recovered in the 20th century. Some Japanese temples

constructed with wood date back 13 centuries. These facts show that wood,

in favourable conditions may last for centuries undamaged. Numerous such

facts from the chest of world history are always prepared to prove wood as

a promising material. When surrounded by this material we feel very

comfortable and cozy. Wood, in houses and gardens and in surroundings

gives a really calm and beautiful appearance. This is one of the reasons why

leading designers and building experts prefer wood as a perfect material for

interiors.

According to one of the studies conducted by REMMERS industries

(2011), tree bark in the outer layer of trees not only protect it from outside

climatic disturbances but also helps the wood from drying. It is the gift of

the scientific world that created paints and wood coats that act as a barrier

in the absence of the natural barrier of ‘bark’ when it is in service.

Wood is also described as a biologically derived renewable raw

material with a low processing energy demand (Dubey, M. K., 2010). It is

recyclable and biodegradable. Timber products with prolonged life can be

used as a repository for CO2 (Bruce and Lucy, 2006) and can be considered

as a future-oriented material to achieve the universal goal of sustainable

development and a low carbon future.

FINISHING AND WOOD FINISHES: Every wood work before use require attractive appearance as well as

protection from degradation caused by changing atmospheric conditions like

temperature, alternate wetting and drying, exposure to sunlight, dirt etc.

these twin objectives are generally achieved by application of suitable wood

finishes like paints, varnishes or polishes (Gupta, S. et al. 2008). A wide

variety of organic coatings translucent, transparent or opaque have been

formulated for the purpose and are being used in trade. However, for

furniture and top class joinery work, spirit polishes are generally used which

to a great extent contribute acceptable glossy surface besides protection

from atmospheric changes encountered in interior locations (Badoni, S. P.,

et al. 1990).

Finishing is one of the most important aspects in wood working. The

word finish in wood working usually describes some final surface treatment

that protects the wood and enhances its appearance. Finishing, which is

usually the last step in the manufacture, can ultimately decide the fate of

the product in the market. A product well designed and manufactured can

be completely ruined by bad finishing and also an inferior product can be

upgraded by a fine finishing work (Badoni, S.P., 1987). Wood finishing has

a history of many thousands of years. It dates back to the time when mighty

kings ruled the lands and built great monuments. The difference between

the finish of that period and today is those finishes were natural origin and

pure whereas today’s finishes are mostly synthetic and very few are natural

based (Hoadley, 2000).

Finishes may also protect against abrasion and prevent changes in

colour due to light or atmospheric pollutants. But their most important

function is to control the exchange of moisture with the atmosphere, thus

helping to avoid the dimensional change and seasonal swelling and

shrinkage. Finishes also provide cleanable wood surfaces and a surface that

does not accumulates dirt easily. Finishes also protect wood from colour

changes due to UV and other light radiations (Hoadley, 2000).

The process of wood finishing is quite simple, it involves few steps like,

surface preparation and applying coats of finish on top. Be it manually or

mechanically done, the basic process remains the same. Surface

preparation itself involves a number of steps. So does the application of

finishing coats. Depending upon the substrate, the finish desired, the

materials used and the method of application some of the steps can be

skipped or added on.

Any finish is only as good as the surface on which it is applied.

Therefore preparation of the surface is very important to obtain a good

finish. Surface preparation could involve a number of steps such as sanding,

bleaching, where necessary, staining, filling and sealing.

Once the surface is prepared, topcoats of finish need to be applied in

further processing. There is a wide range of finishes available and an

appropriate finish for the end use has to be selected.

Finishes are of two main groups –penetrating and film forming

finishes. Penetrating finishes are usually oils that do not cure as hard

surface layers. Film forming finishes cure into hard surface layer and can

be built up into any desired thickness. Finishes can also be classified into

evaporative (like lacquer, shellac, and water based finishes) and reactive

finishes (like linseed or tung oil, catalyzed lacquers, varnishes) on the basis

of how they cure or dry. They can further be classified on a practical scale

as traditional and modern finishes. The former include waxes, linseed oil,

tung oil, etc while the latter include lacquers, varnishes, nitro cellulose

lacquers, polyurethane lacquers, etc.

Despite so many modern finishes being available, India is still

traditionally a market where French polish is the most used finish. Over

90% of the furniture is still made in the craftsmen workshop. Lacquers like

acid curing melamine lacquers as well as polyurethane are now making an

entry into the market. No doubt wood can be used both outdoors and

indoors without finishing but unfinished wood surfaces exposed to the

weather change colour, are roughened by photo-degradation and surface

checking, and erode slowly. Unfinished wood surfaces exposed indoors may

also change colour also unfinished wood is more difficult to clean than the

finished wood.

In the context of wood finishing, Badoni et al. (1990), made a

preliminary study on moisture excluding efficiency of some pore filling

treatments and polishing of Terminalia mannii (black chuglam). Wood

finishing is a two-step operation consisting of surface preparation or pore

filling followed by application of coating of choice. Both these steps are

complimentary to each other and contribute to the efficiency of the coating

system. Therefore, they considered it worthwhile to assess MEE of some pore

filling treatments for their comparative performance after subsequent

polishing. They conducted Preliminary studies for various polished surface

of black Chuglam samples which revealed marked variations when exposed

to 60% and 90% R.H. at 350 C. They observed that:

Linseed oil application gave higher protection against moisture as it

possessed moisture curbing properties.

Two coats of spirit polish on wood surface were also effective.

Chalk powder filler treatments give good initial gloss but do not

possess moisture curbing properties and should be applied

judiciously for polishing wood.

HARDWOOD AND SOFTWOOD ANATOMY: A COMPARISON Jane et al. (1970) Softwoods are composed of only a few significant cell types

whereas hardwoods have many. Long cells known as longitudinal tracheid

comprise 90 – 95 percent of the volume of softwoods. Ray cells (either ray

tracheids or ray parenchyma) constitute the remainder of softwood xylem.

Although a few other types of cells may occur, they make up an insignificant

part of the volume of softwoods. Hardwoods are composed of at least four

major kinds of cells each of these may constitute a significant portion of

hardwood volume.

Only hardwoods contain vessels, a structure composed of vessel

elements. In hard wood tyloses increase the resistance to flow along vessels

and they account low permeability of white oaks such as Quercus alba

(Comstock, 1984). Hardwood ray widths vary within and between species.

They are often wider than the (mostly) uniseriate rays found in softwoods.

Except for fusiform rays, softwood rays are one cell (or occasionally two) in

width when viewed tangentially. Collectively, ray cells comprise about 5 – 7

percent of total softwood In Conifers, the xylem, or water-conducting tissue,

is made up exclusively of tracheids. Water-transport in conifers depends on

very small columns of cells, without perforations at the ends as in vessels of

hardwoods. Tracheids rely on pits in their walls for the passing of water from

cell to cell. Parenchyma, uni-seriate and multi-seriate.

MOISTURE CONTENT IN WOOD Glass, S. V.; Zelinka, S. L (2010) the moisture content of wood is the amount

of water contained in the wood. Moisture content includes both water

absorbed into the wood cell wall and free water within the hollow centre of

the cell, and it is expressed as a weight percentage. The amount of water

that wood can absorb (that is, that can be bound in the cell wall) depends

on the wood species; most species can absorb about 30% water. This limit

to the amount of water that can be bound in the wood cell wall is called the

fiber saturation point. Wood can reach the fiber saturation point by

absorbing either liquid water or water vapour. The amount of water vapour

that can be absorbed primarily depends on the relative humidity (RH) of the

surrounding air. If wood is stored at zero RH, the moisture content will

eventually reach 0%. If wood is stored at 100% RH, it will eventually reach

fibre saturation (about 30% water).If kept at a constant RH between these

two extremes, the wood will reach a moisture content between 0 and

30%.The moisture content is controlled by the RH, and when the moisture

content is in balance with the RH, the wood is at its equilibrium moisture

content. This rarely happens because as the RH changes so does the

moisture content of the wood, and atmospheric RH is almost always

changing. It varies through daily and seasonal cycles, thus driving the

moisture content of wood through daily and seasonal cycles.

Wood when left as such without any finishing absorbs a lot of

moisture. This becomes one principal cause of weathering is frequent

exposure of the wood surface to rapid changes in moisture content (Fiest,

1982) (Fiest et al, 1984) may it be coated or uncoated. Rain or dew falling

on unprotected wood is quickly absorbed by the surface layer through

capillary action, followed by adsorption within the wood cell walls. Water

vapor is taken up directly by the wood by adsorption under increased

relative humidities, and the wood swells. Stresses are set up in the wood as

it swells and shrinks because of moisture gradients between the surface and

the interior. The steeper the gradient, the greater the stress. Stresses are

usually the greatest near the surface of the wood. Unbalanced stresses may

result in warping and face checking (Coupe, C. et al. 1967) mathematically,

moisture content by the oven-dry method for industrial testing Jim Reeb

Mike Milota Oregon State University Corvallis,

Where IW=Initial weight

OD= Oven dry weight

MC=Moisture content

SHELLAC: Shellac, or Lac, is a natural animal-produced resin and wax mixture

(Derry, 2012), it is the purified product of the resin lac (Farag, y. and

Leopold, C. S., 2011). Which is utilized in a broad spectrum of applications,

and within a variety of fields. When applied as a finish to wood, shellac

imparts a depth, glow and beauty hard to match with any other product. In

the 17th and 18th centuries, artisan furniture makers applied shellac to

finish only their most exclusive creations, before it became commonplace on

European furniture from the early 1800s and on. (Rivers et al, 2003). Within

restoration and conservation work, shellac is often used as ahigh gloss

finish, applied as a varnish, or padded on with a French polishing technique.

Shellac is also used as an adhesive, or as a film-forming finish for wooden

objects, metals and frames, as well as floors and walls, as the versatility of

the resin has proven invaluable for a variety of applications. (Mills et al.

1994), (Farag, Y. and Leopold, C. S., 2011).

After harvesting, the so-called “stick lac” is chopped and separated

from wood and resin. A washing step extracts the water-soluble dye, laccaic

acid, yielding the raw material “seed lac.” There are three different processes

used for refining, resulting in different shellac qualities: The melting

filtration process, where melted seed lac is filtered through a cotton hose,

leads to wax containing shellac. Bleached shellac is obtained by treating the

dissolved polymer with sodium hypochlorite. The most suitable type of

refining is the solvent-extraction process, in which the raw material is

dissolved in alcohol, decolorized by treatment with activated carbon, filtered,

and cast to a film. After cooling, the film breaks into flakes giving shellac its

typical appearance (Penning, 1990)

Shellac is a hard, brittle and resinous solid. It is practically odourless

in the cold but evolves a characteristic smell on heating and melting. This

smell can partially be referred to aleuritic acid which is known to be a

starting material for the production of flavours (Mathur H. H. et al, 1963),

(Mishra, 1983). Its color is dependent on the type of seedlac and the refining

process and can range from pale yellow to deep red. The color of the material

is usually characterized by the Gardener (Möller-Kemsa, J., 1992) or

Lovibond scale (Nowak, M., 1990). Shellac films provide high gloss (Trezza,

T.A., 2001), a low permeability for water vapor and gases (Hagenmaier et al.,

1991) and good dielectric behaviour (Goswami, D.N., 1979). Shellac is water

insoluble. However, by addition of alkali translucent aqueous solutions can

be obtained. Shellac is soluble in ethanol, methanol and partially soluble in

ether, ethyl acetate and chloroform (Bose et al., 1963).

POLYURERTHANE:

During the 1930s the german chemist Otto Beyer laid the foundation

of polyurethanes and found their utilities. Now-a-days it is a chief

component of most of the wood paints. P. Nylen, and E.Sunderland (1965)

in his research on “Modern Surface Coatings” discussed the numerous

reasons for the popularity of polyurethane coatings for wood applications.

They have a high level of quality and fit perfectly with the natural properties

of wood. In addition, they combine outstanding resistance to solvents and

chemicals with unique toughness and flexibility. It is possible to formulate

both clear coats and - because of their good pigment wetting properties -

pigmented coatings, which yield high-gloss, high-bodied films with excellent

flow properties. The films also have outstanding mechanical properties and

provide the ideal balance of hardness and flexibility, even at low

temperatures. Good scratch resistance is another feature of polyurethane

coatings (INDUS, 2014).

DESCRIPTION OF WORKABILITY OF THE SPECIES: TEAK:

Teak is one of the world’s best-known hardwood timbers. Teak is renowned

for its marine applications, including boat building, and a wide variety of

decorative uses.

OTHER NAMES: Genuine Teak, True Teak, Asian Teak, Java Teak, Tek,

Teck, Jati

ORIGIN: Native to India, Burma, Thailand, Indochina, including Indonesia,

particularly Java

APPEARANCE: Heartwood dark golden yellow, turning a dark brown with

exposure (Kokutse et al. 2006), often very variable in color when freshly

machined showing blotches and streaks of various shades; sapwood pale

yellowish, sharply demarcated. Grain straight, sometimes wavy; texture

coarse, uneven (ring porous); dull with an oily feel; scented when freshly cut.

Dust may cause skin irritations. Silica content variable, up to 1.4% is

reported

DENSITY: 639 kg/m³ (>675kg/m3) (Miranda I. et al. 2011, Bhat KM, 1998)

WEIGHT: 41 lbs/ft3 (655 kg/m3)

DRYING: Dries slowly but with little or no degrade, large variations in drying

rates reported

WORKABILITY: Easily worked with both hand and machine tools (Miranda

I. et al. 2011) and dresses to a very smooth finish if tools are kept sharp;

glues moderately well despite its oily nature. Blunting of cutters can be

rather severe. As noted, may cause dermatitis some individuals

DURABILITY: Heartwood is rated as very durable (Willeitner and Peek, 1997)

(Cabrera Y.2010) with respect presence of toxic extractives to decay fungi

(Sandermann and Dietrichs, 1957) and termites (Wolcott, 1955); not

immune to marine borers.

PRESERVATION: Heartwood extremely resistant to preservative

treatments, sapwood also of low permeability

FINISHING: Finishes well, Teak oil is a standard finish

DEODAR:

The name “Deodar” is derived from the Sanskrit work “Devadar” meaning

tree of the gods. Hindus consider this tree sacred. Lord Ganesha is offered

this leaf during the 21 patra (leaves) pooja and the chanting that is

accompanied with the leaf is as follows: “Om Sarveswarayanamaha,

Devadaru Patram Samarpayammi”. Deodar tree and Deodar forests are

mentioned in many Hindu epics.

OTHER NAMES: Himalayan Cedar, Devadar, East Indian Cedar, Deodar,

The Himalayan Tree of God

ORIGIN: These evergreen coniferous trees are native of Pakistan and

Himalayas

APPEARANCE: The wood is white to light yellowish brown, with a

characteristic odour and oily feel. It is straight-grained, medium fine and

somewhat uneven-textured. As the inner wood of this tree is aromatic, it is

used to make incense sticks. This inner wood is also processed to get an

essential oil.

DENSITY: 800 kg per cubic meter

WEIGHT: Its average weight is 560 kg/m3.

WORKABILITY: it is very soft wood so very easy to be worked on. Because

of its easy workability and high durability it is a highly demanded wood in

construction industry. It is also in demand in plywood industry.

DURABILITY: Deodar wood is extremely durable and rot-resistant.

FINISHING: The wood has a fine close grain capable of receiving a high

polish

CHAPTER 3

MATERIALS AND METHOD:

The broad objective of this study was to analyse the effect on different

polish in the finish of the wood surface on different samples of Deodar and

Teak. A total of 60 sample planks of Teak and Deodar were taken for the

study with a dimension of 15 X 9 X 1 cm3 deodar, 15 X 7 X 1.5 cm3 teak.

Than they were oven dried and treated in humidity chamber. Sanding was

done for all 10 samples each with sandpapers of 60, 80, 100 and 120 grit

size. Making a total of 30 samples. The dimensions and weight data for all

the samples were taken. All the samples were placed in the humidity for

conditioning at 35°c and 30% R.H. water level was maintained in the

humidity chamber always. Proper care has been taken while placing the

samples in the humidity chamber that the samples should not touch each

other; and no samples should be placed in the bottom shelf where water

accumulates in case of leakage.

Of the 30 samples of teak 10 samples were coated with polyurethane

(PU), 10 samples were coated with shellac and 10 were kept as constant; the

same was done for deodar. The polyurethane applied was prepared by

diluting polyurethane with turpentine oil in the proportion of 10 ml of

Turpentine oil for every 50 ml of polyurethane.

The samples coated with polyurethane 3 coats were applied by spray gun

for even application of the coat and placed in sun for drying. Gloss was

measured for all the samples after each coat was applied. Coat thickness

was measured in 3 random samples after each coat so as the sample once

taken for coat thickness should not be repeated. 10 samples of each species

were coated with 6 coats of shellac. The shellac applied was prepared by

mixing 60 gm of shellac in 1liter of spirit and placing it in sun. Proper care

has been taken so that shellac should not be applied when the weather is

cloudy. The bottle has been kept closed when not in use to avoid drying of

spirit. Gloss was measured for all the samples after each coat was applied.

Coat thickness was measured in 3 random samples after each coat so as the

sample once taken for coat thickness should not be repeated. This is done

to to study the relation between coat thickness and gloss. After application

of the coating, weight, coat thickness and gloss were measured for all the

samples. 10 samples of each species were kept as control. Proper care has

been taken for all the coated samples; they should not be placed one above

another when they are not fully dry. The samples are than placed in the

humidity chamber again at elevated humidity levels, i.e., at 35°c and 85%

R.H. At this elevated humidity moisture has been taken by the coat applied.

Than moisture uptake of the coat in hardwood and softwood has been

calculated to compare the difference. Weight were taken for all the samples

continuously for 3 days after placing the samples at elevated relative

humidity and then taken at a gap of 3 days, 7, and 15 days.

CHAPTER 4

Results & discussions:

Thickness

The effect of thicknesses were studied in two stages viz. effect of coating

material on thickness formed on either species and effect of species on the

thickness obtained for the same coating.

Coating material effect

Fig 1. Shows the comparison of thicknesses of PU and shellac coatings on

the samples of teak and deodar.

0

50

100

PU Shellac

Th

ick

ne

ss

Coat

Avg Thickness

Teak

Deodar

Fig 1: Average coat thicknesses of PU and shellac coatings on the samples of teak and

deodar.

Figure 1 presents coating thickness for Teak and Deodar for PU and shellac

compositions in general the trend is similar with these compositions.

However, the relative increase in Deodar wood with these compositions is

the meter of interest, had these been an ideal surface like glass sheet the PU

and shellac coating could not have shown such a prominent variation these

variation wood have existence in PU and shellac coating thickness due to

the linearity and degree of freedom of linking molecules in other words PU

being a cross linked molecules would have produced a three-dimensional

surface. Which however could not have possible with shellac. In other words

there is a threshold minimum thickness with a single PU coat.

Now in case of Teak and Deodar PU has shown higher thickness in

comparison to shellac sustaining varying nature of coating. Beside this

deodar has shown tremendous increase in coating thickness which cannot

be attribute through coating and is rather suggestive of surface phenomenon

of a hardwood and a softwood.

It is evident that after planning hard teak surface does not contain raised

grain which is always present in softwoods. This is due to the variability of

earlywood (springwood) and latewood fibers.

It is visually evident that in case of teak samples, the thicknesses are almost

similar in the case of both the coatings. In case of deodar it is seen that there

is a considerable difference on average thickness of coating. Interestingly,

the three coats of PU seem to be giving a much thicker coat on Deodar

compared to the six coats of shellac used. The differences in thicknesses of

coatings of the two coats in case of teak and deodar were analysed through

one-way ANOVA at 95% confidence interval. The details of the statistical

analysis of the two species are as follows:

Table 1: ANOVA of coating thicknesses of PU and shellac on Teak and deodar

surfaces

Species Source of variation df Mean Square F Sig.

Teak Coatings 1 82.82 58.32 0.000

Error 18 1.42

Deodar Coatings 1 3751.06 372.12 0.000

Error 18 10.08

Table 1 reveals that the two coatings used in the study result in significantly

different thicknesses on both the surfaces. From fig. 1 it can be clearly stated

that the thicknesses of three coats of PU is significantly greater than the film

formed by six coats of shellac.

Rajput et al. (2014) reported 60-70 μm thicknesses for bio-based PU

coatings on wood panels. In the present study, the thickness of PU on the

softwood (Deodar) is 81 μm against 35 μm on teak wood.

Species effect

Table 2. Gives the mean values of thicknesses obtained by the two coating

materials on either species.

Table 2: Mean thicknesses (μm) of PU and Shellac on the two species studied

Coating material Teak Deodar

PU 35 (1.4) 81 (3.8)

Shellac 31 (0.9) 54 (2.4) *Values in parentheses give the standard deviations)

Table 2 indicates that the coating thickness is always higher on Deodar.

Analysis of this data also proved that the thicknesses formed by either

coating on Deodar were significantly higher than those on teak surface (p

<0.05). Teak is a ring porous hardwood and Deodar is a non-porous

softwood. Hence it is expected that any deposition in liquid or semi liquid

form on the surface of the porous wood may percolate into the wood. Thus

the higher thickness on the softwood is not surprising. The average

thickness obtained on chestnut and pine surfaces for two coats of an acrylic

varnish containing polyurethane were about 55 μm and 66.5 μm which was

attributed to the greater volume of voids in pine (Fernandez et al., 2013).

Gloss

The gloss data also were studied in two stages viz. effect of coating material

on gloss on either species and effect of species on the gloss obtained for the

same coating.

Coating material effect

Table 3 gives the mean values of gloss of PU and shellac coatings on the

samples of teak and deodar.

Table 3: Mean Gloss values (GU) obtained on the two species with PU and

shellac

Species PU Shellac

Teak 79.5 (3.1) 32.7 (3.5)

Deodar 86.7 (3.4) 27.6 (2.6)

*Values in parentheses give the standard deviations)

It is seen that the polyurethane coating gives considerably more gloss than

shellac coating. This is in spite of the fact that in the present study, only

three coats of PU seems to be give a much higher gloss on Deodar and a

slightly higher gloss in teak were used whereas six coats of shellac were used

to coat the samples. The mean values of gloss of PU coated samples (79.5

GU and 86.7 GU on teak and deodar respectively) are much higher than

those reported on eucalyptus surfaces by Ghosh et al. (2015) mainly due to

the fact that in the present case the thickness of PU coating was perhaps

higher. On the other hand, the gloss value for shellac are lower than reported

for eucalyptus illustrating the role of substrate also in achieving gloss levels.

The differences in gloss of the two coats in case of teak and deodar were

analysed through one-way ANOVA at 95% confidence interval and the

differences were indeed significant(p<0.05).

Species effect

Fig 2. Shows the comparison of gloss values of PU and shellac coatings on

the samples of teak and deodar.

Fig 2: Mean gloss of the two coatings on teak and Deodar surfaces

It can be seen from fig 2 that the polyurethane coating gives

considerably more gloss than shellac coating on both the surfaces. This is

in spite of the fact that in the present study, only three coats of PU was used

as against six coats of shellac. However, the gloss values obtained by a

particular coating (either PU or shellac) seems to be similar on either species.

To understand any species effect, the gloss data was analysed using one-

way ANOVA and the results are given in Table 4.

Table 4: ANOVA of gloss values (GU) of PU and shellac on Teak and deodar

surfaces

Species Source of variation df Mean Square F Sig.

PU Species 1 261.37 24.31 0.000

Error 18 10.75

Shellac Species 1 130.56 14.00 0.001

Error 18 9.32

0

10

20

30

40

50

60

70

80

90

Teak Deodar

Glo

ss (

GU

)

Species

PU

Shellac

The above statistical analysis for comparing the effect of gloss between the

two species shows highly significant differences for both the coating

materials. On either species, the PU gave higher gloss values.

MOISTURE STUDIES

Table 5 gives the moisture contents attained by the samples after

conditioning and at the end of the experiment.

Table 5: Initial and final MC of Teak and Deodar.

Species Conditioned MC FMC MC Increment %

Teak 8.7 10.10 16.09

Deodar 11.8 14.83 25.67

Table shows that the softwood samples had a higher initial MC. In addition,

these samples have taken up more moisture (25.67 %) as against that taken

up by teak (16.09 %). This may be attributed to the higher permeability of

Deodar.

Moisture gain

Fig 3. Shows the comparison of moisture gain values of PU and shellac

coatings on the samples of teak and deodar.

Table 6: Percent Moisture gain of Teak and Deodar samples.

% moisture gain

Species PU Shellac Non-coat

Deodar 20.92 22.08 25.72

Teak 13.69 10.09 16.14

Fig 3: Percent Moisture gain of PU and Shellac coatings on Teak and Deodar.

It can be seen from fig 3 that moisture gain is highest in the non-coated

control samples in case of deodar. Wood being hygroscopic in nature is

always prone to swell/ shrink on the absorption of moisture. Swell refers to

intake of moisture, shrink refers to loss in moisture content of wood. In this

study, we have compared the amount of moisture intake on the two coatings

(PU and shellac) in different samples of teak and deodar. The statistical

analysis details of comparison of each species are given in table 7. Before

running the analysis, the percent increment data were transformed to its

square roots as the values were below 30 % (Ahrens et al 1990).

Table 7: ANOVA of moisture increment of PU and shellac on Teak and deodar

samples

Species Source of variation df Mean Square F Sig.

Teak Moisture 2 1.78 7.41 0.002

Error 27 0.24

Deodar Moisture 2 0.74 3.52 0.047

Error 21 0.21

0

5

10

15

20

25

30

pu shellac non-coat

MC

in

Coating Material

% moisture gain

deodar

teak

Table 4 shows that there is a difference between the moisture increments

exhibited by the two finishes on either wood species. The MC increment

values were grouped through Duncan’s subsets using SPSS. The results are

given in tables 8 and 9 for teak and deodar respectively.

Table 8. Duncan’s subsets for moisture gain in teak

Coat teak No of samples

Moisture Subsets

1 2

PU 10 3.2

Shellac 10 3.3

control 10 4.0

Sig. 0.669 1.000

When we compare the moisture increments of PU and shellac coated

samples of teak, we find that both the coatings are allowing increase in MC

similarly. However, when we compare it with the control (non-coated

samples) it is found that the MC increment is significantly lesser for the

coated samples. Thus both shellac and PU (in thicknesses of 31 and 35 µm)

are equally efficient in blocking moisture entry into teak.

Table 9: Duncan’s subset for moisture gain in deodar

Coat Deodar No of samples

Moisture Subsets

1 2

PU 8 4.4865

Shellac 8 4.5448

control 8 5.0406

Sig. 0.801 1.000

Table 9 reveals a very similar result for Deodar also. Here it is to be noted

that the shellac coating had 81 um thickness compared to 54 µm for PU. It

is actually the higher coat thickness for shellac which has helped in

reducing moisture intake in Deodar in comparable terms with PU. In teak,

both the finishes ad almost similar thicknesses (31 µm for shellac and 35

µm for PU).

Change in gloss studies:

Table 10: comparison of coat thickness before and after exposure to

adverse Condition (85% R.H)

Coat

Materia

l

Teak Deodar

Before

Gloss

After

Gloss

Change

%

Before

Gloss

After

Gloss

Change

%

PU 79.5 62.6 21.2 86.7 63.6 26.6

Shellac 32.7 14.7 54.7 27.6 10.9 60.3

Table 11: % change in gloss on exposure to adverse conditions (85% R.H)

Coat Teak Deodar

PU 21.2 26.6

Shellac 54.7 60.3

Figure 4: % change in gloss on exposure to adverse conditions

0

10

20

30

40

50

60

70

Teak Deodar

Glo

ss (

GU

)

Species

% change in gloss on exposure to adverse conditions

PU

Shellac

From the above figure we can observe that gloss in PU coating offers a

greater resistance to adverse condition as compared to Shellac coating. The

retention provided by PU is more than double the amount of retention

provided by shellac coated samples. It means gloss reduction in shellac is

very high in adverse climatic condition in both hardwood and softwood.

Coat thickness studies:

Table 12: comparison of coat thickness before and after exposure to adverse

Condition (85% R.H)

Coat

Material

Teak Deodar

Before

Thickness(µm)

After

Thickness(µm) Change

%

Before

Thickness(µm)

After

Thickness(µm) Change

%

PU 35.1 34.9 32.6 81.0 56.7 29.8

Shellac 31.0 26.5 14.4 53.6 44.0 17.8

Table 13: %change in coat thickness on exposure to adverse conditions at

85%R.H.

Coat Teak (%) Deodar (%)

PU 32.6 29.8

Shellac 14.4 17.8

Fig.5: % change in coat thickness on exposure to adverse conditions.

0

10

20

30

40

Teak Deodar

% C

han

ge

Species

%change in coat thickness on exposure to adverse conditions at 85%R.H.

PU

Shellac

From the above figure we can analyse, in both the species Teak and Deodar

shellac coated samples offer higher retention in coat thickness on exposure

to adverse condition, i.e., 85% Rh for a prolonged period as compere to PU.

Similar experiment was done by Arno et al 1984 but the results obtained

were different, the reason may be the difference in the humidity conditions

of the experimental setup. And similar results were obtained by Richard

(1978) who studied the effectiveness of some commonly used conservation

materials in reducing dimensional movement of wood samples under

cyclically varying RH conditions.

CHAPTER 5

Conclusions: The coating thickness is always higher on Deodar. The thicknesses

formed by either coating on Deodar were significantly higher than

those on teak surface.

Three coats of PU seems to be give a much higher gloss on Deodar and

a slightly higher gloss in teak were used whereas six coats of shellac

were used to coat the samples.

Moisture gain is highest in the non-coated control samples in case of

deodar. The MC increment is significantly lesser for the coated

samples. Thus both shellac and PU (in thicknesses of 31 and 35 µm)

are equally efficient in blocking moisture entry into teak. The shellac

coating had 81 um thickness compared to 54 µm for PU, the higher

coat thickness for shellac which has helped in reducing moisture

intake in Deodar in comparable terms with PU. In teak, both the

finishes ad almost similar thicknesses (31 µm for shellac and 35 µm

for PU).

Gloss in PU coating offers a greater resistance to adverse condition as

compared to Shellac coating. The retention provided by PU is more

than double the amount of retention provided by shellac coated

samples.

In both the species Teak and Deodar shellac coated samples offer

higher retention in coat thickness on exposure to adverse condition,

i.e., 85% Rh for a prolonged period as compere to PU.

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