the effect of solvents on the chemical...

1

The Effect of Solvents on the Chemical Composition

Of Archaeological Wood

S.S. Darwish and N.M.N. El Hadidi

Conservation Dept. - Faculty of Archaeology - Cairo University

Summary

Solvents are widely used in wood conservation for either dissolving polymers for

consolidation purposes or for removing dirt or foreign matter, which was applied during

previous conservation. Solvents may cause temporary swelling of the wood, and when

they evaporate wood returns back to its original size. They may form complexes with

wood components when unlimited swelling arises as a consequence of breaking the

adjacent bonds. These complexes have been shown to be stable for long periods of time

at elevated temperatures or under high vacuum, while they are not stable with regard to

moisture. Wood absorbs organic solvents, which are retained in the wood cells for short

periods of time only in normal conditions. During the short presence of solvents inside

the wood, wood components are slightly affected, and after evaporation of the solvent the

chemical composition of wood may undergo some changes. Using FTIR, the molecular

bonds in wood samples that were treated with three different organic solvents were

closely studied.

Keywords: solvents effect; archaeological wood; FTIR

Introduction

Different types of dirt such as grease, old varnish, paints, glue and mildew stains are

often found on archaeological wooden artifacts. It may often be difficult to choose a

solvent which is both effective and safe. However, wood has giant molecules with either

primary or strong secondary bonds linking them together. These are more difficult to

2

dissolve than the small dirt molecules. It has always been believed that the consequence

for cleaning non deteriorated wood is that organic solvents, in general, are likely to be

innocuous as far as any risk of dissolving the main structural materials of wood such as

cellulose and lignin. One can be rather less sure about the supplementary materials of an

object such as varnishes, colours and pigments ( Moncrieff and Weaver, 1994).

In cases where wood is deteriorated, cleaning may become a very difficult matter,

because major wood polymers may have deteriorated due to different factors. Usual

cleaning solvents do not only dissolve dirt or other foreign matters, moreover they can

also remove some of the deteriorated outer layers of the wood.

Solvents are used for many purposes in conservation including cleaning and the

application or removal of coatings, consolidants and adhesives. Making the most of any

solvent requires familiarity with the basic principles of molecular bonding and an

understanding of how the structure of solvents affects their physical and chemical

properties. Chemical cleaning of wooden surfaces involves the use of reagents, which are

chemicals that break primary molecular bonds, converting dirt, varnish or other unwanted

material to a different form in order to remove it from the surface. After solvent cleaning,

original material cannot be recovered in the same way as it was, when the archaeological

object was first made in the past (Rivers and Umney, 2003).

The aim of this study is to find out how the two major wood components are affected by

solvents commonly used in cleaning archaeological wood.

Materials and Methods

Ancient deteriorated samples taken from the Mashrabieh of Bazarah (Ottoman period),

which had been previously identified as oak wood (El Hadidi, 2003) were used for

studying the effect of three solvents commonly used for either cleaning wood or during

3

wood consolidation in Egypt at the present time. The three solvents chosen were:

Ethanol, Acetone and Toluene.

Three wood samples were immersed in every solvent separately for one hour. Samples

were then removed and left to dry out in normal room temperature and humidity

conditions.

Samples were then divided into three groups, each group consisting of 4 samples; i.e.

archaeological sample before immersion in solvent and archaeological sample after

immersion in one of the three solvents. The first group was studied by FTIR spectroscopy

(JASCO FTIR plus 460). The second group was aged using UV radiation (Spectroline

UV A lamp, wave length 365 nm) for 100 hours in normal room temperature at a distance

of 15cm and the third group was aged using heat for 100 hours at105+3˚C. Samples from

the second and third groups were also studied by FTIR spectroscopy, so as to study and

compare the changes that had occurred in the chemical bonds of both wood cellulose and

lignin before and after ageing.

Results and Discussions

I- Effect of Heat and U.V. ageing on Wood Samples

I.1- Heat Ageing: Heat ageing of wood is expected to undergo hydrolysis of glycosidic

bonds of cellulose and oxidation of functional groups of glucopyranose rings. Lojewska,

et al. (2005b) found that oxidation and hydrolysis of cellulose are supposed to proceed at

temperatures not higher than 100oC. At higher temperatures the reaction scheme would

have to include dehydration, condensation or transglycosidation reactions.

I.1.1- Hydrolysis: is indicated by splitting of the hemiacetal bond between the two

glucopyranose rings C1 & C4. The terminal rings giving rise to the cleavage of C1-O-C5

bond in the same ring. On opening the ring, the C5-OH formed becomes available for

oxidation and the formation of CHO group.

4

I.1.2- Oxidation: Carbon atom occupying various positions in the ring C1, C2…..C6

gradually transforms by oxidation into various carbonyl groups, therefore intensities of

C-O bands decrease. Oxidation was detected as fairly broad and overlapping bands in

FTIR spectroscopy.

Shafizadeh & Chin (1977) and Englund & Nussbaum (2000) studied some minor changes

that can occur in wood at temperatures above 50° C, such as elimination of water and

release of volatile components (i.e. monoterpenes). Hancock (1963) and Nuopponen, et

al. (2003) observed migration of wood resin onto the surface of wood at temperatures

between 120-160° C.

Heat ageing also caused some modifications in lignin structure including

depolymerisation and condensation reactions. The first thermal changes in lignin can be

detected at temperatures above 150°C (Fengel and Przyklenk (1970); Faix (1988) &

Nuopponen (2005)). Molecular weight of lignin has been reported to decrease extensively

at temperatures above 180°C in various thermal treatments as a result of breaking down

of aryl-ether interunit linkages (Westermark, 1977). The amount of methoxyl groups in

lignin diminished when wood was heated at temperatures higher than 180°C. At elevated

temperatures (> 200°C) structure of lignin becomes more condensed (Wikberg and

Maunu, 2004).

Nuopponen (2005) found that of the structural components, hemicelluloses are the most

vulnerable to thermal degradation. Degradation rates of hemicelluloses have been

reported to be four times higher at 150°C than that of wood or α-cellulose. Sundqvist

(2004) revealed that acetic and formic acids liberated from wood during thermal

treatment enhanced hydrolysis of hemicelluloses and cellulose. Noticeable decrease in

the content of polysaccharides occurs at temperatures above150°C. Fengel and Wegener

5

(1989) found that hydrolyzed sugars are further dehydrated and great varieties of volatile

compounds are formed, such as furfural and hydroxymethyl furfural.

The results in figures (1,2,3,4&5) clarified the effect of both heat and U.V. ageing on the

archaeological wood samples. The results showed that the band at 1645 cm-1

due to

bending modes of water molecules disappeared, which is evidence of complete water

desorption. These findings were noted in the spectrum of the wood samples that were

heated for 100 hours at 105+3˚C. Similar results were recorded in previous research in

the field of degradation of wood components (Lojewska, et al. (2005b); Englund and

Nussbaum (2000); Hatakeyama, et al. (1976); Zhou, et al. (2001) & Lojewska, et al.

(2005a)); where they had noted the disappearance of adsorbed water by the vanishing of

the 1640 cm-1

bond from the samples that were being monitored, and at elevated

temperatures water desorbs from wood and does not reabsorb again.

We may summarize the changes in our samples due to heat ageing as follows:

- In the archaeological sample sharp OH stretching band appeared at 3782 cm-1

due to

free OH; i.e. heat broke H-bonds. A carbonyl band at 1621 cm-1

appeared in the sample as

a result of natural ageing of the sample. This band was due to conjugated carbonyl groups

resulting from partial oxidation of C-OH groups at C2 and C3 in the glucopyranose ring.

- Heat ageing caused sharp decrease in C-O stretching band intensities at 1112 cm-1

and

1056 cm-1

and the disappearance of the band at 1033 cm-1

. These findings are attributed

to the oxidation of CH-OH groups to carbonyl groups which appeared at 1635 cm-1

leading to broadening of the band.

- Lignin bands at 1509 cm-1

(aromatic >C=C< stretching) and 1269 cm-1

(C-O-R

stretching) decreased as a result of its degradation. This result agreed with previously

published research (Westermark, et. al., 1997) which noted that degradation of lignin

6

results from breaking down of aryl-ether interunit linkages, so the amount of methoxyl

groups in lignin diminishes.

- The intensity of various bands observed in the OH bending and CH deformation zone

(between 1400 cm-1

-1200 cm-1

) also decreased. Similar studies were done by other

researchers (Nuopponen, 2005) who had examined the thermally induced changes in pine

wood with Fourier transform infrared (FT-IR) and UV resonance Raman (UVRR)

spectroscopy. The Spectroscopic data revealed that the structure of thermally treated

wood was extensively modified at temperatures above 200oC. These modifications

included the depolymerisation and condensation of lignin, degradation of hemicelluloses

as well as the removal and/or decomposition of the wood resin components.

I.2- U.V. ageing: U.V ageing showed a slight variation compared to heat ageing.

Hydrolysis and oxidation occurred in limited cases. Exposure of the sample to 100 hours

of U.V. radiation caused complete water desorption and disappearance of the water band

at 1645 cm-1

. U.V. radiation had a similar effect as heat on the H-C-OH groups that were

oxidized to carbonyl groups, leading to the decrease in C-O intensity at 1117 cm-1

and its

disappearance at 1033 cm-1

in addition to the broadening of the carbonyl band. A

decrease in the lignin band (aromatic C=C) at 1509 cm-1

was noticeable.

II- Effect of solvent treatment on archaeological wood samples

Figures (6,7,8,9&10) showed the effect of two polar solvents, ethanol and acetone, and a

moderately polar solvent like toluene on the stability of archaeological wood samples.

Wächter (1974) suggested that the treatment of paper with an organic solvent during the

conservation treatment might result in the formation of a permanent cellulose-solvent

complex. The formation of such a complex might increase the reactivity of the paper and

accelerate its rate of aging. Other researchers (Wiertelak and Garbaczowna (1935);

Staudinger (1953); Wade and Creely (1974) & Arney and Pollack (1980)) have

7

demonstrated that these complexes have shown some stability for long periods of time at

elevated temperatures or under high vacuum, while they are not stable with regard to

moisture.

Horvath (2006) suggested that the swelling of cellulose in organic solvent is related to the

swelling of wood. The swelling of cellulose appears to be intercrystalline (the solvent

enters into the amorphous areas) and intracrystalline (the solvent penetrates in the

crystalline regions). The solvent forms complexes with cellulose when unlimited swelling

arises as a consequence of breaking the adjacent bonds. The extent of swelling depends

on the solvent as well as on the nature of the cellulose sample. The resulting separation of

the polymer chains indicates the beginning of the solubility. The dissolving ability entails

formation of a complex with the two secondary hydroxyl groups in cellulose and with

breaking of hydrogen bonds. The swelling and solubility of lignin is greater with

hydroxylated solvents (swelling solvents), e.g., methanol, ethanol, phenol, and water than

non polar solvents (non swelling solvents) like benzene and toluene. The hydrogen-

bonding capacities of various solvents are proportional to the shift in wave length of the

infrared region of the spectrum.

II.1- Unaged alcohol treated sample: The results in figures (6,7,8,9&10) showed that

asymmetric and symmetric stretching modes of water molecules at 3534 & 3406 cm-1

disappeared and typical OH stretching resulted due to the formation of wood- alcohol

complex; i.e. alcohol displaces water molecules. The results agreed with that of Horvath

(2006) who proved the formation of this complex in case of swelling solvents (polar

solvents, e.g. ethanol, acetone,….). The formation of wood-alcohol complex accelerated

the rate of wood ageing. Intensity of C-O stretching bands at 1112, 1057 and 1032 cm-1

decreased (in comparison to the untreated sample) due to the oxidation process on C2–

8

OH, C3–OH and C6–OH and the formation of enolic group-carbonyl group tautomor at

1646 cm-1

(Mosini, et al .(1990); Ali, et al.(2001) & Calvini and Gorassini (2002)).

A new additional band appeared at 1160 cm-1

(in comparison to the untreated sample).

This band may be due to opening of the terminal rings and cleavage of C1-O-C5 bond and

formation of C5-OH group. All the bands between 1500-1200 cm-1

decreased. These

bands were due to OH bending, CH deformation, aromatic >C=C< stretching of lignin

and C-O-R stretching in lignin.

II.2- Unaged acetone treated sample: Acetone accelerates wood oxidation leading to

decrease of C-O stretching band at 1119 cm-1

and disappearance of C-O bands at 1056

cm-1

and 1033 cm-1

due to complete oxidation of C-OH groups. Asymmetric and

symmetric stretching modes at 3534 & 3406 cm-1

and bending modes at 1646 cm-1

of

water molecules slightly decreased as some acetone replaced water and formed wood-

acetone complex. A complex vibrational pattern of various carbonyl groups due to partial

cellulose oxidation products appeared at 1682, 1646 and 1621 cm-1

. Lignin bands

decreased as a result of lignin degradation.

II.3- Unaged toluene treated sample:

Formation of toluene – wood complex is limited due to its lower polarity. So, its effect on

wood reactivity and on the ageing of wood components is small compared with that of

alcohol and acetone.. Toluene may accelerate hydrolysis of both cellulose and lignin and

whose effect on lignin bands was more than that of cellulose. Asymmetric and symmetric

stretching modes of hydroxyl groups as well as C-O stretching bands slightly increased.

These findings may result from opening some of the glucopyranose rings or/and splitting

few of the hemiacetal bonds between the two glucopyranose rings C1 & C4 and formation

of C1-OH, C4-OH and C5-OH groups. Lignin bands at 1509 and 1267 cm-1

decreased due

to its degradation.

9

III- Effect of heat ageing on wood treated samples

Figures (11,12,13,14&15) clarified the heat effect on the wood treated samples that were

heated for 100 hours at 105+3˚C

III.1- Heat aged alcohol treated sample: New bands due to free OH stretching

appeared in the region between 3710 and 3565 cm-1

. These bands were formed as a result

of heat breaking down of intermolecular hydrogen bonding. Various carbonyl groups

bands (CO-CHO-COOH groups) were formed due to partial oxidation occurring

predominantly on C-OH groups in glucopyranose rings. These bands were reasonably

broad and overlapping, and their intensities increased in comparison to similar bands in

the heated untreated samples. The band at 1732 cm-1

is presumably from the ester groups

which may arise at this position of the spectrum and may form in the reaction of the

carboxylic groups with unreacted alcoholic group or with residual ethyl alcohol. Similar

results were obtained by Inari, et al.(2007) who stated that compared to lignin,

holocellulose exhibits important infrared absorptions of about 1,730 cm−1

, characteristic

of ester or urethane linkages. This hypothesis is confirmed by the presence of additional

newly formed C-O-C vibration from ester at 1155 cm-1

. The band at 1716 cm-1

may

represent carboxylic groups (the final oxidation step of C-OH groups). Rutherford, et

al.(2004) recorded the same band in the case of charred lignin spectra. Bands at 1844cm-1

and 1771cm-1

fit the pattern observed in five-member ring cyclic anhydrides (Colthup, et

al., 1990). Band at 1683 cm-1

could be attributed to ß-diketones similar to quinone-type

vibrations described by Agarwal (1998). Lignin degraded faster when treated with

alcohol i.e. band at 1268 cm-1

disappeared and at 1509 cm-1

decreased compared to heat

untreated sample. Intensity of C-O band at 1112 cm-1

increased as a result of hydrolysis

of the hemiacetal bond between two glucopyranose rings C1-O-C4. The terminal rings

may open giving rise to the cleavage of C1-O-C5 band in the same ring and to the

11

formation of CHO groups. On opening the ring, the C5-OH groups were formed and this

increased the C-O intensity. The above results showed that oxidation accompanied

hydrolysis, because residual oxygen is always present in wood, and conversely,

hydrolysis cannot be avoided during oxidation because residual water is present in wood

structure and also because water is a product that occurs during wood oxidation. The

same results were obtained by Lojewska, et al. (2005b) who proved that oxidation

accompanied hydrolysis during cellulose degradation.

III.2- Heat aged acetone treated sample: The results obtained were nearly the same as

in case of alcohol. New band at 1156 cm-1

appeared (in comparison to the untreated

sample). It may be due to C-O group of ester formation or new C-OH groups resulting

from opening of the pyranose ring. More carbonyl groups were formed as a result of

further oxidation of C-OH groups of cellulose molecules.

III.3- Heat aged toluene treated sample:

Heat ageing of toluene treated samples showed slight variations compared to heat aged

untreated ones. More decrease in C-O stretching bands, lignin bands at 1509 &1267cm-1

and increase in C=O bands. While, in comparison to unaged toluene treated samples, heat

increased the effect of toluene on wood components, i.e. more oxidation and hydrolysis.

Sharp decrease in C-O and lignin bands; and an increase and broadening in C=O bands

occurred.

IV. Effect of U.V. ageing on wood treated samples

Exposure of wood treated samples to U.V. radiation for 100 hours had a great effect on

wood components as shown in figures (16,17,18,19&20).

IV.1- U.V. aged alcohol treated sample: C-O band intensity at 1121cm-1

increased in

comparison to U.V. aged untreated sample and to the alcohol treated sample. This

11

increase is due to the combination of new C-O of C5-OH resulting from the opening of

the pyranose ring and C-O of residual unoxidized C2-OH and C3-OH.

Carbonyl group due to C2 and C3 oxidation had the same intensity compared to U.V.

untreated sample. Lignin bands at 1509 cm-1

decreased and at 1268 cm-1

disappeared, i.e.

alcohol increases the effect of U.V. ageing on wood.

IV.2- U.V. aged acetone treated sample: As in case of alcohol, intensity of C-O

stretching band increased due to the combination of new C-O of C5-OH resulting from

the opening of the pyranose ring and C-O of residual unoxidized C2-OH and C3-OH.

Hydration band at 1646 cm-1

appeared again as some water molecules replaced solvent in

wood-acetone complex. i.e. U.V ageing occurred in normal (humid) conditions. Intensity

of carbonyl groups band at 1623 cm-1

increased as a result of oxidation process. Lignin

bands decreased as a result of lignin degradation.

IV.3- U.V. aged toluene treated sample:

Like heat ageing, U.V. increased the effect of toluene on wood components. Absorption

of C-O groups decreased while that of C=O increased (compared to both unaged treated

& U.V. aged untreated samples) as a result of conversion of C-O-H to C=O by oxidation.

Also, intensities of lignin bands at 1509 & 1267 cm-1

decreased.

Conclusion

It was found that the chemical composition of the two major wood components is

affected by organic solvents commonly used in cleaning archaeological wood. Ethyl

alcohol and acetone accelerated oxidation and hydrolysis of both cellulose and lignin.

Toluene showed a slight change compared to the other solvents used. So, it can be used

safely in conservation treatment. More over, it is an environmentally friendly compound.

12

All cellulose and lignin

bands decreased as a

result of heat and U.V

ageing. Some changes

in position or shape of

bands are noticeable. Some bands disappeared

and new bands were

formed.

(Fig.1): Effect of heat and U.V. ageing on wood sample

Heat ageing; accelerated hydrolysis and

oxidation processes. New band was formed

at 1158 cm-1 (in comparison to the untreated sample) as a result of ring

cleavage i.e. C5-OH was formed. The

intensities of all C-O bands decreased.

(Fig.2): C-O stretching zone

(Fig.3) : OH bending and CH deformation zone

The intensity of various bands observed in

the OH bending and CH deformation zone

(between 1400 cm-1 -1200 cm-1) decreased.

Heat & U.V. ageing increased the

intensity of carbonyl groups as a result of

partial oxidation of various C-OH groups

to C=O groups. Water bending modes

band at 1645 cm-1 was also removed. A decrease in the lignin band (aromatic C=C)

at 1509 cm-1 was noticeable. A carbonyl

band at 1621 cm-1 appeared in the sample

as a result of natural ageing of the

archaeological sample.

(Fig.4): C=O stretching zone

Asymmetric & symmetric water stretching

modes were present in both archaeological

sample & U.V. aged sample. As a result of

heat ageing water stretching bands were

removed and typical O-H stretching band was formed.

(Fig.5): O-H stretching zone

13

(Fig.6): Effect of solvent treatment on unaged archaeological wood samples

Solvents displaced water

molecules forming

solvent-wood complexes

and accelerated the rate

of wood ageing. Formation of these complexes depends on

solvent polarity.

Ethanol treatment decreased the intensity of

C-O stretching bands at 1112, 1057 and

1032 cm -1. A new additional band (in

comparison to the untreated sample) appeared at 1160 cm-1. Acetone treatment caused disappearance of

C-O bands at 1056 cm-1 and 1033 cm-1 due

to complete oxidation of C-OH groups.


(Fig.8): OH bending and CH deformation zone

Lignin bands at 1269 cm-1 decreased as a

result of its degradation. The intensity of

various bands observed in this zone also

decreased.

Hydration band at 1646 cm-1 decreased due

to formation of wood-solvent complex.

Various carbonyl groups appeared at 1682,

1646 and 1621 cm-1 as a result of acetone

treatment. Lignin bands at 1509 cm-1 decreased as a result of lignin degradation.

(Fig. 9) C=O stretching zone

(Fig.10) O-H stretching zone

Intensities of water stretching modes

decreased due to the formation of wood- solvent complexes.

14

(Fig.11): Effect of heat ageing on wood treated samples

Heat ageing accelerated

oxidation and hydrolysis

of wood treated samples

compared to untreated

ones. i.e. more new

bands and more carbonyl

groups were formed.

Lignin degraded faster when treated with

alcohol & acetone i.e. band at 1268 cm-1

disappeared and at 1509 cm-1 decreased

compared to heat untreated sample.


Various carbonyl groups bands were formed in case of heat ageing of alcohol

and acetone treated samples.

(Fig.14): C=O stretching zone (Fig.15): O-H stretching zone

New bands due to free OH stretching appeared in the region between 3710 and

3565 cm-1in case of heat ageing of alcohol

treated sample. These bands were formed

as a result of heat breaking down of

intermolecular hydrogen bonding.


New band (in comparison to the untreated

sample) appeared at 1156 cm-1. This band may be due to C-O group of ester

formation or opening of the pyranose ring.

15

(Fig.16): Effect of U.V ageing on wood treated samples

U.V. ageing of wood treated

samples increased wood oxidation

compared to wood untreated ones.


Lignin bands at 1509 cm-1 decreased and at

1268 cm-1 disappeared, i.e. alcohol increases

the effect of U.V. ageing of wood.

C-O band intensity at 1121cm-1 increased in

comparison to U.V aged untreated sample and

to the alcohol and acetone treated samples.


(Fig.20): O-H stretching zone

Asymmetric and symmetric water stretching

bands were formed as water replaced solvents.

U.V ageing occurred in normal (humid)

conditions.

(Fig.19): C=O stretching zone

Intensity of carbonyl groups bands of acetone

and alcohol at 1623 cm-1 increased as a result

of oxidation process.

16

References:

- Agarwal, U.P., Assignment of the photoyellowing -related 1675 cm-1 Raman/IR band to p- quinones and

its implications to the mechanism of color reversion in mechanical pulp, J. Wood Chem. Technol.,18,

(1998) ,381-402.

- Ali, M.; Emsley, A. M.; Herman, H. and Heywood, R. J., Polymer, 42: (2001), 2893-2900.

- Arney, J.S. and Pollack, L.B. , The retention of organic solvents in paper, JAIC, Volume 19, Number 2,

Article 2, (1980),pp. 69-74.

- Calvini, P. and Gorassini, A., FTIR- Deconvolution spectra of paper documents, Restaurator, 23,

(2002)48-66.

- Colthup, N.B., Daly, L.H., and Wiberley, S.E., Introduction to infrared and Raman spectroscopy:

Boston, Academic Press, (1990) , p.547. - Englund, F. and Nussbaum, R.: “Monoterpenes in Scots pine and Norway spruce and their emission

during kiln drying”, Holzforschung, 54 (2000), pp.449-456. - El Hadidi, N.M.N; ―A Study on some Physical, Mechanical and Chemical Changes of Deteriorated

Archaeological Wood and it’s Consolidation, with the Application on some Selected Artifacts at the

Islamic Museum of the Faculty of Archaeology‖. Doctoral Thesis. Cairo University, Faculty of

Archaeology, (2003)

- Faix, O.; Jakab, E.; Till, F. and Székely, T.: “Study on Low Mass Thermal Degradation Products of

Milled Wood Lignin by Thermogravimetry-mass-spectrometry”, Wood Sci.Technol., 22: (1988), pp. 323-

334.

-- Fengel, D. and Przyklenk, M.: “On Changes in Wood and Its Components at Temperatures up to

200°C”- Part V: Influence of Thermal Treatment on Lignin in Spruce wood, Holz Roh Werks., 28 (1970),

pp. 254-263.

- Fengel, D. and Wegener, G. : Influence of Temperature, Wood Chemistry, Ultra structure, Reactions,

Walter de Gruyter, (Berlin, 1989), pp. 319-344.

- Hancock, W.V.: “Effect of Heat Treatment on the Surface of Douglas-Fir Veneer”, Forest Prod. J.

(1963), pp. 81-88.

- Hatakeyama, H; Nagasaki, C. and Yurugi, T.: Carbohydrate Research ;48: (1976)149e58.

- Horvath, A. L., Solubility of Structurally Complicated Materials, J. Phys. Chem. Ref. Data, Vol. 35, No. 1

(2006).

- Inari,N. G.; Petrissans, M. and Gerardin, P., Chemical reactivity of heat treated wood, Wood Science

and Technology, Volume 41, no.2, (2007,)157-168(12).

- Lojewska, J.; Lubanska, A; Lojewski, T.; Miskowiec, P. and Proniewicz, L. M., Kinetic Approach to

Degradation of Paper. In situ FTIR Transmission Studies on Hydrolysis and Oxidation, Directory of Open

Access Journal ,2,(2005b), 1-12.

- Lojewska, J.; Miskowiec, P.; Lojewski, T. and Proniewicz, L., M., Cellulose oxidative and hydrolytic

degradation: in –situ FTIR approach, Polm. Degrad. Stab., 88, in press. (2005a ) .

17

- Moncrieff, A., and Weaver, G.; Cleaning, Science for Conservators, vol.2; The Conservation Unit &

Routledge (1994) , pp. 13-15.

- Mosini,V.; Calvini, P. ; Mattogno,G. and Righini, G., Derivative infrared spectroscopy and electron

spectroscopy for chemical analysis of ancient paper documents, Cell. Chem. Technol., 24, (1990),263- 272.

- Nuopponen, M., Thermal Modification of Wood and FT-IR and UV Raman Spectroscopic; Studies of its

Extractable Compounds, PhD Thesis, Helsinki University of Technology Laboratory of Forest Products

Chemistry, Reports, Series A 23, Espoo, Finland. (2005) - Nuopponen, M., Vuorinen, T., Viitaniemi, P. and Jämsä, S.: “Effects of heat treatment on the

behaviour of extractives in softwood studied by FTIR spectroscopic methods”, Wood Sci. Technol.,

37(2003), pp.109-115.

- Rivers, S. and Umney, N.; Conservation of Furniture, Butterworth Heinemann (2003), pp. 504-511.

- Rutherford, D. W.; Wershaw, R. L. and Cox, L. G., Changes in Composition and Porosity Occurring

During the Thermal Degradation of Wood and Wood Components, Scientific Investigations Report 2004-

5292—ONLINE ONLY. http://pubs.water.usgs.gov/sir20045292 (2004 )

- Shafizadeh, F., Chin, P.S.: “Thermal deterioration of wood‖, ACS Symposium Series, 43 (1977), pp.

57-81.

- Staudinger, H. , Staudinger, Makromol. Chem., 10, (1953), 254 .

- Sundqvist, B.: “Colour Changes and Acid Formation in Wood During Heating”, Doctoral Thesis, Luleå

University of Technology, (Sweden, 2004) , p. 50.

- Wächter, Mitteilungen, 4(4), (1974), p. 189.

- Wade, R. H. and Creely J. J., Text. Res. J., 44, (1974), 941.

- Westermark, U.; Samulesson, B. and Lundquist, K.: “Homolytic Cleavage of the β-ether Bond in

Phenolic β-O-4 ether Structures ant Its Significance in High-yield Pulping and Lignin Analysis”, Nord.

Pap. Res. J., 12: (1997) pp. 150-154.

- Wiertelak, J. and Garbaczowna, I., Ind. and Eng. Chem., 7, (1935), 110 .

- Wikberg, H. and Maunu, S.L.: “Characterization of Thermally Modified Hard- and Soft woods by 13C

CPMAS NMR”, Carbohydr. Polym., 58: (2004) pp.461-466.

- Zhou, S; Tashiro, K; Hongo, T; Shirataki, H; Yaman, C. and Ii ,T.: Macromolecules; 34: (2001)

1274 e80.
http://pubs.water.usgs.gov/sir20045292

the effect of solvents on the chemical...

Documents