NEW PROCESSES FOR THE STABILIZATION OF LIGNOCELLULOSIC MATERIALS DEVELOPED IN LAST FEW YEARS

Abstract

Traditional stabilization techniques often struggle with limitations such as the need to sort documents prior to modification, the inability to mass deacidify books for aqueous systems, economic difficulty, environmental concerns etc [1, 2]. The period in recent years on which the paper focuses highlights the current efforts to advance the resolution of these challenges through innovative approaches. These newer methods encompass a range of techniques including the utilization of nanotechnology, environmentally friendly chemicals, and advanced mechanical processes to ensure the deacidification, antioxidation, and reinforcement of paper materials. One of the traditional methods works on the basis of dispersions. The particle size of these dispersions is on the micrometer level. Standout features of the new developments is the use of nanotechnology in the conservation process. Nanoparticles, such as calcium hydroxide and magnesium oxide, have been modified to improve their efficiency in deacidification and paper strengthening. These nanoparticles exhibit unique properties that allow for a deeper penetration into the paper matrix and a more uniform distribution, thereby ensuring a comprehensive stabilization effect without compromising the paper's structural integrity. A emphasis is also placed on the ecological and health safety of these methods, alongside their effectiveness in preserving the integrity and extending the lifespan of paper-based information carriers. The advancements discussed in this article not only offer more efficient and safer alternatives for paper conservation but also underline the ongoing need for research in this vital field of heritage preservation. This contribution aims to summarize the main findings, methodologies and advantages of the 18 newly developed procedures. The paper presents in detail results of one of the newly developed methods whose deacidifying agent is hydrotalcite (HTC) dispersed in a mixed solvent (prefluoroheptane (PFH), isopropanol (IPA) and water). The effectiveness of the method to stabilise the lignocellulosic material during accelerated ageing is evaluated by measuring chemical (surface pH, glycosidic bond cleavage), mechanical (folding ndurance-coefficient of relative increase of the lifetime), optical (colorimetry) and spectral properties (FTIR) [3, 4].

Full text

NEW PROCESSES FOR THE STABILIZATION OF LIGNOCELLULOSIC
MATERIALS DEVELOPED IN LAST FEW YEARS
Eva Guzikiewiczová, Soňa Maleková and Katarína Vizárová
Slovak University of Technology, Faculty of chemical and food technology, Radlinského 9, Bratislava, 812
37, Slovak Republic
eva.guzikiewiczova@stuba.sk
Abstract
Traditional stabilization techniques often struggle with limitations such as the need to sort documents prior to
modification, the inability to mass deacidify books for aqueous systems, economic difficulty, environmental
concerns etc [1, 2]. The period in recent years on which the paper focuses highlights the current efforts to advance
the resolution of these challenges through innovative approaches. These newer methods encompass a range of
techniques including the utilization of nanotechnology, environmentally friendly chemicals, and advanced
mechanical processes to ensure the deacidification, antioxidation, and reinforcement of paper materials.
One of the traditional methods works on the basis of dispersions. The particle size of these dispersions is on
the micrometer level. Standout features of the new developments is the use of nanotechnology in the conservation
process. Nanoparticles, such as calcium hydroxide and magnesium oxide, have been modified to improve their
efficiency in deacidification and paper strengthening. These nanoparticles exhibit unique properties that allow for
a deeper penetration into the paper matrix and a more uniform distribution, thereby ensuring a comprehensive
stabilization effect without compromising the paper's structural integrity.
A emphasis is also placed on the ecological and health safety of these methods, alongside their effectiveness
in preserving the integrity and extending the lifespan of paper-based information carriers. The advancements
discussed in this article not only offer more efficient and safer alternatives for paper conservation but also underline
the ongoing need for research in this vital field of heritage preservation.
This contribution aims to summarize the main findings, methodologies and advantages of the 18 newly
developed procedures. The paper presents in detail results of one of the newly developed methods whose
deacidifying agent is hydrotalcite (HTC) dispersed in a mixed solvent (prefluoroheptane (PFH), isopropanol (IPA)
and water). The effectiveness of the method to stabilise the lignocellulosic material during accelerated ageing is
evaluated by measuring chemical (surface pH, glycosidic bond cleavage), mechanical (folding ndurance -
coefficient of relative increase of the lifetime), optical (colorimetry) and spectral properties (FTIR) [3, 4].
Keywords: stabilization, deacidification, processes, paper

Criteria for evaluation the effects of deacidification processes
Nowadays, there are no comprehensive, unified criteria to evaluate the process of mass deacidification [1].
P. G. Sparks was the first to formulate general requirements for mass neutralization processes in his work [2].
The main emphasis is on an in-depth analysis of six technical evaluation factors:
1) deacidification efficiency: the ability of the process to achieve complete and permanent neutralization of strong
and weak acids and acid-forming chemicals; the deposition of an adequate and uniform amount of alkaline
reserve; how well the treated paper is stabilized when subjected to accelerated aging conditions due to heat and
moisture; whether the process is effective in handling a variety of formats such as transparencies, boxed
manuscripts, and maps;
2) preventing undesirable changes in materials: chemical compatibility with materials commonly used for paper,
packaging, book bindings and other documents; compatibility with materials such as inks and dyes; effect of
the process on the brightness of the paper and the degree of photosensitivity; the strength of the paper should
not be significantly impaired by the treatment...;
3) toxicity,
4) environmental impact,
5) unit treatment cost/economic considerations,
6) user friendly method.
For an objective evaluation, it is essential to select several appropriate criteria based on self-designed
assessments [3]. In most cases, the basic criteria are considered to be the pH; the content, distribution and
homogeneity of the alkaline reserve and the influence of the deacidification system on the treated material [4, 5].
Library of Congress, Pittsburgh has selected the following as criteria suitable for evaluating the deacidification
process [5]: deacidification efficiency based on folding endurance, completeness of deacidification (post-treatment
pH between 6.8 - 10.4), alkaline reserve 1.5% CaCO3, process harmlessness (must not cause undesirable changes),
environmental impact, and toxicology.
Others take into account criteria such as surface pH as well as the pH of the aqueous cold extract, alkaline
reserve, discolouration or paint and ink spillage [6].
Later, the KnihaSK project developed criteria for evaluating the effectiveness of deacidification processes,
which include sustainability of the technology, preservation efficiency, heritage safety, quality compared to
competing technologies, environmental sustainability and risks, economic considerations, and supplementary data
(to support the quality of the process) [7, 8].

Deacidification processes developed from 2018 to 2024
The deacidification process is still a debated issue. Every year, new publications dealing with the subject are
added, bringing new knowledge and information on newly developed processes for deacidification and
stabilization of paper carriers. A brief overview of this information is given in Table 1.
Table 1 Deacidification processes developed from 2018 to 2024
Process
Environment
Deacidification Agent
Carrier/Solvent
Note
Dispersion of Ca(OH)2 in
subcritical 1,1,1,2-
tetrafluoroethane
(R134a) [9]
Aqueous
dispersion
CaOH2
Solvent: water, Carrier:
subcritical 1,1,1,2-
tetrafluoroethane
(R134a)
Advantages: possibility to
integrate cleaning and
deacidification into one
workflow
Dispersions of MgO
nanoparticles modified
with oleic acid in non-
polar solvent [10]
Non-aqueous
dispersion
MgO
cyklohexán
Addition of surfactant: oleic
acid. After deacidification,
the surface pH is around 8,
tensile strength values
remained stable after
accelerated aging. The
modification does not
adversely affect the sample's
appearance.
Aqueous colloids of
magnesium
oxyhydroxide [11]
Aqueous
dispersion
Magnesium
oxyhydroxide
Mg5O(OH)8 (Mg-NSs)
Water
pH of paper increased to the
neutral range after treatment
and remained stable after
artificial aging. Whiteness
of paper increased by 10%,
and paper strength increased
by 25%.
Deacidification and
strengthening of paper
in situ by quaternization
[12]
Partly
aqueous
dispersion
MgO
HMDO
(hexamethyldisiloxane),
2,3-epoxypropyl
trimethyl ammonium
chloride (ETA),
isopropanol (IPA),
water
Paper is strengthened and
deacidified in situ via
quaternization. pH range is
7.5 – 9.0. Tensile strength
and folding endurance
increased by 280.5% and
80%, respectively.
Brightness fluctuation and
chromatic aberration range
is 0.14 and 1.27. Treated
paper had good antibacterial
effects.
Extracts from plants of
Lemna gibba and
Eichhornia crassipes
[13]
Gaseous
Lemna gibba and
Eichhornia crassipes
(active ingredient:
polyphenolic
compounds)
Cellulose substrate
(Whatman paper)
Advantages: scavenges free
radicals, metal chelation,
antioxidant and fungicidal
effects.
Strengthening paper
using aqueous cellulose
solution [14]
Aqueous
solution
Strengthening agent:
cellulose (filter paper)
NaOH (7% wt), urea
(12% wt), and water
(solvent needs to be
cooled to -12°C before
adding cellulose)
Alternative method based
on paper strengthening.
Advantages: application by
spraying, improved
mechanical properties.
Disadvantages: slight
change in paper appearance,
high alkalinity of cellulose
causes immediate paper
degradation – pre-treatment
is necessary.

Alkaline-exchanged Y
zeolites [15]
Aqueous
dispersion
Y zeolite (active
ingredient: negative
oxygen atom charge in
zeolite)
Water
pH of paper increased to 6.5
– 7.5 range and slightly
decreased under accelerated
aging. Prevents color
changes in pH-sensitive
pigments (fading,
darkening, and whitening).
Hexamethylenetetramine
(HMT) in alcohols and
supercritical carbon
dioxide [16]
Non-aqueous
polar solution
Hexamethylenetetramine
(HMT) (active
ingredient: amine)
Alcohol
pH shift to neutral area (pH
6.7 – 7.0), improved
mechanical properties.
Chitosan nanoparticles
[17]
Non-aqueous
polar
dispersion
Chitosan (active
ingredient: amine)
Isopropanol
Advantages: application by
spraying, quick process,
antimicrobial activity.
Epoxy ethane - argon
system [18]
Gaseous
Ethylene oxide
Gaseous argon
Advantages: economically
accessible, effective
deacidification, safe
process, no pre-selection
required, environmentally
friendly. Disadvantages:
insufficient improvement in
mechanical properties.
Halloysite nanotubes
filled with MgO [19]
Non-aqueous
dispersion
MgO
Solvent: hydroxypropyl
cellulose (HPC),
Carrier: halloysite
nanotubes
Improves mechanical
properties by approximately
8% and raises pH to the
neutral range. The
modification does not affect
the color of the paper.
Hydroxyapatite
nanoparticles [20]
Partly
aqueous polar
dispersion
Hydroxyapatite
(Ca10(PO4)6(OH)2)
Water: alcohol (50:50)
Advantages: application by
spraying, effective
deacidification, and
increased mechanical
properties.
Highly stable organic
coatings of nano
magnesium oxide [21]
Non-aqueous
dispersion
MgO
Carrier: TMSC
(trimethylsilylcellulose),
IPA (isopropanol),
Solvent: HMDO
(hexamethyldisiloxane)
Advantages: modification
does not adversely affect the
sample's appearance,
provides sufficient alkaline
reserve, antifungal effect.
Superhydrophobic and
deacidified granulated
coating derived from
cellulose /CaCO3 [22]
Non-aqueous
dispersion
CaCO3, Strengthening
agent: cellulose
nanocrystals (CNC)
PDMS
(polydimethylsiloxane),
THF (tetrahydrofuran)
Self-cleaning properties,
strong mechanical strength,
ph values between 7.50 and
7.77. The modification does
not change the appearance
of the paper.
Composite of bacterial
cellulose with zinc oxide
nanoparticles [23]
Aqueous
dispersion
ZnO
Strengthening agent:
nano bacterial cellulose
Water
Significant improvement in
mechanical properties,
increase in pH by about 2
units after modification. Has
antifungal properties.
Nanocellulose is a
renewable resource.
Two-phase
deacidification based on
impregnation of organic
dispersion of nano MgO
combined with
ultrasonic atomization of
saturated aqueous
Ca(OH)2 solution [12, 21,
24]
Non-aqueous
and aqueous
solution
MgO a Ca(OH)2
HMDO, IPA, water and
ETA (2,3-
epoxypropyltrimethyl
ammonium chloride)
Improves mechanical
properties, good optical
stability, strengthening of
the microstructure of paper
fibers, alkaline reserve 2-
3%, effective
deacidification

Atomized sodium
carbonate and latex
composite [25, 26]
Aqueous
dispersion
Ca(OH)2
Water
Uniform deacidification by
atomized solution, no paper
wrinkling during the drying
process, increases pH and it
remains above 7 even after
aging, the color difference
of the paper after treatment
was not visible.
Disadvantages: the method
is not suitable in terms of
mechanical resistance.
Hydrotalcites [27, 28]
Partly
aqueous
dispersion
Hydrotalcite (active
ingredient: Mg)
Perfluoroheptane
(PFH), isopropanol
(IPA), and water
(89.3%, 10.0%, 0.7%)
Increases surface pH,
improves optical properties,
slows down rate of
glycosidic bond cleavage,
improves mechanical
properties, decrease of
oxidation products. Health-
safe, easy-to-apply method,
odorless.
Refereces
[1]
Banik, G. - Doering, T. - Hähner, U. , Current efforts to establish an effective quality management
for mass deacidification, Bern: Swiss National Library, 2006.
[2]
Sparks, P. G., Technical considerations in choosing mass deacidification processes, Washington,
DC, 1990.
[3]
Ladomerský, J., Oponentský posudok riešenia úlohy: Záchrana, stabilizácia a konzervovanie
tradičných nosičov informácií SR, 2007.
[4]
Grossenbacher, G., Paper deacidification as a measure for preserving originals, Bern: Swiss
National Library, 2006.
[5]
Anonym, Library of Congress Technical specifications for mass deacidifications, Preservation
Directorate Library of Congress, 2004.
[6]
Ďurovič, M., Hromadné odkyslování papírových archiválií, Praha: Státní ústřední archiv, 2000.
[7]
Králik, M. a kol., Kritická analýza literárnych a patentových poznatkov o
stabilizačných/deacidifikačných systémoch pre prírodné a syntetické polymérne materiály., Bratislava:
FCHPT STU, 2019.
[8]
Potthas A. - Henniges U., Vertrauen ist gut, Kontrolle ist besser – Kriterien für Testpapiere zur
Qualitätskontrolle in der Mengenentsäuerung nach der neuen ISO / TS 18344, ABI Technik, 2016.
[9]
Jiajia Wenget al., Deacidification of aged papers using dispersion of Ca(OH)2 nanoparticles in
subcritical 1,1,1,2-tetrafluoroethane (R134a), China: Journal of Cultural Heritage, 2018.
[10]
Jie Huang et al., Conservation of acidic papers using a dispersion of oleic acid-modified MgO
nanoparticles in a non-polar solvent, China: Journal of Cultural Heritage, 2018.

[11]
A.L. Nemoykina et al., Restoration and conservation of old low-quality book paper using aqueous
colloids of magnesium oxyhydroxide obtained by pulsed laser ablation, Russia: Journal of Cultural
Heritage 39, 2019.
[12]
Bei He et al., A new and highly efficient conservation treatment for deacidification and strengthening
of aging paper by in-situ quaternization, China: Carbohydrate Polymers, 2019.
[13]
W.A. Mohamed et al., Lemna gibba and Eichhornia crassipes extracts: Clean alternatives for
deacidification, antioxidation and fungicidal treatment of historical paper, Egypt: / Journal of Cleaner
Production 219, 2019.
[14]
Yan Li, Zhenxing Li, Guopeng Shen, Yuzhong Zhan, Paper conservation with an aqueous
NaOH/urea cellulose solution, China: Springer, 2019.
[15]
Zhang H. et al., Alkali-exchanged Y zeolites as superior deacidifying protective materials for paper
relics: Effects of accessibility and strength of basic sites, China: Microporous and Mesoporous Materials
293, 2020.
[16]
Ting Wu, Wei Tan , Mengru Liu, Yanxiong Fang, Yingtao Lin, Deacidification of Papers with
Hexamethylenetetramine (HMT) in Alcohols and Supercritical Carbon Dioxide, Journal of chemical
engineering of Japan, 2020.
[17]
Zhihui Jia, Chun Yang, Fangnan Zhao, Xiaolian Chao, Yuhu Li, Huiping Xing, One-Step
Reinforcement and Deacidification of Paper Documents: Application of Lewis Base—Chitosan
Nanoparticle Coatings and Analytical Characterization, Coatings, 2020.
[18]
Yunpeng Qi, Zhihui Jia, Yong Wang, Guangtao Zhao, Xiaolian Chao, Yajun Zhou, Yuhu Li, Ethylene
Oxide for the Mass Deacidification of Paper Relics, China, 2020.
[19]
Lorenzo Lisuzzo, Giuseppe Cavallaro, Stefana Milioto, Giuseppe Lazzara, Halloysite nanotubes
filled with MgO for paper reinforcement and deacidification, Italy, 2021.
[20]
Rodica-Mariana Ion, Ramona Marina Grigorescu, Mădălina Elena David, Carmen Adriana Cirstoiu,
Morphological and Mechanical Properties of Book Cellulose-Based Paper (XXth Century) Treated with
Hydroxyapatite Nanoparticles, Heritage, 2022.
[21]
Bei He et al., Highly stable nano magnesium oxide organic coatings for nondestructive protection of
acidic paper documents, China: Progress in Organic Coatings, 2022.
[22]
Xiaochun Ma et al., Superhydrophobic and deacidified cellulose/CaCO3-derived granular coating
toward historic paper preservation, China: International Journal of Biological Macromolecules, 2022.
[23]
Yanli Li, Jianwei Wang, Zhihui Jia et al., „Deacidification and consolidation of brittle book paper
using bacterial cellulose composite with zinc oxide nanoparticles,“ Journal of Cultural Heritage, zv. 64,
pp. 83-91, 2023.
[24]
Bei He, He Zhao, Li Weiying et al., „Enhancing capillary action of acidified paper to achieve uniform
deacidification and long-lasting aging resistance,“ Journal of Cultural Heritage, zv. 67, pp. 23-31, 2024.
[25]
Huiming Fan et al., „Deacidification and Reinforcement of Old Books Using Sodium Carbonate and
Latex Composites,“ BioResources, zv. 15, %1. vyd.1, pp. 302-316, 2020.

[26]
Huiming Fan et al., „Extending the Durability of Old Books by Atomized Deacidification and
Reinforcement Treatments,“ BioResources, zv. 15, %1. vyd.1, pp. 276-289, 2020.
[27]
Jurišová, J., Danielik, V., Malečková, S., Guzikiewiczová, E., Králik, M., Vizárová, K., Ambrová,
M., & Fellner, P., „Preparation and characterisation of hydrotalcites colloid dispersions suitable for
deacidi cation of paper information carriers,“ Chemical Papers, %1. vyd.https://doi.org/DOI:
10.21203/rs.3.rs-2816963/v1, 2023.
[28]
Eva Guzikiewiczová, Soňa Malečková, Jana Jurišová, Milan Králik, Svetozár Katuščák, Katarína
Vizárová, „Development of new systems based on hydrotalcites for stabilization and deacidification of
paper information carriers,“ Submitted to Bioresources, Under Revision, 2024.