Dariusz SOBKÓW*, Joanna BARTON, Krystyna CZAJA, Marek SUDOŁ, Beata MAZOŃ – Division
of Chemical Technology and Polymer Chemistry, Faculty of Chemistry, University of Opole, Opole,
Poland
Please cite as: CHEMIK 2014, 68, 4, 347–354
Atmospheric ageing
Recently manufacturers of products developed on polymer
basis put a lot of focus in the safety of their products, including
their durability under use conditions, especially outdoors, where
due to number of external factors appearance may change (e.g.
discolouration, tarnishing or cracking) and/or loss of desired
properties e.g. mechanical. This occurs usually as a result of material
degradation due to the change of its chemical structure (including
oxidation, reduction of molecular weight due to the breaking of
macromolecular chains or its increase as a result of their crosslinking and branching) [1, 2].
Change process occurring in materials induced by set of
external environmental factors is called atmospheric ageing [3].
Usually it is induced by sunlight (mainly by light from UV range
– photodegradation), and its rate might be increased by heat (varying
temperature – thermodegradation), precipitation (hydrolytic
degradation), air pollution, or even by wind and stress (mechanical
degradation) [4÷8]. Atmospheric ageing is a physicochemical
process causing gradual destruction of materials [9], usually as
a result of change in chemical structure induced by simultaneous and
interdependent radical photo- and thermooxidation processes [10].
Thermooxidative degradation occurs in the whole bulk of polymer,
while photodegradation occurs mostly in its surface and subsurface
layer, due to the limited possibility of UV radation penetration
to deeper layers of material [11].
The type and intensity of material property changes during
the exploitation of product manufactured from it depends mostly
on material’s structure and structural defects, morphology, mainly
content of crystalline phase, type and content of other substances
(e.g. fillers, modificators, contaminants), as well as product shape and
dimensions, type and intensity of factors causing changes in polymer,
and finally the exposure time [4]. Polymeric material degradation
might be also initiated or assisted by present additives, including
catalyst residues, as well as environmental contaminants. Moreover,
important role is played by such factors as even low content of
hydroperoxide, carbonyl groups as well as content of double bonds
that by might generated additionally during material processing and
storage. The main light absorbers, responsible for the initiation of
photochemical reactions are carbonyl groups. The degradation
reaction usually starts from absorbing UV radiation by carbonyl groups
and progresses further with assistance of generated radicals, causing
cross-linking or breaking of macromolecule chains. Both mentioned
processes are main and competitive degradation mechanisms. The
physical effect of photodegradation is surface cracking and loss of
material rigidity and strength [12].
The intensity of sun radiation that reaches Earth surface is not
a constant value. The value of intensity depends on latitude, time of
year and day, cloudiness and atmosphere permeability. Due to that,
atmospheric ageing of the same composite might progress differently
depending on the climate zone or current conditions [10]. In order
Corresponding author:
Dariusz SOBKÓW – M.Sc., e-mail:dariusz.sobkow@uni.opole.pl
nr 4/2014 • tom 68
to evaluate composite materials resistance against external factors
it is necessary to carry out ageing tests in natural conditions. Such
tests, carried out in testing ground stations equipped with climate
factor measurement instruments shall last for at least one year,
although due to the variability of natural environmental conditions,
the longer, few year period is recommended [2]. Such tests are very
time-consuming and thus it was necessary to develop methods for
accelerated ageing under laboratory conditions. The time reduction
of lab tests is usually possible due to the intensification of UV
radiation, usually emitted by xenon lamps equipped with suitable
set of filters, imitating sun light spectrum. Lab tests are performed
in various climate chambers, that allow programming and constant
control of radiation intensity, temperature and humidity inside test
chamber, temperature of sample surface, time of water sprinkling
(imitating rain) as well as airflow (imitating wind). Lab tests have also
another advantage – they might be repeated in identical conditions,
what is practically impossible in the case of ground testing.
In order to evaluate the degradation progress of the material
subjected to ageing process, it is usually necessary to determine
the change in its functional properties, i.a. mechanical ones (tensile
strength, impact strength or hardness). In this case, it is understood that
deterioration of measured property by more than 50% disqualifies the
material for further use. By using the additional set of complementary
analyses regarding morphology and structure changes preceding the
change of functional properties, it is possible to predict more precisely
the duration of safe material use.
The group of researchers from the Division of Chemical
Technology and Polymer Chemistry of the University of Opole for
several years has been carrying out evaluation of durability of various,
mainly polymeric materials of varying structure and composition (in
case of composites and other multi-component compositions) and
their field of application. The tests are performed on their own
testing ground station equipped with set of measurement sensors
registering sun radiation intensity in whole spectral range and in most
destructive UV range, ambient and sample surface temperature and
air humidity. The aforementioned climate data have been archived
since 2002. The lab tests are performed using apparatuses Xenotest
Alpha HE and Wezerometr Ci4000, according to standards or in
other, set conditions. The most frequent tests concern reproduction
of environmental conditions in lab tests for materials used outdoors
or simulation of sun light spectra passing through the window for
materials used indoors. At the same time, we have number of
apparatuses for morphology and structure tests and for evaluation of
functional properties of studied polymeric materials.
Authors’ works involve ageing tests for various materials, including
workpieces made of various plastics used in automotive industry,
polyurethane and polystyrene foams, paints and varnishes, packaging
foils, labels and stickers, composite materials, including numerous
wooden-polymer composites (WPC) of varying composition.
The example of spectrum cascade (Fig. 1) for selected WPC
presents increasing intensity of carbonyl and ether bands that
correspond to various oxidation products that form in the material.
• 351
50 Years of Chemistry in Opole
Studies of material resistance against natural
environmental factors
50 Years of Chemistry in Opole
Fig. 1. Set of spectra for WPC produced on base of PEHD and wood flour
Lignocel 9 with marked characteristic bands generated during ageing
process under natural conditions (ageing time – from 3 to 61 months)
Micrographs (Fig.2) confirm surface cracking for similar composite
with ageing progress, while visible cracks are systemically deepening
and widening creating wide-spread mesh of cracks, that with time forms
separates fragments of structure. Changes of wood flour morphology
in WPC were also observed – the flour swelling is visible in form of
formed clusters.
Fig. 2. SEM micrographs of WPCs based on PEHD matrix with wood
flour Lignocel C120 (ageing under natural conditions)
Properly developed accelerated ageing tests in ageing chambers
allow to accelerate ageing process of materials and obtain definitely
faster answer to a question how given material will behave during the
exposure to natural conditions. These methods are also applicable
to comparative studies of various materials (Fig. 3)
Fig. 3. Changes of carbonyl band of WPCs on polyolefin matrix
subjected to ageing under ground (HDL, LDL, PPL) and lab conditions
(xHDL, xLDL, xPPL)
Biodegradation
Degradation of plastics and composites occurring in the
environment due to microorganisms is called biodegradation [13,
14]. This type of degradation might be caused both by bacteria and
by fungi that grow in favorable growth conditions [15].
The correct growth of fungi is ensured by the access to sufficient
amount of nutrients. The optimum environmental conditions are:
approx. 70% humidity, suitable temperature and pH in range 5.6–6.5
[16]. The growth of particular species of fungi is determined also
by type and properties of base, on which they grow (contents of
various minerals, salinity) [17].
352 •
The biodegradation processes can be divided into aerobic and
anaerobic. In former case, the main products of decomposition
occurring in the presence of oxygen are CO2, water and biomass. In
anaerobic conditions methane is also generated [14].
Activity of microorganisms to a great extent affects functional
value of materials (wood, paper products, plastics, ceramic
construction materials, paints and varnishes) exposed to contact with
microbes [18,19] Currently used materials show varying resistance
against destructive action of biofactors. Meanwhile this is the quality
that determines their potential application range. Susceptibility
of polymer material to biodegradation processes results, among
others form chemical structure and polymer molecular weight, its
physicochemical properties, as well as type and intensity of impact
of microorganisms [20, 21].
The matrix of polymeric composites is usually made of synthetic
polymers showing none or negligible susceptibility to biodegradation
processes [22]. It is a result of i.a. chemical structure and hydrophobic
nature of their surface. However, the number of factor effecting
acceleration of biocorrosion processes, i.e. presence of easily
hydrolysing functional groups (ester, amide), low degree of crystallinity
and large content of amorphous phase, hygroscopy (easy transport of
of enzymes produced by microorganisms) or low molecular weight
[23÷25].
Biodegradation of polymeric materials include number of
processes of chemical and biological nature. As a result of interaction
between material and enzymes produced by microorganisms,
the polymer chains are shortened, what causes the reduction of
molecular weight as well as change of physicochemical and mechanical
properties. This results in increased susceptibility of material to other
degradation processes [26].
Depending on the application field of polymeric materials, it is
desirable that it shows particular resistance against biodegradation.
On one hand there are efforts aiming at development of new materials
showing increased susceptibility to biodegradation processes (e.g.
packagings and other materials short-living), while on the other
hand there is an ongoing research on improvement of construction
materials durability (construction, automotive industry). While it is
obvious that seeking to increase biodegradation rate for different
types of materials is intended to i.a. improve waste management
systems, the desire to protect materials from microorganisms is
mostly a result of two different factors. Firstly, material corrosion
caused by biodegradation might pose a threat to life and health of
materials’ users [27]. What’s more, the toxic impact of fungi might
turn out to be even more dangerous [28, 29]. Many of fungi species
produces mycotoxins (e.g. aflatoxins) that even in a single dose might
lead to irreversible, precancerous and cancerous lesions. Other
diseases include: allergic rhinitis, bronchial asthma, fungal dermatitis,
allergic pulmonary alveolitis and food allergies [16].
Current tendency in material engineering is related to the
search for materials that could be an alternative for synthetic
polymeric materials. Performing various modifications that give
materials new, unique properties or developing materials containing
renewable plant materials. However, it is believed that content of
plant materials reduces lifetime of these materials making them
susceptible to biocorrosion caused by hyphal fungi. For this reason,
the research aiming to evaluate factors causing deterioration of
material properties under conditions of their potential application
is an attractive scientific field determining future application field of
developed composites.
The subject of research in scope of evaluation of biological
resistance performed by group from the Division of Chemical
Technology and Polymer Chemistry in collaboration with employees
of the Division of Analytical and Ecological Chemistry of UO are
all types of materials: composites and polymer coatings, foils or
nr 4/2014 • tom 68
3.
4.
5.
6.
7.
8.
9.
Fig. 4. a) an example of culture grown on liquid mineral medium
Czapek-Dox, b) an example of culture grown on solid medium
– observation of colonization effect
Presented in Figure 5 representative test results regarding
composite biodegradation have proven that both environment of
culture growth, as well as different composition of composite material
(type, content of filler, presence of compatibiliser) are of importance
to course of mycelium growth.
10.
11.
12.
13.
14.
15.
16.
17.
Fig. 5. Mass balance obtained for culture grown on full Czapek-Dox
medium and glucose-free Czapek-Dox medium (polymer materials based
on PE-HD with 40% content of floud Lignocel C-120 and/or possible 5%
content of compaitibiliser) expressed in grams of dried mycelium
Summary
Carrying out complex studies on photo-, thermo- and biodegradation allows to determine lifetime of products manufactured
from studied materials under conditions corresponding to their potential area of application. Moreover, the research is also of cognitive
nature in the scope of understanding the ageing processes nature
and mechanisms and are essential part of works on development
and implementation to exploitation new materials or their variations
modified chemically or physically.
Joanna Barton is a recipient of the scholarship under project “Ph.D.
scholarships - investment in scientific staff of Opole voivodeship” co-funded by the
European Union, within the European Social Found.
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* Dariusz SOBKÓW – M.Sc., is a graduate of the University of
Opole in the field of chemistry in 2000, as well as in the field of
economics (2003). He works at the Division of Chemical Technology
and Polymer Chemistry, Faculty of Chemistry, University of Opole.
Specialization: studies of material ageing under natural conditions and
in accelerated laboratory tests, modification of polyolefins for their
stabilization or degradation acceleration.
e-mail:dariusz.sobkow@uni.opole.pl; phone: +48 77 452 71 07
Joanna BARTON – M.Sc., is a graduate of the Faculty of
Chemistry of the University of Opole (2011). Currently, she a
student of Environmental Doctoral Studies organized at the
Faculty of Chemistry, Wroclaw University of Technology and
the Faculty of Chemistry, University of Opole. Specialization:
production and characterization of composites with renewable
plant fillers and study on biodegradation processes of materials
including evaluation of fungistatic properties.
e-mail:jbarton@uni.opole.pl; phone: +48 77 452 71 35
Professor Krystyna CZAJA – (Ph.D., Eng.) is a graduate of the
Faculty of Chemical Technology and Engineering of the Silesian
University of Technology (1970). She has received academic degrees
from the Faculty of Chemistry of Warsaw University of Technology
in the field of chemical sciences: She obtained Ph.D. degree in 1977
After obtaining a doctorate, he earned habilitation in 1992. The title
of full professor of chemical science was conferred on her in 2002 .
She has been working at Opole academy since 1973, currently as a
full professor at the Faculty of Chemistry of the University of Opole.
Specialization: polymer chemistry and technology, mostly polyolefins
including synthesis of metalloorganic catalysts and low-pressure (co)
polymerization of olefins with the use of such catalysts, physical
and chemical modification of polymers, polymer matrix composites
and nanocomposites, characterization of molecular structure and
polymer functional properties, particularly study of their thermo-,
photo- and biodegradation.
e-mail: krystyna.czaja@uni.opole.pl; phone: +48 77 452 71 40
Marek SUDOŁ – Ph.D., is a graduate in the field of chemistry of
the State Higher Pedagogical College (currently University of Opole).
Since his graduation, he has been working at the Faculty of Chemistry
(till 2008 Institute of Chemistry) of this University. Scientific field:
identification of micro- and macromolecular compounds by means
of infrared spectroscopy and chemical and physical modifications of
polyolefins for specific practical applications.
e-mail:marek.sudol@uni.opole.pl; phone: +48 77 452 71 38
Beata MAZOŃ – M.Sc. in 1991 has graduated from the Institute
of Chemistry of the University of Wroclaw. Since her graduation
she has been working at the Division of Chemical Technology and
Polymer Chemistry, University of Opole. Specialization: molecular
characteristic of macromolecular compounds, mostly polyolefins by
means of high-temperature gel permeation chromatography.
beata.mazon@uni.opole.pl, +48 77 452 7110
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Dokończenie ze strony 350
Przeciwbakteryjne metalopolimery
Popularnie stosowane antybiotyki stają się coraz mniej skuteczne,
ponieważ bakterie bardzo szybko stają się na nie odporne. Dla przykładu, co roku 2 miliony pacjentów amerykańskich szpitali ulega zakażeniom szpitalnym, a aż 99 000 z nich umiera. Ok. 30% tych zakażeń jest
spowodowanych bakteriami Staphylococcus aureus. Obecnie nawet 60%
szczepów Staphylococcus aureus znajdowanych w szpitalach jest odporna
na penicylinę, metycylinę i wiele innych antybiotyków beta-laktamowych.
Dlatego też wankomycyna i amoksycylina/kwas klawulanowy są jednymi z najbardziej powszechnie stosowanych antybiotyków do leczenia
infekcji spowodowanych Staphylococcus aureus. Choć antybiotyki te są
najsilniejsze w swojej klasie związków, to częste stosowanie spowodowało ich zmniejszoną aktywność przeciwbakteryjną. W celu uniknięcia
antybiotykooporności, projektowane są nowe inhibitory β-laktamazy,
w tym pochodne kwasu boronowego i fosfoniany. Inną możliwością jest
używanie odporna jako środków przeciwbakteryjnych odporna. Związki
te działają poprzez przerywanie grubych ścian komórkowych lub błon
i wykazują skuteczność w walce z Staphylococcus aureus.
354 •
Naukowcy ze Stanów Zjednoczonych, na łamach JACS, przedstawiają klasę naładowanych metalopolimerów, które wykazują nie
tylko wysoką skuteczność w zmniejszaniu aktywności β-laktamazy, ale
również zwalczają komórki bakteryjne. Wyniki pokazują, że metalopolimery atakują enzymy β-laktamazy i ściany komórek oraz chronią
sprzężone z nimi antybiotyki poprzez oddziaływania jonowe pomiędzy polimerami i antybiotykami. Metalopolimery zbudowane są z kationowych polimerów zawierających kobaltocen. Dzięki wyjątkowej
zdolności kobaltocenu do kompleksowania anionów karboksylanowym, różne komercyjne antybiotyki β-laktamowe, w tym penicylina-G, amoksycylina, ampicylina i cefazolina, mogą być chronione
przez tworzenie stabilnych jonowych par z polimerem. Co więcej,
metalopolimery wykazują wysoką skuteczność wobec Staphylococcus aureus, natomiast nie wykazują aktywności hemolitycznej ani toksyczności in vitro i in vivo. (kk)
(Jiuyang Zhang, Yung Pin Chen, Kristen P. Miller, Mitra S. Ganewatta, Marpe Bam, Yi Yan, Mitzi Nagarkatti, Alan W. Decho, Chuanbing Tang, Antimicrobial
Metallopolymers and Their Bioconjugates with Conventional Antibiotics against
Multidrug-Resistant Bacteria, J. Am. Chem. Soc., DOI: 10.1021/ja5011338)
nr 4/2014 • tom 68