Addition of unmodified nanoclay to improve the performance of unsaturated
polyester resin coating on natural stone
Vero
´
nica Morote-Martı
´
nez, Rafael Torregrosa-Coque, Jose
´
Miguel Martı
´
n-Martı
´
nez
n
Adhesion and Adhesives Laboratory, University of Alicante, 03080 Alicante, Spain
article info
Article history:
Accepted 3 December 2010
Available online 9 December 2010
Keywords:
Composites
Microscopy
Cure/hardening
Impact
abstract
In this study, an unsaturated polyester resin (UPR) thin coating containing styrene monomer has been
used to consolidate Brown Emperor natural stone pieces. Different amounts (0.5–2 wt%) of nanoclay was
added to reduce shrinkage during cure and to impart both stiffness and toughness. The uncured UPR–
nanoclay hybrids were characterized by rotational rheology, the gelation was monitored by means of a
texture analyzer and the viscoelastic and thermal properties were determined in the cured UPR–nanoclay
films. Transmission electron microscopy (TEM) was used to establish the degree of dispersion of the
nanoclay in the UPR–nanoclay composites. The mechanical performance of the UPR–nanoclay thin coated
natural stone pieces was measured by means of 3-points bending and impact strength tests.
Addition of nanoclay (0.5 and 1 wt%) increased noticeably the viscosity to the UPR resin. The gel time
of the UPR resin was significantly decreased by adding small amounts of nanoclay due to the interactions
between the filler and the styrene in the UPR resin. Moreover, addition of nanoclay decreased the
shrinkage degree during curing of UPR resin. In the cured composites, improved thermal properties in UPR
were reached by adding nanoclay due to the creation of a network between the filler and the polymer
matrix. Bundle nanometric size nanoclay agglomerates were observed which did not affect the glass
transition temperature but increased the viscoelasticity of the UPR–nanoclay composites. Furthermore,
the improved properties of UPR by adding nanoclay produced enhanced impact strength to coated natural
stone pieces, as both stiffness and toughness were improved by nanoclay addition. Finally, good adhesion
of nanoclay filled UPR to the surface of natural stone was reached.
& 2010 Elsevier Ltd. All rights reserved.
1. Introduction
The natural rocks suitable for construction and ornamental
elements are called natural stones. The global industry of natural
stone is under expansion and an exponential growth is estimated in
the next years. In Spain, the production of natural stones is mainly
located in three areas: Almerı
´
a (Macael), Murcia (Caravaca de la
Cruz, Cehegı
´
n and Lorca), and Alicante (Mono
´
var, Novelda). One of
the most important commercial natural stone in Alicante province
is the Brown Emperor.
Natural stone blocks obtained from quarries are transformed in
different materials (floor or wall tiles, stair steps, decorative stones)
for use in the building industry. Four main processes are needed for
natural stone pieces elaboration: tailoring of the blocks, polishing,
cutting and finishing. The natural stone blocks extracted from the
quarries have 2.2–3 m height and 1.2–1.5 m width, and they are
tailored in smaller pieces (sheets) by means of steel wire or
diamond disc cutter machines. Water is used during cutting
to refrigerate and evacuate the calcium carbonate wastes
(natural stone mud). After tailoring, the natural stone pieces are
polished with abrasive millstones of decreasing sizes to obtain
smooth polished surface. Then, the polished natural stone sheets
are cut into smaller pieces by means of diamond cutter discs. The
edges of the natural stone pieces are bevelled and polished. If some
imperfections on the natural stone surface exist or special finishing
is required, additional surface treatments (such as hammering or
sanding) can be applied. Finally, the natural stone pieces are cleaned,
dried and packaged for storage and transportation.
During polishing, bending stresses are applied to the natural
stone pieces, and during transportation they suffer impact stresses.
As a consequence, during manufacturing several natural stone
pieces are broken (in some cases 50% production), and a noticeable
material loss and an increase in the price of the natural stone tiles
are produced. The Brown Emperor natural stone is particularly
fragile due to the presence of clay and sand as impurities and to the
existence of porosity holes due to geological defects. As a con-
sequence the number of Brown Emperor pieces broken during
industrial operation is higher than for other natural stones [1].In
this work, the mechanical reinforcement and structural integrity of
Brown Emperor natural stone pieces was improved by adding thin
thermoset polymeric coatings on one of their surfaces that are well
adhered creating strong stone-coating interfaces.
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/ijadhadh
International Journal of Adhesion & Adhesives
0143-7496/$ - see front matter & 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijadhadh.2010.12.001
n
Corresponding author. Tel.: +34 96 5903977; fax: +34 96 5903454.
E-mail address: jm.martin@ua.es (J.M. Martı
´
n-Martı
´
nez).
International Journal of Adhesion & Adhesives 31 (2011) 154–163