STUDY OF THE PLYWOOD PANELS PROPERTIES USING
GEOSTATISTIC
Cleverson Pinheiro
IFSP - Federal Institute of Education, Science and
Technology of Sao Paulo; UNESP - Univ. Estadual Paulista, Brazil
E-mail: cleverson.pinheiro@ifsp.edu.br
Cristiane Inácio de Campos
UNESP - Univ. Estadual Paulista, Brazil
E-mail: cristiane@itapeva.unesp.br
Carlos Alberto Oliveira de Matos
UNESP - Univ. Estadual Paulista, Brazil
E-mail: carlos@itapeva.unesp.br
Manoel Cléber de Sampaio Alves
UNESP - Univ. Estadual Paulista, Brazil
E-mail: manoelcsa@feg.unesp.br
Ivaldo De Domenico Valarelli
UNESP - Univ. Estadual Paulista, Brazil
E-mail: ivaldo@feb.unesp.br
Marcos Valério Ribeiro
UNESP - Univ. Estadual Paulista, Brazil
E-mail: mvalerio@feg.unesp.br
Simone Simões Amaral
UNESP - Univ. Estadual Paulista, Brazil
E-mail: simonesimoessi@gmail.com
Submission: 10/03/2016
Revision: 22/03/2016
Accept: 12/05/2016
ABSTRACT
Plywood panels have multiple
applications in construction, in the furniture industry and packaging. There is
a need to improve techniques for assessing quality of these products. This
paper proposed the use of geostatistics to evaluate the behavior of the of the
plywood panel. The physical properties were analyzed (moisture content, density
and water absorption) in the full extent of the plywood panel of Eucalyptus sp., bonded with adhesive
single-component polyurethane. For analysis, three panels of five layers, with
dimensions of 350 x 350 x
Keywords: plywood;
moisture content; density; water absorption; geostatistics
1. INTRODUCTION
In
order to maintain its competitiveness, the company has invested in innovative
tools focused on the process management, production process and product, as
discussed by Petter et al. (2013). Petter et al. (2013) found that the highest
concentration of innovative activities, in furniture, is focused on the product
(54%). In this context, new products have been development and improved, as is
the case of the plywood panels.
Plywoods
are veneers overlapped and joined by adhesives in presses. The bonding of the
wood veneers is taken orthogonally with the objective of increasing the
dimensional stability of the panel, as described by Watai (1987). According to
Iwakiri et al. (2012), one of the species of wood used for the production of
plywoods are, principally, the species of the genus Eucalyptus sp. and Pinus sp.
Tomaselli
(1998) classified the plywood panel according to their use in: internal use
plywood, glued with urea formaldehyde resins; plywood for the use of external
use, glued with phenol formaldehyde resins.
In
furniture industry, the use of quality plywoods is a fundamental requirement.
However, to maintain the quality of plywood, Iwakiri (2005), commented that the
process of gluing the wood veneer, which form the plywood, must be strictly
controlled. To maintain quality during the gluing process. Iwakiri (2005)
recommends the following variables control: formulation of the adhesive,
thickness of wood veneer and pressing cycle parameters (temperature, pressure
and time of pressing).
Vick
(1999), Frihart (2005) and Frihart and Hunt (2010) reported that the process of
glue is influenced also by the anatomical, physical, chemical and mechanical
properties of wood.
Due
to large amount of factors that can affect bonding of the plywood and
compromising its quality, a strict control of the properties of these panels is
required. For analysis of physical and mechanical properties of plywood panels,
some authors have used the traditional statistic (Bortoletto Júnior and Garcia (2004), Arruda et al.(2013), Albino et al. (2015)). However,
despite its importance, the use of traditional statistic is not sufficient to
analyze the variations that can occur in all regions of the panel.
A
method used to analyze the changes in a particular region and between regions
is the geostatistics method. Geostatistics is a name associated with a class of
techniques used to analyze and infer values of a variable distributed in space
and/or time (CAMARGO, 1997). In this way, the analysis of the panel properties,
involving the method of geostatistics, enables higher understanding of their
variability and assists in the identification of the causes of the defects,
ensuring the quality of the product.
In
this context, the present study aims to assess the variability of physical
properties in the entire size of the plywood panel Eucalyptus sp., using geostatistics.
2. MATERIAL AND METHODS
2.1.
Plywood panels preparation
Three
plywood panels, composed of five layers, were produced. To make the plywood
panels were used woods veneer of Eucalyptus
sp. and polyurethane single component adhesive "supertackplus".
Woods
veneer, employed in the manufacture of panels, had an average thickness of 3.32
mm and were squared in 40 x 40 cm. Squaring of the wood veneer was conducted in
the Wood Machining Laboratory (UNESP, campus
of Itapeva- SP). The production of the panels was held at Wood Processing
Laboratory (UNESP, campus Bauru).
The
average weight of the adhesive used for gluing the wood veneer was 427g /m2
on each double glue line (bonding pressure: 1:47 MPa). Table 1 shows the
conditions and characteristics of manufactured panels.
Table 1: Conditions and characteristics of the
plywoods.
Source:
author.
Four
weeks after its manufacture, the panels were squared on the dimensions of 350 x
350 mm and samples were taken for testing of characterization of physical
properties: specific mass, moisture content and water absorption, as shown in
Figure 1.
|
|
|
|
Figure 1: Specimen layout on the panels (mm).
Source:
author.
2.2.
Characterization of plywood panels
For
the physical characterization of the panels were employed with standards EN
323-2000 (determination of specific mass), EN 322-2000 (determination of
moisture content) and standard ABNT NBR 9486-2011 (determination of water
absorption).
2.3.
Statistical analysis
Statistical
analysis was done using the geostatistics method. According to Ribeiro Júnior
(1995), the geostatistics does not refer to a special type, different or alternative
of statistics. In geostatistics, samples are described by its value as a
function of its position in a coordinated data system. This method
characterizes the spatial distribution, differing locations with higher
aggregation of individuals of the localities with less aggregation and also the
areas devoid of individuals (LIMA et al.,
2006).
Camargo (1997)
described the study involving geostatistics techniques must follow some steps:
(1) exploratory analysis of the data; (2) structural analysis (calculation and
variogram modeling); and (3) realization of inferences (kriging or simulation).
For Huijbregts
(1975) apud Camargo (1997), the variogram is a basic technical support tool of
kriging, that allows you to represent the variation of a regionalised phenomenon
in space. For Camargo (1997) it is necessary to fit a model for the estimates
obtained from the "kriging" are more accurate and therefore more
reliable.
According to
Delfiner and Delhomme (1975), the factors that differentiate the
"kriging" of other interpolation methods are: the estimate of a
spatial covariance matrix that determines the weights assigned to the different
samples; the treatment of data redundancy; the neighborhood to be considered in
the inferential procedure; and the error associated with the estimated value.
In addition to these factors, the "kriging" also provides accurate
estimators with no bias and efficiency properties.
Camargo (1997)
mentioned that among the models most used in geostatistics are the potential
model, spherical model, exponential model and Gaussian model, as shown in
Figure 2.
Figure 2: Semivariogram example: parameters and models
employed.
Source: adapted from:
http://xongrid.sourceforge.net/
In Figure 2, are
also showed the semivariogram parameters:
- Range:
distance within which the samples are spatially correlated.
- Sill: is the
value of the semivariogram corresponding to its range. From this point on it is
considered that there is no more space dependence between samples, because the
variance of the difference between pairs of samples does not vary with the
distance.
- Nugget: Reveals the discontinuity of the
semivariogram for distances smaller than the small distance between samples.
The parameters for modeling the behavior of
the samples were calculated with the aid of the geoR software, which is a free
software environment for statistical computing and graphics. According to
Ferreira (2013) R program is one of the best to existing statistical analysis
today. All the console window contents can be saved, checked and eliminated
using Windows and Toolbar resources. A widespread way to use R is type programs
and macros that will run in a window called script. The main advantages of R is
the fact of being a free program, and packages (libraries / packages) are
written and developed by researchers from different areas of knowledge. Among
the packages, it stands out the geoR used for geostatistical analysis.
3.
RESULTS AND DISCUSSIONS
3.1.
Plywood panel characterization
The
apparent density of the plywood panels of Eucalyptus
sp. was 652.09±6.31 kg/m3. The moisture content was 10.66±0.27
%. The percentage of absorbed water was 50.50±1.23 %. In table 2 were shoed
values found in the literature for moisture content, specific mass and water
absorption.
Table 2: Comparative summary of the values obtained on
this work and literature.
|
Source |
Specie |
Adhesive |
Specific mass (kg/m3) |
Moisture
content (%) |
Water
absorption (%) |
|
This work |
Eucalyptus sp. |
Polyurethane |
652.09±6,31 |
10.66±0.27 |
50.50±1.23 |
|
Bortoletto
Júnior (2003) |
Eucalyptus sp. |
Phenol
formaldehyde |
767- 973 |
9.18- 10.24 |
17.51-36.79 |
|
Almeida (2002) |
E. grandis |
Urea
formaldehyde |
680 |
10.55 |
38.85 |
|
Almeida (2002) |
E. urophylla |
Urea
formaldehyde |
640 |
11.11 |
43.76 |
|
Kollmann
(1975) |
_ |
_ |
550 |
7.30- 12.70 |
_ |
Source:
author.
The
results of specific mass and moisture content, obtained from this work, were
very similar to those found in the literature.
The
water content absorbed was 7% higher than that obtained by Almeida (2002),
which was of 43.76%. Possibly, the high water absorption in the plywood panels
is associated with the surfaces conditions of the veneers of Eucalyptus sp., which were with some
cracks.
3.2.
Variability analysis of the samples in the
panel
The
variability analysis of the samples in the panel was performed using the concepts
of geostatistics. The variation of the regionalised phenomenon in space was
quantified through the semivariogram.
First,
the parameters for modeling the behavior of the samples in the semivariogram
were calculated and showed in Table 3.
Table 3: Samples modeling parameters.
|
Properties |
Nugget effect |
Sill |
Range |
Least square |
|
Moisture
content |
0.00 |
0.11 |
55.00 |
0.13 |
|
Specific
mass |
42.78 |
247.09 |
218.63 |
707,945.40 |
|
Water
absortion |
0.00 |
66.11 |
30.00 |
811.31 |
Source:
author.
From
the parameters showed in Table 3, the semivariogram was constructed for water
absorption, moisture content and specific mass, as Figures 3 (a), 3 (b) and 3
(c), respectively. The semivariograms curves were adjusted by the method of
least squares.
(a) (b)
(c)
Figure 3: Semivariograms to: (a) water
absorption; (b) moisture content; (c) specific mass.
Source:
author.
With behavior of the semivariogram and the kriging
method was possible the interpolation and extrapolation of results at certain
points of the Panel to the other regions.
In figures 4 (a), (b) and (c) it is possible to
observe the behavior of the samples for water absorption, moisture content and
specific mass, respectively. The behavior of the samples is represented by the
level curves of the properties and their extrapolations.
(a)
(b)
(c)
Figure 4: Samples behavior:
(a) Water absorption samples behavior; (b) Moisture content samples
behavior; (c) Specific mass samples behavior.
Source:
author.
In
Figure 4 (a) it is possible to observe the existence of areas with darker
points. These points correspond to the places of higher absorption of water.
Alongside these points are located the curves of levels, which are the
extrapolations from measured values for the property "water absortion”.
This staining pattern occurred in at least seven points in the panel, and
almost always on the edges. Two possible explanations for this pattern of
behavior are related to surface cracking and movement of the adhesive. The
adhesive can have migrated to areas with surface cracks, leaving gaps in the
line of glue fill, which favored the absorption of water. Another possibility
is the adhesive drive towards the edges, through the action of pressing and
temperature. Adhesive drive facilitates their evaporation and subsequent
absorption of water. The evaporation of the adhesive can be confirmed by
measurements of the panels mass (Table 1). The panel 2, for example, lost about
60 g of adhesive. The points of lighter color, in Figure 4 (a), represent the
sites of low water absorption.
In
Figure 4 (b) was presented the behavior of the samples for the moisture
content. The darker regions correspond to the higher moisture content and
lighter regions represent the lower moisture content.
The
behavior of the specific mass along the panel can be displayed in Figure 4 (c).
The darker region represents the higher points of specific mass.
Comparing Figures 4 (b) and 4 (c) it is observed that,
the region of higher moisture content value corresponded to the maximum
specific mass region. According to Almeida (2002), the moisture content
influences the specific mass of the panel, which explains the result.
May have occurred the accumulation of wood veneer with
larger thicknesses, in the region of higher density and moisture content of the
panels. The accumulation of wood veneer may result in increased wood density,
during the pressing process.
Almeida (2002) mentioned that the resistance of the
plywood panel is directly linked to the thickness of the wood veneer. Wood
veneers with heterogeneous thickness can result in regions of higher pressing
pressure, causing differences in the amount of glue, which impairs the degree
of adherence of the wood veneers, which may occur the so-called "bonding
failure".
The variability found in the panels can also be
related to manufacturing process parameters such as temperature and pressure.
The values of the temperatures and pressures used in
the press have followed the recommendations of specialized literature. However,
may have been a non-uniform distribution of temperature and pressure on the
surface of the press, causing several anomalies along the entire area of the
panel.
The
behavior of the three analyzed variables (moisture content, specific mass and
water absorption), did not reach the desired expectations, because these
properties should have uniformity within the plywood panel. Unlike the expected
result, the plywood panels showed large variations of its physical properties.
4.
CONCLUSION
The
average values of the water absorption were 7% higher compared to other papers.
Thus, these panels can only be applied indoors.
The
average moisture content and specific mass were within the average values found
in the literature.
The
behavior of the properties analyzed by geostatistical model does not present
homogeneity, undermining the possible application of plywood in the manufacture
of furniture products.
Possibly the lack of homogeneity of the analyzed
properties, can be related to undesirable variations in the used pressure and
temperature parameters. The values of the temperatures and pressures used in
the press have followed the recommendations of specialized literature. However,
may have been a non-uniform distribution of temperature and pressure on the
surface of the press, causing several anomalies along the entire area of the
panel.
The
behavior of the properties analyzed by geostatistical model does not present
homogeneity, undermining the possible application of plywood in the manufacture
of furniture products.
The
method of analysis by geostatistics technique seems to be suitable for the
study of the properties of the plywood panels and it can be applied for better
quality control.
5.
ACKNOWLEDGE
The
authors acknowledge the UNESP - Universidade Estadual Paulista, campus of Itapeva-SP, for providing your
Wood Machining Laboratory and Wood Processing Laboratory, in UNESP of Bauru-SP.
REFERENCES
ALBINO, V. C. S. et al..(2015) Avaliação das propriedades físico-mecânicas de painéis
compensados de Toona ciliata M. Roem. var. australis. Cerne, v. 17, n. 1,
p. 103–108.
ALMEIDA, R. R. (2002) Potencial da madeira de
clones do híbrido Eucalyptus grandis x Eucalyptus urophylla para produção de
lâminas e manufatura de painéis compensados. Dissertation
(Master in Forest Resources with option
Technology Forest Products). Piracicaba: - Escola Superior de
Agricultura Luiz de Queiroz, Universidade de São Paulo. Available: http www.teses.usp.br.
Access: 28 out.2008.
ARRUDA, L. M. et al. (2013) Estudo preliminar das propriedades de compensados
produzidos com lâminas de paricá (Schizolobium
amazonicum Huber ex Ducke) modificadas termomecanicamente. Revista
Ciência da Madeira (Brazilian Journal of Wood Science), v. 3, n. 2.
ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS - ABNT.
NBR-9486. Painéis de madeira compensada: determinação da absorção de água.
Rio de Janeiro, 1986.
BORTOLETTO
JÚNIOR, G. E. (2003) Produção de compensados com 11 espécies do gênero Eucalyptus,
avaliação das suas propriedades físico-mecânicas e indicações para utilização.
Scientia Forestalis, n. 63, p. 65-78. Disponível em: <
http://www.ipef.br/publicacoes/scientia > Acesso em: 21 de out. 2008.
BORTOLETTO
JÚNIOR, G. E.; GARGIA, J. N. (2004) Propriedades de resistência e rigidez à
flexão estática de painéis OSB e compensados. Revista Árvore, v. 28,
n.4, p. 563-570. Disponível em: http://www.scielo.br/scielo. php Acesso em: 21
de out. 2008.
CAMARGO,
E. C. G. (1997) Desenvolvimento, implementação e teste deprocedimentos
geoestatísticos (krigeagem) no sistema de processamento deinformações
georreferenciadas (spring). Dissertation
(Master in Remote sensing). São José dos Campos: INPE, Available:
httpwww.dpi.inpe.brteseseduardoapres.pdf. Acesso em: 26 out.2008.
DELFINER
P.; DELHOMME, J. P. Optimum interpolation by kriging. In: J.D.Davis and
M.J.McCullagh (eds), Display and
Analysis of Spatial Data. New York, John Wiley and Sons, 1975, p. 96-114.
EN
322:2000 Painéis derivados de Madeira. (2000) Determinação do teor de
umidade. EuropeanStardard (versão portuguesa), Bruxelas
EN
323:2000 Painéis derivados de Madeira. (2000) Determinação da massa
específica. European Stardard (versãoportuguesa), Bruxelas.
FERREIRA,
D. F. Estatística computacional
utilizando R. Universidade Federal de Lavras, Departamento de Ciências
Exatas, 2013, 125 p.
Frihart,
C. R. (2005) Wood adhesion and adhesives. In: Rowell, R.M., ed. Handbook of wood chemistry and wood
composites. Boca Raton, FL: Taylor & Francis. P. 215–278.
FRIHART,
C. R.; HUNT, C. G. (2010) Adhesives
with Wood Materials Bond Formation and Performance, in: Wood Handbook- Wood
as an Engineering Material,
Madison: U.S. Department of Agriculture, Forest Service, Forest Products
Laboratory, cap. 10, p. 2-23.
IWAKIRI,
S. (2005) Painéis de Madeira
reconstituída. Curitiba: FUPEF, p. 247.
IWAKIRI, S.; MATOS, J. L. M.; FERREIRA, E. S.;
PRATA, J. G.; TRIANOSKI, R. (2012) Produção de painéis compensados estruturais
com diferentes composições de lâminas de Eucalyptus salignae pinus
caribaea. RevistaÁrvore, v. 36, n. 3, p. 569-576.
KOLLMANN,
F. F. P.; KUENZI, E. W.; STAMM, A. J. (1975) Principles of wood science and technology. Berlin:
Springer-Verlag, v. 2. p. 703.
LIMA,
J. S. S. et al. (2006) Estudo da viabilidade de métodos geoestatísticos na
mensuração da variabilidade espacial da dureza da madeira de paraju (manilkara
sp). Revista Árvore, Viçosa-MG, v. 30,
n. 4, p. 651-657. Disponível em:< http://www.revistaarvore.ufv.br php>
Acesso em: 26 out.2008.
PETTER, R. R. H.; RESENDE, L. M.; ANDRADE
JUNIOR, P. P. (2012) Comparative
analysis on the adoption of innovation in furniture companies. Independent Journal of Management &
Production, v. 4, n. 1, p. 111-125.
RIBEIRO
JUNIOR, P. J. (1995) Métodos
geoestatísticos no estudo da variabilidade especial de parâmetros do solo.
Dissertation (Master) Piracicaba: Escola Superior de Agricultura Luiz de
Queiroz, Universidade de São Paulo,
TOMASELLI,
I. A. (1998) Indústria de painéis no Brasil e no mundo: tendências de mudanças
do perfil de produção e usos. In: SEMINÁRIO INTERNACIONAL SOBRE PRODUTOS
SÓLIDOS DE MADEIRA DE ALTA TECNOLOGIA, 1, Belo Horizonte-MG, Proceedings…Viçosa-MG: SIF/UFV/DEF,
1998. p. 55-64.
VICK, C. B. (1999) Adhesive bonding of wood materials. Forest Products Laboratory.
Wood handbook–Wood as an engineering material. Gen. Tech. Rep. FPL–GTR–113.
Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products
Laboratory. cap. 9, p. 199-222.
WATAI, L. T. (1987) Painéis
derivados da madeira. São Paulo. ABPM (Associação Brasileira de Painéis de
Madeira).