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Physical evidence obtained at crime scene is important basic evidence in forensic
science. In such examination along with classical methods, instrumental
analysis plays a major role. Very few studies have been performed for cardboard
comparison as physical evidence with reference to forensic examination.
Examination and comparison of cardboard found in murder case was successfully
performed using thermal methods of analysis. The results were also matched with
control samples. The analysis is found to be helpful in identification and
linking of physical evidences at crime scene. The results obtained from the
simultaneous thermal analysis of cardboard seized at crime scene and company
office showed that all the three layers in cardboard show similar thermal
properties and differences found in the thermal properties were due to their
treatment in making originating from binder in cardboard making. The adhesive
material used in preparation of corrugated card board box results in exothermic
degradation peak while endothermic peak was observed for corrugated card board
box without adhesive material. The differences in results are found out with
help of control sample as well as simulated study.
Keywords: TG, DSC, Cardboard comparison, Cellulose
INTRODUCTION
Forensic science is an
integrated part of judiciary system. The collection, sampling, preservation and
analysis of evidences are important aspects of forensic investigations.
Forensic evidences may be biological, physical or audio-visual and generally
involve detection or comparison method. Most of the cases submitted in Forensic
Science Laboratories (FSL’s) need comparison between articles collected from
crime scene and from accuse or victim. Analysis of those evidences requires
specific method and technique to reach final conclusion. Analytical
instrumental techniques are valuable and integrated part in forensic
investigations. The physical evidences that are commonly submitted to FSL are
earth, metals, glass, fiber and polymer, etc. A rare case of cardboard
comparison has become an important as linking evidence in murder case. Thermal
analysis of card board box has become imperative and is been done using
simultaneous thermal analysis. Corrugated cardboard is stiff, strong and
lightweight and hence mainly due to the strength, cardboard boxes are generally
used for packaging and transportation purposes. Cardboard boxes are generally
made from pine tree’s bark. The bark mainly composed of cellulose,
hemicelluloses and lignin. The pine bark chips are treated in a pressurized
tank containing sodium hydroxide to remove its glue like material called lignin
which holds wood fibers together. The process is called Kraft process thus
breaks down wood chips in to fibrous pulp and used for making cardboard. The
cardboard has two flat liner sheets on either side of the corrugated sheet
(medium) in the middle, bound together with corn starch glue.
Thermal properties of cardboard
have been extensively studied with relevance to its recycle and reuse, safety
purposes in storehouses and environmental impact [1-3]. The present case gives
emphasis on comparison of two cardboard boxes found at crime scene and from
accuse, using simultaneous thermal analysis.
In present case accused used a
cardboard box to dispose of a body in murder case. A cardboard piece along with
label stick to it was seized from riverside. The cardboard box piece thrown in river
to dispose the body has company label stick on it. The same label was observed
on the cardboard boxes seized from the export company office. Thermal
properties of cardboard boxes at crime scene and from suspected site were found
to be different. The peak observed at about 357°C was of opposite nature. A
study for this difference was performed using different conditions and using
different cellulose based materials. The results of analysis revealed that the
cardboard used to dispose the body was obtained from the same office.
EXPERIMENTAL
Preliminary analysis
Label examination: Details of printed words such as hue, font size,
background color and words printed on labels were compared on intact cardboard
box in ex 1 and piece of cardboard in ex 2. Similarly colors of words were also
observed under UV cabinet. Thermal properties of label were studied using STA.
Cardboard examination: Three layers of each corrugated cardboard
(outer layer- liner, middle layer- medium/flute, and inner layer- liner) in ex
1 and ex 2 were separated and assigned as (a) (b) and (c), respectively. Each
layer was observed under Motic SMZ-168 series stereomicroscope. Physical
parameters such as thickness and weight of known dimensions were studied using
Digimatic Vernier Calliper, and digital balance (Metter Toledo) respectively
for comparison. The thermal properties of each layer were studied using STA.
Simultaneous thermal analysis
The STA measurements were
performed using NETZCSH STA 449, aluminium crucible with pierced lid and nitrogen
as purge gas at a flow rate of 40 ml/min. About 4-5 mg samples used in this
study were heated in the range of 50°C at the rate of 20 K/min to 600°C. Data
was analyzed using NETZCSH STA 449 protease software.
RESULTS AND DISCUSSION
Label stick on both cardboard in describe ex 1
and 2 have same hue, wordings and physical appearances as shown in Figure 1, similarly STA analysis of
label found on ex 1 and 2 also show similar TG as well as DSC curves as shown
in Figure 2. Thus labels on
cardboard box from company office in ex 1 and cardboard piece seized from
riverside tally with each other in morphological and thermal characteristics.
Each layer of cardboard as
described above was studied for hue and microscopic appearance. All layers of
cardboard in exhibit no 1 and 2 resembles with each other on the basis of hue.
The images under stereomicroscope of each layer are shown in Figure 3. The results of physical
parameters indicate that the width and weight known dimensions of cardboard
piece are same. Thus on the basis of preliminary examinations the pieces of
cardboard on ex 1 and 2 appears to be same.
Thermogravimetric analysis
The thermal stability of cardboard is determined by testing the onset of degradation temperatures. TG curve for all the layers for ex no 1 and 2 (Figures 4-6) show decrease in the curve at about 300°C. Cellulose absorbs moisture and this moisture loss generally found in the range 75°C-127°C. Cardboard generally consist of cellulose fibers. The decrease in weight of the cellulosic fibers was observed at 206°C-400°C with the maximum decrease in weight loss about 60-65% in these temperatures. Literature on thermal degradation study of cellulose fiber reveals that decomposition of major components of the cellulose fibres4 and the depolymerization of hemicellulose occurs between 180 and 350°C [5] and the random cleavage of the glycosidic linkage of cellulose between 275°C and 350°C [6]. The cellulose molecule is a very long polymer of glucose units and its crystalline regions improve the thermal stability of fibers [6,7]. Higher thermal stability of Celluloses is attributed to the hydrogen bonds between cellulose chains that can lead to more ordered and packed cellulose regions and hence increasing the thermal decomposition temperature of cellulose [8].
The cardboard piece obtained
from river side was wet and STA was performed on drying the exhibit. The DSC
analysis of each layer of cardboard box namely a, b and c obtained from river
side show endothermic peak at 354-357°C, however the exothermic peak was
observed at same temperature from cardboard box seized from office. The
discrepancy in the DSC results was found for both exhibits. Hence similar
control samples were used from fresh cardboard box. The piece of cardboard was
wet in water for 24 h and then dried. The results are presented in Figures 7-9. The DSC of the control
sample was performed and it was found that the nature of peak at 357°C was
endothermic. Thus it was found that cardboard box show exothermic peak at 357°C
while after getting moistened followed by drying, it shows endothermic peak.
The water extract of the residue of cardboard box was tested. Water extract was
alkaline (pH 9) along with sulphate and traces chloride.
The probable reason for the
phenomenon is hidden in formation of cardboard box. When cardboard piece get
moistened with water, the glue used to stick the medium or corrugated sheet get
dissolved in water and only cellulose left behind and show endothermic peak
instead of exothermic peak for the same cellulose without glue. The phenomenon
was again confirmed using cotton and filter paper as control sample. Whatman
filter paper is made up of high quality cotton linters which have been treated
to achieve a minimum alpha cellulose content of about 98%. The DSC of pure
whatman paper show endothermic peak at 358°C in absence of glue and when the
glue is stick to it an exothermic peak is observed at 388°C. The same
experiment was performed using cotton and the similar results obtained are
shown in Table 1.
The decrease in temperature in
endothermic peak with respect to exothermic peak is due to loosening cellulose
carbon hydrogen bond and less energy is absorbed to break the bond. The present
study successfully interprets the cause of differences in thermal properties
during analysis and thus helpful in forensic investigations of comparison of
exhibits to come to the final conclusion.
TG results
Generally decomposition
temperature of any material is found to be low due to less moisture content in
dry condition and it shifts to higher value.
CONCLUSION
In a murder case cardboard box
was used to dispose of the body. The results of comparison of cardboard box
obtained in the present study show similar STA results for label. In exhibit
but show discrepancy in cardboard box results. DSC results show first
endothermic peak for moisture loss and second degradation peak show opposite
nature. The adhesive material used in preparation of corrugated cardboard box
results in exothermic peak while endothermic peak was observed for the
corrugated cardboard box without adhesive material. The differences in results
were found out with the help of control samples as well as simulated study.
Hence the observations are further useful in solving and establishing evidence
of cardboard box in similar type of medico-legal case.
ACKNOWLEDGEMENT
The authors are thankful to Director, Directorate of Forensic Science Laboratories and Director General (legal and technical) Mumbai, Government of Maharashtra, for their valuable guidelines and encouragement for the preparation of this paper.
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