Journal of Radiation Research and Applied Sciences Physico ... · then impregnated in unsaturated polyester resin. These impregnated particleboards were subjected to various doses

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J. Rad. Res. Appl. Sci., Vol. 3, No.2B , pp. 537 -551 (2010)

Physico-mechanical Properties of Electron Beam Irradiated Particleboards Based on Wood flour/ Polyethylene/Cement Kiln Dust Impregnated with Unsaturated Polyester H.A. Abdel-Rahman, Magdy M. Khattab and M.R. Ismail Radiation Chemistry Department, National Center for Radiation Research and Technology Nasr City, Cairo, Egypt. E-mail:[email protected] Received: 20 /05 /2010. Accepted: 20 /07 /2010.

ABSTRACT Particleboards were fabricated by mixing wood flour (WF), low density polyethylene (LDPE) and cement kiln dust (CKD) under hot pressure; and then impregnated in unsaturated polyester resin. These impregnated particleboards were subjected to various doses of electron beam irradiation up to 50 kGy. The physico-mechanical properties were characterized in terms of flexural strength, impact strength, water absorption, thickness swelling, and the thermal stability. The results showed that the partial replacement of wood flour with cement kiln dust up to 20% by weight improved the values of flexural strength, and impact strength. However, the water absorption percentage and thickness swelling values decreased with increasing the CKD ratio up to 40%. Furthermore, the treatment with electron beam irradiation doses improved the physico-mechanical properties of the impregnated particleboards up to 50 kGy. The improved results were confirmed by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Key word: Cement kiln dust, wood flour, thermal stability, polymer,

electron beam irradiation.

INTRODUCTION

Reinforcing fillers are resistant materials that, due to their properties and interaction with many polymeric materials; bring about favorable changes in the mechanical properties of the composite, such as impact strength, stress resistance, hardness, etc. Examples of this kind of fillers are fiber glass, carbon black, natural fibers (sisal, cotton, wood flour) and synthetic fibers (nylon, rayon, polyester). The quality of filler depends

H.A. Abdel-Rahman, et al., J. Rad. Res. Appl. Sci., Vol. 3, No.2(B) (2010)

538

upon factors such as distribution and average size of the particles, their shape and porosity, chemical nature of the surface and content of impurities. The use of wood flour as a filler is a choice offering an economical solution for the increasing costs of wooden products and construction materials. There is a considerable commercial interest in thermoplastic composites filled with wood flour, due to the potential opportunities of combining the attractive characteristics and properties of both components.

Recently the production and application of thermoplastic polymers reinforced with wood flour and natural fibers increased considerably(1,2). The increase in the use of wood as filler and/or reinforcement in thermoplastics is due to many advantages e.g. low price, low density thus offering economically advantageous solutions(3,4). The main application area of wood flour filled composites not only in the building and automotive industry, but they are applied for packing, furniture office appliances and convenient wide range of applications (5-6). Many different modifications of thermoplastic wood composites have been used to reduce the wood-wood interaction and increase the wood-polymer one(7). Magnus Bengtsson et al. (8)studied the possibility of using silanes as a coupling agent for crosslinking properties of wood flour/polyethylene composites. On the other hand, the influence of synthesized nano-silica/low density polyethylene (LDPE) on the thermal and mechanical properties of wood flour composites in the presence and absence of dicumyl peroxide were investigated(9-10). Scanning electron microscopy showed a uniform dispersion of nano-silica particles in the matrix also, fourier transform infrared spectroscopy results indicated an interaction between the nano-silica and LDPE matrix (11-12).

The impregnation of cement-bonded particleboard with styrene/acrylonitrile copolymer and monomer was studied to produce a new type of composite material; the effect of polymer impregnation on the various strength properties and the thickness of these boards were investigated(13-14). Compressive strength, tensile strength, flexural strength and impact strength were increased, while thickness swelling of polymer-impregnated cement bonded particleboard was less than for ordinary cement bonded particleboard. Thomas el al. (15) investigated the properties of wood plastic composites, which prepared using locally available


539

softwood and commercial monomer by vacuum and subsequent polymerization by gamma radiation. It reported that, the radiation dosage required for maximum conversion of monomer into polymer was less than 20 kGy except styrene, which required a much larger dose of about100 kGy. Reyes et al. (16-17) studied the effect of gamma irradiation on the mechanical properties of thermoplastic polymer filled with wood flour. The results obtained showed that general behaviour of the polymer blends was similar, being 10 to 50 kGy the most favourable irradiation range due to the remarkable improvement the studied mechanical properties experience within it (18). The goal of our research is studying the effect of both the cement kiln dust and electron beam irradiation on the physico-chemical and mechanical properties of the prepared composites from low density polyethylene and wood flour.

EXPERIMENTAL

Materials

Low-density polyethylene (LDPE) powder supplied by Cidasa Egypt, 6th October City, Egypt; with specific gravity 0.924 gm/cm3, grain size 350m and it has a molecular weight ranging from 2000 to 5000 g.mol-1. Cement kiln dust (CKD); a by-product of the manufacture of ordinary Portland cement Type I supplied by National Cement Company (NCC), Egypt. It has a particle diameter less than 200m. Wood flour (WF) obtained from the sawmill wastes; it has a particle diameter of about 300m. The chemical composition of both CKD and wood flour are cited in Table 1. The unsaturated polyester resin (UPE) used in this investigation is a general-purpose resin and contains 40% styrene monomer; supplied by the Saudi Industrial Resins Company (SIR) Ltd., Jeddah and commercially sold under the name Sirpol 8230. It has a viscosity of 450 cP and a specific gravity of 1.08 g/cm3 at 25oC.

Preparation and processing

Firstly, the wood flour was washed with water to remove surface impurities and dried for 24 h at 105oC. The particleboard samples were prepared by mixing a ratio of 80% wood flour with 20% of low-density polyethylene powder (by weight); then a partial replacement of the dried wood flour (WF) with different ratios of CKD namely (10%, 20%, 30% and 40%) took place. The raw materials were mixed and then pressed in a


540

mould of dimensions 16x16x0.8 cm, using an electric hot press type Carver-M-154. Hot pressing was performed at 140oC for 5 minutes preheating followed by 10 minutes under press at a 2000 psi and the specimens were then allowed to cool at the same pressure for 5 minutes. The particleboard sample compositions are designated as WF:LDPE:CKD (70:20:10), WF:LDPE:CKD (60:20:20), WF:LDPE:CKD (50:20:30), and WF:LDPE:CKD (40:20:40). Another group of samples were prepared under the same previous conditions; impregnated with unsaturated polyester resin (UPE) under vacuum for 3h, then subjected to different doses of electron beam irradiation namely, 10, 20, 30, and 50, kGy.

Table (1): Chemical Composition analysis of cement kiln dust and wood flour.

Cement kiln dust Wood flour

Oxides % Composition %

SiO2 14.1 Dry matter as: 97.3

CaO 56.3 Crude fiber 64.4

Al2O3 3.42 Acid detergent fiber 30.4

Fe2O3 2.3 Crude protein 1.1

MgO 2.1 Ash 1.4

SO3 6.6

Na2O 2.4

K2O 2.7

Cl 0.7

L.O.I. 1.3

Measurements

The mechanical measurements include flexural strength, was tested according to ASTM standards (D-1037-11, 1987) and impact strength was carried out according to ASTM standards (D 256, 1987). The physical properties such as water absorption percentage and thickness swelling were tested on the various samples using standard procedures according to ASTM Designation: (D 1037-100, 1987). The morphology of the fractured surface of some selective samples was investigated by scanning electron microscopy (SEM) model JSM-5400 (JEOL/Japan). Thermogravimetric


541

analysis (TGA) was performed using TG-50 instrument from Shimadzu (Japan). were carried out in a platinum sample pan in the presence of nitrogen atmosphere and a temperature ranging from 20 to 600oC and heating rate of 10oC/min,.

RESULTS AND DISCUSSIONS

Flexural strength

Figure1 illustrates the effect of electron beam irradiation dose on the flexural strength of low-density polyethylene (LDPE)/wood flour (WF) containing different ratios of cement kiln dust (CKD) impregnated with unsaturated polyester liquid resin. The results show that, at zero irradiation dose (un-impregnated composite) the values of the flexural strength for the particleboard samples (un-impregnated) increase with increasing the ratio of CKD up to 20%. This is due to a sort of physical or chemical interaction takes place between the components under pressing at 140oC. Firstly, the chemical interaction between WF and the particles of CKD through hydrogen bond formation, secondly, LDPE interact with/and WF and Si+4 present in CKD (19-21). Beyond the ratio 20% of CKD the flexural strength values of the composite decrease as a result of a segregation between the particles of composite components (22). This is leading to a weaker adhesion between the composite components, and consequently, the flexural strength of the composite is reduced.

Several techniques have been developed to obtain crosslinked polyethylene composites by peroxide, irradiation techniques and silane cross-linking methods; as well as, vinyl trimethoxy silane and peroxide were used to crosslink composites of polyethylene and wood flour (23). Moreover, studies revealed that irradiated thermoplastic polymer exhibits higher hydrophilicity than non-irradiated thermoplastic, due to the oxygen content in the irradiated samples(24). Theses studies also indicated that the oxygen containing groups, such as carbonyl, carboxylic and ether, have been introduced onto thermoplastic chains (25). Based on this, the behvaiour of the mechanical properties, such as flexural strength for the impregnated composites can be due to several reasons: first, to cross-linking which may be experienced by LDPE, and second to the higher polymer-filler interaction due to hydrophilicity of LDPE when it is irradiated, which is due to the functional OH groups. In addition, the wood flour has high concentration of OH groups, which may signify interactions of the


542

I r r a d i a t i o n d o s e ( k G y )

0 1 0 2 0 3 0 4 0 5 0

Flex

ural

stre

ngth

(kgf

/cm

2 )

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

F i g . 1 . E f f e c t o f e l e c t r o n b e a m i r r a d i a t i o n d o s e a s w e l l a s C K D c o n t e n t o n t h e f l e x u r a l s t r e n g t h o f W F : L D P E : C K D c o m p o s i t e .

hydrogen bridge type between the wood flour and LDPE. As well as the presence of unsaturated polyester leads to the increase of crosslinking density along the composites; these is associated with a strong adhesion between all components in the composite (26-27). Consequently, the flexural strength of the composites is improved.

Impact strength

It can be defined as the energy to break sample per unit thickness (or, it is the work done to fracture under shock loading). The results in Fig. 2 showed that, the maximum value of impact strength of the un-impregnated composites (at zero irradiation dose) was obtained for the composite containing 20% of CKD while, further increase in the cement kiln dust up to 40% is accompanied with a decrease in the impact strength. Lin et al. (28) stated that the effect of reinforcement by the wood fibers in the cement matrix might be attributed to the flexible and conformable structure of the wood fibers. This allowing the fibers to accommodate a certain amount of volume change, which reduced the stress on the cement matrix

and a successful bridging role as the wood fiber restricted further extension of a crack in the cement matrix under stress from wet-dry cycles. In general, the reduction of impact strength of WF:LDPE:CKD composite with increasing the CKD content up to 40% in the composite accompanied with a decrease of the WF ratio in the composite which is associated with a further extension of cracks as well as particles agglomeration, which cause easier crack propagation. This leads to further reduction of the values of


543

impact strength. The results showed that the impact strength of all the impregnated composites based on different CKD ratios; increased with increasing of irradiation dose. This behaviour is related to the presence of polymeric material which has ability to be crosslinked under the effect of irradiation process; leading to the formation of a net work structure beside that increase the adhesion force between the components of the composite and consequently both toughness and interfacial strength are significantly improved.

I r r a d i a t i o n d o s e ( k G y )

0 1 0 2 0 3 0 4 0 5 0

Wat

er a

bsor

ptio

n (%

)

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

F i g . 3 . E f f e c t o f e l e c t r o n b e a m i r r d i a t i o n d o s e a s w e l l a s C K D c o n t e n t o n t h e w a t e r a b s o r p t i o n ( % ) o f W F : L D P E : C K D c o m p o s i t e .

Irrad iation dose (kG y)

0 10 20 30 40 50

Impa

ct st

reng

th (J

ole/

cm2 )

0.5

1.0

1.5

3.0

F ig . 2 . E ffect of electron beam irrad iation dose as w ell as CK D content on the im pact s trength of W F :LD PE:C K D com posite


544

Irradiation dose (kGy)

0 10 20 30 40 50

Thic

knes

s sw

ellin

g (%

)

5

10

15

20

25

30

Fig.4. Effect of electron beam irradiation dose as well as CKD content on the thickness swelling of WF:LDPE:CKD composite.

Water absorption and thickness swelling

The changes in water absorption and thickness swelling percentages for all WF:LDPE:CKD composites with increasing the CKD content as well as the electron beam irradiation dose are graphically represented in Figs. 3 and 4, respectively. The results indicated that, at zero irradiation dose (un-impregnated composites) the water absorption and thickness swelling tended to decrease as the amount of cement kiln dust was increased from WF:LDPE:CKD (80:20:0) to (40:20:40). This may be due to the greater the CKD content the lower the wood flour ratio and as a result, the amount of absorbed water by the composite decreases with increase the CKD content (29-31). Since the tendency of the mineral filler as CKD towards the water absorption is lower as compared to the natural fiber as wood flour which has a great ability to absorb water due to its hydrophilic nature. Thus the composite of composition WF:LDPE:CKD (80:20:0) has the greatest value of both water absorption and thickness swelling. In addition, the effect of electron beam irradiation dose on the values of water absorption and thickness swelling percentages for all impregnated composites with unsaturated polyester resin are shown in Figs. 3 and 4, respectively. The results showed that, a significant reduction of water absorption and thickness swelling percentages takes place. This is mainly due to the consumption of unsaturated group, present in the polyester resin under the effect of irradiation doses; leading to an increase in cross-linking density and more dense structure is formed between the composite components.


545

Thermal stability

The decomposition thermograms obtained in TGA for WF:LDPE:CKD (80:20:0) composite, un-impregnated WF:LDPE:CKD (60:20:20) composite, and an impregnated WF:LDPE:CKD (60:20:20) composite with unsaturated polyester resin and irradiated at 30 kGy are showed in Fig. 5 and Table 2. It is observed that, the variation of remaining weight percentage at the beginning temperatures up to 200oC is limited, after this temperature a sharp decrease was observed in the temperature range 250oC-500oC leaving residues approximately 6.9, 25.9 and 31.2%, respectively and started leveling off in a plateau at a temperature range 500oC-600oC. In addition, the rate of the thermal decomposition reaction dw/dt (taken from the initial TGA thermograms) for different composites was plotted versus the temperature in Fig. 6. The results showed that, the maximum value of the reaction rate of thermal decomposition of these three composites are located at 332oC, 355oC and 387.5oC, respectively. The maximum rate of the thermal decomposition reaction of impregnated WF:LDPE:CKD (60:20:20) composite, which irradiated at 30 kGy is shifted towards a higher temperature (387.5oC) as compared to the un-impregnated WF:LDPE:CKD (60:20:20) composite i.e. the impregnated composite WF:LDPE:CKD contains 20% CKD is thermally the most stable.

Temperature (oC)

0 100 200 300 400 500 600

Rem

aini

ng w

eigh

t (%

)

0

20

40

60

80

100

120 WF:LDPE:CKD (80:20: 0) un-impregantedWF:LDPE:CKD (60:20:20) un-impregnatedWF:LDPE:CKD (60:20:20) impregnated and irradiated at 30 kGy

Fig.5. TGA thermograms of W F:LDPE:CKD composites


546

Table (2): Weight remaining percentages for un-impregnated and impregnated WF:LDPE:CKD composites at different temperatures.

Temperature

(oC)

Weight remaining (%) for different type of mix

WF:LDPE:CKD (80:20:0)

Un-impregnated WF:LDPE:CKD

(60:20:20)

Impregnated WF:LDPE:CKD

(60:20:20) 100 97.6 98.5 97.8 200 96.9 97.1 97.3 300 80.7 84.1 85.1 400 31.5 44.7 50.3 500 6.9 25.9 31.2

Tmax 332 355 387.5

Scanning electron microscopy

SEM micrographs of WF:LDPE:CKD (80:20:0), un-impregnated WF:LDPE:CKD (60:20:20), and impregnated WF:LDPE:CKD (60:20:20) composite with unsaturated polyester resin irradiated at 30 kGy are shown in Fig. 7 (a,b,c), respectively. The micrograph of the control composite WF:LDPE:CKD (80:20:0) as seen in Fig. 7a, displayed a considerable fiber

Fig.6. Rate of decomposition reaction (dw/dt) of both un-impregnated compoiste and polymer impregnated composite irradiated at 30 kGy.

Temperature ( oC)

200 250 300 350 400 450 500 550 600

Rat

e of

dec

ompo

sitio

n re

actio

n, d

w/d

t(mg/

min

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14WF:LDPE:CKD (80:20:0) un-impregnatedWF:LDPE:CKD (60:20:20) un-impregnatedWF:LDPE:CKD (60:20:20) impregnated and irradiated at 30 kGy


547

pull-out together with fiber tearing as well as some particles appearing on the surface of the fiber and large amounts of the voids leading to a poor adhesion between the polyethylene and wood flour. On the other hand, the micrograph 7b, illustrated that, the composite WF:LDPE:CKD (60:20:20) has a dense structure due to the interaction between the particles of cement kiln dust and cellulose fibers with the LDPE. After the impregnation of this composite with unsaturated polyester resin followed by irradiation at 30 kGy is shown in Fig. 7c; it displayed the formation of agglomerated structure which reflects the improvement in the flexural strength as a result of the reaction takes place between the unsaturated polyester and the matrix under the effect of the irradiation process.

Fig.7. SEM micrographs of particleboards made of: (a) WF:LDPE:CKD (80:20:0), (b) WF:LDPE:CKD (60:20:20), and (c) impregnated and irradiated at 30 kGy WF:LDPE:CKD (60:20:20).

CONCLUSION

The present work illustrated the following:

At zero irradiation dose, the replacement of wood flour composite with cement kiln dust up to 20% is accompanied with an improvement in the physico-mechanical properties in term of flexural strength, and impact

(a) (b

(c)


548

strength, however, the values of water absorption and thickness swelling percentages decreased with increasing the CKD ratio up to 40%.

The impregnated composite with unsaturated polyester resin and irradiated with different electron beam irradiation doses ranging from 10 to 50 kGy; is accompanied with an improvement in the physico-mechanical properties as compared with the un-impregnated composites.

Thermogravemetric analysis (TGA) illustrated that, the impregnated composite containing 20% cement kiln dust WF:LDPE:CKD (60:20:20) is thermally more stable than the un-impregnated composite.

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)2010( 551 - 537 ص ص )ب(2 عدد 3 مجلد

ولى ب، الب ارة الخش ن نش ة م بیة المؤلف واح الخش ة لألل واص الفیزیقومیكانیكی الخزم أیثیل عة الح ععة بأش تر والمش البولى أس ربة ب منت والمش ران األس راب أف ین، ت

االلكترونیة ، محمد رجب اسماعیلمحمد مجدى منصور، ھدى عطیة عبد الرحمن

اء ـ - اإلشعاعـ قسم كیمیاء اإلشعاعھیئة الطاقة الذریة ـ المركز القومى لبحوث وتكنولوجیا واد البن د 3معمل م أحم 29: ب. القاھرة ص –ة نصر مدین –الزمر

منت األلواحتم تحضیر الخشبیة بواسطة خلط نشارة الخشب والبولى أیثیلین وتراب أفران األس

رارى غط الح ت الض ر . تح م غم د ت واحوق بع األل ر مش تر الغی ولى اس ول الب ى محل رة ف بیة المحض الخشات ھا لجرع عاعیة وتعریض ن إش راوح م ة تت ى 10مختلف و 50إل عاع كیل تخدام أش طة اس راى بواس جبیة المحضرة . المعجالت االلكترونیة ة وقد تم دراسة الخواص الفیزیقومیكانیكیة لتلك األلواح الخش والممثل

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ستبدال نشارة الخشب بنسب مختلفة من تراب أفران األسمنت تصل إلى إلنتائج على أن وقد دلت اائج . لھ تأثیر جید على كًال من قوة االنحناء والقوة التصادمیة% 20 ا أظھرت النت ھ أبینم ًا أن ادة یض د زی عن

اخ % 20نسبة تراب أفران األسمنت عن مك االنتف اء وس ى . قلت النسبة المئویة لإلمتصاص الم الوة عل وعة واص الفیزیقومیكانیكی ان الخ ك ف واحذل ععة ألل بع والمش ر المش تر غی ولى أس ى الب ورة ف بة المغم الخش

وقد تأكدت .كیلو جراى 50إلى كیلو جراى 10من اإلشعاعیةقد تحسنت بزیادة الجرعة إشعاعیةبجرعات .تلك النتائج بواسطة الماسح االلكترونى والتحلیل الحرارى التفاضلى

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Journal of Radiation Research and Applied Sciences Physico ... · then impregnated in unsaturated polyester resin. These impregnated particleboards were subjected to various doses