Effects of pyrolysis bio-oil derived from palm kernel shell on modified bitumen properties

Economical and environmental friendly materials that able to replace petroleum based binder has become an urgent demand in road industry. Bio oil from palm oil waste is relatively more economical and has the potential to used as bitumen replacement as bio asphalt. The performance of bio asphalt derived from different source and process to produce bio oils are varies. Hence, this study aims to investigate the effects of palm kernel shell bio-oil in terms of physical properties, the chemical functional group, and the morphology. The bitumen properties were evaluated by the conventional physical tests, Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy. The palm kernel shell bio-oil was added into the bitumen by weight of bitumen at 0%, 2%, 3%, 5%, 10%, 15%, and 20% and blended using mechanical stirrer. From the conventional physical test, it was found that bio-oil modified bitumen increased in penetration and ductility with decreased softening point. This indicate that direct addition of bio oil soften the modified bitumen. The change of the functional group in FTIR is significantly influenced by the increasing content of bio-oil. The morphology of the modified bitumen showed inhomogenous surface with noticeable wrinkles as the bio oil content increase. Based on the physicochemical evaluation, 3% bio oil replacement passed all the physical tests requirement with less changes in FTIR result. Therefore, 3% bio oil content is proposed for further tests for direct inclusion of bio oil into bitumen for local road construction utilization.


Introduction
Sustainability in road industry are related the feasibility to utilize resources effectively and conserve the ecosystems in the environment.Previous research reported the potential of waste recycling from the byproducts of industrial activities or regular output in daily life as a replacement of bitumen to reduce the reliance on consuming non-renewable resources [3].For example, the waste products from palm oil industry.Malaysia is currently known as one of the world's top producers and exporters of crude palm oil [4].It is known that 90% of the plantations' biomass in Malaysia are including oil-palm trunks (OPT), oil-palm fronds (OPF), empty fruit bunches (EFB), palm kernel shell (PKS), and palm-oil mill effluent (POME) is environmentally dangerous if these biomasses are let as solely residues [5].In the study of [4], palm oil tree has the highest oil production efficiency for about 4000 kg/ha, said to be the most productive plant among the major oil-producing plants.Palm oil trees have a lifespan of more than 200 years that it is suitable to be shifted as renewable energy in the context of oil production [4].The output of palm oil industry wastes has the potential to be utilized as bio-materials in road industry and be converted to bio-oil from pyrolysis technology that can be used in modified bitumen.Based on a study bio-oil produced from oil palm-based pyrolysis process is more environmentally friendly as compared to the conventional thermal process from the environmental perspectives, [11].Many researchers had concluded that bio-oil has excellent properties that it could be used as a binder in the road construction, thus gives reason on the increasing number of studies and researches of bio-oil and bio-asphalt recently [7].The performance of bio-oil from various biomass wastes such as waste cooking oil, soybean oil, cotton stalk bio-oil and wood bio-oil shows improvement in terms of physical properties of bitumen including the penetration, softening point, and ductility [1], [3], [8]- [12].According to a review on bio binder, the performance of bio oil modified bitumen and mixtures derived from different sources are varies [13].This means that the source of bio bio will affect the resultant modification.
Therefore there is a need to study the performance of each source of bio oil such as bio oil derived from PKS .Additionally, chemical test is not widely studied in bitumen modification using biomaterials as have been researched by [1] and [3].Therefore, this study aims to determine the effects of pyrolysis bio oil derived from PKS on the physical properties of the bio-oil modified bitumen, chemical analysis by using Fourier Transform Infrared Spectroscopy (FTIR) and morphological.

Materials and Samples Preparation
The materials used in this study were bio-oil and bitumen.The bio-oil used for this research is PKS biooil which is obtained from the local palm oil industry at Lahad Datu, Sabah, namely Verde Resources(Malaysia) Sdn.Bhd., as shown in Figure 1(a).The bitumen used is bitumen grade 60/70 which is obtained from Astenpave Sdn.Bhd, as shown in Figure 1(b), which is based in Kota Kinabalu, Sabah.There are seven samples with 2%, 3%, 5%, 10%, 15%, and 20% of bio-oil by the weight of bitumen to be compared with original bitumen.One bitumen sample without the addition of bio-oil is referred as the control bitumen.The sample preparation in which bitumen with penetration grade 60/70 is blended with bio-oil at temperature of 140°C.The blending process is done by using mechanical stirrer with constant speed of 500 rpm for 25 minutes until the mixture is in uniform condition.The bitumen is first heat in the oven up to 140°C and the PKS bio-oil is slowly added into the bitumen.Correspondingly, Table 1 and 2 show the physical properties of bitumen and PKS bio-oil respectively.

Experimental Procedure
Experiments were conducted to evaluate the physical properties of bitumen using penetration, softening point, and ductility tests.The penetration test of bitumen was conducted according to ASTM.Softening point test was carried out based on the ASTM D36.The ductility test was performed in accordance with ASTM D113 standard.All specimens for physical properties test were based on average of three samples.The chemical analysis was done by using FTIR test according to the standard ASTM E168 and ASTM E1252 at room temperature between 22°C and 27°C.The IR spectra were observed and analyzed in the range of 2000cm -1 and 500cm -1 [2], [3].The morphological test was performed with the use of Scanning Electron Microscopy (SEM) to evaluate the effect of the modification of bio-oil on asphalt materials with the magnification of 200x, the accelerating voltage used is 15.0kV and electron emissions of 120 micrometers.

Results and Discussions
The result is obtained from laboratory works which is divided into three sections namely the effect of bio-oil to the physical properties of the modified bitumen supported with statistical analysis by simple linear regression analysis, effect of bio-oil to the functional group of the modified bitumen by FTIR test, and the effect of bio-oil to the morphology of the modified bitumen by SEM test.

Effects of Bio-Oil Modification on Physical Properties of Bitumen
The conventional physical tests consist of penetration test, softening point test, penetration index (PI), and ductility test are analysed.The findings from each test are shown in Table 3. From Table 3, a code designation was adopted to indicate the bitumen modification with the respective percentage of PKS bio-oil added to the bitumen.The first letter denotes the bitumen, and the number that follows indicates the percentages of PKS bio-oil by weight of bitumen.For example, B2 indicates the bitumen is added with PKS bio-oil at 2% by weight of bitumen.The penetration increases as the content of PKS bio-oil increases for the increment of 2% up until 20%.The increasing penetration depth of the samples indicates that the PKS bio-oil has soften the bitumen grade since 2% of bio-oil has shown 75dmm penetration which is not within the range of the control bitumen grade.Therefore, the replacement of bitumen with different percentages of PKS bio-oil significantly increases the bitumen grade.Since the pavement grade of 60/70 is the standard grade used in Malaysia, it can be said that the bio-oil modification using 1% of PKS bio-oil has the potential to meet the bitumen 60/70 specifications as it may be nearly similar to that of the control bitumen.
A decreasing trend can be observed as the content of bio-oil increases, the softening point decreases up until 35 for the replacement of bitumen with 20% bio-oil.It can be concluded that the high amount of PKS bio-oil give effect to the bitumen that it has low temperature susceptibility and resistance to deformation over elevating temperature.For the Penetration Index obtained, most of the bitumen have values of penetration index within the range of -2 until +2 [10].The modified bitumen with 2% and 3% of bio-oil has PI values that are within the range of standard PI values.Nevertheless, the PI values decreases as the bio-oil content increases and are vulnerable to high temperature and high possibility to form cracking.As for the ductility, all samples have passed the minimum standard of 100cm ductility that the average ductility obtained is more than 130cm.The reference groups which also referred to aliphatic group are seen at both peaks of approximately 1456cm - 1 and 1376cm -1 for all respected bitumen samples.This complies to the studies of [2] and [3] that the CH2 and CH3 bends are within the range of 1350 to 1525cm -1 .On the other hand, the C=C stretch bend which depicts the aromatic group of the bitumen lies at 1600 cm -1 as indicated.Significant difference can be seen in this aromatic group as increasing peak is shown as the increasing content of PKS bio-oil to the bitumen.The carbonyl group lies in the range within 1660 to 1753cm -1 .The spectrum of control bitumen exhibits small peaks at 1700cm -1 .This means that the carbonyl functional group does exists within the bitumen sample even though the functional group is in a smaller amount.Comparably, the spectra for sample of modified bitumen with 20% of PKS bio-oil is relatively different at this wavenumber, since it can be noted that the peak is significantly increasing in shape.The difference may be caused by the intensification of bio-oil added to the sample.As palm-based bio-oil contains probably more carbon in its elemental composition as in the research of [8], it most likely affects the carbonyl functional group of the modified bitumen.

Scanning Electron Microscopy
The SEM image for control bitumen is shown in Figure 3(a) as studied by [9].Control bitumen has no phase separation and little to no white form, which portrays a homogenous structure.This is because control bitumen is known as new bitumen without any modification done into it as well as no aging of bitumen occurred [9]. Figure 3(b) indicates the morphology of the modified bitumen with 5% PKS biooil presents a smooth surface with an almost homogenous structure which indicates the bitumen is well blended with the bio-oil.However, the wrinkle parts with little white phase of the bitumen exists which may be caused by the incorporation of PKS bio-oil as the light components of the bitumen increased.
Next, the structure of modified bitumen with 10% of PKS bio-oil showed that there are notable agglomerations of white parts on some locations of the bitumen as captured in Figure 3(c).The SEM image showed that the bright parts as the bio-oil-rich phase, while the dark phase is the bitumen-rich part.This could be caused by the increased content of bio-oil blended to the bitumen that the phase separation shown is significant.Another significant change on the morphology of the bitumen can be seen in Figure 3(d) when modified with 15% of bio-oil as there are scattered white parts on most of the locations captured of the bitumen, though no coherent images of these white parts are found other than the captured ones.
The SEM image for 20% PKS bio-oil modified bitumen shown in Figure 3(e), the white parts are scattered as well but not as abundant as in the bitumen with 15% PKS bio-oil.Besides, the bitumen surface has noticeable wrinkles that are relatively smooth.Nevertheless, some parts of the bitumen have no white parts on the structure, which stipulates equivalent structure formed as in the bitumen modified by 5% PKS bio-oil.This may be justified as the modified bitumen has been enhanced with the blended bio-oil into it and improved.

Statistical Analysis
The independent variable for statistical analysis are the values for penetration, softening point, and ductility.Meanwhile, the dependent variable is the PKS bio-oil content.Regression statistics was performed and the summary of result is shown in Table 5.The adjusted R 2 is used to determine if a linear relationship between the independent and dependent variables satisfactorily match [6].Adjusted R 2 that closer to 1.0 indicates that the linear relationship between the two variables fit the data well.The adjusted R 2 of the penetration test is 0.985 and 0.778 is obtained for softening point.Therefore, the linear regression model for penetration and softening point is acceptable.The adjusted R 2 of ductility test is 0.278 thus conclude that ductility test does not fit the linear regression.
As the confidence level is 95% which also indicates the alpha is 0.05, the result shows that the analysis of ductility is not significant as the P-value obtained is more than 0.05, which corresponds to the null hypothesis that the relationship between the two variables is not linear.Meanwhile, the penetration and softening point are significant with P-value is 0.00000609 and 0.00536, respectively.Therefore, it is concluded that there is a linear relationship between bio-oil content with penetration, as 7 well as between bio-oil content with softening point value.Figure 4 shows the graph of liner regression for penetration, softening and ductility

Conclusion
In conclusion, the effect of the bio-oil from PKS to bitumen conventional properties are determined from physical tests showed increase penetration, decrease in the softening point with improvement in .$#'"0$#1"0')'03 '+$ ..$#'"0$# 1"0')'03 the ductility.Meanwhile, the effect of bio-oil from PKS to the chemical composition of the bitumen evaluated through FTIR analysis indicated that the functional group such as carbonyl group, sulfoxide group, esters, aliphatic and aromatic group has influenced in the transposition of the chemical structure of the bitumen.As for the SEM test, the images observed showed that the bitumen modification using PKS bio-oil has altered the morphology of the bitumen.However, the PKS bio oil content above 3% was too soft.Hence, for local road construction addition of 3% bio oil is suggested.

Figure 2 .
Figure 2. FTIR spectrum of control bitumen PKS bio-oil modified bitumen

Figure 4 .
Figure 4. Linear regression fitting of penetration, softening point and ductility.

Table 2 .
Typical Properties of PKS Bio-oil

Table 5 .
Simple Linear Regression Statistics