The combined chemical and mechanical modifications of cigarette: a novel methodology to reduce harmful effects

Without hindering the taste, making a cigarette less harmful by reducing the percentage of toxic and carcinogenic compounds in the smoke of the cigarette is a challenging task for the current generation of researchers. In the current work, by implementing mechanical, chemical and combined modification techniques, the above stated is tried to mitigate. In addition to the above, the optimum suction pressure, burning time and the number of puffing are also determined. Mechanical modification technique considers filter to cigarette ratio and filter design as the controlling parameters. The mathematical calculation reveals that puffing should stop when the cigarette length reaches 0.15 times of its original length. Furthermore, it is also identified that the concentrations of suspended solids and droplets in the smoke decrease significantly (separation efficiency = 56.81%) if the cigarette to filter ratio is maintained at 2.32. In case of chemical modification, by using various types of adsorbents such as charcoal and Zeolite 13X, the harmful effects are further reduced. These processes depict significant reduction in harmful effect (separation efficiency up to 62.1%) by showing the decrement in the suspended solids and droplets in the smoke due to the adsorption on the active sites of adsorbents. In case of combined modification, the achieved separation efficiency is 66.51%. For the experimentation, an experimental setup fitted with artificial lungs was used.


Introduction
Cigarette smoking is one of the most plausible reasons for the increment in the number of deaths worldwide. Cigarette smoke is a mixture which contains approximately 5000 chemicals. As per the information reported by the World Health Organization (WHO), 5.4 million premature deaths occur worldwide due to smoking. Talhout et al. 2011 predict-ed that by 2025, around 10 million smokers could die annually. In addition to the above, cigarette smoke also causes air pollution. Among all the components of cigarette smoke, air pollution is mainly caused by polyaromatic hydrocarbons (PAHs). The neural network(RNN) model developed by and its percentage in the total smoke depends on the combustion efficiency and methodology (Russell et al. 1980;Schick and Glantz 2006;Benowitz et al. 2010;Schick et al. 2012, andYu et al. 2019).
The above stated harmful chemicals present in the smoke either in the form of droplets or in the form of suspended solids which settle at various locations of the lungs, mouth and throat due to the sudden changing in the direction during the flow of smoke. The settlement mechanism is described with the help of a schematic diagram (Fig. 1). The rapid expansion of smoke in the mouth and lungs and sudden changes in flow direction at the throat and in the lungs enhance the pressure drop. Due to this, the suspended solids settle. Furthermore, the droplets agglomerate due to the temperature variation.
To reduce the harmful effect, the suspended solids, droplets settling rate and condensation rate of smoke must be minimum. The phenomena described above depend on the residence time, quality of tobacco, the efficiency of the filter and the methodology of smoking. The residence time depends on the flow pressure, and it is proportional to velocity. For the attainment of minimum settling, the pressure drop must be low.
To attain enhanced separation efficiency, chemical, mechanical or combined modification methodologies are used.
In the absence of any information in the open literature regarding the above stated modification processes, in the current work, an attempt has been made to develop an efficient modification process to achieve the maximum separation efficiency.
In the mechanical modification, the filter's design, packing density and cigarette to filter ratio are altered. The improper selection of any parameter discussed above augments the carcinogenic effect by decreasing the separation efficiency. Therefore, proper selection of the parameters mentioned above is required to minimize the carcinogenic effect without hampering the taste and feeling of the smoker. In this regard, the literature does not disclose any information in open literature.
The chemical modification includes the use of various adsorbents as a filter to enhance the separation efficiency. It is also be noticed from the previous work that various additives are used in the tobacco mixture to reduce the carcinogenic effect of smoking; However, the harmful effect of burning of additives and catalyst are not considered in the modifications (Bombick et al. 1997;Muscat et al. 2005;Miyamoto et al. 2012;Firas et al. 2014;Martins et al. 2015;Campo et al. 2016;Moura et al. 2016;Abdul Kareem et al. 2018). In the case of commercially available electronic cigarette, the disadvantages reported in the literature had been tried to eliminate. However, the survey conducted by UNICEF and WHO reveals that the use of electronic cigarette does not mitigate the requirement of the consumers (Badea et al. 2018).
For the chemical modification, charcoal, 13X-Zeolite and the mixture of both were used to separate the significant number of suspended solids and droplets (Zhang et al. 2010;Mopoung et al. 2015). However, these study were not carried out at the optimum conditions. In the current manuscript, at the optimum conditions, the removal efficiencies of the various carcinogenic elements by the adsorbents and filters have been reported. In addition to the above, the effect of both chemical and mechanical modifications on removal efficiency has also been tried to disclose.

Procedure
In the current work, an indigenously designed and fabricated experimental setup and lungs were used. The schematic diagram of the experimental setup is depicted in Fig. 2. The experimental setup contains a suction chamber, filtration unit, data recording subsection, artificial lungs and an imaging unit with an illumination system. The suction chamber mimics the role of the mouth.
Experiments were performed at room temperature (~25°C) and atmospheric conditions (1 atm). For all the experiments, King's Gold Flake brand cigarettes were used. The cigarette before ignition was fitted with the suction chamber (63 cm 3 ) which is connected with a suction pump (capacity = 30 kPa). Thermistor 1 is attached to the mouth cavity and it measures the temperature of the inlet smoke to the mouth. At the suction chamber's entry point, the smoke samples were collected as the inlet smoke to the cavity for the further analysis. To identify the quality of outlet smoke, smoke from the lungs was collected. During the experimentation, the pressure and the flow rate of the inflow were measured by using the pressure gauge and rotameter, respectively. The measuring instruments associated with the experimental setup have the following specifications: (1) Rotameter: 10-1000 ml/min, (2) Pressure Gauge: 0.1-0.2 bar and (3) Thermistors: 25-150°C.

Particulate collection methodology
The schematic diagram of the fabricated separator is presented in Fig. 3. After collection of the smoke, it is sent to the separator for the determination of solid and droplet concentrations in the smoke. The separator has two sections: (1) Retentate and (2) Permeate. Both sections have equal volume that is 40 ml. The length and diameter of each section are 2.38 cm and 46.2 mm, respectively. Both the sections are separated by a  Schematic of the setup used to separate the suspended solids and droplets filter paper (2 μm PTFE 46.2 mm filter) and the sections are joined by using a sealant. The stereo image and the photograph of the used filter papers are presented in Fig. 4a and b, respectively.

Materials
In the current work, the following raw materials were used (Table 10). For the experimentation, standard cigarettes available in Indian open markets were used. In addition to the above, various adsorbents such as Charcoal and Zeolite-13X were also used and the details of the manufacturer have also been provided in Table 10.

Characterization of raw materials
In the raw material characterization, moisture analysis was performed to identify the expected amount of condensate presents in the smoke. In addition to the above analysis, SEM, XRD, FESEM and EDS analysis were also performed to determine the carcinogenic compounds present in the cigarette. Furthermore, analysis of the filter was also performed. Finally, the thermal and flow behaviour were modeled to map the various process controlling the harmful effects.

Moisture analysis
For the moisture analysis, one gram of raw tobacco was taken in a known weight of crucible. Then, the sample was kept in an oven for 1.5 h at 110°C. Finally, the sample was brought out from the oven and kept in a desiccator. After the sample cooled down to room temperature in the desiccator, the weight of the sample was measured. Finally, the percentage of moisture is determined by following Eq. 1.
Packing density For the calculation of the above stated parameter, cylindrical shape is assumed for the cigarette. Without filter, the diameter and length of the cigarette are 0.7 cm and 5.45 cm, respectively and the calculated weight is 0.7012 gm. Based on the above information, the packing densities of cigarette and filter are calculated using Eq. 2 and the obtained values are 333.9 kg/ m 3 and 180 kg/m 3 , respectively.
Characterization of the filter In the current work, the commercially available filters were used. The fibres arrangement and its porosity are determined using the images captured by a Leica microscope. This characterization helps to define the flow pattern of the smoke. Furthermore, in Table 1, the physical properties and the compositions of the filter have also been presented. The optical and FESEM images of the cigarette filter after different modifications are depicted in Fig. 5.

Composition analysis
In terms of compound For the raw cigarette tobacco, charred part and ash collected after burning, XRD analysis was performed and obtained results are presented in Fig. 6(a-c). From the XRD analysis of the cigarette ash and raw material, it is identified that both ash and raw material contain carcinogenic compounds. However, for the quantification of the above stated, elemental analyses were performed.

In terms of elements
As the process deals with combustion, the proximate and ultimate analyses are initially performed (Table 2). From the analysis, it is identified that the raw tobacco contains very high amount of moisture and therefore, the smoke contains fine droplets in the form of aerosol. During the flow of smoke Images (Top view of the exposed part) Schematic of filter Cross-sectional view by Leica Microscope 1.6 cm 0.7 cm inside our body, these are expected to agglomerate and deposit. Furthermore, the ultimate analysis indicates that flakes of gold leaf contain very small amount of sulphur. For the elemental analysis in detail, EDS analysis was performed for each sample and the obtained results are presented in Fig.  7(a-c).
For the detection of traced components in the composition, chemical analysis was performed. In this case, the dried and pulverized samples were chemically digested in the mineral acids such as HCl and HNO 3 . The digested sample was then filtered using filter paper (Whatman filter paper 42) to separate any insoluble residues. Furthermore, to separate all the heavy metal ions from the residue, the filter paper was at least washed 3 times. Finally, the collected mother liquor was analysed using ICP-OES (Perkin Elmer 8300). The primary wavelength for each element was selected during the analysis work. The instrument's standards were purchased from Merk (India) Ltd and used after suitable dilution. The obtained compositions are reported in Table 3.
From the above stated information, the smoke and ash compositions are calculated by using Eqs. (3)-(6).

Raw tobacco→
The compositions of raw tobacco, smoke and ash indicate that the significant percentage of the carbon present in the raw material goes to the gaseous phase after burning (Table 4). The C in the gaseous stream as CO and CO 2 are very much harmful to human health. In addition to the above, elements such as Pb, Cr, Hg and Cd also transform to smoke. Therefore, along with the carcinogenic compounds, the above stated compound or elements intensities also need to reduce. The transformation rate of elements enlisted in Table 4 depends on the surface texture.
Surface morphology and texture SEM analysis of raw tobacco, charred part and ash is presented in Fig. 8(a), (b) and (c), respectively. These depict that after combustion, the coarse solids present in the raw material convert to comparatively finer solids. The raw tobacco pores are not visible as these are filled by volatile matter and moisture. With the progress of burning, the moisture and volatile matters become smoke and as a result, the pores are visible ( Fig. 8(b)). In case of complete burning of tobacco ( Fig. 8(c)), the agglomerated form of the ash is noticed. Furthermore, it also observed that tobacco after burning converts to finer particles. In addition to the cigarette part, the filter's properties also play a significant role and decide the separation efficiency.

Role of suction velocity and pressure drop
The following are the assumptions for the establishment of a relationship between pressure drop and velocity: & Uniform smoke and air distribution & The composition of tobacco is uniform & Cigarette and filter are considered as packed bed  7 Elemental analysis of (a) raw tobacco, (b) charcoal and (c) ash parts Before modelling, few terms which are used in the modelling need to describe and these are sphericity and void fraction. For the calculation of void volume, the required data are the diameter of a tobacco particle (0.1 cm), length of a tobacco particle (0.31 cm) and the calculated volume(V p ) of one cigarette particle (9.82 × 10 −3 cm 3 ). The surface area (A ps ) of one tobacco particle is 0.41 cm 2 and the equivalent radius (r o ) is0.133 cm. With the help of the above information, sphericity of a tobacco particle is determined using Eq. 7.
Without filter, the volume of a cigarette is 2.097 cm 3 and the volume of water displaced is 1 ml when a cigarette without filter is dipped in water. With the help of the above information, the void fraction is calculated by using the following formula: From the filtration unit, the volume is found to be 0.596 cm 3, and the volume of water displaced is 0.2 ml. Hence, the void fraction is: Finally, with the help of information represented in Eqs. (8) and (9) and velocities reported in Table 5, the pressure drop is calculated using Eq. 10 (30).
The enhancement in velocity is observed with the rise in pressure drop (Table 5) due to the alteration of flow pattern from laminar to transition. In addition to the above, the  augmentation in residence time is also noticed and this promotes step-up in combustion efficiency, which is a desirable criterion to achieve minimum harmful effect. The following modelling work needs to be performed to identify the role of pressure drop in inspiration and expiration during smoking. Equation 10 is modified to Eq. (11) for simplicity, According to Boyle's law, During expiration, 500 ml is discharged. The inspiration and expiration volumes during cigarette smoking are presented through a P-V diagram (Fig. 9) using Eqs. (11)-(15) (Kim et al. 2005;Brown 2015). V suction amount retains in the lungs after expiration and releases during subsequent breathing. It is the reason for the getting cigarette smoke smell even after smoking completes. Due to the additional residence time in the lungs, the settling of droplets and suspended solid augments. Higher suction pressure indirectly increases the residence time and settling velocity. The above stated is consistent with Eq. (17) according to the information reported in literature (Kim et al. 2005).
In addition to the P-V relationship describing the harmful effect of cigarette, combustion, condensation and distillation effects also need to be determined (MacIntyre and Branson 2001). For this, the thermal modelling is performed: Heat released during combustion reaction ¼ Heat absorbed by the gold leaf flakes þ Heat loss due to radiation þ Heat absorbed by filter The heat generated by tobacco during combustion is 9.75 MJ/kg, and therefore the total heat generated by one cigarette is 9.75 MJ/kg × 0.7012 × 10 -3 kJ heat.

Heat absorbed by filter unit
Heat loss due to radiation from cigarette, ¼ 2:182 Â 10 −12 Â 973 4 −298 4 À Á = 1:938 J s Â t (23) Heat loss due to convection from cigarette smoke to flakes is: Using Fig. 10 and the above stated equations (Eqs. (18)-(24)), at any time 't', it can be written that ΔT = 850°C -T (x, t) and T (x, t) is determined by solving the fallowing partial differential equations: b a þ c …… : : a b c ::… : : :a b c:… : : :: : : :… : : :: : : :: :: : : :: : : :: :a b c :: : : :: ::a þ c b For the calculation of temperature distribution along the cigarette's length, the cigarette's geometry is initially discretized. For this, Crank-Nicolson and Fully Implicit formula are utilized. The discretized forms and the original equations are mentioned above. In addition to the above, the solution is converted into a tridiagonal matrix. For the calculation, the following assumptions are used: 1. After the grid independency test, it is found that the values of Δx and Δt are 0.006 m and 0.1 s, respectively 2. The temperature variation along the radial direction is assumed to be insignificant 3. At t = any time; x = L ′ and T = 850°C 4. At t = 180 sec; x = L = L ′ = 0 cm and T = 120°C 5. At t = 90 sec ; x = L = 0.855 cm and T = 850°C 6. The thermo-physical properties of gold leaf are given as the input 7. L = 5.7 = nΔx; t = 180 = nΔt and L 0 t 0 ¼ nΔx nΔt 8. The tri-diagonal matrix is solved for the known heat flux, and from that, the temperature at different locations is determined by following the methodology presented in INTEMP software.
For the different time intervals, by using information reported above (Eqs. (18)-(22)), the absorption zone, distillation and condensation zone lengths are also determined ( Table 6).

Optimization of the process parameters
For this investigation, the cigarette was burnt at various suction pressures. The suction was provided at an interval of 12 s and it continues for 3 s. During the burning of cigarette, the whole process was recorded using a high-speed motion analyser and thereafter, by using an image processing software, the transient nature of the images was determined. Finally, by using the following formula (Eq. (38)), the burning time is determined.
The variation of burning time with the suction pressure is presented in Fig. 11 and it shows a decreasing trend with the increasing suction pressure up to 10 kPa due to the rise in airflow which generally promotes the burning process. However, above 10 kPa, as the suction pressure increases, the burning time depicts accelerating trend due to the decrement in the residence time of fresh air in the cigarette. In this case, incomplete combustion is expected. In addition to the above, Table 7 depicts that the separation efficiency increases up to 10 kPa suction pressure. Further increment in suction pressure, the separation efficiency declines. The above-stated investigation discloses that the optimum burning time and suction pressure are 135 s and 10 kPa, respectively. From the information reported above, the calculated optimum number of strokes is 9. In the current work, stroke represents one cycle of puffing. To verify the above mentioned, experiments were conducted by altering the number of strokes at the optimum burning time. The obtained results are presented in Table 8. In this analysis, instead of considering separation efficiency, the unburnt carbon percentage has been considered as the controlling parameter.

Mechanical modifications
In mechanical modifications, the ratio of filter to cigarette length (F/C) is varied. In the current work, the cigarette length of 5.4 cm is considered as the one unit and the filter of 1.55 cm length is taken as the one unit. For this study, at 10 kPa suction pressure and around 10 strokes, the cigarette was burnt. In per suction, the smoke enters the lungs, and the smoke from the lungs is collected using the methodology described earlier.
The analysis depicts that with the increasing F/C ratio from 0 to 1.5, the separation efficiency enhances significantly (Table 9). It could be due to the entrapment of significant amount of suspended solids in the filter's pores. Although beyond 1.5, the above-stated parameters follow the same trend line; however, the cigarette's taste deteriorates, and the consumer gets insufficient smoke due to very high resistance for   flow created by the higher length filter. Therefore, up to 1.5 F/ C ratio is acceptable. From the XRD analysis ( Fig. 12(a-d)), it is concluded that the peak intensity of certain carcinogenic compounds decreases as the filter length increases. Cellulose fibres of the filter block some part of the smoke particles from entering into the lungs (Fig. 13). For the further improvement in separation efficiency, chemical modification is performed.

Zeolite-13X
In case of chemical modification, within the filter, adsorbents such as charcoal and Zeolite-13X were used as a separate layer (Fig. 13a). The addition of adsorbent layer is expected to reduce the suspended solids and droplets from the smoke due to  13a and 14) depicting the structure of cigarettes and adsorbents for the various cases are presented. In addition to the above, the adsorption mechanism is presented in Fig. 13 (b) and the adsorption capacity of adsorbents is presented in Table 11. Zeolite is considered as the potential solid adsorbents for separation and purification, and it is cost-effective. It also depicts higher lifetime and has eco-friendly nature (Firas et al. 2014;Martins et al. 2015;Campo et al. 2016;Moura et al. 2016). In addition to the above, zeolite also illustrates higher specific surface area and smaller average pore diameter (Tables 10 and 11). Zeolite-13X has also a promising affinity towards CO 2 adsorption (Miyamoto et al. 2012;Abdul Kareem et al. 2018). Various amounts of Zeolite-13X ranging from 0.5 to 2 g were used to fabricate different cigarettes. Then, each cigarette's performance is determined by measuring the suspended solids concentration in the entry and exit smoke. The analysis clearly illustrates that the optimum performance is obtained in the case of 0.1 g Zeolite-13X (Tables 12 and 13). Beyond the stated amount, the 10 kPa pressure is insufficient to create suction for the proper combustion.

Charcoal
In case of modification by charcoal, by following the methodologies described above, finite numbers of cigarettes were prepared (Fig. 15). The performance of each cigarette was determined by measuring suspended solids and the droplets concentrations at the inlet and outlet. Table 14 illustrates that the concentrations of suspended solids at the inlet and outlet decline with the increasing concentration of charcoal up to 0.75 gm and above the stated amount, the suction pressure becomes insufficient. In this case, the reduction in suspended solid, droplets and the carcinogenic compounds in the inlet and outlet streams are also observed. The maximum achieved separation efficiency is 55.68%.

Both chemical and mechanical modifications
In case of both chemical and mechanical modifications, the filter to cigarette ratio is maintained at 1.5 and different ratios of charcoal and Zeolite-13X mixtures were (1:1, 1:2,1:3 and 1:4 ratio) prepared. These mixtures were positioned as shown in the schematic (Fig. 16). During the experimentation, the suction pressure was maintained at 10 kPa.
Table 17 clearly ensures that both chemical and mechanical modification depict the highest separation efficiency. It is further verified by performing the EDS analysis of the solid sample collected from the smoke after filtration. The EDS analysis (Table 16) corroborates the information reported in Table 17 qualitatively.

Consumer comfort
The word "taste" is used to indicate the user's satisfaction level after the modification of cigarette. This was determined by taking the feedback of the consumers after smoking of modified and unmodified cigarette. The testing was conducted with the help of a group of people who consumes cigarettes regularly and according to them, the satisfaction level after the use of modified cigarette was unaltered. The weight increments of the cigarette after modifications are presented in Table 18.

Discussion
For the identification of the efficient methodologies, a comparison has been performed among all (Table 19). For this, the suspended solid removal efficiency is considered as the parameter. The comparison indicates that the combined chemical and mechanical modification methodology separates significant amount of suspended solid from the smoke. However, for the combined case, beyond 1.5 g mixture, the suction pressure becomes insufficient. In addition to the above, the economic analysis also ensures that the increment in the price of the cigarette after modification is about 0.96-6.19 % (Table 20).

Conclusions
Experiments were conducted to investigate the modification methodologies which decline the cigarette's harmful effect without deteriorating its taste. Initially, the role of smoking parameters was disclosed, and then the chemical, mechanical and combined modification processes on the final quality of smoke were studied. Based on current experimental results, the followings are the conclusion:  1. Without any modification, the maximum separation efficiency is achieved if the suction pressure is maintained at 10 kPa and 135 s burning time is maintained. 2. The analysis of ash, flakes and smoke ensures that every stream contains carcinogenic elements in different forms. 3. The P-V analysis indicates that additional (63 ml) smoke goes into the lungs during cigarette smoking. However, only 500 ml comes out during expiration, and the remaining 63 ml comes out in the subsequent breathing. Due to this, the suspended solids and droplet containing 63 ml find sufficient time to settle. Furthermore, the discussed phenomenon enhances the settling velocity up to 5 × 10 4 times. 4. To avoid the distillation and condensation of cigarette smoke within the human body, L/U must be 0.15. 5. In mechanical modification, the optimum F/C ratio is found to be 1.5, and the achieved separation efficiency is 51.13%.  6. In chemical modification, the separation efficiency of 55.68% and 62.5% are achieved in case of charcoal and zeolite 13-X, respectively. 7. The separation efficiency of 66.51% is obtained in the case of combined modifications. 8. The economic analysis indicates that 4.74% rise in the actual cost and per cigarette, the increment in average weight is 0.114 g. Subscript a, Ash; A c , Cross-section area of the cigarette, 3.848 × 10 −5 m 2 ; A es , Surface area of equivalent sphere; A ps , Surface area of particle; d, Dry; e, Determined after EDS analysis; fu, Filter unit; p, Tobacco particle; r, Raw tobacco; r o , Radius of equivalent sphere; w, Wet or sample before drying; T 1 , Cigarette temperature, 1023 K; C P , Specific heat (cellulose with < 0.01 % ash), 1.27 J/ g K; T 2 , Surrounding temp, 298 K; V inspiration , Inspiration volume during smoking; V settling outside , Settling velocity in the environment; V settling in , Settling velocity in lungs; V suction , Suction volume during smoking Greek symbols ε c , Cigarette void fraction; ε fu , Filtering unit void fraction; ΔT, Temperature difference; ΔP, Pressure drop; σ, Stefan Boltzmann constant = 5.67 × 10 −8 J/s · m 2 · K 4 ; α, Void fraction; ϕs, Sphericity Author contribution SSM has conceptualized and designed the experiment. The experiments were carried out and the manuscript was written by KPRK.
Data availability Everything available in the manuscript.

Declarations
Ethics approval Not applicable.
Consent to participate Not applicable.
Consent for publication All authors agreed to publish.

Conflict of interest
The authors declare no competing interests.