Lignin based waste Biomass from Paper mill- A potential substitute for replacing Carbon black to produce Green Rubber Product Dr. R.K. Jain*, Dr A.K. Dixit*, Mrs A.V.Janbade*, Dr N. Shukla # and Dr. Rajkumar # ------Lignin, a naturally occurring poly phenolic biopolymer is generated as a waste biomass from pulp and paper industry. Depending on the nature of raw material and pulping conditions used the nature of lignin laden black liquor generated is varied and becomes a major concern for small paper mills. However, conventionally the black liquor containing dissolved lignin is used as a source of energy and recovering chemical in a process called chemical recovery which also serves the purpose of pollution abatement.
The technological development and promotion of Cleaner & Greener technologies, the paper industry have been using Oxygen Delignification & low kappa pulping to reduce the generation of pollutant in the discharging effluent. As a result these mills are generating more black liquor and it has become difficult for them to manage this extra black liquor due to limited capacity of Chemical Recovery System. Central Pulp and Paper Research Institute (CPPRI) has been doing research on debottlenecking of the capacity of the Chemical Recovery System by way of partial removal of lignin from the black liquor so that load on chemical recovery could be reduced. Thus this provide an opportunity to generate this valuable bio polymer as a by-product.
Due to inherent chemical nature and functional groups present in the lignin it is felt that it may find application in rubber industry. In view of this CPPRI in association with Indian Rubber Manufacturer’s Research Association (IRMRA), studied the possible application for replacement of carbon black in rubber product and the findings were highly encouraging. It has been found that it improved certain important properties of rubber products beside helping in conserving energy during curing and masticating. The present paper highlights the joint efforts made by CPPRI and IRMRA in application of lignin based waste biomass from paper industry in rubber manufacturing & substitution of carbon black in rubber thereby reducing petroleum based product and helping in producing green product.
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• *Central Pulp & Paper Research Institute Saharanpur • #Indian Rubber Manufacturer’s Research Association, Thane
Introduction
Lignin is a complex natural polymer characterized by wide range of functional groups. It is known for its chemical versatility and is considered as an excellent starting material for conversion into value added products that find use in various industrial applications including the rubber industry. Indian Rubber Industry has been growing along with the strength and importance, as a part of India’s burgeoning role in the global economy. India is the world’s biggest producer and third largest consumer of natural rubber. Rubber is normally used in auto tires, cycle tires, shoe and other miscellaneous uses. Automotive tire sector is the major consumer of rubber (50% of total consumption) followed by cycle tires and footwear. Styrene Butadiene Rubber or SBR is a general purpose elastomer that is widely used in the rubber industry. However SBR is non-polar and non-crystalline with low gum tensile strength. Hence fillers like carbon black are added to improve the physico-mechanical properties of SBR. During manufacturing of carbon black hazardous air pollutants (HAP) like carbon di-sulphide, carbonyl sulphide and hydrogen cyanide are produced. These hazardous air pollutants cause health hazard to human beings. Further carbon black after oxidation causes generation of carbon di-oxide which creates detrimental effect on environment and living organisms. Lignin a naturally abundant wood derivative obtained as a by-product of the paper industry possesses strong mechanical properties and is known to have a potential as partial substitute for carbon black.
There are more than 800 pulp and paper mills producing around 15 million tons of paper. A major portion of this production (64%) is coming from waste paper and remaining (36%) from virgin pulp produced from wood and agro residue based mill. These mills based on wood and agro residue & around 150 in numbers are pulping fibrous raw material employing drastic alkaline conditions at high temperature to separate fibre and lignin. Lignin is dissolved in hot alkaline conditions and gets separated as lignin rich black liquor. Due to promotion of green technologies and mounting pressure from pollution authorities these mills are adopting low kappa pulping and oxygen delignification in order to reduce pollution load generated from bleaching section. As a result these mills are generating more black liquor per ton of pulp comparing to mills following traditional pulping methods. Black liquor is highly colored & polluting liquid and traditionally is being managed in Chemical Recovery System. Installation of chemical recovery system is highly capital intensive and capacity expansion in the existing system is also not possible. Therefore it has become difficult for these mills to manage this extra black liquor due to limited capacity of Chemical Recovery System.
Looking in to above Central Pulp and Paper Research Institute (CPPRI) has been doing research work on marginal expansion of the capacity of the Chemical Recovery System by way of partial removal of lignin from the black liquor so that quantity of black liquor to be processed in chemical recovery could be reduced. This provide an opportunity to generate this valuable bio polymer as a by-product from paper mills. Lignin produced as by product was characterized and modified at CPPRI and send to IRMRA for its application studies in Rubber industry. IRMRA has conducted studies on utilization of this lignin as a replacement of carbon black in Styrene Butadiene Rubber (SBR). The present paper highlights the results obtained in the above mentioned joint study conducted by CPPRI and IRMRA.
Materials and Methods Black liquor used for the studies was collected from two mills located in Northern and Central part of India. The black liquor was subjected to lignin separation process developed by CPPRI and lignin was generated. Samples of lignin were send to IRMRA for utilization in rubber industry. Another sample of lignin was derived as by product from bio ethanol process. A paper mill waste lingo cellulosic waste was utilized for bio fuel generation. The residual biomass which is around 40% of the biomass was modified for application in rubber industry.
Results and Discussions
Partial Separation of Lignin from Black Liquor
Black liquor collected from mill was subjected to lignin removal and partial lignin was separated. Black liquor was subjected to acidification to reduce pH for lignin separation. pH was reduced to around 2.0 by addition of Sulphuric acid. Precipitated lignin was allowed to settle and separated through filtration. Lignin was washed and dried and was subjected to mechanical treatment for powdering and to obtain uniform size. The lignin powder was passed through 100 mesh for uniform size and to obtain higher surface area.
Table 1 shows the characteristics of as received black liquor and after lignin separation.
Table 1 Characteristics of Black Liquor S. Parameter Before LRP After LRP No. 1 Total solids, % w/w 8.53 7.23 2 pH, at room temperature 12.05 2.30 3 Inorganics as NaOH, % w/w 33.29 43.02 4 Organics, % w/w 66.71 56.98 5 Silica as SiO2, % w/w 3.11 3.97 6 Sodium as Na, % w/w 15.80 17.78 7 Potassium as K, % w/w 3.25 4.15 8. lignin , % w/w 28.5 6.5
The above indicates that more than 75% lignin is separated from black liquor. Dry solids concentration of the black liquor is also reduced by 15%. This shows that by adopting LRP we can marginally increase the capacity ( 15%) of the chemical recover system by reducing dry solids load. Other parameters of the black liquor have shown this black liquor after mixing with the untreated black liquor can effectively used in chemical recovery system.
Characterization of Black Liquor and Biomass Lignin
Lignin separated from black liquor and received as residual biomass of bio ethanol production were characterized prior to application in SBR. Table 2 and 3 shows this lignin analysis marked as lignin 1 and lignin 2 respectively.
Table 2 Analysis of Black Liquor Lignin Parameter Lignin – 1 Ash, % w/w. 32.37 Lignin Purity, , % w/w. 54.76 Inorganics as NaOH, , % w/w. 18.30 Organics (BY difference) 81.70
Sulphate as SO 4, , % w/w. 18.39 Iron as Fe, µg/gm 32.40 Lead as Pb, µg/gm 0.91 Chromium as Cr, µg/gm 1.65
Table 3 Lignin Rich Residual Biomass from Scarification of Bagasse Pith
Parameter Lignin – 2 Ash, % w/w. 28.14 Lignin Purity, , % w/w. 58.9 Inorganics as NaOH, , % w/w. 16.39 Organics (BY difference) 83.61 Sulphate as SO 4, , % w/w. 0.91 Iron as Fe, µg/gm 89.90 Lead as Pb, µg/gm 1.82 Chromium as Cr, µg/gm 18.60
The above results indicate that impurities like Fe, lead etc. are in traces and this lignin can be tried in rubber industry.
Utilization of Lignin in Styrene Butadiene Rubber Manufacturing
Central Pulp & Paper Research Institute submitted above two samples of Lignin marked as Lignin sample 1 and Lignin sample 2 for evaluation in rubber compound at Indian Rubber Manufacturer’s Research Association. IRMRA conducted study regarding the use of lignin and evaluating its potential in rubber compounding. Results obtained are shown in table 4, 5 & 6.
Table 4 Application of Lignin Rich Residual Biomass from Rice-Straw
Ingredients Blan 100% 5phr 10phr 50:50 100% k Black Lig1 Lig1 Lig1 Lig1 SBR1502 100 100 100 100 100 100
Zinc Oxide 3 3 3 3 3 3
Stearic Acid 2 2 2 2 2 2
SRF Black 0 50 50 50 25 0 (N774) Lignin 0 0 5 10 25 50
TDQ 1 1 1 1 1 1
CBS 1.5 1.5 1.5 1.5 1.5 1.5
TBBS 1.5 1.5 0.5 0.5 1.5 1.5
Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 Table 5 Application of Lignin from Agro-based Black Liquor Ingredients Blank 100% 5phr 10phr 50:50 100% Black Lig2 Lig2 Lig2 Lig 2 SBR1502 100 100 100 100 100 100
Zinc Oxide 3 3 3 3 3 3
Stearic Acid 2 2 2 2 2 2
SRF Black 0 50 50 50 25 0 (N774) Lignin 0 0 5 10 25 50
TDQ 1 1 1 1 1 1
CBS 1.5 1.5 1.5 1.5 1.5 1.5
TBBS 1.5 1.5 0.5 0.5 1.5 1.5
Sulfur 1.5 1.5 1.5 1.5 1.5 1.5
Table 6 Impact of Lignin on Properties of SBR rubber Compound
Properties Blank 100% 5phr 10phr 50:50 100% 5phr 10phr 50:50 100% Checked Black Lig1 Lig1 Lig1 Lig1 Lig2 Lig2 Lig2 Lig 2 Rheometric Properties at 160°c MH (Lbs. inch) 59.75 86.39 70.03 73.37 46.03 32.50 80.65 77.37 44.08 13.53 ML(lbs. inch) 7.61 12.76 11.19 12.9 11.64 11.78 12.03 12.65 8.99 6.44 Ts2 (minutes) 8.83 3.58 2.63 2.11 1.92 2.62 4.16 4.23 4.06 8.63 Tc90 14.64 9.17 7.37 7.25 5.19 6.84 10.59 11.85 15.30 34.14 (minutes) Slab Molded 15 10 8 8 6 7 11 12 16 35 at 160°c for (mints.) Surface finish Ok OK Ok Ok Minor Rough Ok Very small Very Rough & Sticky, air bubbles Adhering to mold of cured defects Sample Physical Properties 100% 9 27 19 24 16 9 20 19 Modulus (kg/cm 2) 300% 16 118 70 75 28 13 83 69 Modulus (kg/cm 2) Tensile 18 159 125 139 77 17 178 158 Strength (kg/cm 2) Elongation@ 350 370 470 500 750 710 510 530 Break Hardness 46 66 62 66 62 49 63 64 (Shore-A) Tear Strength 14 60 62.2 68.5 43.5 17.3 64.6 64.6 (kg/cm)
Studies on application of lignin as replacement of carbon black in rubber industry were conducted on different replacement ratio starting from 10% to 100% replacement. Both the lignin sample has shown encouraging results.
Studies conducted with biomass lignin are shown in table 4 & 6 have shown following advantages over carbon black.
i. It reduces curing time, so there will be reduction in time during molding and ultimately production rate will increase ii. Nearly 35% curing time is decreased at same conditions indicating 35% reduction in energy consumption.
iii. It also reduces the viscosity of rubber compound and thus helps in energy reduction required to masticate/process the compounding during mixing and molding stage, thus it saves energy.
iv. Elongation, tear strength and hardness of rubber compound also improve
v. Hardness of rubber compound decreases.
Studies conducted with black liquor lignin are shown in table 5 & 6 have shown following advantages over carbon black.
i. It reduces curing time, so there will be reduction in time during molding and ultimately production rate will increase and energy demand will be reduced.
ii. Scorch time is high therefore such compounds after mixing can be stored for long time at room temperature before further processing on the same.
iii. It also reduces the viscosity of rubber compound and thus helps in energy reduction required to masticate/process the compounding during mixing and molding stage, thus it saves energy.
iv. Elongation, tear strength and hardness of rubber compound also improve
v. Hardness of rubber compound decreases.
Conclusion
The studies conducted on application of waste lignin generated as by product in paper industry have shown encouraging results. It is observed that curing time is decreased indicating less energy demand and higher throughput. Reduced viscosity of rubber compound help in reduction of energy required during masticate and compounding. Elongation, tear strength and hardness of rubber compound also improve. The studies have shown lignin biomass, a waste product of paper mill can be effectively used in SBR rubber as a replacement of carbon black.
Replacement of carbon black by waste byproduct of paper mill i.e. Lignin reduces use of petroleum based product and helping in producing green product.
Acknowledgement The authors express their sincere thanks to Petroleum Conservation Research Association, New Delhi for providing financial support to CPPRI for conducting the study.