BIO-RESOURCE, PAPER AND COATINGS TECHNOLOGYSCHOOL OF INDUSTRIAL TECHNOLOGY UNIVERSITI SAINS MALAYSIA

IWA 383/2PAPER TECHNOLOGY LABORATORY II

Experiment 3 : Chemical Effects in Kraft Pulp Recycling Group : 5

Group Members: Lee Ying Fang 107979 Farid Aiman Bin Nasir107970 Mohd Arif Bin Mohamad Samsudin 107990

Lecturer: Dr. Arniza bt Ghazali

1. AbstractThe main concept of this experiment is to determine the chemical effect in Kraft pulp recycling.The type of recycled paper used is paper from Kraft pulp.The paper sample was tear into small piecess and soak into four litres of water for at least four hours before disintegration.Somehow,when the first soaking hour is up,the water is adjusted to the appropriate desired pH by using diluted acid HCL and NaOH.The group which deal with chemical hydrogen peroxide(H2O2) and alkaline peroxide (AP),the pH is maintain by resultant pH.Then, the sample is disintegrated by disintigrator at 5000rpm and diluted the pulp slurry to 0.3% consistency with filtered tap water and stir the diluted stock to ensure proper mixing.The stock consistency and pulp freeness is then determine before forming handsheets in 400 ml total fluid. The optical,mechanical and physical testing is carried out such as brightness, opacity,thickness, tensile strength, bursting strength, tearing resistance and folding endurance as recommended by the standard TAPPI procedure.Thus the amount and quality of fibre bonding is the most important factor affecting the strength. Increased in bonding caused by chemicals used also contribute in increasing the tensile strength as the fibre contact area is increased.2. IntroductionPaper recycling basically is the process of reused by taking the required fibrous raw materials (pulps) and non- fibrous component (additives),treat and modify each furnish constituent, and then combined all the ingredients continuously and uniformly into the papermaking stock to produce paper.Usually for the enhancing the strength of paper, it will mixed with fresh wood pulp or virgin pulp due to its long fiber properties. There are three categories of paper that can be used as feedstock for making recycled paper which are mill broke, pre-consumer waste, and post-consumer waste. Paper cannot be recycled over and over again because since it turns into secondary fibers, the strength properties surely will be drops due to case of fiber shortening. That is why virgin pulp (long fiber) is usually mixed with recycled paper to support back the strength properties of the paper. The repulping of the recycled paper is different from the virgin pulp pulping process. More steps of removal contaminants are required to make sure the pulp will be free from impurities. This is due to the raw material used in recycle paper is secondary fiber which contain ink, stickiest, adhesive and etc. Thus, repulping process of secondary fibre consume more chemical and high energy than virgin pulp pulping process. Repulping is an important part for papermaking process because it will affect the final yield for papers especially the strength properties. The purpose of repulper is to produce low consistency pulp slurry usually ranges from 4.5-5% to broken down fiber particles, and rendering the pulp more uniform. There is no cutting action on fibers.Optional chemicals such as NaOH, HCL, AP or H2O2 are added by observing percentage of fibers swelling to improve slushing by absorbing water to separate the fibers and thus high temperature are not required, unless there is significant level of wet strength additive presents. In general, the pulping process is continuous thus it will be agitated to form a slushy pulp of fiber. In pulping system, the concept of disintegrated is done by vortex and shear forces which cause the fibre to separate. The shearing forces only causing the fiber to swell due to water absorption and tend to separate.In addition, the present of chemicals will contribute to the disintegrating of fibres. The vortex intensity is dependent on pulp consistency. Thus, it provides more fiber separation, control the level of consistency and increase uniformity of stock. One noticeable effect of repulping is the spectacular alter on dewatering properties of the pulp. Pulp freeness (CSF) is rapidly reduced as repulping proceeds, mainly due to the increased concentration of fines. The freeness testing is to measure the freeness of pulp stock and stage of absorption water for pulp. The pH value for the aqueous medium is usually alkaline. The alkalinity results in the softening and swelling of the paper fibers by saponification or hydrolysis which has to be carefully determined for each furnish. The brightness increases with increasing pH but too high pH will cause decrease in brightness. This phenomenon, called alkali darkening, has been determined as due to the formation of chromophores in lignin. In the acidic condition, low pH will also cause low brightness as acidic condition prevents the water penetration inside fibre, hence, the fibre may not swell and the fiber will hard to disintegrate into individual fibres. When the pH is neutral, there are no much different in brightness. Thus, a careful balance is required in maintaining the right pH so that the fibers soften and swell up, hydrogen peroxide performance is improved and formation of chromophores is minimized. The handsheets was cut according to Figure 1 in Appendix B. Test of normal tensile, folding endurance, burst, tearing strength, brightness and opacity were carried adapted from TAPPI 220.i. Bursting StrengthSpecimen was placed and clamp between two concentric platens of Mullen tester, with each having a circular opening in the centre. Pressure was applied to the underside of the specimen by a rubber diaphragm which expands by the hydraulic pressure showed by the pressure gauge.ii. Tensile StrengthSpecimen was aligned and clamps between two jaws neatly an upper, moveable jaw and a lower, stationary jaw. The upper jaw traverses upward at a constant rate when the test started. The load (N) is recorded when the specimen break and calculated the tensile strength (N/m), tensile index (Nm/g) and breaking length (km).iii. Tearing ResistanceMovable pendulum sector arc of Elmendorf tear test was fixed prior test in position from which it can be released. The test specimen was fastened (a pile of 2 or 4 sheets) between the two clamps with the bottom edge against nicely to the clamp bottom. An initial slit was made and the sector arc was released from its fixed position. The energy required to tear the specimen (mN) was recorded and the tear index based on the number of sheets used was calculated.iv. Folding EnduranceThe spring-loading jaw of the MIT testes was pressed with the appropriate weight (0.5-1.5 kg) and fastened the screw to fix jaw at level. The upper edge of the specimen strip was clamped to the spring-loading upper jaw and the bottom edge was clamped to the oscillation folding head firmly and neatly. The fold counter was reset and the screw of the upper jaw was released. Folding test was started and recorded the folding endurance as a number of double folds as shown by the counter.

3. Natural phenomenon Recycling means repulp the fibers so many times and has been thought the fibre swelling capability, and the flexibility of fibres will be reduce. The restricted swelling of recycled fibres has beenscribed tohornification. Hornification imply both a reduction in the amount of water that fibers hold within their cell walls, and also a tendency for rewetted fibers to be stiffer and less conformable than before being subjected to drying or other kinds of stresses.Hornification also can be used when cellulosic fibers are subjected to other kinds of stresses, including heating without drying as long as there is a simultaneous loss of water-holding ability and strength potential.According to this concept the process of repulping tends to open up submicroscopic spaces within the lamellar structure of the fiber cell walls.Evidence of fibrillation during repulping includes swelling in the thickness direction of fibers and also an increase in wet fiber flexibility. In repulping system, the concept of disintegrated is done by vortex and shear forces which cause the fibre to separate. The shearing forces only causing the fiber to swell due to water absorption and tend to separate. The vortex intensity is dependent on pulp consistency. In addition, the present of chemicals will contribute to the disintegrating of fibres.The chemical added cause the fiber to swell. During the repulping process, the higher pH (alkaline condition) is more preferable. This is because alkaline condition promotes the fibers to swell easily than acidic condition. When the fibers swell, the water absorption of fibers increase, thus the fibers become more flexible to disintegrated into individual fiber. 4. Methodology4.1. Materials and apparatusPaper from Kraft Pulp, HCl (1.2M), NaOH, H2O2, pH meter, filtered tap water or deionised water, pail, 1L plastic beaker, disintegrator, analytical balance, handsheet making equipment.4.2. Procedures1. The provided papers made from kraft pulp were examined. Their features such as colour, coarseness in comparison to the given A4 papers were recorded. Their brightness, opacity and thickness were measured. The papers density was determined from the grammage value.2. With clean hands, the provided samples were tore down to small size of 1.5cmx1.5cm. Moisture content was determined.3. 48g OD of sample in (1) was weighed and soaked in 4L water for at least 4 hours. When the first soaking hour is up, the suspension was stirred and had it pH measured. Observation was recorded. The pH was controlled to desired values. The pH value for every hour was recorded.4. The suspended pulp was disintegrated at 5000rpm. Colour was recorded. Pulp slurry was diluted to 0.3% consistency and stirred well.5. The consistency of pulp stock for forming handsheet in 400ml total fluid was calculated. Stock consistency was adjusted accordingly. The pH of the prepared stock solution was measured. Colour change was recorded.6. After pulp freeness was determined, handsheet was made in the amount recommended by the standard TAPPI procedure.7. The wet handsheet which adheres on the blotting paper was dried by placing the wet handsheet and the blotting paper on the hot plate. A dry blotting paper was put on the wet handsheet and the handsheet was dried by ironed. After the handsheet was fully dried, the hot dry handsheet was removed from the blotting papers and cooled down in a desiccator for 10 minute. A dry 100ml beaker was placed in a digital analytical balance and the tare button was pressed. The dry handsheet was taken out from the desiccator and was placed into the tared beaker. The weight of the handsheet was written down to the nearest 0.01g.8. The drying and weighing steps were repeated until a constant weight was obtained. The pulp consistency was calculated based on the weight of the moisture-free handsheet. Based on the pulp stock consistency calculated earlier:i. The volume of pulp stock required for producing a handsheet with 60 grammage (60g/m2) was calculated orii. The volume of the water which should be added or removed from the pulp stock in order to adjust the consistency to 0.30% was calculated.9. The mesh and cylinder of the handsheet machine was cleaned and the cylinder was then locked tightly. The pulp stock in the bucket was stirred thoroughly and the required volume of pulp stock was immediately measured by using a graduated cylinder. The measured amount of the stock was poured into the sheet machine (cylinder) and the start button was pressed to fill the cylinder with water. At the same time, the graduated cylinder was rinsed with water and the rinsed was poured into the sheet cylinder.10. The handsheet machine automatically release air bubble when the water reach to the required level and then the water was drained out from the handsheet cylinder to form a wet sheet on the mesh. The cylinder was immediately unlocked and opened after the water had drained from sheet. Two pieces of standard blotting papers was placed on the drained sheet. The flat couch plate was laid centrally on the blotting papers and couch roll was placed gently on the middle of the plate. Without applying other pressure, the roll was rotated backward and forward for five complete roll within the range of 8 to 12 seconds. After that, the roll was lifted. The handsheet, blotters and covering couch plate was removed from the wire mesh. The sheet was adhered to the underside of the lower blotter. The blotter with the adhered handsheet (handsheet side up) was placed on two fresh blotters and was located centrally on the press plate by using the press template. The handsheet was covered with a polish plate (polished side down) and followed by two fresh blotters which was ready to receive next couch blotter and handsheet. The mesh in the sheet machine in positioned was washed by turning on the water, occasionally the surface of the mesh was rubbed with fingertips, and then the next test sheet was made as described. About 10 sets of blotters, handsheet and plate were stacked in the press plate.11. For first pressing, the cover of the press was placed in position and the wing nuts were screwed hand-tight. The 1st cycle button was pressed and the pressure increased to 435kPa (50psig) in 30 seconds for duration of 5 minute. After the first pressing, the whole stack was removed to one side. The plate and the sheet (handsheet side up) were laid centrally on two dry blotters by using the press template as a guide. The sheet was covered with two blotters and the plate, sheet and blotters was laid continuously. The order of the sheet was reversed in the second pressing. The cover was placed on position as before and the pressure was raised within 30 second to 345kPa (50psig) for 2 minute.12. The stack was removed from the press and each plate with the handsheet was fitted into the drying rings. The edge of each handsheets was ensured to be in contact with the rubber of the next ring above it. A heavy weight was placed on the pile of rings after the whole stacks were fitted on the rings. The sheets were dried in a standard conditioning room (as specified in TAPPI 402: 502% RH and 231C). The sheets were left to become fully dried in position in the rings before they were removed from the plates.13. Steps 2 to 12 is repeated using 24 od weight of pulp for second recycling stage along with 2L of water for soaking.4.3. Paper testing procedures4.3.1. Bursting StrengthSpecimen was placed and clamp between two concentric platens of Mullen tester, with each having a circular opening in the centre. Pressure was applied to the underside of the specimen by a rubber diaphragm which expands by the hydraulic pressure showed by the pressure gauge.4.3.2. Tensile StrengthSpecimen was aligned and clamps between two jaws neatly an upper, moveable jaw and a lower, stationary jaw. The upper jaw traverses upward at a constant rate when the test started. Recorded the load (N) when the specimen break and calculated the tensile strength (N/m), tensile index (Nm/g) and breaking length (km).4.3.3. Tearing ResistanceMovable pendulum sector arc of Elmendorf tear test was fixed prior test in position from which it can be released. The test specimen was fasten (a pile of 2 or 4 sheets) between the two clamps with the bottom edge against nicely to the clamp bottom. An initial slit was made and the sector arc was released from its fixed position. The energy required to tear the specimen (mN) was recorded and the tear index based on the number of sheets used was calculated.4.3.4. Folding EnduranceThe spring-loading jaw of the MIT testes was pressed with the appropriate weight (0.5-1.5 kg) and fastened the screw to fix jaw at level. The upper edge of the specimen strip was clamped to the spring-loading upper jaw and the bottom edge was clamped to the oscillation folding head firmly and neatly. The fold counter was reset and the screw of the upper jaw was released. Folding test was started and recorded the folding endurance as a number of double folds as shown by the counter.5. Function of Chemical UsedNaOH : To maintain the alkalinity of the solutionHCl : To maintain the acidity of the solutionH2O2 : Using hydrogen peroxide to delignify chemical pulp requires more vigorous conditions than for brightening mechanical pulp. Both pH and temperature are higher when treating chemical pulp. The chemistry is very similar to that involved in oxygen delignification, in terms of the radical species involved and the products produced. Hydrogen peroxide is sometimes used with oxygen in the same bleaching stage and this is gives the letter designation Op in bleaching sequences. Metal ions, particularly manganese catalyse the decomposition of hydrogen peroxide, so some improvement in the efficiency of peroxide bleaching can be achieved if the metal levels are controlled

6. Results and Discussion6.1. Comparison on features of kraft and A4 paperBased on Table 1, kraft paper has darker colour compared to A4 paper since the virgin pulp of kraft paper undergo unbleached kraft chemical pulping process. Additionally, this causes kraft paper to have lower brightness value, 18.12% compared to A4 paper, 86.47% since A4 paper is usually used on printing and writing purposes, while A4 paper also have smoother surface compared to kraft paper since it contains more additive like starch to prevent flaking due to its commercial usage. Meanwhile, opacity for both papers is about the same along with their thickness. However, A4 paper has higher grammage and density compared to kraft paper because the fibre content found in single sheet of A4 paper is more than kraft paper. This is because the fibres in A4 paper undergo better fibre consolidation and bonding due to its commercial purpose.

Table 1: Comparison on features of kraft paper and A4 papersType of paperColourBrightnessCoarsenessTappi Opacity, %Print Opacity, %Grammage, g/mThickness, mmDensity, g/cm

Kraft paperBrown18.12Slightly rough92.3996.6351.990.08760.59

A4 paperWhite86.47Smooth91.1793.1972.720.09950.73

6.2. First recycling processIn this experiment, group 5 used kraft pulp that had undergone alkaline disintegration using alkaline peroxide with 0.5% NaOH and 0.6% H2O2.6.2.1. CFS Freeness testingBased on Graph 1, pulp freeness value for group 2, 3, 5, 6 and 7 shows higher freeness value compared to group 1. This is because disintegrate kraft paper under acidic condition promotes delignification causing lignin removal as acidic condition made the hydrolysis of lignin to be easier. The presence of cellulose which have hydroxyl group will absorb water giving lower freeness value. Meanwhile, other group uses either neutral or alkaline pH to disintegrate the pulp where there will be less water absorption since there are still lignin content surround the cellulose.

Graph 1: Pulp freeness among groups

6.2.2. Optical propertiesBased on Table 2, the increase in pH caused increase in brightness of kraft paper under alkaline condition for alkaline peroxide shown by group 7, 26.08%. This is because pH has an effect on water penetration into the fibre whereby the fibre will swell. The increase in pH will also give deinking effect where there will be removal of ink from pulp giving brighter handsheet. Other than that, the alkaline condition with presence of peroxide will also provide delignification resulting less light absorption by chromophores. Meanwhile, low pH will prevent water penetration into fibre and high pH will cause the fibre to be slippery. In acidic condition, low pH caused lower brightness since acidic condition prevents water penetration whereby group 1 has the lowest brightness value, 23.46%. This is because there is no fibre swelling due to the fibre pores does not enlarge and the fibres are not slippery resulting absent formation of foams. Moreover, neutral pH does not give much different in brightness value since the condition is neither alkaline nor acidic. On the other hand, opacity for group undergo alkaline recycling process has lower value compared to those in acidic conditions (Graph 2). This is because soaking pulp in alkaline condition promotes fibre swelling where the fibres will be more flexible and this improves the bonding ability between fibres. The fibres will have better comformability giving better bonding and less light scattering during the handsheet formation. Thus, there will be lesser light being scattered around the fibres giving lower opacity for handsheet produced from acidic recycling.Furthermore, brightness of non-recycle handsheet has lower brightness than recycled ones (Table 1)(Table 2). This is because the usage of chemicals either acid or alkaline will give delignification effect causing the reduction in chromophoric structure that absorbs blue light. On the contrary, pulp that undergo recycling under neutral pH does not show much changes since there is less swelling effect experience by fibres.Table 2: Final pH value of pulp stock for handsheet making and brightnessGroup 1234567

Condition Acidic Neutral Alkaline Neutral Alkaline Alkaline Alkaline

Chemicals HClNaOHNaOHH2O2APAPAP

Final pH value4.077.257.116.4010.1210.5410.22

Brightness, %23.4623.3923.4323.9822.7023.5626.08

Graph 2: Tappi and print opacity of handsheet among groups

6.2.3. Physical propertiesInitially, non-recycled kraft paper posses density, thickness and grammage with values 0.59 g/cm, 0.0876 mm and 51.99 g/m respectively. Based on Graph 3, the thickness for handsheets from all groups is about the same since similar disintegration is carried our which is 5000rpm resolution whereby the rate of fibres distribution is quite similar from each other. Meanwhile, group 7 has the least thickness, 0.1290 mm compared to other group because the pulp undergo greater revolution compared to other groups causing greater fibre dispersion and fibre consolidation. However, all the recycled kraft paper shows increment in thickness value compared to non-recycled ones. This is because the rate of revolution undergone by recycled pulp is insufficient to break the pulp into individual fibres causing the stacking of fibres resulting voids in between fibres. Next, density and grammage (Table 3) for group 4 indicates the highest value that the porosity in the handsheet is lower than other group and the fibre undergo better hydrogen bonding with each other due to higher contact area. Meanwhile, handsheet from group 1 has the lowest density and grammage compared to other group because kraft recycling in acidic condition inhibits fibre swelling causing lesser fibre contact area along with less chemical bonding. This creates voids between the fibres. In contrast, there is reduction in density compared to non-recycled kraft paper with value 0.59 g/cm due to weaker fibre consolidation since the pulps had undergone acidic chemical treatment.

Table 3: Grammage of handsheet among groupsGroup 1234567

Grammage, g/m59.3960.9164.5070.5064.3460.4260.97

Graph 3: Density and thickness of handsheet among groups

6.2.4. Mechanical propertiesBased on Graph 4, the strength properties such as tensile index, tearing index and burst index of recycled handsheet of kraft paper increased as pH increased because alkaline pulping condition will promote fibre swelling. This can be observed from handsheet produced by group 5, 6, and 7. Water molecules will penetrate into the fibre wall causing the fibre to swell and increase the flexibility of fibre. This increament in fibre flexibility allow the improvement of fibre comformability during handsheet formation resulting the contact area and bonding between fibres to increase as well. In addition, the treatment of pulp with alkaline peroxide gives better pulp strength due to better delignification compared to other condition. Thus, the strength properties of handsheet will increase. Likewise, paper recycling at lower pH gives lesser strength increment due to lack of fibre swelling and less delignification effect. However, group 1 shows higher tensile index even though the pulp undergo acidic recycling process. This is due to error in setting up the experiment and pulp contamination. Furthermore, folding endurance for paper undergo neutral recycling carried out by group 2 and 3 is lower compared to those undergo alkaline recycling because there is hardly any changes in fibre properties since neutral condition does not lead to any fibre swelling. Handsheet undergone alkaline peroxide recycling such as group 5, 6 and 7 will have better folding endurance because the fibres in handsheet are flexible due to water absorption and delignification leading to increment of fibre flexibility. Overall, there is reduction in burst index and folding endurance of recycled handsheet (Graph 4) compared to non-recycled kraft paper whereby burst index and fold endurance of non-recycled kraft paper is 3.08 kpa.m/g and 13.8 folds respectively. This is because there is some loss in fibre strength after recycling causing the bursting effect of recycled handsheet decrease. Same goes to the folding properties of recycled handsheet since the fibre strength decrease and the handsheet produced is brittle compared to non-recycled ones. Pulp that undergoes neutral disintegration does not show much change in their properties.Meanwhile, tensile index for recycled handsheet also decreased in general compared to non-recycled ones, 35.49Nm/g. This is because there is some reduction in fibre length by slushing during disintegration causing less contact area for bonding after recycling. However, the tearing index of recycled handsheet shows increment in value compared to non-recycled ones, 6.78mN.m/g due to the increase in fibre flexibility since it undergoes chemical processing resulting swelling of fibre especially in alkaline treatment. Thus, force applied during tearing will distribute to larger area causing more work required to overcome the frictional force.

Graph 4: Mechanical properties of handsheet among groups

6.3. Comparison between first and second recycling6.3.1. Optical propertiesBased on Graph 5, there is increased in brightness value after secondary recycling compared to first recycling. This is because the fibre had undergo further chemical process by lignin removal where the chromophoric structure is reduced causing the light absorption reduce significantly. In other words, NaOH, H2O2 and alkaline peroxide gives reduction in chromophoric structure or the alternation of chromophoric structure.Based on Graph 6, there is reduction of opacity value for tappi and print opacity after second recycling. This shows that further chemicals usage during pulp disintegration shorten the fibre length since the fibres is experiencing hornification effect because the fibres had undergone several recycling stages. However, the contact area between adjacent fibres increased since fibres moved closer to each other due to fibre shortening. This gives less light scattering due to lower porosity between fibres. Other than that, the removal of lignin in alkaline treatment exposed cellulose chain causing the fibres to be more flexible results better consolidation during handsheet formation. This gives lesser light scattering effect.

Graph 5: Brightness of handsheet among two recycling stages

Graph 6: Opacity of handsheet among two recycling stages6.3.2. CSF Freeness testingBased on Graph 7, the pulp freeness increased gradually after second stage recycling. Although pulp that undergoes alkaline treatment can experience swelling and water absorption, but the fibre undergoes second recycling stage does not show much swelling power. This is because the fibres has experienced hornification effect whereby the bonding between fibres is not broken during rehydration process due to high degree of crosslinking between microfibril during the drying of handsheet after first recycling process. Thus, fibre only swells to certain extent causing less swelling and flexibility.

Graph 7: Freeness of pulp stock among two recycling stages6.3.3. Mechanical propertiesBased on Graph 8, most of the tensile index of handsheets after secondary bleaching reduced. Although alkaline peroxide treatment can improve the mechanical properties of handsheet by delignification, subsequent recycling of pulp caused hornification whereby fibre will lose its swelling ability resulting from previous drying effect. In addition, these dried fibres will lose their comformability and swelling capacity causing less interfiber bonding. The lack of fibre bonding causes reduction in fibre contact area resulting weak handsheet produced. Furthermore, acidic treatment on pulp gives further lignin and cellulose hydrolysis resulting fibre losses its strength and bonding strength. Thus, the tensile index of handsheet reduced after second recycling whereby the ability for the test sample to resist rupture has lessened.Based on Graph 9, burst strength and folding strength of handsheets decreased after second recycling. This is because the hornification effect after subsequent recycling and drying caused the fibre to loss its ability to absorb water causing the fibre swell to certain extent only. Since this phenomenon caused reduction in interfibre bonding, burst strength of handsheet after second recycling drops since the fibres unable to withstand the pressure applied onto the handsheet. Meanwhile, the folding strength of handsheet decreased after second recycling occurred because the fibre has loss its flexibility since the fibre unable to swell during the rehydration process as there is no breaking of bond from fibres. The latter fibre appears to be stiffer.Furthermore, tearing strength of handsheet produced from second recycling also decreased slightly compared to first recycling because the effect subsequent drying from previous paper making process caused thermaldegradation of cellulose chain. Besides, the frequent chemical treatment caused the fibre to become brittle and lack of flexibility as well as loss in bonding strength since the fibres only swell to certain extent. This caused the handsheet produced to be rigid and the force applied onto handsheet during tearing test only focus on small region resulting less work required to overcome the frictional force between fibres.

Graph 8: Tensile strength of handsheet based on two recycling stages

Graph 9: Mechanical properties of handsheet based on two recycling stages

6.3.4. Physical propertiesBased on Graph 10, the density of handsheet produced after second recycling are about the same since there is less fibre swelling occured to improve the interfibre bonding after rehydrating of the pulp sheet. Meanwhile, the same thing goes to thickness of handsheet as well where the consolidation of fibre is at its minimum due to rigidity of fibre because the bonding between fibres is not broken even the pulp sheet had undergone rewetting process. However, the thickness of handsheet after second recycling still shows slight decrement since the weak fibres undergo shrinkage during drying process whereby hydrogen bond formed between fibres even though the strength is weaker.

Graph 10: Density and thickness of handsheet based on two recycling stages6.4. Colour feature of kraft paper

Top kraftTest

LLightness61.5860.79

ARedness6.184.01

bYellowness19.8115.61

7. Calculations7.1. Alkaline Peroxide (AP) Recycling First and Second Recycling

1. 0.5% NaOH Weight of pulp (OD) = 48g Weight of NaOH required, g

2. 0.6% H2O2 Given H2O2 = 10% Weight of full strength bleach charge (A)

Weight of chemical in 100ml solution (C) = 10g H2O2 Volume of chemical solution required

7.2. Handsheet Making (First Recycling)OD weight of bleached pulp from second stage bleaching = 48gMoisture content = 58.42%Weight of wet pulpWater in wet pulp=115.44-48.00=67.44g=67.44ml

To Achieve Consistency 0.3% for HandsheetVolume pulp = 16 000mlTotal volume required = 16 000ml.: Volume of water needed to add= 16 000 4000 67.44=11932.56mlHandsheet TestingWeight of pulp pad = 1.05g.: The new volume of pulp required to produce 1.2g handsheet:7.3. Pulp Freeness Testing (First recycling)Corrected CFS Freeness at 0.3% ConsistencyTemperature of pulp stock = 29OCVolume of water = 530ml.: value to be subtracted = 37Pulp OD weight, g = 2.61g, volume used for freeness testing = 1000ml

Pulp freeness consistency.: Based on T227, points of freeness to be subtracted = 28Thus, correct CFS at 20OC, 0.3% consistency= 430-37-28=465ml7.4. pH change during pulp soaking (First Recycle)Time (hour)pH

010.73

110.47

210.35

310.27

410.12

Observation : pulp turn from dark brown to light brown after soak with alkaline peroxide

7.5. Handsheet Making (Second Recycling)OD weight of bleached pulp from second stage bleaching = 24gMoisture content = 61.56%Weight of wet pulp61.56Water in wet pulp=62.43 - 24.00=38.43g=38.43mlTo Achieve Consistency 0.3% for HandsheetVolume pulp = 8 000mlTotal volume required = 8 000ml.: Volume of water needed to add= 8 000 2 000=6 000 mlHandsheet TestingWeight of pulp pad = 1.2305g.: The new volume of pulp required to produce 1.2g handsheet: 400ml

7.6. Pulp Freeness Testing (Second recycling)Corrected CFS Freeness at 0.3% ConsistencyTemperature of pulp stock = 29OCVolume of water = 510ml.: value to be subtracted = 38Pulp OD weight, g = 2.72g, volume used for freeness testing = 1000mlPulp freeness consistency.: Based on T227, points of freeness to be subtracted = 21Thus, correct CFS at 20OC, 0.3% consistency= 510 - 38 - 21=451ml

7.7. pH change during pulp soaking (Second Recycle)Time (hour)pH

010.85

110.68

210.54

310.35

410.23

Observation : pulp turn from light brown to yellowish-brown after soak with alkaline peroxide

7.8. Handsheet Testing7.8.1. First recycling7.8.1.1. Physical properties

I. Weight SamplesWeight (g)

11.2879

21.2992

31.2360

41.2892

51.3213

Average1.2867

II. Thickness SampleThickness (mm)Average

12345

10.13710.17830.14000.13250.13780.1451

20.14290.17290.14240.13130.15500.1529

30.13590.14560.13110.13090.14340.1374

40.20090.14500.13540.14280.13310.1514

50.17810.14400.14980.14200.14400.1516

Average sum of 5 samples thickness0.1477

III. Grammage where area of handsheet=0.02m2SampleWeight (g)Grammage (g/m)

11.287964.40

21.299264.96

31.236061.80

41.289264.46

51.321366.07

Average1.286764.34

IV. DensitySampleWeight (g)Volume (cm)Density (g/cm)

11.28792.9020.4438

21.29923.0580.4249

31.23602.7480.4498

41.28923.0280.4258

51.32133.0320.4358

Average1.28672.9540.4356

Volume, cm = (0.02 m x 100 cm) x (thickness, mm x 0.1 cm)

7.8.1.2. Mechanical properties

I. Tensile Strength*paper width=15mm=0.015m

, where um --> kg/m (divide by 9.807)

SampleLoad, NExtension, mmTensile strength, N/mGrammage, g/m2Tensile index, Nm/gBreaking length, km

120.33.71353.3364.4021.022.14

219.73.41313.3364.9620.222.06

319.23.4128061.8020.712.11

417.92.71193.3364.4618.511.89

512.11.5806.6766.0712.211.25

Average17.842.941189.3364.3418.531.89

II. Tear Resistance

SampleTear strength (mN)Grammage, g/m2Tear index (mN.m2)/g

1509.94664.407.9184

2542.21164.968.3468

3504.06261.808.1563

4502.10664.467.7894

5515.83066.077.8073

Average514.83164.348.0017

III. Folding EnduranceSampleFolding Endurance

15

24

33

44

55

Average4.2

IV. Burst Testing

1kgf/cm = _X98.0665_> kPa

SampleBurst strength, kgf/cm2Burst strength, kPaGrammage, g/m2Burst index, kPa.m2/g

12.058201.8264.403.13

21.392136.5164.962.10

31.725169.1661.802.74

41.654162.2064.462.52

51.579154.8566.072.34

Average1.682164.9564.342.56

7.8.2. Second recycling7.8.2.1. Physical properties

I. Weight SamplesWeight (g)

11.2017

21.1959

31.2386

41.2570

51.2623

Average1.2311

II. Thickness SampleThickness (mm)Average

12345

10.14970.12360.13920.14470.13790.1408

20.20250.13610.13350.14330.13660.1505

30.14470.13610.14420.13690.13020.1387

40.13930.14300.13670.13230.14780.1400

50.14300.14580.14110.13580.13520.1404

Average sum of 5 samples thickness0.1419

III. Grammage where area of handsheet=0.02m2SampleWeight (g)Grammage (g/m)

11.201760.085

21.195959.795

31.238661.930

41.257062.850

51.262363.115

Average1.231161.555

IV. DensitySampleWeight (g)Volume (cm)Density (g/cm)

11.2017200.4267

21.1959200.3976

31.2386200.4471

41.2570200.4496

51.2623200.4502

Average1.2311200.4338

Volume, cm = (0.02 m x 100 cm) x (thickness, mm x 0.1 cm)

7.8.2.2. Mechanical properties

I. Tensile Strength*paper width=15mm=0.015m

, where um --> kg/m (divide by 9.807)

SampleLoad, NExtension, mmTensile strength, N/mGrammage, g/m2Tensile index, Nm/gBreaking length, km

115.32.11020.0060.08516.981.731

214.22.1946.6759.79515.831.714

317.92.11193.3361.93019.271.965

418.83.11253.362.85019.942.033

510.51.5700.0063.11511.091.131

Average15.342.181022.6761.55516.611.694

II. Tear Resistance

SampleTear strength (mN)Grammage, g/m2Tear index (mN.m2)/g

1418.74460.0856.96919

2490.33359.7958.20023

3467.77761.9307.55332

4445.22262.8507.08388

5450.12563.1157.13183

Average454.44061.5557.38769

III. Folding EnduranceSampleFolding Endurance

13

22

34

44

53

Average3.2

IV. Burst Testing

1kgf/cm = _X98.0665_> kPa

SampleBurst strength, kgf/cm2Burst strength, kPaGrammage, g/m2Burst index, kPa.m2/g

11.508147.88060.0852.461

21.357133.08059.7952.226

31.463143.47061.9302.317

41.488145.92062.8502.322

51.397136.99963.1152.171

Average1.443141.51061.5552.299

7.8.3. Brightness and opacity of handsheet from first and second recycling

8. ConclusionBased on the experiment conducted, the effect of chemicals on subsequent paper recycling shows reduction in papers properties in terms of strength but the brightness of paper after recycled shows increment after treated with chemicals. The reduction in papers strength is due to hornification effect causing the fibres unable to swell and flexible. Thus, rapid recycling process under chemical treatment cause the paper properties to be lower since there is lack of interfiber bonding between fibres. Meanwhile, paper brightness increases because there is reduction in chromophoric structure and delignification effect by the chemicals used.However, the strength properties of handsheet produced from first recycling still shows increment compared to non-recycled ones since chemical used like alkaline peroxide promote better delignification compared to normal alkaline treatment. Even so, other condition also showed increment in paper strength but the impact is not as obvious as alkaline peroxide treatment.

9. Reference1. http://www.ncsu.edu/bioresources/BioRes_02/BioRes_02_4_739_788_Hubbe_VR_Recycling_Cellulosic_Fibers_Review.pdf2. http://upcommons.upc.edu/e-prints/bitstream/2117/6356/1/effects-of-drying.pdf3. Gary A. Smook, second edition, Handbook for Pulp & Paper Technologists.4. http://www.cellulosechemtechnol.ro/pdf/CCT1-3-2009/p.65-69.pdf5. Wistara, N. and R. Young, Properties and treatments of pulps from recycled paper. Part I. Physical and chemical properties of pulps. Cellulose, 1999. 6(4): p. 291-324