Experimental study on the drying of natural latex medical gloves

Transcription

1 IOP Conference Seres: Materals Scence and Engneerng PAPER OPEN ACCESS Expermental study on the dryng of natural latex medcal gloves To cte ths artcle: Mano Chankrachang et al 2018 IOP Conf. Ser.: Mater. Sc. Eng Vew the artcle onlne for updates and enhancements. Ths content was downloaded from IP address on 15/05/2018 at 08:43

2 Expermental study on the dryng of natural latex medcal gloves Mano Chankrachang 1, Pst Yongyngsakthavorn 1, Attaya Tohsan 2 and Udomkat Nontakaew 1, * 1 Department of Mechancal & Aerospace Engneerng, Faculty of Engneerng, Kng Mongkut's Unversty of Technology North Bangkok, Bangkok, 10800, Thaland 2 Department of Materals and Producton Technology Engneerng, Faculty of Engneerng, Kng Mongkut's Unversty of Technology North Bangkok Bangkok, 10800, Thaland * Correspondng Author: udomkat.n@eng.kmutnb.ac.th Abstract. The purpose of ths research was to study latex flm dryng at 70 ºC usng a laboratory dryng oven. Two dfferent total sold content (TSC) latex compounds, whch 45% TSC and 35% TSC were used. The undred latex flms were prepared accordng to the common procedures used n latex gloves manufacturers, that s, by dry coagulant dppng process. The expermental results such as ntal mosture content, the amount of mosture and dryng tme of latex flms n each latex compound formula were determned. After that, the results were projected to calculate on the producton capacty expand by 1 mllon pece/day of natural latex medcal gloves. Fnally, the rate of mosture enterng the latex dryng oven and the energy consumpton of the dryng oven were estmated. The results ndcated that when the 35% TSC of latex compound was used. The ntal mosture content of latex flm was hgher than 45% TSC of latex compound about 7%. The dryng tme of 35% TSC was longer than 45% TSC for 2.5 mn and consume more energy about 10%. As a result, the 45% TSC latex compound was the better way to savng energy and managng humdty n the producton lne. Therefore, t was found to very useful to an approxmate desgn length and sze of actual of latex dryng oven and the rate of mosture enterng the oven as well. 1. Introducton Nowadays, natural latex medcal gloves ndustry are wdely used n the clncal and medcal settng and for varous objectves, whch helps to protect the dsease nfecton or contamnaton. The man reasons of ncrement for usng the medcal gloves s due to people are now becomng more hygene awareness and want to be prevented them from mpurty and chemcals substance [1]. In ths way, the demand for latex rubber gloves ndustry s vewed to ncrease steadly. It s reported that a demand of medcal gloves s ncreasng around 5-10% per year [2]. Concentrated natural rubber (NR) latex s the man raw materal to produce the dppng products such as medcal glove, npple, hot/cold bag, balloon, sportng goods and so on. Thaland s the world largest producer and exporter of the concentrated latex, accountng for one-thrd of the total exports volume n the Content from ths work may be used under the terms of the Creatve Commons Attrbuton 3.0 lcence. Any further dstrbuton of ths work must mantan attrbuton to the author(s) and the ttle of the work, journal ctaton and DOI. Publshed under lcence by IOP Publshng Ltd 1

3 Nomenclature P W t W d W m W d W m n M r M M f Wd Producton rate of latex flms (g/s) Weght of undred latex flm from each former (g/pece) Weght of dry matter from each former (g/pece) Weght of mosture from each former (g/pece) The amount of dry matter enterng the oven (g/s) The amount of mosture enterng the oven (g/s) Number of formers enterng the oven (pece/s) The amount of mosture to be removed (g/s) Intal mosture content of latex flms (% wb) Fnal mosture content of latex flms (% wb) Weght of dry matter on ceramc plate (g) W m, t Q Q d Q m Q e T T f C pw Weght of mosture on ceramc plate at tme = t (g) Total heat energy requrement (kw) Sensble heat of dry matter (kw) Sensble heat of mosture (kw) Latent heat of vaporzaton of water (kw) Intal Temperature of latex flms (ºC) Fnal Temperature of latex flms (ºC) Specfc heat capacty of water (kj/kg K) C ps Specfc heat capacty of rubber h v (kj/kg K) Latent heat of vaporzaton of water (kj/kg) world [2]. Although, Thaland s the number one producer and exporter of concentrated NR latex but n term of the products of concentrated NR latex, for examples, medcal gloves, Thaland has the proporton only 22 percent of the world market. The man reason of the slow progress n the development of rubber product ndustry of Thaland s the lack of contnuous mprovement n research and development. The methods of makng medcal gloves va dppng process are conssted of the followng steps [2,3]: frst, a former s dpped nto the latex compound, wthdrawng a former, dryng and vulcanzng the latex flm, respectvely [4]. In all actualty, the dryng process s nvolved n the several producton lnes, for example: dryng process was appled to cleanng, dppng coagulant and latex compound, leachng and chlornaton secton. The hot ar was suppled to each dryng oven n order to remove mosture and also mantan the temperature of formers and latex flms properly. Thus, the dryng process not only takes nto account the dppng process producton lne but also consumes amount of heat energy n ths process more than 80% of total energy consumpton [3]. The objectve of ths work was to study latex flms dryng usng a laboratory dryng oven by measurng amount of mosture of latex flm on the ceramc plates. The latex flms were prepared accordng to the common procedures used n latex gloves manufacturers, that s, by dry coagulant dppng process. The expermental data were projected to calculate the rate of mosture enterng the actual latex dryng oven n the factory, and also determne dryng knetcs of the undred latex flm to antcpate how long s the undred latex flms keep stay n the actual dryng oven. Last, the heat energy requred for actual oven also calculated when the producton capacty expand by 1 mllon pece/day. Consequently, by conductng ths experment, we wsh to elucdate the energy of dryng characterstc of medcal rubber gloves, whch can be a great advantage for development of the gloves ndustry n Thaland. 2

4 2. Dryng Knetcs of Latex Flm The hot ar was suppled by varous heat sources such as thermal hot ol and fred burner that transferrng heat from a heat exchanger to fresh ar. The undred latex flm on the formers were enterng nto the latex dryng oven and the mosture content n the latex flms were removed to hot ar. The most mportant thng has to concern, whch determnes the flow rate of hot ar supply n the oven that could be mantaned the dryng knetcs of the latex flm frmly. Therefore, mass and heat balance were appled to ths study Mass Balance In order to ncrease the productve capacty to 1 mllon pece/day, t means that about 12 peces of glove must be pass through the latex dryng oven per second. Each of undred latex flm at ntal mosture content and temperature needs to be dred to a fnal mosture content at a temperature, thus the latex gloves producton rate nto the latex dryng oven can be calculated as follows: [5] P nw t (1) The weght of undred latex flm from each former conssts of weght of dry matter and weght of mosture n latex flm s calculated as follows: The rate of mosture enterng the oven s calculated as follows: W W W (2) t d m M P W m (3) 100 The rate of dry matter that passes through the oven s calculated as follows: Hence, the rate of mosture to be removed s calculated as follows: M W d P 1 (4) 100 M M f M r P (5) Heat Balance In the classcal concepts for dryng process the total heat requrement comes from 2 types of heat: [6] that s, the combnaton of sensble heat of mosture and dry matter, n ths case stand for dry rubber and latent heat of vaporzaton of mosture. For ths study, the rate of requred heat calculaton was focused on the rate of mosture and dry matter enterng the latex dryng oven. Other mechancal parts such as former holder, conveyor chan, dryng oven wall were neglected. Therefore, the rate of requred heat for dryng latex flms can be calculated as follows: 3

5 Heat Heat requred = Sensble heat of dry requred = matter to ncrease + temperature from T to T f Sensble heat of mostureto ncrease + temperature from T to T f Latent Heat requred to evaporate the mosture at temperature T f (6) (6) For ths model, e.g. 6 can be wrtten as follows: M M M M f Q P Cpd 1 Cpm T f T Ph v (7) The fnal dryng temperature of the latex flms was assumed to be 70 ºC referrng to the manufacturng procedure. A summary of the parameters used n the estmaton s shown n table 1. Table 1. Calculaton Parameters used for the dryng process. [6, 7] Parameter M f T T f C pm C pd h v n Parameter Value 5.00 % wb 25 ºC 70 ºC 4.19 kj/kg K 3.20 kj/kg K 2333 kj/kg 12 pece/s 3. Materals and Methods 3.1. Materal NR latex was an ammonacal latex contanng 0.7 % NH 4OH wth a dry rubber content (DRC) of 60 %, whch was purchased from Tha rubber latex publc Co., Ltd., Thaland. Potassum hydroxde dsperson, potassum laurate dsperson, sulfur dsperson, znc dbutyl dthocarbamate dsperson (ZDBC), wngstay-l dsperson and ZnO dsperson and calcum ntrate were prepared from the commercal grade reagents Latex Compoundng Preparaton The NR latex was strred at room temperature usng strrng speed of 300 rpm, then t was frstly mxed wth 20% Potassum laurate soluton and 10% Potassum hydroxde soluton whch were functoned as stablzer. Next, 50% sulfur dsperson, 50% Znc dbutyl dtho carbamate dsperson, 50% Wngstay L dsperson, 50% ZnO dsperson were respectvely added nto the latex mxture. Fnally, the DI water 4

6 was added to obtan TSC = 45% and 35% of latex compound, respectvely. The amount of the chemcals were lsted n table 2. After the mxng was completed, the latex compound was strred at 30 rpm for 24 hrs maturaton tme. Table 2. The amount of chemcals n 45% and 35% TSC latex compound Chemcals Undred weght (g) 45% TSC 35% TSC 60% Concentrated Latex % K-laurate soluton % KOH soluton % Sulfur dsperson % ZDBC dsperson % Wngstay L dsperson % ZnO dsperson DI water Flm Preparaton The undred latex flms were prepared accordng to the common procedures used n latex gloves manufacturers, that s, by dry coagulant dppng process. The ceramc plates that used n ths experment were cut from the palm and the back of the hand area of medcal gloves ceramc dppng formers. The szes were set on a 30 mm x 40 mm. It s mportant to clean up and dry n an oven before starng the experment. Frst, the clean ceramc plates were heated up at 60 C and dpped by usng 10% calcum ntrate as the coagulant and dred n an oven at 120 C for 5 mn then cooled down n desccator untl the temperature reached 60 C. Next, the ceramc plates were dpped nto the latex compound for 8 seconds. After reachng a dwell tme, the ceramc plates were slowly wthdrawn and nstantly weghted by an analytcal balance n order to record the ntal mass of undred latex flm. After that, the undred latex flm were dred n the oven wth a tme step equal to 2.5 mnute and weghted the latex flm agan also repeat the dryng process untl the mass of latex flm was constant to complete the experment. Thus, the mosture content of the latex flm at each tme step s calculated by rato between amount of mosture and the total weght of undred latex flm at each tme step as follows: 4. Results and Dscusson M W m, t t (8) Wt 4.1 The Amount of Mosture In ths study, two dfferent total sold content (TSC) latex compounds, whch 45% TSC and 35% TSC were used. From table 2, t s shown that DI water n 35% TSC latex compound was larger than 45% TSC latex compound 65.2 g or 125%. The surface area of ceramc plate was m 2. To fnd the total surface area of the medum sze medcal gloves former, the 3D scanner was used for measurng the surface area so that the dpped surface area of the former s about m 2. After calculatng the expermental data shown n fgure 1. The weght of mosture of 45% TSC and 35% TSC latex compound was about and g/pece and ntal mosture content of latex flms s about 50.37% and 56.91%, respectvely. As a result, the rate of mosture to be removed whch was calculated by usng e.g. (5) were about and g/s for 45% TSC and 35% TSC, respectvely. 5

7 12.5 W m M 60% % Wm (g/pece) % 30% 20% 10% M (%wb) % TSC latex flm 35% TSC latex flm 0% Fgure 1. W m and M value of each former dpped by 45% and 35% TSC latex compound 4.2 Flm Formaton and Dryng Tme Some prevous research [8 10], They ndcated that there are 3 steps of the latex flms formaton. Step 1, a lnear cumulatve mosture loss occurs overtme and ends when rreversble contact between latex partcles s acheved. Durng ths moment, the evaporaton rate s smlar to the evaporaton of pure water. The mass transfer lmtaton s localzed n the gaseous phase [8, 11]. Step 2, Latex partcles deform and come nto close contact wth so-called honeycomb structure, whch s assocated wth a sharp decrease n the water evaporaton rate. The overall rate of evaporaton decreases consderably [8]. Step 3, a homogenous flm s formed and the evaporaton rate strongly decreases and the mass transfer lmtaton s also clearly wthn the flm. The remanng mosture leaves the flm by dffuson through the ar/dred latex layer nterphase [8, 11] In ths experment, the weght of undred latex flms on the ceramc plates and dryng tme were recorded. The result of change n mosture content of the latex flm dpped by 45% TSC and 35% TSC compound were represented n fgure 2. Each of mosture content value was calculated by e.g. (8), whereas the cumulatve mosture loss of the latex flm dpped by 45% TSC and 35% TSC compound were shown n fgure 3. The amount of mosture loss at each tme step were recorded and counted to plot the cumulatve mosture loss. 6

8 60% Mosture Content (%wb) 48% 36% 24% 12% 45% TSC 35% TSC 0% Dryng Tme (mn) Fgure 2. Change n the mosture content of the latex flm dpped by 45% TSC and 35% TSC latex compound 0.25 Cumelatve mosture loss (g) % TSC 35% TSC Dryng Tme (mn) Fgure 3. Change n the cumulatve mosture loss from latex flm dpped by 45% TSC and 35% TSC latex compound From the expermental data, t was observed that, when the dryng tme ncreased from mn, the mosture content and cumulatve mosture loss are dramatcally decreased and ncreased, respectvely. It can be seen that, when dryng tme s reached 5 mn for 45% TSC and 7.5 mn for 35% TSC, a constant weght of latex flm was detected. These results can be explaned that the mosture content of latex flm and the humdty rato of hot ar were balanced. In term of the flm formaton, the honeycomb structure was completely formed and become to a homogenous flm. Consequently, the 5 mn and 7.5 mn dryng tme from dpped latex flm by 45% TSC and 35% TSC latex compound was appled n ths study. 7

9 4.3 Energy Requrement As the prevous secton, the rate of requred heat for dryng latex flms was focused on the latex flm. Other mechancal parts were not ncluded. In order to ncrease the producton capacty expand by 1 mllon pece/day, the bg problem that has to deal wth the massve of mosture n the undred latex flm. The rate of requred heat n e.g. (7) was calculated by usng parameters value from varous research [6,7,11] about kw and kw for 45% TSC and 35% TSC, respectvely. For more detals, the rate of requred heat was dvded nto three parts as follows from e.g. (6), sensble heat of dry matter, sensble heat of mosture and latent heat of mosture to evaporate. Sensble heat of dry matter was about kw for 45% TSC and kw for 35% TSC compound. Smlarly, sensble heat of mosture was about kw for 45% TSC and kw for 35% TSC compound. Meanwhle, latent heat of mosture to evaporate was about kw for 45% TSC and kw for 35% TSC compound. As a result, t should be noted that the latent heat of evaporaton takes on an mportant role about 86% of the rate of requred heat as shown n fgure 4. 45% TSC latex flm 35% TSC latex flm The rate of heat (kw) Qd Qm Qe Fgure 4.The rate of requred heat for dryng latex flm dpped by 45% and 35% TSC latex compound 5. Concluson For ths study, the amount for mosture enterng, dryng tme and total energy usage of latex dryng oven were determned. The effect of dfferent TSC of latex compound causes mpact to the ncrease of energy consumpton about 10% and dryng tme for 2.5 mn. It also affects to expand the whole length of producton lne as well. At the present, the most of latex compound formula try to reduce operatng cost by reducng TSC of latex compound. The energy supply for dryng oven also has to ncrease nevtably. Therefore, t was found to be very useful to an approxmate desgn length and sze of actual of latex dryng oven and the amount of mosture enterng as well. Acknowledgement Ths research was funded by and the Thaland Research Fund (TRF) (Project No. RDG ). 8

10 References [1] Ken Research 2017 Global Natural Latex Gloves Industry In-depth Investgaton and Analyss Report (Inda) [2] Thaplastc (Plastcs Insttute of Thaland) 2014 Rubber ntellgence unt (Bangkok) [3] DEDE (Department of Alternatve Energy Devolpment and Effcency) 2007 Project on Studyng of Energy Effcency Index n Rubber Industry (Thaland) [4] Sadur R and Mekhlef S 2010 Appl. Energy 87 pp [5] Ghaly A E and Macdonald K N 2012 J. Eng. Appl. Sc. Publ. Onlne 5 pp [6] Cengel Y A and Boles M A 2006 Thermodynamcs: An Engneerng Approach (McGraw-Hll) [7] Kl S 2006 Prog. Org. Coatngs [8] Steward P a., Hearn J and Wlknson M C 2000 Collod Interface Sc. 86 pp [9] Kedde J L and Routh A F 2010 Fundamentals of Latex Flm Formaton Processes and Propertes (New York: Sprnger Dor) [10] Ludwg I 2008 Dryng, Flm Formaton and Open Tme of Aqueous Polymer Dspersons (Demand: Unverstätsverlag Karlsruhe) [11] Bouyer D, Phlppe K, Wsunthorn S, Pochat-Bohater C and Dupuy C 2009 Technol