ME 8883 Physical Properties of Paper MeasurementCobb test detailCobb test continuedContact angleContact angle equipmentContact angleContact angle detailWater absorbencyWVTR detailWVTR detailWVTR detailT 464 WVTR “Tropical” conditionsT 464 temperature set pointsHecules size testHercules size test detail1ME 8883 Physical Properties of Paper MeasurementLecture 14: Water Absorption Properties: Cobb, Drop Absorption/Penetration, Contact Angle, WVTR, SizingTest2This is the fundamental water absorption test for linerboard2 minutes is the usual duration of the testFor testing water barrier properties, 30 minutes is the test durationFor sized linerboard 100 gsm fro 30 minutes is a good valueFor coated/treated water resistant linerboard 40 and lower is a good value3The problem:wax replacement polymer coatings must be of sufficient thickness to cover the surface features of rough linerboardBottom of a coated box after an ice-pack trial Cobb test of coated paperHow can the coat level be reduced or made less costly ?4Issues with conventionally applied polymer coatingsNeed 10 gsm or more to cover the fibers, surface pits, air bubbles are a problemSEM shot of a polymer coated linerboard surface5Top polymer coatings made with drawdown Mayer rod, IR lamp dried Clay base coatings in this study were applied with a CLC 6000 coater, 2000 fpm, smooth rod applicator Mayer wire rod coater, rod size and coating solids determines the coat weight on a substrate, typically use <40% solids coating, #8 rod to get a coating about 10 gsmCalendering linerboard helps024681012141679111315Surface roughness P P S S-10 microns85909510 010 5110115Coat weight gmsCobb gms/30minWVTR gms/24hrsLinear (WVTRgms/24 hrs)Linear (Coatweight gms)Linear (Cobbgms/30 min)WVTR gms/24 hrsCobb, WVTR, coat weight versus the PPS of a coated kraft linerboard changed through increasing the density by calendering. Note that WVTR increases although the coating method is the same in all cases. 67However, calendering compromises other propertiesSTFI, Bending Stiffness, Predicted ECT versus PPSGM BS = 0.648 (PPS) - 0.81R2 = 0.93ECT lb/in = 1.69 (PPS) + 32.939R2 = 0.84STFI (lbs/msf) = 0.36 (PPS) + 19.6R2 = 0.462121.52222.52323.52424.52525.579111315PPS S-10 micronsGeometric mean Bending Stiffness (mN-m)0102030405060STFI lbs/inSTFI lbs/inBending Stiffness (N-m)Predicted ECT frommodelLinear (Bending Stiffness(N-m))Linear (Predicted ECTfrom model)Linear (STFI lbs/in)Physical properties of linerboard calendered to various densities (decreasing surface roughness) and coated with a #8 rod of a commercial aqueous polymer coating.8Difference with a clay base coating:Fiber crossings and pits are covered by the clay base coating, more uniform coverage with a top coatSEM top shot: clay base coat 13 gsm, polymer top coat 8 gsm, linerboard substrateThe small holes don’t matter for water passage but do let water vapor through9Cobb test detailRubber pad underneath sample, Rubber O-ring on top of sampleScrew down steel ring tightlyPour 100 cc of 23 degree de-ionized water, start timer,10Cobb test continuedWhen the time interval is up, drain the water, remove the sample place between blotters and roll twice with the roller to remove excess waterTake blotted sample to the balance, weigh to 4 figuresCobb value = (weight after interval – weight before) x 100 = gsm absorbed water11Contact angle1213Contact angle14Contact angle equipment Backlight Translation stageTelescope with crosshair reticle and protractor We now also have an automated video based goniometer “Fibrodat”– yet to be installed and set up15Contact angle16Contact angle detail Turn inner cross hair to be horizontal with the translation stage, the cursor will be on the left hand sideRead the interior drop angle using the outer cross hair adjustment17Use a digital pipette to make the droplet volumes required1819Water absorbencyLight source with condensing lensLight box has a light switch and a mirror for viewing droplet penetration underneath2021WVTR detail Use Vapometer cups, O ring on borrom of sample, another O ring on top of sample, secure seal by tightening screws in a clockwise fashion at least 2 rotations22WVTR detailSample for Vapometer cups are punched out using a mallet and a circular punch against a soft Plexiglas sheet23WVTR detailCaclium chloride dessicant is always kept at 105 degrees C in the dry oven,Recycled dessicant has to be “baked”at 205 degrees C prior to re-use24Vapometer cups filled with dessicant and sealed with test specimens are weighed upon assembly and again after 24 hours to determine the amount of absorbed moisture throughthe specimen per unit area25T 464 WVTR “Tropical” conditionsThe test is conducted in the Blue M over, environmental conditions are set using the dry and wet bulb temperature set-points26T 464 temperature set pointsDry bulb set at 37.8 deg CHold up/down arrows to change Wet bulb set at 36.3 deg C27Usually a 50/50 mix of 2% formic acid and Hercules green dye aremixed.Poured onto the specimen in its hlder and the timer started on the Hercules testerThe Hercules size tester measures the time taken for the underside of the sample to have its reflectance decrease due to the penertration of the green dye28Hecules size testEssnetiall a resiatncebridge circuit measures the drop in reflectivityThe bridge must be balanced before each test by adjustment of front panel knobs29Sample window light source and photocellsGalvanometer with red (set point) and black (signal level) hands.At start of test move red hand 5 points to left of zero switch on CALIBRATEAdjust CALIBRATE knob for zero with black cover and sample in sample holder on windowSwitch to TEST, set red hand to zeroSet REFLECTANCE knob to desired reflectance (usually 80%)Remove black cover from sample holderPour 10 ml of solution, switch to AUTO at the same timeTimer starts replace black cover30Place dye/formic acid mix in this metering squeeze bottle Sample holder, specimen is claped in this, machine direction along the handle lengthCalibration green and white tiles31Hercules size test