Experimental investigation into the cushioning properties of ...

Packaging Technologyand Sciencewhere e is the compressive strain of honeycombpaperboard; s is the compressive stress of honeycombpaperboard; and E is the deformation energyper unit volume, where compressive strain is e.With rapid changes of market requirements andescalating competition, honeycomb paperboardmanufacturers frequently and swiftly need toupdate their cushioning pad structure to meetthe low-cost demands of industrial packaging.However, manufacturers always provide acommon honeycomb paperboard structure to theirclients, not because of their production capacity,but because of a lack of basic knowledge of materialcushioning properties. This work is intendedto assist a packaging designer to produce a honeycombpaperboard pad design that represents thelowest cost for clients.The main aim of this paper is to research theeffect honeycomb paperboard structures, relativedensity of paper honeycomb cores, liners andlayouts of cushioning pads have on cushioningproperties. A further objective is to establish abasic and fundamental knowledge of cushioningproperties of honeycomb paperboards.EXPERIMENTAL METHODSD.-M. WANG AND Z.-W. WANGSamples of different heights (10, 20, 30, 40 and50 mm), different kraft liners (250, 300, 350 g/m 2basis weights), different basis weights of the honeycombcell-walls (112, 127, 150,180 g/m 2 ; the correspondingthickness of the honeycomb cell-wallswere 0.20, 0.22, 0.25, 0.29 mm, respectively) anddifferent honeycomb cell types (A, B, C and D; thelengths of the honeycomb cell-walls were 5.8, 8.7,12.1, 14.4 mm, respectively) were made.The experiments were conducted at theShenzhen Control and Test Centre for PackagingQuality and Packaging Test Centre of ShenzhenPolytechnic. The test equipment included a KBFtest chamber for constant temperature and constanthumidity (manufactured by Binder Company,Tuttlingen, Germany) condition, and a CMT universalmaterial tester from SANS Company (locatedin Shenzhen, China). The reference test standardsinclude Testing Method of Static Compression forPackage Cushioning Materials GB8168–87; 7 PolymericMaterials, Cellular Flexible – Determination of StressstrainCharacteristics in Compression – Part 1: LowdensityMaterials ISO 3386/1; 8 Packaging – TransportPackages – Temperature and Humidity ConditioningISO 2233–1986; 9 and Paper, Board and Pulps – StandardAtmosphere for Conditioning and Testing ISO187:1990. 10All test samples were approximately 200 ×200 mm 2 . The tests were conducted in an environmentof 23 ± 1°C, 50 ± 2% relative humidity, andunder a constant displacement velocity of 12 ±2 mm/min. Every compression test was effectivelyconducted in five repeats, and the mean value calculatedfrom the five test values is shown in thestress–strain curves of Figures 2, 3, 7, 9 and 11.EXPERIMENTAL SAMPLESAND RESULTSCushioning properties of paperhoneycombs with and without linersThe structure of experiment samples is shown inFigure 1. The experiment samples and characteristicsare listed in Table 1. 180B paper honeycombcore indicates the honeycomb cell is B type, andthe basis weight of base paper made into paperhoneycombs is 180 g/m 2 . 450/180B/450–50 indicatesthat the basis weights of the liners bondedto 180B paper honeycomb are 450 g/m 2 and theheight of paper honeycomb core is 50 mm. Figure2 shows the effect of liners on the cushioning propertiesof honeycomb paperboard. The stress–straincurves of paper honeycomb cores with and withoutliners are similar, but the strength of the paperFigure 1. The structure sketch map of experiment samples.Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

INVESTIGATION INTO THE CUSHIONING PROPERTIESPackaging Technologyand ScienceTable 1. Experiment samples and characteristicsSamplesPaperhoneycombcoreLiner(g/m 2 )LinerpresentHeight(mm)180B-50 180B – No 50450/180B/450–50 180B 450 Bonded 50150B-40 150B – No 40300/150B/300-40 150B 300 Bonded 40Stress σ /MPaa0.50.450.40.350.30.250.20.150.10.050180B-50450/180B/450-500 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Strain εStress σ /MPaStrain ε(a) 180 B-50 (b) 150 B-40b0.50.40.30.20.1300/150B/300-40150B-4000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Figure 2. Comparison of paper honeycombs with and without liners.honeycomb core with liners is significantly largerthan that of without liners. However, a recentpaper 11 shows that the compressive strength ofmetallic honeycomb with and without liners typicallydoes not change. It can be concluded that theeffect of liners on the compressive strength of honeycombpaperboard must be taken into considerationand that of metallic honeycomb can be ignored.This is because the restrictions of liners on paperhoneycombs play an important role in the bucklingof the paper honeycombs.Cushioning property comparison forhoneycomb paperboard withdifferent densitiesThe relative density of paper honeycomb cores isdetermined by honeycomb structure factors, e.g.thickness and length of cell-wall and drawingangle. The relative density 12 of hexagonal paperhoneycombs isρc= ⎛ tρ ⎝ ⎞ 1 + hl(2)⎠s l ( hl+sinθ)cosθwhere r c is the density of paper honeycomb cores;r s is the density of base paper made into paperhoneycombs; t is the thickness of the base papermade into paper honeycombs; l is the length of thesingle-cell-wall of hexagonal honeycomb; h is thelength of the double-cell-wall of hexagonal honeycomb;and q is the drawing angle of paper honeycombcores, here, q = 30°.The experimental samples and their characteristicsare listed in Table 2. The experimental resultsare shown in Figure 3. Figure 3 illustrates thatrelative density has a significant effect on cushioningproperties. With the increase of relative density,the compressive stress significantly increases.Therefore, when optimizing honeycomb paperboardstructures, we can increase the relativedensity of paper honeycomb cores; however, thisincreases costs.Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

Packaging Technologyand ScienceD.-M. WANG AND Z.-W. WANGTable 2. Experiment samples and characteristicsSamplesRelativedensityr c /r sHoneycombcoreHeight(mm)Liner(g/m 2 )Energyper unitvolume E(N/m 2 )Density(kg/m 3 )250/150A/250 0.066 150A 20 250 0.1619 64.6350/180B/350 0.051 180B 20 350 0.1154 66.6250/150B/250 0.044 150B 20 250 0.0929 51.4250/150C/250 0.032 150C 20 250 0.0637 44.2350/150D/350 0.026 150D 20 350 0.0523 50.6Stress σ /MPa0.40.320.240.160.08250/150A/250350/150B/350350/150C/350250/150D/250250/180B/25000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Strain εFigure 3. Effect of relative density of paper honeycombcores on the cushioning properties of honeycombpaperboards.Energy abosorption perunit volume E/N/m 20.180.160.140.120.10.080.060.040.0200.02 0.03 0.04 0.05 0.06 0.07Relative density r c /r sFigure 4. Relationship between the maximum deformationenergy per unit volume and the relative density of paperhoneycomb cores.Research on cushioning properties of paper honeycombcores with different relative density isimportant to reduce cost. The relationship betweenmaximum deformation energy per unit volumeand relative density of paper honeycomb cores isshown in Figure 4.A further research is to determine the relationshipbetween the maximum deformation energyper unit volume and the density of honeycombpaperboard, which can directly evaluate the cushioningcost. The density r of honeycomb paperboardcan be written aswhere r is the density of honeycomb paperboard;r f is the basis weight of liner; S is the load area,here, S is 7850 mm; 2 H is the height of paperhoneycomb core; and t 1 is the thickness of theliner – here, t 1 is enough less than H, so we oftenignore t 1 in Equation 3.r s can be described by basis weight r ss of the basepaper for paper honeycombs asρ = ρ t (4)sssFrom Equations 3 and 4, we obtainρρ + ⎛ ρ + ρ⎝ ⎜ c ⎞2 fρ ⎠⎟ ρ sH2 fScSHsρ ==St+H t + H( )1 1(3)ρ =ρρ + ⎛ ⎝ ⎜ ⎞ρ ⎠⎟ ρsH2 fcssHt(5)Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

INVESTIGATION INTO THE CUSHIONING PROPERTIESPackaging Technologyand ScienceAccording to Figure 2, the relationship betweenthe maximum deformation energy per unit volumeand the density of honeycomb paperboard isshown in Figure 5.Figures 4 and 5 show that the relative density ofpaper honeycomb cores has a significant effect onthe maximum energy absorption of honeycombpaperboards. With the increase of the relativedensity, the maximum energy absorption increases.However, there is no direct relation between themax deformation energy per unit volume andthe density of honeycomb paperboard. In fact, thebasis weight of the liners has a significant effect onthe stiffness of honeycomb paperboard. Therefore,we can improve the cushioning property ofhoneycomb paperboard by increasing the relativedensity of paper honeycomb core, and improve thestiffness by increasing the basis weight of liners.Cushioning property of multilayerhoneycomb paperboardThe experimental samples and their characteristicsare listed in Table 3. The mode of the compressiveEnergy abosorption perunit volume E/N/m 20.180.160.140.120.10.080.060.040.02040 50 60 70 80Density of honeycomb paperboard r/kg/m 3Figure 5. Relationship between the maximum deformationenergy per unit volume and the density of honeycombpaperboard.load is shown in Figure 6. The cushioning propertiesof multilayer honeycomb paperboard agreewith the stack theory, 13 and the strain e of multilayercushioning materials isε = αε 1 + βε 2 (6)where e is the strain of multilayer honeycombpaperboard; e 1 , e 2 is the strain of two monolayerhoneycomb paperboards; and a, b is the thicknessproportion of two monolayer honeycomb paperboardin total thickness.Figures 7 and 8 show the difference betweenmultilayer and monolayer honeycomb paperboards.During compression on multilayer honeycombpaperboards, the one with the lower strengthis always crushed first, and then the other. Thestrength of the 10 + 10 mm multilayer is significantlylarger than the 20 mm monolayer; however,the strength of the 20 + 10 mm multilayer is partlylower than the 30 mm monolayer, even though the20 + 10 mm multilayer possesses two additionalliners. In energy absorption, the deformationenergy of the 20 + 10 mm multilayer is also lowerthan the 30 mm monolayer honeycomb paperboard.Therefore, the cushioning and energyabsorption properties of multilayers are not alwayshigher than monolayer honeycomb paperboardsof the same total thickness. It must be noted thatthe compressive stress–strain of the 20 + 10 mmmultilayer has a second peak, which can withstandsecond impacts.aFigure 6. Load and stack confi guration of honeycombpaperboard. (a) multilayer; (b) monolayer.bTable 3. Experiment samples and characteristicsSamples Paper honeycomb core Liner (g/m 2 ) Height (mm)250/127B/250-30 127B 250 30250/127B/250-20 127B 250 20250/127B/250-10 127B 250 10Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

Packaging Technologyand ScienceStress σ/MPaa0.30.250.20.150.10.05010mm+10mm20mm0 0.2 0.4 0.6 0.8Strain εStress σ/MPab0.40.320.240.160.0800 0.2 0.4 0.6 0.8D.-M. WANG AND Z.-W. WANGStrain ε20mm+10mm30mm10mm20mmFigure 7. Comparison of multilayer and monolayer honeycombpaperboard. (a) 10 ± 10 mm stack; (b) 10 ± 20 mm stack.Energy absorption per unit volumeE /(N/m2)0.140.120.10.080.060.040.02010 20 10+10 20+10 30Height of honeycomb paperboard H/mmFigure 8. Energy absorption histogram of multilayer andmonolayer honeycomb paperboards.Cushioning properties of honeycombpaperboards with different heightsThe experimental honeycomb paperboards havedifferent heights (10, 20, 30 and 50 mm, respectively)and with the same 127B paper honeycombcore and 350 g/m 2 liner. The compressive stress–strain curves are shown in Figure 9.The 30 mm height honeycomb paperboard has ahigh critical stress; the 10 mm height honeycombpaperboard has a high plateau stress; and the20 mm height honeycomb paperboard has thelowest cushioning ability. From theory, the ratio ofthe height of honeycomb paperboard to length ofhoneycomb cell-wall has an effect on its cushioningproperties when the ratio is less than four. 14The above results agree with this theory 14 anddynamic compression test results from the document.3 Therefore, properly selecting the height isvery important to improve the properties of honeycombpaperboard.Cushioning properties of honeycombpaperboard with differentcompressive directionsThe three load directions of honeycomb paperboardare shown in Figure 10. The 150B paperhoneycomb core with 50 mm height bonded toliners was used in the experiment. The compressivestress-strain curve is given as Figure 11.The three orientation compression results showthat the flat compressive stress is significantlyhigher than the side and vertical compressivestress, and the side and vertical orientation energyabsorptions are similar and smaller.CONCLUSIONSMany experiments were conducted to investigatethe cushioning properties of honeycomb paperboard.The liners, density, height of honeycombpaperboard, multilayer honeycomb paperboardand compressive orientations have been discussedin detail.The stress–strain curves of honeycomb coreswith and without liners are similar, but the strengthand energy absorption of paper honeycombs withliners is significantly larger than those of withoutliners.Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

INVESTIGATION INTO THE CUSHIONING PROPERTIESPackaging Technologyand ScienceStress σ/MPa0.30.250.20.150.10.0500 0.2 0.4 0.6 0.8 1Strain εH=50H=30H=20H=10Figure 9. Stress–strain curves of honeycomb paperboards with differentheights.flat0.15sideverticalsideverticalStress σ/MPa0.10.05flatFigure 10. Load direction.The relative density of paper honeycomb coreshas a larger effect on the cushioning property ofhoneycomb paperboard. Changing the structure orincreasing the relative density of paper honeycombscan improve the cushioning properties.However, the basis weight of the liners has littleeffect on the cushioning properties of honeycombpaperboards.The energy absorption of the multilayer honeycombpaperboard is not always higher than themonolayer honeycomb paperboards, although itpossesses two additional liners.The height of honeycomb paperboard has aneffect on its cushioning properties; therefore, properlyselecting its height is beneficial to optimizingproperties.The flat compressive stress is significantly higherthan the side and vertical, and the side and verticalorientation energy absorptions are similar andsmaller.00 0.1 0.2 0.3 0.4 0.5Strain εFigure 11. Three orientation compressions of 50 mmhoneycomb paperboard.ACKNOWLEDGEMENTSThe authors are grateful to Dr Wang Wenming ofHelisheng (Guangzhou) Paper Products Company andgeneral manager Wang Shangduan of Jinglong PaperHoneycomb Products Company for their help in theexperiments.REFERENCES1. Wang M. The research of the honeycomb fibreboardcushioning performance and the application. Packag.Eng. 2000; 21(4): 5–9 (in Chinese).2. Zhang GM. Study on the buffering property of thehoneycomb board. Packag. Eng. 2001; 22(5): 7–9 (inChinese).Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts

Packaging Technologyand Science3. Guo YF, Zhang JH. Shock absorbing characteristicsand vibration transmissibility of honeycomb paperboard.Shock Vib. 2004; 11(5): 521–531.4. Sek M, Rouillard V. High-speed videographic studyof engineered composite paperboard cushioningsystems. Proceedings of the 15th IAPRI World Conferenceon Packaging. Tokyo, Japan, 2006; 258–262.5. Sek M, Rouillard V. Behaviour of multilayeredcorrugated paperboard cushioning systems underimpact loads. Appl. Mech. Mater. 2005; 3–4: 383–388.6. Miltz J, Gruenbaum G. Evaluation of cushion propertiesof plastic foams compressive measurements.Polym. Eng. Sci. 1981; 21(15): 1010–1014.7. GB 8168. Testing Method of Static Compression forPackage Cushioning Materials. China, 1987 (inChinese).8. ISO 3386/1. Polymeric Materials, Cellular Flexible – Determinationof Stress–strain Characteristics in Compression– Part 1: Low-density Materials. 1986.D.-M. WANG AND Z.-W. WANG9. ISO 2233. Packaging – Transport Packages – Temperatureand Humidity Conditioning. 1986.10. ISO 187. Paper, Board and Pulps – Standard Atmospherefor Conditioning and Testing. 1990.11. Ĉoté F, Deshpande VS, Fleck NA, Evans AG.The out-of-plane compressive behaviour of metallichoneycombs. Mater. Sci. Eng. 2004; A380: 272–280.12. Gibson LJ, Ashby MF. Cellular Solids: Structure andProperties, 2nd edn. Cambridge University Press:Cambridge, UK; 1997.13. Peng GX. Transport Package. Printing Industry Press:Beijing; China 1999 (in Chinese).14. Yang YH. Master Thesis of Southern Yangtze University.Study of Environmental Protection PackagingMaterials for Transportation. Wuxi; China 2003:45–49 (in Chinese).Copyright © 2008 John Wiley & Sons, Ltd. Packag. Technol. Sci. (2008)DOI: 10.1002/pts