j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69

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Mechanical deterioration of polyethylene greenhousescovering under arid conditions

Abdullah M. Alhamdan ∗, Ibrahim M. Al-HelalDepartment of Agricultural Engineering, College of Food and Agricultural Sciences,King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia

a r t i c l e i n f o

Article history:

Received 22 July 2007

Received in revised form

6 January 2008

Accepted 19 January 2008

Keywords:

Polyethylene

Greenhouses

Deterioration

Mechanical properties

Arid

a b s t r a c t

One of the most common greenhouse covering materials in Saudi Arabia is polyethylene

film. However, polyethylene films are susceptible to mechanical failure due to harsh condi-

tions of high temperature, solar radiation, and wind as occurs in Riyadh, Saudi Arabia. This

study examined effects of ambient conditions on the deterioration of mechanical properties

of polyethylene films over 14 months, using an experimentally cooled empty greenhouse

(3.6 m length, 2.4 m width, and 3.6 m height) covered with a single layer of 200-�m thick

polyethylene.

Three mechanical tests were conducted on the polyethylene samples: penetration, shear,

and tension utilizing a SMS texture analyzer. The force–distance curves produced were

characterized by two stages, the elastic and plastic regions. Mechanical properties were

determined, including modulus of elasticity, rupture point, and total work for each stage of

the three tests. Generally, mechanical resistance of the samples decreased with increased

exposure time. The results of the tension tests were preferable to penetration and shear

tests. For tension tests, work decreased from 21,693 N mm for new samples, to 6658 N mm

after 14 months. Based on elongation at break data, the shelf life of polyethylene covers

was 12 months under the tested environmental conditions. This illustrates the effect of arid

conditions and age on the mechanical deterioration of polyethylene films. The presented

data can be utilized to predict the deformation and mechanical behavior of greenhouse

polyethylene covers at different exposure times under arid conditions.

1

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as glass to short wave transmission but much higher perme-ability to long wave radiation. In addition, polyethylene covers

0d

. Introduction

here is 5150 ha of greenhouses in Saudi Arabia, produc-ng 487,614 metric tons of vegetables in 2006 (Ministry ofgriculture, 2007). Greenhouses provide better environmentalonditions for plant growth and productivity. The importantnvironmental factors affecting plant growth are temperature,

elative humidity, light level, and carbon dioxide (Al-Ayedhnd Al-Doghairi, 2004).

∗ Corresponding author. Tel.: +966 14678458; fax: +966 14678458.E-mail address: Alhamdan@ksu.edu.sa (A.M. Alhamdan).

924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2008.01.052

© 2008 Elsevier B.V. All rights reserved.

Greenhouses are covered with transparent material thattransmits visible light (400–700 nm), which is the main sourceof energy for photosynthesis. Lozano et al. (1996) emphasizedthe importance of good light permeability in increasing green-house crop production. Polyethylene has similar permeability

are easy to handle and are the cheapest greenhouse covers.A general problem with polyethylene is the short shelf life,

i n g

64 j o u r n a l o f m a t e r i a l s p r o c e s s

especially in harsh weather conditions such as high tempera-ture, high solar intensity, and dust, all of which are commonin arid regions (e.g. central region of Saudi Arabia). In suchconditions, mechanical resistance and light transmission maydeteriorate rapidly.

The many factors affecting physical and mechanical prop-erties of polyethylene films used in greenhouse coveringscan be grouped into three categories; product manufacturingand process specifications, climate and external conditions,and microclimate conditions. Important processes in themanufacturing of plastics include temperature of the melt,die parameters, blow-up ratio, drawn ratio and frost-lineheight and cooling conditions that produce different mechan-ical properties of the film (Dilara and Briassoulis, 1998).Molecular orientation during film blowing influences tensileproperties; higher in the direction of the covalently bondedcarbon–carbon chain than in the transverse direction dom-inated by weaker van der Waals bonds (Gruenwald, 1992;Vishu, 1995). Climatic conditions such as solar irradiation,temperature, humidity, rain, and wind loads, and environ-mental pollution influence ageing and mechanical propertiesof low density polyethylene (LDPE) greenhouse covers. UVradiation (290–400 nm) is the high energy part of the solarspectrum, and can be absorbed by the polyethylene. Thisleads to bond cleavage and polymerization, causing photo-degradation (oxidation) and thus mechanical degradation(Khan and Hamid, 1984). Cyclic temperatures, high when incontact with metal greenhouse frames during hot and sunnydays, but low at night might increase degradation (Dilaraand Briassoulis, 1998). Other external weathering factorsinclude photo-induced degradation, thermal and mechani-cal stresses, ultrasonics and vibration, and hydrolysis (Dilaraand Briassoulis, 2000). The third group influencing mechanicalproperties of greenhouse polyethylene is microclimate condi-tions such as internal humidity and temperature, biologicalactivity and agrochemicals. A combination of such harmfulfactors can eventually alter the properties of the polymer andcompromise its mechanical and optical properties. It shouldbe considered that researchers’ various testing methods andapproaches possibly introduce variations in data. The avail-able tests for mechanical and physical properties of plasticsused as greenhouse covering materials are mainly for generalpurpose and are not in European Union standards (Dilara andBriassoulis, 1998). There is little information on the type oftests recommended for greenhouse covers. Mechanical degra-dation of greenhouse polyethylene can be of several formsthat include rupture, tearing, shearing, penetration, impact,or excessive elongation. Much effort is needed to standardizemechanical tests for greenhouse covers, especially to accountfor degradation from aging.

Mechanical properties for three types of greenhousepolyethylene films have been tested for recycling purposes(Dintcheva et al., 2002). These films were subjected to cli-mate conditions and solar radiation for 3 years in Ragewasia,Italy. The tensile mechanical properties were measured usinga texture analyzer instrument, which showed there were two

regions, the first had a linear relationship and the other hada constant or decreasing stress value with increased strain.Other means of measuring deformation utilized strain gauges(Briassoulis and Schettini, 2002). These strain gauges were

t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69

fixed on polyethylene sheets and when subjected to mechan-ical stress, the electronic instrument measured the deforma-tion value of the sample; however, limited deformation valueswere obtained. Salem (2001) examined the effect of UV radia-tion on mechanical properties of LDPE films containing blackcarbon titanium oxide. The UV radiation has changed theelongation and shear stress of the samples. Merah (2007) con-ducted an interesting study of the effect of 9 months of weath-ering in the harsh conditions of Saudi Arabia on the mechani-cal properties of tensile and three point bend fracture tests ofchlorinated PVC pipes. The exposure time had a limited effecton tensile strength and modulus of elasticity but a notice-able effect on elongation. Unprotected LDPE films failed (50%retained elongation) after the equivalent of <2 months expo-sure (Ram et al., 1980), while linear LDPE (LLDPE) films had a50% reduction in tensile strength at break after only 3 monthsof natural exposure in a hot region (Qureshi et al., 1990).

Addition of starchy materials to LDPE films decreased thevalues of mechanical properties but increased the water vaporpermeability of the films (Psomiandou et al., 1997). Veverka etal. (1997) found improved mechanical and thermal propertiesfor three treated types of plastic films compared to the con-trol. Geoola et al. (1999) examined the mechanical propertiesof polyethylene films with different additives. A greenhouseceiling was divided into 30 slides, each constructed on analuminum frame to facilitate sample collection. The ten-sile properties for each slide were measured and reported.Sanchez et al. (1994) found films made of blends of LDPE andLLDPE treated with UV absorbent possess superior mechanicalproperties; these blends with appropriate stabilizers had sat-isfactory resistance and extended shelf life to 3 years in severeclimate conditions.

Pacini (2001) emphasized the importance of keeping theplastic greenhouse cover in good conditions and examinedcovers’ properties including total permeability to solar radi-ation, mechanical properties, shelf life, effect of climate, andthe homogeneity of film thickness and width. Shen et al. (2000)developed a simulation model to calculate the structural dis-tribution inside a greenhouse, calculating yield and elasticityto predict the maximum ice and storm loads on the green-house structure. Nijskens et al. (1990) discussed the effectof age on the mechanical properties (tensile force, elonga-tion, and breaking) of greenhouse polyethylene covers; UVradiation, external pressure, humidity, and high temperatureshortened the shelf life of the covers.

Most studies have been conducted on polyethylene films inmoderate climates. There is little information of the influenceof arid environmental conditions and aging on the mechanicalproperties of greenhouse polyethylene covering. The objectiveof this study was to investigate the effect of climate conditions(for 14 months) on the mechanical properties (tensile, pene-tration, and shear tests) of a greenhouse polyethylene cover inRiyadh, Saudi Arabia.

2. Materials and methods

A small truss shape greenhouse model was constructed (3.6 mlength, 2.4 m width, and 2.6 m height) oriented in an east–westdirection. The greenhouse was covered with 200 �m thick

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2.1. Tension tests

Tensile grips (A/T6 plunger) were hooked to the SMS textureanalyzer to run tension tests. The method described in ASTM

j o u r n a l o f m a t e r i a l s p r o c e s s i n

olyethylene sheets produced by Al-Watania Plastics factoryRiyadh, Saudi Arabia). An evaporative cooling system in thereenhouse consisted of a ventilating fan, water pump andooling pads. The cooling pads (CELdek®, Munters Corp., Swe-en) were placed in a vertical position to the east side ofhe greenhouse with pad dimensions of 2.35 m length, 1 midth and 10 cm thick. On the other side, four small fans were

nstalled, each with a rated capacity of 0.17 m3/s.To facilitate collecting polyethylene samples for testing,

0 (20 cm × 20 cm) and 24 (30 cm × 30 cm) samples of sepa-ate polyethylene sheets were installed (Fig. 1) on woodenrames (similar to previous study (Geoola et al., 1999) butsing wooden rather than metal frames to avoid heat effects).his enabled replacing a new polyethylene slide in theame location as the removed samples on the greenhouseeiling. Samples were collected monthly, starting from 16anuary 2002, to measure their mechanical properties. Col-ected polyethylene samples were cut into five sheets for theension experiment (6 cm × 3.8 cm), five sheets for the penetra-ion test (5 cm × 4 cm), and five sheets for shear experiments11 cm × 12 cm). Monthly measurements were taken for 14

onths. For comparison purposes, other polyethylene sam-les were taken from a 28-month-old greenhouse that wasearby the model greenhouse.

A SMS texture analyzer (TA-HDi, Model HD3128, Stableicro Systems, Surrey, England) was used for the mechani-

al tests. A software package (Texture Expert Exceed, version.5, Stable Micro Systems) was used with a PC interfaced withhe texture analyzer. The instrument is equipped with differ-nt plungers and tools used for the tension, penetration, and

ig. 1 – View (outside and inside) of the polyethyleneheets used for the mechanical tests.

e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69 65

shear tests. Important information concerning a material’selastic and plastic properties including modulus of elasticity,work, bioyield, and rupture (breaking or apparent) points canbe determined from stress–strain (force–distance) curves. Forall tests, the plunger speed was 1.5 mm/s and return speed of10 mm/s with a load cell of 2500 N. All mechanical tests wererepeated five times at room temperature (∼23 ◦C).

Fig. 2 – Mechanical tools used for tension (top), penetration(middle), and shear (bottom) tests utilizing texture analyzer.

66 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69

Table 1 – Averages (standard deviations) of polyethylene tensile properties for different periods of exposure

Exposure period(month)

First stage Second stage

Tension modulus(N/mm)

Tensionforce (N)

Distance(mm)

Work(N mm)

Force atbreak (N)

Distanceat break

(mm)

Total Work(N mm)

0 −12(3.7) 106.1(4) −5.5(0.4) 536.6(51.2) 164.4(12.8) 169.2(14.5) 21,693(2674)1 −25(2.9) 77.2(4.2) −2(0.2) 140.2(19.1) 141.9(3.0) 156.2(3.6) 17,214(2920)2 −1.22(6.8) 65.2(5.9) −2(0.3) 119.1(24.2) 135.4(11.4) 131.6(23.5) 11,329(1664)4 −9.54(5.3) 86.4(3.1) −4.9(0.6) 312.3(36.1) 144.7(2.4) 91.7(10.2) 9940(2088)5 −6.37(6.14) 91.9(2.6) −5.1(0.4) 366(35.5) 131.8(12.8) 73.8(9.8) 7002(1203)8 −9.26(4.6) 93.1(11.3) −2.1(1) 179.5(79) 150.7(2.8) 101.7(3.4) 10,128(470)

12 −6.35(5.18) 93.4(8.9) −2.3(0.7) 191.4(55.8) 138.4(9.5) 94.6(3.1) 9695(1243)7(0.2)6(0.5)4(0.2)

sure. The distance at break decreased from 169.2 mm for thenew sample to 25.4 mm after the 28-month exposure. Totaltensile work needed to break the samples decreased from21,693 N mm for new plastic to 1854 N mm after exposure of

13 −7.51(7.6) 91.8(4.7) −4.14 −7.48(3.11) 96.7(3.5) −7.28 −2.44(3.5) 77.8(9.3) −2.

D 882 (ASTM, 1991) is suited for films <250 �m thick and wasused in the present study. This method employs special upperand lower grips on samples of uniform width and thickness toprevent slippage of LDPE films, which can lead to prematurebreakage and test failure. Fig. 2 (top) shows a sample betweenthe two grips during the tension process.

2.2. Penetration tests

Fig. 2 (middle) shows the penetration test for a sample using aneedle probe (P/2 N) of 2 mm diameter to penetrate the sampleup to 20 mm depth. This test was a modified version of ASTMD 732 (ASTM, 2002) with a smaller probe. The polyethylenesample was carefully fixed between the upper and lower holedplates to minimize elongation of the sample before the onsetof penetration.

2.3. Shear tests

This test was comprised of a Warner Bratzler blade, areversible blade, a slotted blade insert and a blade holder(Fig. 2, bottom). The reversible blade had a knife-edge at oneend and a flat guillotine edge at the other. The polyethylenewas carefully fixed to the slotted upper and lower blades tominimize slippage of the sample before shearing took place.

3. Results and discussion

The effect of climatic conditions for different periods of expo-sure on tension, penetration, and shear properties of thepolyethylene greenhouse covers follows. Tables contain aver-age mechanical properties, determined and calculated fromfive force–distance curve replicates for each test.

3.1. Tension test

Averages and standard deviations of the mechanical proper-ties for tension tests for different exposure periods are shown

in Table 1. The data was obtained and calculated from aver-age force–distance curves (e.g. Fig. 3) where negative valuesfor force and distance indicate tension direction was oppositeto gravitational direction.

398.2(23.5) 114.1(3.1) 68.1(6.7) 6669(798)551.5(14.3) 119.1(67.4) 72.3(8.5) 6658(1160)165(14.4) 67.4(8.6) 25.4(16.6) 1854(1363)

The tension curves were characterized by two regions, thefirst was the elastic region (in which the sample may returnclose to its original shape after load removal). The elasticdistance was relatively short (2–7 mm) with higher values ofmodulus of elasticity up to the yield point. Hence, polyethy-lene films subjected to storm or other mechanical stressesat this stage might return close to their original length. Thesecond region of the tension curves was plastic deformation.Constant elongation was followed by higher tension resis-tance, which ended with the sample being cut (the rupturepoint). This stage is undesirable and should be consideredwhen evaluating the influence of harsh climate conditions(e.g. high solar radiation, strong wind, and high temperatures)on polyethylene.

The effect of up to 28 months of exposure on the mechani-cal behavior of tension tests is shown in Fig. 3 and Table 1. Themodulus of elasticity varied between −12 and −2.44 N/mmand tensile strength 106.1–77.8 N with a decrease of elas-tic work from 536.6 N mm for new plastic to 165 N mm after28 months of exposure. For the plastic deformation region,rupture force decreased with increased exposure time from164.4 N for new plastic to 67.4 N after 28 months of expo-

Fig. 3 – Mechanical behavior curves of polyethylene sheetsfor tension tests for different periods of exposure.

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69 67

Table 2 – Averages (standard deviations) of polyethylene penetration for different periods of exposure

Exposure period(months)

First stage Second stage

Penetrationmodulus (N/mm)

Penetrationforce (N)

Distance(mm)

Work(N mm)

Penetrationforce (N)

Total work(N mm)

0 1.02(0.03) 1.04(0.05) 1.14(0.04) 0.80(0.02) 1.86(0.21) 35.70(0.99)1 10.70(0.08) 1.61(0.03) 1.19(0.04) 0.92(0.03) 1.58(0.07) 36.78(1.7)2 3.02(0.40) 1.90(0.12) 1.22(0.08) 0.86(0.0) 1.27(0.0) 21.55(0.0)4 1.71(0.04) 2.26(0.04) 3.17(0.26) 1.57(0.03) 1.89(0.15) 32.74(1.22)5 1.96(0.32) 2.15(0.05) 0.98(0.03) 1.28(0.04) 1.51(0.02) 38.46(0.6)8 1.57(0.27) 1.80(0.04) 0.95(0.06) 1.04(0.05) 2.10(0.15) 38.26(0.97)

12 1.93(0.22) 1.75(0.1) 0.88(0.05) 0.99(0.1) 1.75(0.13) 35.50(2.8)111

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Total shear work was 3892–10,047 N mm. There was no cleartrend for the effect of polyethylene exposure time on work ofshear tests, except that samples at 28 months had the lowestwork values (Table 3).

13 1.65(0.09) 1.94(0.05)14 1.67(0.09) 2.02(0.06)28 1.60(0.30) 2.00(0.1)

8 months (Table 1). This represents a considerable degrada-ion of the sample; in which the total work required on theew sample was double that after 12 months, and 12 timeshat after 28 months of exposure. In general, elongation atreak decreased considerably, from 1600% for new plastic, to50% at 12 months, and finally to 150% after 28 months ofxposure (Table 1). These values of elongation at break areithin the upper ranges of LDPE reported by Henninger and

edrazetti (1988). As a practical rule, the useful life of a plas-ic is reached when initial mechanical resistance is reducedy 50% (Briassoulis et al., 1997). Thus, approximate shelf lifef the polyethylene cover under these weathering conditionsas 12 months. The elongation at break (expressed as a per-

entage) can be used to predict an index of degradation. Someesearchers (Amin et al., 1995; Liu et al., 1995; Qureshi etl., 1990) have shown that decreased mechanical propertiesf exposed greenhouse film were associated with increasedarbonyl content, lower molecular weights, and substan-ially increased crystallinity. The rate of photo-oxidation inolyethylene is temperature dependent and roughly doublesor every 10 ◦C of temperature increase (Rabek, 1995). Thus,here is a need for molecular dynamic studies to investigatehe effect of harsh weathering conditions on the polyethylene

icrostructure to improve its resistance and quality.

.2. Penetration test

he averages and standard deviations of mechanical prop-rties for penetration tests at different exposure times areresented in Table 2. There were local fluctuations in theorce–deformation curves (Fig. 4) compared to the relativelymooth curves in tension tests (Fig. 3). This may be due tohe elongation of the tested samples before penetration takeslace. Similarly to the tension tests, the force–deformationurves were characterized by two stages. The first region washe elasticity stage of stretching the sample before the onsetf penetration. The second region was the plasticity regionhere penetration of the probe occurred. Tree branches near

reenhouses or equipment pricking may cause holes in green-

ouse polyethylene, and the mechanical resistance to suchamage is dependent on exposure time. The yield force rangeas 1.27–2.19 N and the work required for penetration ranged

ver 21.6–38.5 N mm, both based on the age of the polyethy-

.25(0.05) 1.18(0.03) 1.68(0.08) 32.59(1.05)

.26(0.06) 1.25(0.05) 2.19(0.08) 38.45(0.86)

.30(0.04) 1.20(0.1) 1.70(0.1) 32.60(1.2)

lene. The effect of exposure time on the mechanical behaviorof penetration (Fig. 4) was not clear in comparison to the ten-sion test, possibly due to a considerable portion of the loadtransferred by bending rather than pure penetration.

3.3. Shear test

Average values of mechanical properties for shear tests(Table 3) were calculated from force–deformation curves(Fig. 5) for up to 28 months of exposure to environment. Similarto the two mechanical tests, two stages can be characterizedin which yield point represents the end of the elasticity stageand the beginning of the plasticity stage. Modulus of elasticityof the first stage was 77.9–124.8 N/mm, corresponding to shearforce of 290.7–392.6 N, and distance of 5.2–8.4 mm. Comparedto penetration curves, shear curves were smoother and fluc-tuated less, which may be due to the larger area exposed toshearing.

There was a trend of decreased mechanical resistance withincreased exposure time (Fig. 5), e.g. after 2 months of expo-sure the curves had a long elongation and low shear force.

Fig. 4 – Mechanical behavior curves of polyethylene sheetsfor penetration tests for different periods of exposure.

68 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 9 ( 2 0 0 9 ) 63–69

Table 3 – Averages (standard deviations) of polyethylene shear properties for different periods of exposure

Exposureperiod(months)

First stage Second stage

Shearmodulus(N/mm)

Shearforce (N)

Distance(mm)

Work (N mm) Elongation force (N) Distance(mm)

Total Work (N mm)

0 105.6(19.4) 307.3(12) 5.7(2) 725.6(224.5) 345.9(28.5) 23.9(7.1) 6746.5(2069)1 124.8(36.3) 352.6(21.9) 8.4(0.4) 566.6(77.5) 410.7(26.3) 23.0(1.2) 4335.5(410)2 123.4(26) 333.2(19.5) 5.2(0.4) 425.5(76.6) 145.4(189.6) 30.1(2.1) 6045(353)4 102.0(11.2) 344.3(10.7) 4.6(0.5) 786.6(10.3) 92.4(42.4) 27.2(1.2) 8106.6(708)5 93.0(18.5) 361.4(63.6) 6.4(2.4) 973.9(206.2) 382(54.7) 14.4(3.3) 4044(1184)8 86.3(9.5) 384.3(20.6) 6.4(0.82) 953.6(143.2) 149.7(42.8) 28.9(2.1) 9035.6(933)

12 96.6(5.3) 392.6(22.2) 6.3(1.45) 892.8(121.3) 106.6(15.7) 31.3(4.7) 10047.7(1456)13 105.3(14.7) 334.7(21.2) 7.6(0.95) 783.3(129.5)14 115.1(20.4) 352.9(40.6) 6.5(1.5) 896.6(432.2)28 77.9(9.3) 290.7(18.2) 6.4(1.1) 644.9(98.2)

Fig. 5 – Mechanical behavior curves of polyethylene sheets

r

the strain gauge problems. Polym. Test. 21, 507–512.

for shear tests for different periods of exposure.

Such discrepancies of shear tests have been noted byother researchers (Henninger and Pedrazetti, 1988), probablybecause a considerable portion of the load was transferred bybending rather than pure shear. Nevertheless, the present datamight be useful in predicting average shear resistance valuesof polyethylene exposed to external mechanical stresses indifferent arid climate conditions. The set up and techniqueshould be improved, to minimize sample bending prior topenetration or shearing. However, tension tests can success-fully characterize the influence of weathering and aging on themechanical behavior of the polyethylene covers. Moreover, useof other techniques such as scanning electron microscopy andthermal analysis (using a differential scanning calorimeteror DSC) may increase understanding in micro-level investi-gations.

4. Conclusion

The effect of different exposure times to an arid climate

on the mechanical properties (of three tests; tensile, pene-tration, and shear) of a polyethylene greenhouse cover wasinvestigated. Mechanical resistance of polyethylene films wasreduced when exposed to harsh environmental conditions

13.7(1.7) 49.9(0.07) 8311.2(1560)28.1(9.3) 36.8(7.4) 9652.7(607)8.9(0.6) 49.9(0.13) 3892.4(988)

(e.g. high levels of solar radiation and temperatures). Therewere elastic and plastic regions characterizing force–distancecurves for tension, penetration, and shear tests. The ten-sion test was preferable to penetration and shear tests in thecurrent study. Mechanical properties, especially in the ten-sion test, helped in exploring the mechanical behavior of thepolyethylene samples after exposure for 14 months. Based on50% of elongation at break, the recommended shelf life of thecurrent greenhouse plastic under these arid conditions was 12months. It is recommended that micro-level techniques suchas scanning electron microscopy and DSC analysis be used infurther investigations.

Acknowledgments

This work has been financially supported by Saudi Basic Indus-tries Corporation (SABIC). Authors express thanks to SABICand Agricultural Research Center, College of Food and Agricul-tural Sciences at King Saud University for their contributions.

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