LABORATORY REPORT

FOOD PACKAGING AND STORAGE TECHNOLOGY

PLASTIC PACKAGING

Written by:

Priscilla Destiana (03420120026)

Stevannie Christie (03420120060)

Cely Hoesada (03420120066)

Bella Natasha (03420120076)

Ferix Jonathan (03420120082)

FOOD TECHNOLOGY DEPARTMENT

FACULTY OF SCIENCE AND TECHNOLOGY

UNIVERSITAS PELITA HARAPAN

KARAWACI

2015

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CHAPTER I

RESULT AND DISCUSSION

1.1 Polypropylene (PP)

Polypropylene (PP) is the first notable plastic type, which has high

molecular weight as the result of modification and development from the utilization

of the olefin propylene or propene from the alkene class. It is basically defined as a

thermoplastic material that is produced by polymerizing propylene molecules,

which are the monomer units, into very long polymer molecule or chains.

Structurally, PP is a linear hydrocarbon polymer containing little or no saturation.

Generally, polypropylene has excellent and desirable physical, mechanical, and

thermal properties when used in room-temperature applications. It is relatively stiff

and has a high melting point, low density, and relatively good resistance to impact.

Compared to ethylene, it has higher density and boiling point due to its greater mass.

Polypropylene (PP) is basically classified into 2 main categories,

homopolymer and copolymer. Homocopolymer is polypropylene containing only

propylene monomer in the semicrystalline solid form. It is made by polymerising

propylene in the presence of a stereospecific catalyst. Homopolymers are more rigid

and have better resistance to high temperatures than copolymers but their impact

strength at temperatures below zero is limited. For copolymer, it is further divided

into random copolymer and impact copolymer. Random copolymer contains

ethylene as a comonomer in the PP chains at levels in about the 1–8% range, while

impact copolymer has the commixed random copolymer phase that has an ethylene

content of 45–65%. Due to many classifications of polypropylene, the properties of

polypropylene actually vary in a relatively simple manner by altering the chain

regularity (tacticity) content and distribution, the average chain lengths, the

incorporation of a comonomer such as ethylene into the polymer chains, and the

incorporation of an impact modifier into the resin formulation.

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Table 1.1. Polypropylene mechanical characteristics (unmodified/homopolymer) based on literature

Parameter Polypropylene quality

Young modulus 1500 MPa

Tensile strength 33 MPa

Strain at max 10%

Strain at break 350% (>50%)

Thickness -

Source: Brydson (1999) and Tripathi (2003)

Table 1.2. Polypropylene (PP) mechanical characteristics based on observation

Parameter Polypropylene quality

Young modulus 899.02 MPa

Tensile strength 23.77 MPa

Strain at max 11.54%

Strain at break 644.30%

Thickness 0.11 milimeter

Mechanical properties of plastic polymer product are important to be

observed beside the thermal properties and rheological properties. Several

parameters in mechanical properties are Young modulus, tensile strength,

percentage strain at maximum (strain yield), and percentage strain at break (strain

break).

These parameters actually represent the stiffness of the plastic material and

mostly used to predict the properties of molded articles. For application in food

industry, these parameters are prior to be taken into account to suit its intended use

for the specific product where packaging function as the container and barrier for

the food (Brydson, 1999; Karian, 2003; Tripathi, 2002).

Comparing Table 1.1 and Table 1.2, it can be inferred that the Young

modulus and tensile strength values of PP observed are lower than in the literature,

while the percentage of strain at maximum and at break are higher than the values

stated in the literature. These differences between the values obtained by

observation compared to the literatures may be due to the many variations exist in

polypropylene nowadays where different company producing it may have different

standards and formulations, including the amount and the type of monomer used as

co-monomer for making PP random and impact copolymer, instead of homo-

polymer. It is known that the addition of ethylene will result in improved toughness

of PP but at the expense of much reduced rigidity, an inevitable consequence, since

the crystallinity is reduced by the inclusion of the second monomer. Furthermore,

for the percentage of strain at break, this parameter standard is highly varies

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between one product to the other, but commonly it is assumed to be higher than

50% (Brydson, 1999; Tripathi, 2002).

For application as food packaging, polypropylene actually possesses good

water vapor barrier and fat resistance properties which are demanded. However,

normal polypropylene films have limited food packaging applications such as its

application for bread. It is due to their low cold temperature resistance. Therefore,

copolymer mixtures with ethylene are used to improve cold resistance and heat

sealability as well as material strength and the most important one, the seal strength.

This could be one reason of the developing modification for polypropylene to

contain other monomers beside propene that also includes the intenton for

improving mechanical properties so that the usage of PP will be more suitable as

food packaging (Birley et al., 1988; Brydson, 1999). Therefore, the polypropylene

plastic used as sample in the experiment may be the modified PP, instead the normal

unmodified one or homopolymer which is intended either to be suitable for food

packaging or to reduce the cost (not necessarily intended to increase the quality for

application to pack foods).

1.2 Polyethylene (PE)

Polyethylene (PE), commonly used as plastic packaging, is having chemical

formula (C2H4)nH2 that consist of similar organic compounds mixture that differ in

terms of value n. Polyethylene is thermoplastic polymer consists of long

hydrocarbon chains. It is made by combining single carbon atoms together to create

long chains of carbon atoms. As thermoplastic, PE have weak forces that attract the

macromolecules together. The melting point and glass transition may or may not be

observable depends on the crystallinity and molecular weight. Plastics with high

amounts of crystalline arrangements are harder and stronger but more brittle.

Density of polyethylene is 0.91-0.96 g/cm3. The melting point temperature depends

on the variety of polyethylene. Medium and high density polyethylene, the melting

point range from 120 to 180oC and 105 to 115oC for low density polyethylene

(Piringer and Baner, 2008).

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Figure 2.1 General structure of polyethylene

Uses polyethylene plastic packaging are for film packaging, bags, industrial

application, container, food packaging, wire and cable applications, laminates, and

many more. The advantage is for food contact acceptability, have good process

ability, have copolymer, antioxidant, high ESCR (stress crack resist), good impact

resistance, good toughness, good stiffness, while the disadvantages are high thermal

expansion, poor weathering resistance, subject to stress cracking, difficult to bond,

flammable, poor temperature capability, low strength or stiffness (Lokensgard,

2008).

Polyethylene classified into several different categories based on the density

and branching. The mechanical properties of polyethylene depend significantly on

variables such as the extent and type of branching, the crystal structure and the

molecular weight. Classification of polyethylene are Ultra High Molecular Weight

Polyethylene (UHMWPE), Ultra Low Molecular Weight Polyethylene (ULMWPE

or PE-WAX), High Molecular Weight Polyethylene (HMWPE), High Density

Polyethylene (HDPE), High Density Cross Linked Polyethylene (HDXLPE), Cross

Linked Polyethylene (PEX or XLPE), Medium Density Polyethylene (MDPE),

Linear Low Density Polyethylene (LLDPE), Low Density Polyethylene (LDPE),

Very Low Density Polyethylene (VLDPE), and Chlorinated Polyethylene (CPE).

Based on the sold volumes, the most important polyethylene grades are HDPE,

LLDPE and LDPE. The degree of branching and crystallinity in PE produce

variations in behavior and properties, and the differences shown in Table 1.3.

Table 1.3. Differences between types of polyethylene

Type

Density

(Specific

Gravity)

Distort

Temperature (oC)

Tensile

Strength

(N/mm2)

Abrasion

Resistance

LDPE 0.91 - 0.92 40 – 50 170 Soft

MDPE 0.93 - 0.94 60 - 70 275 – 450

HDPE 0.94 - 0.96 70 - 90 Over 625

UHMWPE >HDPE >HDPE >HDPE Excellent

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The lower the density of PE, it has good toughness (ability to deform

without breaking) and excellent elongation (ability to stretch) with LDPE stretching

up to 6 times from the original length before breaking. It makes PE useful for

molding and extruding in shapes. PE is clear and goes white and translucent as the

amount of crystallinity increases. Tensile modulus/Young’s modulus of

polyethylene (HDPE) is 0.8 x 109 N/m2, GPa, ultimate tensile strength is 15 x 106

N/m2, Mpa, and elongation 500% while LDPE Young’s modulus is 0.11 - 0.45 Gpa

and 16,000 - 65,000 psi (Berins, 1991).

Table 1.4. Result of polyethylene properties

Group 3 Group 4 Group 5 Group 6

Modulus Young (N/mm2) 206.75 326.67 238.85 245.78

Tensile strength (N/mm2) 17.845 16.534 17.932 20.559

Percentage strain at max (%) 910.23 758.55 887.47 994.47

Percentage strain at break (%) 986 781.11 937.85 1048.9

Thickness (mm) 0.1 0.1 0.1 0.08

The result of polyethylene properties shown on Table 2.4 using all the same

speed (60) and the thickness 0.1 mm, except group 6 which is 0.08 mm. Modulus

Young for the sample of polyethylene varies between 206.75 - 326.67 N/mm2,

which is different from the theory due to unknown type of polyethylene and

different company has different formula to make the polyethylene plastics, thus

resulted in different mechanical and physical properties. Tensile strength of

polyethylene is also not in line with the theory from Berlin (1991). From the

experiment, tensile strength varies between 16.534 - 20.559 N/mm2 which far lower

than the theory. Berins (1991) also stated that the elongation or percentage strain at

max for polyethylene is 500% while the experiment showed that the percentage

strain at max varies between 758.55 - 994.47%. It is higher than the theory that

might be happened due to different thickness, type, and composition of

polyethylene itself.

1.3 Saran

Table 1.5. Properties of saran packaging

Parameter Saran quality

Tensile strength 15.079 N/mm2

Modulus Young 31.960 N/mm2

Percentage strain at maximum 33.01%

Percentage strain at break -

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Saran resin and film, also known as Saran polyvinylidene chloride (PVDC)

have been known and used as wrapping materials for more than 50 years. Saran

works by polymerizing vinylidine chloride with other monomers, such as acrylic

esters and unsaturated carboxyl groups, therefore forming long chains of vinylidene

chloride. This copolymerization leads to a film with tightly bound molecules,

making only very little gas or water may get through. This characteristics result to

the use of Saran as demanding barrier packaging application to minimize the

permeation of oxygen, water vapor, acids, bases, solvent, also odor, which can

protect the food, consumer, and industrial product from further deterioration.

Saran was accidentally discovered by Ralph Wiley in 1933 and further used

as food packaging after World War 2. PVDC was cleared for use as food contact

surface as a base polymer, in food package gaskets, in direct contact with dry foods,

and also for paperboard coating in contact with fatty and aqueous foods. Almost

85% of PVDC is used as a thin layer between cellophane, paper and plastic

packaging, thus improving the barrier performance. Beside food use, Saran can also

be used for molding and melt adhesive bonding. In combination with polyolefins,

polystyrene and other polymers, saran can be coextruded into multilayer sheets,

films, and tubes.

According to Renards (2005), multilayer film or sheet were widely used

since it has an outstanding barrier performances, also resistance to in-use condition

such as humidity and flexes cracking, also specific physical properties given by the

skin polymers. It may possibly increase the shelf life of product as well as reducing

processing steps compared to usual laminated composite products.

Table 1.6. Physical properties of Saran wrap

Parameter Source 1 Source 2

Tensile strength (Mpa) 25-110 90-103

Modulus young (Mpa) 300-550 482-512

Percentage strain at max (%) 15-40 20-40

Percentage strain at break - -

Source: Davletshina and Chremisinoff (2004); Goodfellow (2013)

Table 1.6 shows the physical properties of Saran wrap based on two sources.

The Saran wrap sample has the thickness of 0.02 mm and the speed undergone was

60. Tensile strength indicates the maximum stress withstands while being stretched

or pulled before failing. According to the theory, Saran wrap can endure up to 550

MPa of stress before getting broken. But the sample used only can withstand around

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15.079 MPa. Young Modulus is the elastic modulus used for deformation, which

take place when a force, which is parallel to the axis of the object is applied to one

side while the opposite face is held fixed by another equal force. The experiment

result was also not corresponding to the theory. This might be resulted by the

impurity of Saran wrap in the sample, since nowadays, the pure Saran wrap is rarely

found (Demczyk et al., 2002).

The percentage strain at maximum of Saran wrap based on theory is known

to be around 15-40%. The result of the experiment was supported by the theory.

The experiment Saran wrap has percentage of strain at maximum at 33.01%.

Percentage strain at break was not recorded by the equipment. This might happen

due to the low thickness of the sample, only 0.02 mm.

1.4 Water Vapor Transmission Rate

Table 1.7. Rate of Water Vapor Transmission on Several Plastics

Treatment WVTR (gr/h.m2)

Group 1 (Wet; PP) 0.8319

Group 2 (Dry; PP) 0.9594

Group 3 (Wet; PE) 0.3614

Group 4 (Dry; PE) 1.0476

Group 5 (Wet; PE) 0.118

Group 6 (Dry; PE) 0.782

Group 7 (Wet; Saran Wrap) 0.2272

Group 8 (Dry; Saran Wrap) 1.4323

Table 1.7 shows the water vapor transmission rate from polypropylene,

polyethylene and saran wrap plastics, which treated in wet and dry condition.

Judging by the condition environment, plastics put in a wet condition (group 1, 3,

5, 7) has a lower water vapor transmission rate than plastics put in a dry condition

(group 2, 4, 6, 8). The results prove that environment which surrounds the plastics

is affecting water vapor transmission rate. In wet condition, higher percentage of

humidity present. Means higher amount of water particle in atmosphere, this wet

condition makes the water vapor stay still inside and does not diffuse out to the

atmosphere because the humidity is relatively the same. On the other side, dry

condition has a distinct humidity difference. Silica gel put in dessicator maintain

the atmosphere dryness by absorbing water, this condition would trigger water to

permeate out in order to reach equilibrium humidity thus higher water vapor

transmission rate achieved.

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Data obtained from the experiment reveals that the highest water vapor

transmission was achieved by group 8 with sample of Saran wrap (PVDC) in a dry

environment using silica gel. As many as 1.4323 gr/h.m2 of water vapor transmitted

during 3 days time. Whilst the least water vapor transmitted shown by group 5 with

polyethylene as sample in a wet condition (surrounded by water), lowest rate of

0.118 gr/h.m2

Difference in plastic characteristics plays an important role in water vapor

transmission rate. According to Maier and Calafut (2008), the lowest to highest

water vapor transmission rate was had by saran wrap/PVDC (0.1 gr/day.m2),

followed by high-density polyethylene (0.2 gr/day.m2), propylene (0.3 gr/day.m2),

and low-density polyethylene (0.5 gr/day.m2). This theory by Maier and Calafut

(2008) is on the contrary to the experiment result. As shown in table 1.1, saran wrap

in dry condition is the poorest water barrier with highest WVTR of 0.118 gr/h.m2.

In saran wrap or polyvinylidene chloride, this kind of plastics should be more

impermeable to a wider variety of gases and liquids than other polymers. This is a

consequence of the combination of high density and high crystallinity in the

polymer. An increase in either density or crystallinity tends to reduce permeability.

Also, the high crystallinity of PVDC indicates that no significant amount of

branching can present thus reducing permeability as well.

Water barrier properties of plastics also depend on low solubility and

diffusion coefficients. Polymers of plastics vary in crystallinity and polarity.

Crystallinity is associated with the diffusion parameter, while polarity is associated

with the solubility coefficient. The polarity is usually determined by the kind of

functional group attached to the main polymer. Non-polar materials are usually a

better barrier against water and other polar molecules but poor barriers for non-

polar molecules such as organic flavors. On the other hand, polar polymers are not

a good barrier against water but they are better barriers against non-polar organic

compounds (Romero, 2002).

Referring to Table 1.7, polyethylene as sample from group 4 in dry

condition gives the second highest WVTR rate. While another sample of

polyethylene from group 6 in dry conditions gives the lowest WVTR rate.

Comparing on the polyethylene plastic itself, polyethylene generally divided into

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two, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). The

main difference between these two types lies in its molecular arrangement. HDPE

consists primarily of unbranched molecules. A high degree of crystallinity can be

achieved resulting in resins that have a high density and enable the mobilization of

water molecule. Thus is a good water barrier that indicated by low transmission rate

of water vapor. On the contrary, LDPE is primarily consisting of substantial

concentrations of branches that hinder the crystallization process, resulting in

relatively low densities. The numerous branches characteristics of low-density

polyethylene molecules inhibit their ability to crystallize, reducing resin density

relative to high-density polyethylene (Peacock, 2000). Due to its high level of

branching, mobilization of water is highly possible. LDPE is a poor water barrier

indicated by the high rate of water vapor transmission rate. After all of this

comparison, polyethylene sample from group 4 has higher WVTR (1.0476

gr/hr.m2) than group 6 (0.782 gr/h.m2). So, judging by its WVTR, it is possible to

say that polyethylene from group 4 is LDPE plastic, while group 6 is HDPE.

Polypropylene in dry condition shows the second highest WVTR for 0.9594

gr/hr. . Based on experiment’s result, polypropylene is categorized as good

water barrier. The result is supported by theory from Maier and Calafut (2008),

Polypropylene is a semi-crystalline polymer with varying degrees of crystallization

and different types of crystal structures. Semi-crystalline polymers have high

strength, stiffness, density and sharp melting points. Other properties of

polypropylene is that it has higher branch network than HDPE but less than LDPE.

For those properties, polypropylene is considered as a good water barrier.

1.5 Comparison among Plastics

There were 3 (three) types of plastic which tested; they are polypropylene

(PP), polyethylene (PE), and saran. Thickness of plastic, modulus Young, tensile

strength, percentage of strain at max and strain at break, and water vapor

transmission rate are compared among three types of plastic.

Saran has the thinnest plastic (0.02 mm), while PE and PP has 0.10 mm and

0.11 mm thickness respectively. However, saran has the lowest tensile strength,

modulus Young, and strain value compared to PE and PP. It means that saran plastic

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has the weakest plastic strength and elongation compared to two others. PE and PP

has different strong point against other. PP has the strongest plastic strength

compared to other plastics, it means that PP is the hardest plastic to be changed

from its original shape. In contrast, PE has the highest strain value compared to

others, it means that PE is the plastic with the longest elongation between the other

plastics.

In water vapor transmission rate as shown in Table 1.7, PE has the lowest

rate of transmission whether in dry and wet method. PP in second rank, while saran

in third rank. It means that PE has the lowest water permeability which causing the

water cannot easily pass its polymer network; meanwhile saran has the highest

water permeability.

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CHAPTER II

CONCLUSION

Polypropylene has the highest tensile strength and modulus Young value,

thus it is the strongest plastic among other plastics. Polyethylene has the highest

strain value, thus it has the longest elongation among other plastics. It also has the

lowest water vapor transmission rate; lowest water permeability. Saran has the

thinnest thickness, but the weakest plastic among other plastic. It also has highest

water vapor transmission rate; highest water permeability.

BIBLIOGRAPHY

Berins, M. Plastic Engineering Handbook of The Society of The Plastics Industry.

New York: Springer Science & Business Media, 1991.

Birley, A. W., R. J. Heath, and M. J. Scott, eds. Plastics Materials: Properties and

Applications, 2nd ed. New York: Springer, 1988.

Brydson, J. A. Plastics Materials, 7th ed. Oxford: Butterworth Heinemann, 1999.

Davletshina, Tatyana A. and Nicholas P. Cheremisinoff. Fire and Explosion Hazars

Handbook of Industrial Chemical. USA: PD Library.

Demczyk, B. G. et al. “Direct Mechanical Measurement of The Tensile Strength

and Modulus of Multiwalled Carbon Nanotubes.” Materials Science and

Engineering A334 (2002): 173-178.

Goodfellow. “Polyvinylidenechloride (PVDC) –Properties and Applications.”

Supplier Data, 2013.

Karian, Harutun G. Handbook of Polypropylene and Polypropylene Composites:

Revised and Extended, 2nd ed. New York: Marcel Dekker, Inc., 2003.

Lokensgard, Erik. Industrial Plastics: Theory and Application. Boston: Cengage

Learning, 2008.

Maier, Clive and Calafut, Theresa. Polypropylene: The Definitive User’s Guide and

Databook. Spain: Taylor & Francis. 2008.

Peacock, Andrew. Handbook Of Polyethylene: Structures: Properties and

Applications. USA: CRC Press.

Piringer, Otto G. and Albert Lawrence Baner. Plastic Packaging: Interactions with

Food and Pharmaceuticals 2nd edition. New Jersey: Wiley, 2008.

Romero, Anna. “Evaluation of The Change on Water Vapor Transmission Rate of

Different Propylene Films In Contact With D-Limoneme and The Effect

Such Changes Have On The Shelflife Of Confectionary Products.” Thesis.

Rochester Institute of Technology. 2002.

Tripathi, Devesh. Practical Guide to Polypropylene. Shropshire: Rapra

Technology Limited, 2002.