Food Packaging Technology 3(2+1)

Lesson- 23 Identification of different packaging materials

23.1 Introduction

The basic function of the package is to protect and preserve the contents during transit from the manufacturer to consumer. Protection is required against spillage, dirt, ingress and egress of moisture, insect infestation, contamination by foreign material, tempering, pilferage etc. Identification techniques for different packaging materials are given below.

23.2 Packaging tests are as follows:

23.2.1 Visual Test:

• Fold the film several times to make number of layers.
• Observe the Colour of the film.  E.g. Clear, Hazy Watery, White, Yellowish etc. and compare the results with Table 23.1.

23.2.2 Tear Test:

• Fold the film and Tear it on the fold.
• Try tearing the film from a straight edge.
• Nick the film.
• Compare the results with Table 23.1.

23.2.3 Burning Test:

• Burn a film very carefully at the edge with help of a burner flame.
• Observe the edge of the film as it burns of the smoke and compare the results with Table 23.1.

23.2.4 Solubility Test:

• Cut the film into small pieces.
• If necessary, crush the sheet material to increase the rate of solubility.
• Dissolve this film in a glass beaker using appropriate solvents.
• Amount of the solvent should not be less than 10 times the volume of the    solid material.  If   needed, 25 time volume may also be used.
• Compare the Solubility of the given film with the values given in Table 23.2.

23.2.5 Determination of density:

Weight a small amount of the material in a flask.

• If necessary, cut it into pieces.
• Add water up to the mark on the neck.
• Remove air bubble (if any) trapped with the film using vacuum.
• Weigh the flask containing water and film.

Weigh the same flask filled with only water at the same temperature.

• The difference in weights may be used in calculating the density of the given film.
• Compare the density of the given film with the values given in Table 23.3 which would help in identifying the material.

23.2.6 Melt Test:

• Light a match stick and let the stick to burn for few seconds.
• Extinguish it and make contact of the hot stick to the film.
• Use Table 23.4 for film identification

23.2.7 Water Test:

• Place a drop of water on the flat surface of the film and observe.
• Compare the observations with those given in Table 23.4.

23.2.8 Shrink Test:

• Hold the film I" away from the flame of a match or a burner and observe.
• Compare the observations with those given in Table 23.4.

 23.2.9 Drip Test:

• Roll the film into a tape like and allow to burn.
• Observe the burning and dripping of the film.
• Compare the observations with those given in Table 23.4.

 

23.2.10 Flame hot wire Test:

• Heat a copper wire on flame and allow it to touch to the film.
• Put the wire again into the flame and observe.

• Compare the observations with those given in Table 23.4.
  

Table 23.1: Identification Tests for Plastic Films

No.

Types of Film

Visual Test

Tear Test

Burning Test

Burns slowly with a bead at the edge

Burns poorly

Crystal Clear

Yellowish Clear

Hazy

Easy to Tear (Notched)

Stretches before tearing

Resists Tearing

Burns Explosively

Burns like paper

Burns like wax, Waxy odour

Burns like wax without dripping, white smoke

Vinegar Odour

Rancid Butter Odour

Marigold Odour, Black smoke

Sweet Odour

Pungent odour

Pungent soapy odour, Black smoke

Rubbery odour

Burning Hair odour

Green flame with copper wire

1

Cellophane

X

X

X

2

Cellulose Acetate

X

X

X

3

Cellulose Acetate - Butyrate

X

X

X

4

Cellulose Nitrate

X

X

X

5

Nylon

X

X

X

6

Polyester

X

X

X

X

7

Polyethylene

X

X

X

8

Polypropylene

X

X

9

Polystyrene

X

X

X

10

Polyvinyl Chloride

X

X

X

X

X

11

Rubber Hydrochloride

X

X

X

X

X

12

Saran

X

X

X

X

 

Table: 23.2 Solubility of Plastic films for Identification

No.

Film

Acetone

Amyl formate

Carbon tetrachloride

Cresylic acid

Cyclo hexanone

Dimethyl formamide

Ethyl acetate

Ethyl alcohol

Formic acid

Methyl alcohol

Water

Toluene (Boiling)

1

Acrylic

I

S

I

2

Cellophane

I

3

Cellulose Acetate

S

4

Cellulose Butyrate

S

S

I

5

Cellulose Nitrate

S

S

6

Cellulose Propionate

S

7

Nylon

I

S

I

I

S

I

8

Polycarbonate

S

I

I

9

Polyester

I

10

Polyethylene

I

I

I

I

S

11

Polypropylene

I

I

I

I

S

12

Polystyrene

S

S

S

I

S

13

Polyvinyl Alcohol

S

S

S

14

Polyvinyl Chloride

S

I

I

I

15

Rubber Hydrochloride

S

I

I

S

16

Saran

S

I

S

S

I

I

 

I = Insoluble, S = Soluble

Table: 23.3

 

No.	Film	Density Range (gm/cc)	Flammability (Self Extinguishing)	Colour	Behaviour	Odour
1	Polyethylene	0.91-0.965	No	Top yellow, bottom blue, white smoke	Melts & drips	Burnt Wax
2	Polypropylene	0.90-0.915	No	Top yellow, bottom blue, white smoke	Melts & drips	Burnt Wax & acrid
3	PVC	1.28-1.38	Yes	Yellow orange with green edge	Darkens, softens & decomposes	Chlorine
4	PVDC	1.68	Yes	As above with green spurt	Black, hard residue	Chlorine
5	PVA	1.21-1.33	Yes but slowly	Yellow with gray smoke	Swells, softens & turns brown	Pungent
6	Poly carbonate	1.2	Yes	Yellow orange with black smoke	No drips, decomposes	Pleasant
7	Polyester	1.38	No	Yellow black smoke	No drips, softens, burns steadily	Pleasant
8	Polystyrene	1.04-1.09	No	Yellow orange black shoots	No drips, softens	Floral (Sweet)
9	Nylon	1.06-1.14	Yes	Blue yellow top	Melts, drips & froths, rigid drips	Burnt hair
10	Cellophane	1.48	No	Yellow orange gray and smoke	Burns fast & complete, burnt area brittle	Burnt paper
11	Cellulose Acetate	1.28-1.32	No	Yellow with blue base	Melts, burns quickly & leaves beads	Burnt vinegar
12	Cellulose Nitrate	1.35-1.40	No	Yellow	Burns at once & fully	Acrid

 

Table23.4: Identification of various films

No.	Observation	Inference
1	Melt Test:   Match does not push through readily (film resists melting)     Hot end of the match readily pushes through the film      Film melts readily and does not resist penetration	Plain Cellophane NCC cellophane PVDC coated cellophabe PE coated cellophane PVDC (Saran) Cellulose acetate Polystyrene  Nylon
2	Water Test: Drop flatters, spreads and softens the film Drop does not spread.  Wetting and softening of the film occurs only when it is dipped in acetone and wiped off as compared to the original (undipped) part of the film.	Plain transparent cellophane Nitrocellulose coated cellophane
3	Shrink Test: Film shrinks violently and rapidly to deep wrinkles Little shrinkage is observed	PVDC, Cellulose acetate Polystyrene Polyester, Nylon
4	Drip Test: Film burns with drip like melting wax leaving molten drops Some drip No molten drip but edges tacky when cooled.	Polyethylene (PE) Poly Vinyl Chloride (PVC) Rubber Hydrochloride, Pliofilm
5	Flame Hot Wire Test: Green colour of the flame. Negative test, film unaffected by accetone	Vinyl or rubber type of material Polyethylene coated cellophane