Use of Plastics in Packaging | Materials | Industrial Engineering

Packaging is one single outlet for plastics all over the world and India. Plastics have an inherent advantage over the conventional materials. Being synthetic, these can be tailor-made to meet even the most stringent performance requirement.

Plastics packaging’s in the form of films, blown bottles, moulded containers, laminates and woven sacks have been in use for two decades. The recent materials on the horizon are stretched PVC and PET bottles, multilayer coextruded films, laminated tubes, corrugated PP board and thin-walled disposable cups.

No single polymer can ever meet the entire requirements of a particular product to be packed and in such cases, a combination of various polymers to form a composite structure is used.

All the basic blow moulding processing methods are used with one difference. Firstly, there are additional extruders for extruding one layer each and secondly a very specially designed die to form laminated composite structure of the bottle-wall.

Note that all the polymers can bond to each other and, therefore, an adhesive or bond layer is required to create the bond, which does not delaminate. As a result three or more extruders are required. With the HDPE/EVOH, for example, five layers are actually required: HDPE/adhesive/EVOH/adhesive/HDPE.

EVOH is a relatively more expensive material, but with an excellent barrier. However, it is sensitive to water, which can deteriorate its properties. So, it is sandwiched with HDPE or PP, which are comparatively low-priced, are excellent water vapour barrier, are approved for food-contact applications but are poor oxygen barriers. Thus EVOH and HDPE/PP supplement each other to produce economic package with excellent barrier properties.

Aseptic Blow Moulding is a process where the bottle is extrusion blow-moulded in a commercially sterile atmosphere with a highly modified equipment. In many cases, the product filler is combined with the blow-moulding machine.

The machines are of two types. One is a blow and hold method. The bottle is moulded and sealed in a blow-moulder. The moving plates in the mould close off and seal the blow pin opening after the bottle is moulded.

The bottle is then stored for some time in an ambient atmosphere. At the filler, the outside of the bottle is re-sterilised and the top seal is cut-off. Then the bottle is filled and resealed.

In the second type, blow-fill-seal, the bottle is blown and filled in the cavity itself. In one to two seconds after the bottle is blown with air, a measured amount of product is forced in, filling the bottle. After a few seconds, the mould cavity close onto the parison just above the main bottle cavity, sealing the filled bottle inside.

Another way is, that the bottle is moulded by conventional means and then immediately transferred to a fill station. The moulding, filling and sealing of the bottle take place in the same environment.

The general modifications to the equipment include the use of special stainless steel and plated materials throughout. The moulding and filling area are enclosed in a cabinet. Sterile air with a positive pressure and laminar flow is maintained inside the cabinet.

All internal passages, surfaces, hoses, blow pins, valves etc. are sterilised with special fixturing. Nothing is touched with hands after starting the process. This method is generally used for packaging of medicinal preparations and sensitive food products.

Blow Film Co-Extrusion:

5-layer films for the packaging of edible oils, processed foods beverages, spices, marine products, petroleum products, etc. are being produced. In this process, separate polymers are extruded through 4 or 5 extruders into a circular die with laminar flow so as to form a composite film as the bubble comes out of the die.

Some typical structures are:

i. LDPE bond layers/PA- 6/bond layer ionomer,

ii. LDPE/bond layer/PA-6/primacor.

Other materials that could be used are:

i. LLDPE,

ii. HDPE,

iii. PP,

iv. EVA,

v. EVOH, etc.

PA-6 (Nylon) provides the barrier layer as well as strength. The sealant layer is generally Surlyn or Primacor. The outer layer is generally a low priced and easily processable materials like LDPE, LLDPE, HDPE, etc. For most pouch-making applications, the composite film thickness is between 80 and 110 microns.

Such equipment’s can also be utilised for producting economical structures for utilising the re-processed material as a core layer with virgin materials like LDPE, HDPE, EVA of outside layer and inside layer also likewise.

Laminated Tubes:

A typical laminated tube is containing a plastics layer, aluminium foil and paper with barrier properties for superior to the conventional plastic tube.

The main difference between the conventional plastics tube and the laminated one is the sleeve, made from pre-printed laminated web, which may contain as many as 10 layers, each contributing to the function of the structure.

Fluorinated HDPE Blow-Moulded Containers:

These are generally used for the packaging of very aggressive chemicals like pesticides, because the flourination improves the barrier properties of HDPE to non-polar solvents.

The barrier is created by chemical reaction of the flourine and the polyethylene which forms a thin 20-40 microns fluorocarbon layer on the bottle surface. In the in- process system, flourine is used as a part of parison blowing gas in the blowing operation so as to create a barrier layer only on the inside. The post-treatment system requires bottles to be placed in an enclosed chamber filled with flourine gas so as to form a barrier layer on both the sides.

Bag-in-Box:

Bag-in-box for dry products is already an established concept but a tremendous potential is envisaged for packaging of liquid products like fruit juices, beverages, alcoholic beverages, dispensing medicinal preparations, fruit juice concentrates, bulk milk supply, etc.

Such a pack generally consists of the following main components:

(1) A flexible collapsible, fully sealed bag made from monolayer or a co-extruded multilayer film or laminates.

(2) A closure and a spout through which contents can be filled as well as dispensed.

(3) A rigid outer box container, usually holding one but sometimes more than one bag.

This package offers considerable weight and space saving, resulting in effective saving in transport costs, before filling, components are shipped flat. After filling, the basic cubic shape of the bag in-box outer boxes occupies less space than the comparable metal, HDPE or glass containers.

Flexible Bulk Containers:

Flexible bulk containers upto 1-5 tonne capacity are manufactured from heavy duty PP woven fabric with LDPE or LLDPE liner for the packaging of products like fertilizers, cement, plastics resins, carbon black, etc. In other countries, containers even upto 5-tonne capacity are already in use.

The major advantages are:

(1) Very light weight compared to metal containers.

(2) Returnable for reuse in collapsed folded form resulting in tremendous saving in transport costs of empty containers.

(3) Considerably lower priced.

(4) More convenient for handling.

(5) Even the most aggressive and corrosive chemicals as well as food products could be transported.

Specifications of important components constituting flexible bulk containers are as follows:

i. Lifting Loops:

Nylon, polyester or PP with minimum test strength of 2500 kgs secured to the reinforcing bands.

ii. Body Fabric:

Fabricated from U.V. stabilized PP with special polyester reinforcing bands. Weights of fabrics from 180 g/m² depending upon end used and weight requirements.

iii. Base:

Fabricated from U.V. stabilized PP from 200 gm² to 400 gm² to suit individual requirements.

iv. Liners:

LDPE/LLDPE liners of 80-150 microns.

v. Plastic Pails:

There are several manufacturers of buckets for home use, but its potential for the packaging applications has not yet been explored. The industrial uses of such moulded pails of HDPE/PP are for the packaging or products such as printing inks, paints, building products, adhesives, detergents, janitorial products and even some of the food products.

Such pails could be either open-head containers with removable lids or containers produced as a single unit called tight-head containers. The container top or lid can be injection- moulded of LDPE, HDPE or PP with one or more openings for filling and dispensing.

The pail is generally injection-moulded of HDPE or PP, the handle of PP/ABS and the LDPE/MDPE/HDPE or PP depending on the type.

The performance requirements of filled pails as specified in the U.S.A. are:

a. Drop test with the pail flat on its side and also at a 45° angle on the bottom chime onto solid concrete from a height of 1.22 metres.

b. Pails must be conditioned at 54°C for 4 hours, stacked 3 high, vibrated for 1 hour at ‘1 g’ to a vertical linear motion.

c. Pails filled with product of marked capacity must withstand a static load of 272 kg for a period of 48 hours without deformation or damage.