PET BOTTLES WITH CAP

PET (also named PETE) is a kind of polyester material for fibres, injection molded parts, as well as blow-molded bottles and jars. Special grades are offered with the required properties for the different applications.

PET is linear thermoplastic (long-chain molecule consists of repeating units shown as figure right), white but bluish resin made from terephthalic acid and ethylene glycol through poly-condensation. PET is supplied by the resin manufacturers in the form of small pellets, each about 0.05 grams. PET came into prominence in the 1950s as a textile material. Its strength, temperature tolerance and wear-resistance made it an ideal replacement for, or addition to natural fibres such as silk, cotton and wool.

Bottle Grade PET

Nowadays PET is still widely used for these purposes, but when, in the 1970s a marketing need was identified for larger light-weight, unbreakable bottles to contain carbonated drinks, PET fit the bill perfectly. Unlike simple polymers such as polyethylene, PET is not made by a single stage process, but by the reaction between two chemicals, purified terephthalic acid (PTA) and ethylene glycol (EG). The availability of the first of these has dictated the supply of PET resin in the past, but new capacity coming on stream this year will ensure more than adequate supplies to meet the growing uses of PET over the coming years. Related polyesters are polybutylene terephthalate (PBT) used mainly for engineering applications, and polyethylene naphthalate (PEN). The latter offers significant performance improvements over PET, particularly in terms of barrier properties and heat tolerance. Since PEN can be blended with PET a range of new ‘alloys’ is becoming available for special packaging applications.

As PET (bottle grade) is a kind of transparent, wear-resisting and corrosionresisting plastics with high strength and smooth finish, it is widely used for PET bottles of mineral water, juice, edible oil, pharmaceuticals, cosmetics, etc.

Melting Temperature: 254-256oC

Crystallinity: >=45%

PET products can be made crystallizable or non-crystallizable through controlling crystallization temperature and cooling speed. Usually it’s crystallinity is 0~50%. The higher IV value, the slower crystallization speed.

The key factors that effect PET bottles’ molding process and performance are crystallization and orientation. If PET’s moisture level is high, hydrolysis will happen while molding and it’s IV value will drop which means products’ quality be affected.

Most bottle grades of PET are copolymers, which means that a few percent of a modifier has been incorporated into the polymer chain. Copolymers are easier to injection mold because the crystallinity behaviour is improved.

A remarkable transformation takes place when injection molded PET is stretched at the right temperatures and to the right extent. The long chains undergo strain hardening and strain-induced crystallization, which gives the properly-made PET bottle exceptional clarity, resistance to internal pressure, uniform wall thickness, toughness, and a host of other features. To achieve these useful properties, however, care must be taken in choosing the right grade of resin, as well as the right preform and bottle designs, and good molding practices.

The world food markets are nowadays glutted by a high variety of plastic packaging materials for just as many varied sorts of food products. Only to name a few – Polyethylene, Polypropylene, Polystyrene and Polycarbonate are commonly used in form of foils, bags, boxes and containers. With the introduction of a 2 litre bottle in 1976 Polyethylene terephthalate (PET) steadily conquered the market and emerged as a material of choice for beverage bottles. The characteristic properties of PET like stability, transparency and lower weight have led to the fact that glass bottles are more and more replaced. Due to the stability of the material the multiuse system of PET bottles is common in many countries. The strength and ruggedness of the nearly indestructible PET material is one reason that beverage bottles can achieve high circulation rates between the bottler and the consumer. The use of a rugged material, however, cannot rule out the fact that material changes may occur during the life time of a bottle.

On the account of a direct contact between the PET bottle and the beverage interactions e.g. migration processes can occur during the often long storage time. Plastics have for example the ability to absorb organic compounds easily. For this reason the aspect that a number of refillable PET bottles may be misused by the consumer is very important for the quality assurance and safety-in-use of refillable bottles.

Consumer may “misuse” the bottles for example by filling them with beverages with strong flavour, household chemicals or even pesticides. Compounds absorbed in this way will not be fully removed during the washing and cleaning procedure of a refillable bottle. Therefore these substances may be able to remigrate into a refilled foodstuff or beverage which in turn can result in an off-flavour. Due to the intrinsic interactivity of a refillable plastic bottle with contacting chemicals the question of testing compliance with food regulations arises. To this day there is neither any specific national or EU regulation nor a standard test available which could be applied by industry and enforcement laboratories to cover this problem. One of the main purposes of the EU project SMT4-CT96-2129 was to establish a standardized and easy-to-apply method for general chemical inertness testing in conjunction with the production of a certified reference material of PET applicable not only for the industry but also suitable for enforcement laboratories and therefore having a systematical control possibility to check the food safety of refilled PET bottles taken from the market.

The basic technical and financial parameters of a project on the manufacture PET preforms by injection moulding PET bottle grade resin are described in this profile. This is the first stage in the two stage PET bottle manufacturing process suitable for large scale production and here the pet preform is molded on an injection moulding machine, then in the second stage the preform is reheated and blown on a blow moulding machine. The advantages of PET bottles include exceptional clarity, pure, safe, good barrier to oxygen, carbon dioxide and water, lightweight and therefore less shipping costs, no leakage, design flexibility, recyclable, long shelf life, good chemical resistance etc.