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What are the most commonly used materials for poly bag and packaging?

Poly bag is, by its name, made of poly or in complete form, polyethylene. To general public, people will always call poly bag as plastic bag. They are, in most extend and generally speaking, the very same thing being referring to. But if we look it up closely, we can see that there are indeed a number of different types of poly materials.These poly materials allow us, the manufacturer of poly bags, to produce the poly bag and poly packaging material into various thicknesses and endurance due to their different characteristics.

Since the development of the first polymer over a century ago, the scientists, industrial engineers and technicians have found and further advanced new technical methods to combine the initial basic components into something stronger and more resistant poly materials. Currently, all those different types of poly bags can render very unique characteristics, qualities, value and benefit that allow the user to use them in specific ways all well as allow them to be adaptable to various applications. The production of poly bags and poly packaging will commonly include the use of the following poly materials listing below.

The Most Commonly Used Types of Poly Materials For Bags and Packaging

First of all, we will introduce Low Density Polyethylene (LDPE) and High Density Polyethylene (HDPE) because they are the most extensively used poly material in making poly bag.

Low Density Polyethylene (LDPE)

Low Density Polyethylene or abbreviated as LDPE, or simply named as PE amongst the industrial and factory technicians. LDPE is the polymerization of ethylene; it was formed and found with practical use as early as in the year of 1939. The polymer is short with branched chains resulting in a plastic film that is light weight with low tensile strength. With its low density characteristic, it appears to be opaque and clear. It also has a low melting point, making it ideal for bags to be heat sealed. LDPE is a type of polymer that is found in food packaging and coverings for clothes from dry cleaners.

Below are some examples for LDPE bags. One can see that the bag will look shiny and sharp in appearance.

High Density Polyethylene (HDPE)

High Density Polyethylene or abbreviated as HDPE, or simply named as PO amongst the industrial and factory technicians. It is named as PO, which we can see it take the first two letters from the word polyethylene or poly as it is the most commonly used poly material for the manufacture of poly bags. HDPE material consists of a linear polymer with minimal branches. The chemical structure characteristic of the HDPE material is what creates its high density (compared to the LDPE). But even though it is with high density, HDPE is still light-weighted, durable and almost look opaque (frosty and semi-transparent when made into bag). The characteristics of its high resistance and resilience of HDPE material render it strength to hold heavily weighted item with stronger endurance and tolerance.

See below are the HDPE bag with frosty (semi-transparent) finishing.

Other Variants of LDPE and HDPE

Linear Low Density Polyethylene (LLDPE)

LLDPE is a blended form of LDPE to make a more flexible, softer, and pliable plastic with greater tensile strength and formability. A unique feature of LLDPE is its ability to withstand heavy impact and stress against pressure, puncture or other brute force. Its molecules hold firmly together which allows LLDPE to stretch. The common thicknesses of LLDPE are fromn 0.5 mil to 40 mil. This gauge of LLDPE is lower than HDPE, but still make it featured with the HDPE‘s strength. This makes LLDPE a more cost effective replacement for LDPE.

Medium Density Polyethylene (MDPE)

Simply put, MDPE serve as a choice in-between HDPE and LDPE. It is stronger than LDPE and has a tighter cell structure, which makes it more tear and puncture resistant than LDPE. However, MDPE's density is not sufficient for the storage of bulky and heavy materials. It has low tolerance to chemical exposure and low tensile strength, but still can easily stretches. Factories may usually blend MDPE with LLDPE or LDPE to create a stronger and more resilient bag.

Polypropylene (PP), OPP and BOPP

Polypropylene, also called are polypropene is a semi-crystalline thermoplastic polymer. It has high impact resistance and is strong and tough. It is a thermoplastic made from propylene monomers that was first introduced in 1951. The popular use of polypropylene is due to its ability to retain its shape after torsion, bending, and flexing. It rapidly gained popularity as a material for the production of commercial products and is one of the most popular poly bag materials due to its resistance to chemicals and high melting point as well as its resistance to electricity makes it an ideal material for the storage of electrical components.. The material of PP is non-breathable, which gives it a long shelf life and a safe means for storing food. Popular packaging packets like ziplock pouches, standup pouches, and spout pouches are made from Polypropylene.

Looking at them directly, it is indeed quite difficult to distinguish which bag is made with the PP, OPP, and BOPP plastics. However, one can feel the difference by have a physical touch since OPP feels brittle whereas PP is softer.

The best way to distinguish between PP, OPP and BOPP bags is by understanding their use in the real world objects. The PP bags are used as non-woven bags. These are treated to make them water or moisture absorbent. Sanitary napkins, diapers, air filters, etc are some of the most commonly used PP products nowadays. PP material is also used in the production of thermal clothing due to their temperature bearing feature.

The OPP bags have high tensile strength, and are transparent in appearance. They can resist very high temperatures but will still get wrinkled if roughly used. The popular poly mailer bag's transparent adhesive tapes are also made using the same formulation. They are hard to tear and OPP bags are used in the packaging of fashion and garment products.

The BOPP bags are crystal clear polyethylene bags. Their art of manufacture i.e. bi-axially orientation gives them a transparent appearance and this makes them suitable for branding via printing on their surfaces. BOPP bags are largely used for retail packaging as they are able to carry greater weight and loads. The products inside them can be waterproofed against moisture for a much longer time.

Recycled Plastic / Poly

With the rising concern for the environment and the wide spread propaganda of labelling bad name over to poly bags and in general all plastic packaging, factories and suppliers have to developed alternative yet sophisticated methods to recycle plastic bags so that the used poly bag can be re-used to produce new bags or other plastic products.

First of all the used poly bag will be collected and sorted out into its respective type of material. The company that handle the collection of recycled bag will then bundle the sorted bags and send them to the factory for crushing the bundle of bags. The crushing stage is aimed to remove contaminants and impurities, ie, other than the poly material that can be re-used for recycling. The bags are crushed, chopped, melted, washed and dried to form the pellet-like material. Then, in order to ensure purity, the pellets will undergo a set of purification processes before being conveyed to the extruder for reprocessing. Manufacturers have perfected and improved this recycling process in such a way that in most case, any plastic bag can be applied into this recycling process and again, able to be reprocessed multiple times, ensuring the substantial savings for the environment.

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