LDPE and LLDPE, is considered as one of the most widely used thermoplastics.
In plastic and related industry, LLDPE, LDPE, MDPE and HDPE are the sub-group of the giant PE masterbatch family.
How many people are working in plastic industry and related industries that know clearly about LDPE and LLDPE?
We are going to study about definition of LDPE, LLDPE and comparison of them
Both of these plastic are used the most commonly in the manufacture of plastic bags like carry bags, T-shirt bags, garbage bags, agricultural bags, etc.
First of all, Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its manufacture employs the same method today.
LDPE is defined by a density range of 917-930 kg/m3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 90 °C (194 °F) for a short time. Made in translucent or opaque variations, it is quite flexible and tough.
For plastic bag application, this polymer is made of short and branched chains that are of low density and widely spread. This results in a plastic film that is light in weight and of moderately low tensile strength. The film or ending bag is not stretchable like the HDPE
LDPE comes with a low melting point, making it ideal for heat sealing applications. The light polymer means that the material is almost like transparent. It is therefore quite easy to identify the content carried inside. It is a choice for restaurant and food joints looking to package their food. Dry cleaners, butcheries, and suppliers of consumable produce commonly use this type
Except for above applications, LDPE also is used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic parts for computer components, and various molded laboratory equipment. Other products made from it include:
Secondly, Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.
The production of LLDPE is initiated by transition metal catalysts, particularly Ziegler or Philips type of catalyst. The actual polymerization process can be done either in solution phase or in gas phase reactors. Usually, octene is the comonomer in solution phase while butene and hexene are copolymerized with ethylene in a gas phase reactor. LLDPE has higher tensile strength and higher impact and puncture resistance than does LDPE. It is very flexible and elongates under stress. It can be used to make thinner films, with better environmental stress cracking resistance. It has good resistance to chemicals. It has good electrical properties. However, it is not as easy to process as LDPE, has lower gloss, and narrower range for heat sealing
LDPE and LLDPE have unique rheological or melt flow properties. LLDPE is less shear sensitive because of its narrower molecular weight distribution and shorter chain branching. During a shearing process, such as extrusion, LLDPE remains more viscous and, therefore, harder to process than an LDPE of equivalent melt index. The lower shear sensitivity of LLDPE allows for a faster stress relaxation of the polymer chains during extrusion, and, therefore, the physical properties are susceptible to changes in blow-up ratios. In melt extension, LLDPE has lower viscosity at all strain rates. This means it will not strain harden the way LDPE does when elongated. As the deformation rate of the polyethylene increases, LDPE demonstrates a dramatic rise in viscosity because of chain entanglement. This phenomenon is not observed with LLDPE because of the lack of long-chain branching in LLDPE allows the chains to slide by one another upon elongation without becoming entangled. This characteristic is important for film applications because LLDPE films can be downgauged easily while maintaining high strength and toughness. The rheological properties of LLDPE are summarized as “stiff in shear” and “soft in extension”. LLDPE can be recycled though into other things like trash can liners, lumber, landscaping ties, floor tiles, compost bins, and shipping envelopes.
This polymer used featurers non branding chains but the tensile strength is low compared to that of HDPE. This means that when it is used for blown film, it will be thicker and heavier. The gauge and clarity of LLDPE are slightly lower compared to high-density polyethylene plastic but the strength is maintained. As a result, they are cost-effective and thus preferred compared to low density polyethylene plastics. The plastic bag is common with refrigerator storage and laundry stores.
Except for above applications, LLDPE also is used sheets (where it allows using lower thickness than comparable LDPE), plastic wrap, stretch wrap, pouches, toys, covers, lids, pipes, buckets and containers, covering of cables, geomembranes, and mainly flexible tubing. In 2013, the world market for LLDPE reached a volume of $40 billion
LLDPE manufactured by using metallocene catalysts is labeled mLLDPE.
Finally, manufacturing plastic masterbatch additives or polymer masterbatch couldn’t miss PE resin and two these polymer, LDPE and LLDPE are the most common in this field. This article aims to summarize and categorize some basic information and knowledge about them.