What are the raw materials for stretch wrap?

Polymer

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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.[citation needed]

Production and properties

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The production of LLDPE is initiated by transition metal catalysts, particularly Ziegler or Philips types 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.[citation needed]

Processing

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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.

Application

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LLDPE has penetrated almost all traditional markets for polyethylene; it is used for plastic bags and 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,[1] and mainly flexible tubing. In 2013, the world market for LLDPE reached a volume of $40 billion.[2]

LLDPE manufactured by using metallocene catalysts is labeled mLLDPE.

See also

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References

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• Modern Plastic Mid-October Encyclopedia Issue, page 56 and 61

• Linear low-density polyethylene at Wikimedia Commons
• [1] Example of LLDPE Physical Properties

Stretch film is actually a plastic film, a transparent heat-shrinkable plastic whose main component is polyethylene. It is mainly divided into three categories: linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and high-density polyethylene (HDPE). Most high-performance stretch films contain LLDPE. For traditional LDPE, the current amount is limited. EVA has very high tensile properties. Ethyl acetate is usually used, but it is not as good as polypropylene, so it is rarely used. Different raw materials have different properties of stretched film, so special attention should be paid when selecting materials for stretched film.

Stretch film is a plastic film that people often use. Its raw materials include metallocene polyethylene (mPE), LLDPE, LDPE, EVA, PVC. In addition, the raw materials of stretch film also include polypropylene copolymers. The performance is relatively strong, with tensile resistance, fracture resistance and so on.

At present, the main raw materials for domestic production of stretch films are LLDPE, LDPE, EVA and so on. Most of the domestic products of LLDPE are butene copolymers, which cannot meet the performance requirements of industrial stretched films. However, there are still not many domestic companies that can produce hexene or octene copolymerized LLDPE special materials that can be used for stretched films.

Selection of stretch film raw materials.

1. The stretched film is made by co-extrusion of polypropylene particles to form a sheet, and then stretched in both vertical and horizontal directions. Due to the orientation of the stretched molecules, the transparency of polyethylene decreases to a certain extent with the increase in crystallinity. Under crystallinity, transparency increases with increasing molecular weight.

2. The stretch film is made of polyethylene terephthalate as a raw material, which is made into a thick sheet by an extrusion method, and then biaxially stretched to make a stretch film material. It is a colorless, transparent, glossy stretch film with excellent mechanical properties, high rigidity, hardness and toughness, puncture resistance, friction resistance, high temperature and low temperature resistance.

3. The stretched film material is mixed with high-quality tackifier, heated, squeezed, cast, and then cooled by a chill roll. It has the advantages of strong toughness, high elasticity, tear resistance, high viscosity, thin thickness, cold resistance, heat resistance, pressure resistance, etc. It can save materials, labor, and time during use.

The identification of stretch film mainly depends on the hardness and thickness of its material; a good stretch film material will feel tougher and more elastic when it is held in your hand, on the contrary, a poor film is softer and does not have the above characteristics. In terms of thickness, the thickness of the layer used in a good product will definitely exceed 0.125, and the poor material will be thinner!

Secondly, look at the rainbow pattern; a good stretch film, no matter it is outdoors or under the strong light of an energy-saving lamp, you can hardly see any rainbow pattern. On the contrary, the poor film can be seen very clearly as long as it is under a strong energy-saving lamp. , Just like soap bubbles.

Stretch film is widely used in: foreign trade export, logistics, hardware and plastic products, glass ceramics, building materials, electromechanical castings, etc., the outer packaging of various products.

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