With the development of the times, stretch film has begun to be used in more and more industries, and stretch film makes our life or works more convenient.
So do you know what kind of material stretch film is made of? Let’s learn the raw materials of stretch film today.
There are many different materials for stretch film on the market, such as PE, PVA, polypropylene, nylon, aluminum foil, etc. However, Sinyar stretch film mainly uses PE as the primary raw material. Next, we will introduce PE materials from several aspects.
1. What is PE?
PE is a thermoplastic resin obtained by polymerization and is one of the most common plastics. It produces over 100 million tons of polyethylene resin annually, accounting for 34% of the total plastic market. PE is a typical crystalline polymer with a melting point of 130°C to 145°C. A tasteless, odorless, non-toxic, dull surface and milky white waxy particles characterize it.
2. The advantage of PE
- Low temperature or cold resistance, the minimum operating temperature can reach -100~-70°C;
- Corrosion resistance (not resistant to nitric acid), insoluble in common solvents at room temperature;
- Low water absorption, less than 0.01%;
- Excellent electrical insulation;
- High ductility, impact strength, and low friction exhibit strong creep under continuous force, which can be reduced by adding short fibers.
3. The disadvantage of PE
- Flammable, with an oxygen index of 17.4, low smoke when burning, a small number of molten droplets, yellow on the flame and blue on the bottom, paraffin odor;
- Low water permeability but high air permeability, suitable for moisture-proof packaging;
- The surface is non-polar and difficult to bond and print;
- It is not UV-resistant and has poor weather resistance, and will become brittle in the sun;
- The shrinkage rate is large, and it is easy to shrink and deform (shrinkage rate: 1.5~3.0%)。
4. The different kinds of PE
Polyethylene(PE) is divided into high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) according to the polymerization method, molecular weight, and chain structure.
a. High density polyethylene（HDPE）
HDPE is commonly known as hard, soft rubber, with natural color, cylindrical or oblate particles, insoluble in common solvents at room temperature, but can swell when exposed to aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons for a long time, slightly above 70 ℃ Soluble in toluene and acetic acid. Oxidation occurs when heated in air and under the influence of sunlight. Resistant to most acid and alkali erosion. It has low water absorption, can maintain softness at low temperatures, and has high electrical insulation.
HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg/m3. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder, more opaque, and can withstand somewhat higher temperatures (120 °C/248 °F for short periods).
Uses: It can produce film products, daily necessities, and various sizes of hollow containers, pipes, and calendaring tapes and ligatures for packaging by using injection molding, blow molding, extrusion molding, rotational molding, and other molding methods.
b. Low density polyethylene（LDPE）
HDPE low-density polyethylene (commonly known as soft rubber) is a white resin with a waxy feel. Its structural characteristics are non-linear. The molecular weight is generally 100000~500000. Therefore, compared with medium-density and high-density polyethylene, it has a higher Low crystallinity and softening point, good flexibility, elongation, electrical insulation, transparency, and high impact strength.
Low-density polyethylene has poor mechanical strength and poor heat resistance. Another obvious weakness is poor resistance to environmental stress cracking.
Uses: Most film products made of low-density polyethylene are used for packaging. The other part is used as agricultural film and construction film. Low-density polyethylene packaging film can be used for food packaging such as candy, vegetables, frozen food, etc. In addition, one is used as lining film, shrink packaging film, elastic packaging film, heavy packaging film, and other non-food packaging films.
c. Linear low-density polyethylene（LLDPE）
Since the molecular structures of LLDPE and LDPE are significantly different, the properties are also different. Compared with LDPE, LLDPE has excellent environmental stress crack resistance and electrical insulation, higher heat resistance, impact resistance, and puncture resistance. It is very flexible and elongates under stress. It can make thinner films with better environmental stress-cracking resistance. It has good resistance to chemicals. It has good electrical properties. However, it is more challenging to process than LDPE, has a lower gloss, and has a 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 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 or 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. 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 down-gauged easily while maintaining high strength and toughness. The rheological properties of LLDPE are summarized as “stiff in shear” and “soft in extension.”
Uses： 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, and mainly flexible tubing.
5. Other additives
a. Masterbatch (MB):
MB is a solid additive for plastic used for coloring plastics (color masterbatch) or imparting other properties to plastics (additive masterbatch). Masterbatch allows the processor to color raw polymer economically during the plastics process.
Masterbatch helps plastics to improve many physical properties such as Higher toughness; Flexural stiffness; Adhesion; Printability.
It can also be used for applications where varying levels of permanent electrical conductivity are required for use in applications where an accumulation of static electrical charges can potentially cause problems.
b. Metallocene:
LLDPE manufactured by using metallocene catalysts is labeled mLLDPE. The stretch film mainly adds metallocene material to the machine film, which is mainly used to increase the stretchability and stab resistance of the film. In order to be more suitable for the use of high power of the machine.
c. Chitosan:
The chitin-degradable biofilm contains components that can attract biomass, enabling insects and other microorganisms to digest the chitin-degradable biofilm and decompose it into CO2, H2O, and organics.
The life cycle of chitosan stretch film is 24 months, and the degradation period is 12-24 months, which is more suitable for the needs of stretch film. Its’ physical properties are better than PBAT. The functionality of the stretch film does not change during 24 months of use. It is not only in composting conditions that he can achieve biodegradation. Full biodegradation can also be achieved under natural conditions without any manual intervention and without composting.
We believe that through the understanding of the above information, you can simply distinguish different categories of PE stretch film. When purchasing or using stretch film, you can choose different types of stretch film according to the different needs of the scene.
