MLLDPE

1. What is the core difference between mLLDPE and LLDPE/LDPE?

The core difference lies in the catalyst type and molecular structure. mLLDPE uses a metallocene single-active-center catalyst, resulting in uniform molecular chain length, regular branching, and a narrow molecular weight distribution. LLDPE and LDPE use Ziegler-Natta catalysts or high-pressure free radical polymerization, resulting in molecular chain lengths of varying lengths, disordered branching, and a wide molecular weight distribution.

In terms of performance, mLLDPE far surpasses LLDPE and LDPE in puncture resistance, tear resistance, low-temperature toughness, heat-sealing performance, and optical properties. But it is slightly more difficult to process and has a slightly higher cost. LDPE has better processing flowability and gloss, but poorer mechanical properties. LLDPE falls between the two, with a relatively lower cost, making it suitable for low- to mid-range applications.

2. Why can mLLDPE achieve “low heat-sealing temperature and high heat-sealing strength”?

On the one hand, metallocene catalysts act like “molecular sieves,” ensuring that mLLDPE molecular chains are of uniform length and have evenly distributed branches. Upon heating, all molecular chains melt simultaneously within a narrow melting range, eliminating the need for high temperatures to accommodate molecular chains of varying lengths, thus resulting in a low heat-sealing initiation temperature.

On the other hand, the uniform molecular chains can fully entangle, forming a “three-dimensional network” without weak points. There are no easily slipping short-chain molecules, and the entire network collectively resists tensile forces. Therefore, the heat-sealing strength is high, even exceeding the sealing strength of the film itself.

3. What is the density range of mLLDPE?

The density range of mLLDPE is typically 0.915-0.940 g/cm³.

• mLLDE with desity of 0.915-0.920 g/cm³: Excellent flexibility, suitable for fresh food preservation bags, low-temperature packaging films, silage packaging films, etc.
• mLLDPE with density of 0.920-0.930 g/cm³: Balanced overall performance, suitable for stretch wrap film, heavy-duty packaging film, agricultural greenhouse film, etc.
• mLLDPE with density of 0.930-0.940 g/cm³: High rigidity, suitable for industrial packaging film, pipes, injection molded products, etc.

4. Is mLLDPE more difficult to process than LLDPE?

Yes, mLLDPE is slightly more difficult to process than ordinary LLDPE. The core reason is its narrow molecular weight distribution and lower melt strength. During blown film and extrusion processes, it is prone to problems such as unstable film bubbles and edge tearing. In addition, its processing temperature range is relatively narrow.

It can be blended with LDPE to utilize the good processing fluidity of LDPE to improve the processing performance of mLLDPE without significantly reducing its mechanical properties.

5. Can mLLDPE be recycled?

Yes, it can be recycled. mLLDPE is a thermoplastic and can be reprocessed through crushing, melting, and granulation after recycling, which aligns with the trend of a circular economy in the plastics industry. Recycled mLLDPE, due to a slight decrease in performance, is mainly used in the production of low- to mid-range plastic products, such as recycled plastic films, plastic buckets, plastic pipes, and toy shells. Some, after modification, can be used in non-food grade packaging, achieving resource recycling.

6. Can mLLDPE be used in food packaging?

Yes. mLLDPE is synthesized using metallocene catalysts, resulting in extremely low catalyst residue. The production process involves no harmful additives, has minimal odor, and meets food safety standards. It can be used for packaging that comes into direct contact with food, such as fresh food preservation bags, frozen food packaging, and vacuum packaging for cooked food.

7. What are the main factors affecting the price of mLLDPE?

1) Raw material prices: Fluctuations in the prices of ethylene and α-olefins are the core factor. Changes in oil prices directly impact the raw material end, affecting the cost of mLLDPE.

2) Market supply and demand: Changes in demand from downstream packaging, agriculture, and medical fields, as well as production capacity, affect price trends.

3) Technological costs: The research and development and production of metallocene catalysts are highly complex, and catalyst costs directly affect the pricing of mLLDPE.