COMPOUND LDPE granule for extrusion film

COMPOUND LDPE granule for extrusion film applications involves tailoring the material for properties such as clarity, flexibility, strength, and processability. LDPE films are widely used in packaging, agriculture, and industrial applications, and the compound formulation must match specific functional and aesthetic requirements.

Key Properties for LDPE Film

1. Transparency and Gloss:
   Essential for applications like packaging films where visibility of the product is critical.
2. Flexibility:
   LDPE’s inherent flexibility makes it suitable for stretch and shrink films.
3. Sealability:
   Films require low-temperature heat-sealing properties for packaging applications.
4. Tear and Impact Strength:
   To withstand handling and mechanical stresses during use.
5. Processability:
   The resin must flow easily during extrusion and ensure uniform thickness.

Components in LDPE Compounding for Extrusion Film

Steps in LDPE Compounding

1. Base Resin Selection

• Use LDPE with a density of 0.910–0.930 g/cm³. Lower density provides more flexibility, while higher density improves strength.
• Melt Flow Index (MFI): A range of 0.2–2 g/10 min (190°C/2.16 kg) is typical. Lower MFI is suitable for stronger films; higher MFI enhances processability.

2. Additives and Functions

• Processing Aids:
  Reduces melt viscosity and ensures smoother extrusion. Examples include fluoropolymers.
• Slip Agents:
  Commonly, erucamide or oleamide is added to reduce surface friction and improve film handling.
• Anti-Blocking Agents:
  Fine particles like silica or talc are dispersed to reduce adhesion between film layers, ensuring easy separation.
• UV Stabilizers:
  For outdoor agricultural films, HALS or UV absorbers like benzophenones protect the material from sunlight.
• Antioxidants:
  Hindered phenols or phosphites prevent thermal degradation during processing.
• Fillers:
  Calcium carbonate or talc increases stiffness or reduces cost but may impact transparency.

3. Compounding Process

• Blending:
  The LDPE resin is mixed with all additives using a high-speed blender to ensure uniform distribution.
• Extrusion Compounding:
  The blend is fed into a twin-screw extruder, typically at temperatures ranging from 160–200°C, to melt, mix, and homogenize the compound.
• Pelletizing:
  The molten compound is cooled and granulated into uniform LDPE pellets.

4. Extrusion Film Process

After compounding, the granules are used for film extrusion:

• Blown Film Extrusion:
  Suitable for flexible films with balanced properties in all directions.
• Cast Film Extrusion:
  Produces high-clarity films with controlled thickness.

Typical LDPE Compound Formulation for Film

Key Properties for Quality Control

1. Optical Properties:
   • Measure haze, gloss, and transparency using a light transmission test.
2. Mechanical Properties:
   • Tensile strength, tear resistance, and elongation at break are tested to ensure durability.
3. Seal Strength:
   • Heat-sealing properties are critical for packaging applications.
4. Slip and Blocking Properties:
   • Test for coefficient of friction (COF) and anti-blocking performance to ensure handling ease.
5. UV Resistance:
   • For outdoor films, test UV exposure using accelerated weathering chambers.

Advantages of LDPE Films

1. High Flexibility: Ideal for shrink and stretch applications.
2. Excellent Clarity: Allows visibility of packaged goods.
3. Good Sealability: Simplifies manufacturing for packaging.
4. Customizable: Properties can be tailored with additives for specific uses, such as agriculture or food-grade films.