Study Notes on Major Plastics in Packaging - Polyolefins Family and More

Chapter 4: Major Plastics in Packaging

Part 1: Polyolefins Family

  • Polyolefins are a significant category of polymers used in packaging.

Part 2: PVC and PVDC

  • Introduction to PVC (Polyvinyl Chloride) and PVDC (Polyvinylidene Chloride) as additional types of polymers in packaging.

Part 3: PVOH and EVOH

  • Overview of PVOH (Polyvinyl Alcohol) and EVOH (Ethylene Vinyl Alcohol) as specialized materials.

Part 4: Nylons and Polyesters

  • Discussion on Nylons and Polyesters, their characteristics, and applications in the packaging industry.

Part 5: Polycarbonate, Fluoropolymers, and Acrylonitrile

  • Analysis of Polycarbonate, Fluoropolymers, and Acrylonitrile as important polymers in packaging materials.

Part 6: TPEs and Thermosets

  • Overview of Thermoplastic Elastomers (TPEs) and Thermosets used in diverse applications.

Part 7: Biobased/Biopolymers

  • Introduction to Biobased and Biopolymers as sustainable alternatives in the packaging industry.

The School of Packaging

  • Institution: Michigan State University
  • Course: PKG 323 Packaging with Plastics

Global Plastic Use in the Packaging Industry

  • Inquiry about polymers that belong to the polyolefins family, specifically:
    • Example of Polyolefins: LDPE (Low-Density Polyethylene), LLDPE (Linear Low-Density Polyethylene), HDPE (High-Density Polyethylene), and PP (Polypropylene).
    • Question: Is PET (Polyethylene Terephthalate) part of the polyolefin family? Answer: No, PET is part of the polyester family, which accounts for 10% of polymers produced worldwide. Reference: Rabnawaz et al., 2017. DOI: 10.1039/C7GC02521A

Polyolefins Family

  • Definition of Olefin: An old synonym for alkene, meaning oil-forming.
  • Characterization of Olefins:
    • Structure: Terminal alkenes represented as C=C.
    • In the Plastic Industry: Refers to a family of plastics based on ethylene and propylene (olefinic polymers).
  • Composition of Polyolefins:
    • Encompasses a family of Polyethylene (PE) and Polypropylene (PP).
  • Ethylene monomer chemical formula: H2C=CHH_2C=CH

What Polymers are Called Polyolefins?

  • Categories of Polyolefins include:
    • Linear Polyethylenes:
    • High Density Polyethylene (HDPE)
    • Linear Low-Density Polyethylene (LLDPE)
    • Metallocene Polymers
    • Branched Polyethylenes:
    • Low Density Polyethylene (LDPE)
    • Ethylene Vinyl Acetate (EVA)
    • Ethylene Acrylic Acid (EAA)
    • Ionomers
    • Polypropylene (PP):
    • PP Homopolymer
    • PP Copolymer
  • Polyolefin Family consists of:
    • Linear and branched PE and their copolymers, PP and their copolymers.

Learning Objectives for the Session

  • Focus areas include:
    • Linear Polyethylenes
    • High Density Polyethylene (HDPE)
    • Linear Low-Density Polyethylene (LLDPE)
    • Metallocenes Polymers
    • Branched Polyethylenes (PE)
    • Low Density Polyethylene (LDPE)
    • Ethylene Vinyl Acetate (EVA)
    • Ethylene Acrylic Acid (EAA)
    • Ionomers
    • Polypropylene (PP)
    • PP Homopolymer
    • PP Copolymer

Polyethylene (PE)

  • PE was the original olefinic polymer utilized in food packaging.
  • Reasons for Extensive Use of Polyethylene:
    • Low cost
    • Properties favorable for various applications:
    • Films
    • Closures
    • Moulded containers

Linear PE vs Branched PE

  • Schematic Representation:
    • Linear PE: Straight-chain structure.
    • Branched PE: Long branches leading to decreased crystallinity and density.

Polymerization Techniques

  • Addition Polymerization:
    • Characteristic method for creating linear PE and branched PE.
  • Free Radical Polymerization vs Catalytic Polymerization:
    • Linear PE is obtained via catalytic processes, while branched PE via free radical methods.

Family of PE at a Glance

  • Categorization includes:
    • Branched PE: Low Density PE (LDPE), Medium Density PE (MDPE), Acid (ionomer).
    • Linear PE: High Density PE (HDPE), Linear Low-Density PE (LLDPE), Metallocenes, Acrylate (EAA), Acetate (EVA).

Linear PE Homopolymers vs Copolymers

  • Homopolymers: Consist entirely of a single type of monomer.
  • Copolymers: Composed of two different types of monomers, improving flexibility and altering properties significantly.
  • Example: HDPE (Homopolymer), LLDPE (Copolymers).

High Density Polyethylene (HDPE)

  • HDPE is a homopolymer of polyethylene characterized as a thermoplastic and is non-polar due to the C-H framework.

  • Properties:

    • Affected by Molecular weight (Mw): Higher Mw leads to greater tensile and impact strength.
    • Molecular weight distribution affects mechanical properties; a narrower distribution generally results in superior performance.

  • Physical Characteristics: Milky-white appearance due to high crystallinity, with a barrier to moisture but poor barrier to oxygen and organic compounds.

  • Applications: Uses include containers for milk, detergent, bleach, shampoo, flexible packaging for snacks, pharmaceutical bottles, etc.

  • Processing Methods: Includes extrusion blow molding, blow and cast films, injection molding, and injection blow molding.

Linear Low-Density Polyethylene (LLDPE)

  • Enhanced properties compared to LDPE due to its structure and narrower molecular weight distribution.
  • Applications: Stretch films, grocery bags, heavy-duty shipping sacks.

Metallocene Polymers

  • Utilization of metallocene catalysts leads to polymers with improved and uniform characteristics.
  • Examples: Ultra Low Density PE (ULDPE) and Very Low Density PE (VLDPE).

Branched Polyethylenes (PE)

  • Homopolymers: Low Density PE (LDPE) characterized by lower crystallinity and density.
  • Copolymers of Branched PE:
    • Ethylene Vinyl Acetate (EVA): Enhances flexibility and impact strength at lower temperatures with a polar molecular structure.

Ethylene Vinyl Acetate (EVA)

  • Inclusion of vinyl acetate reduces crystallinity and improves various desirable properties:

    • Flexibility at low temperatures, clarity, impact strength, and adhesion strength.

  • Applications: Used in medical films, cheese wrap, extrusion coating, coextruded layers with PET and BOPP.

Ethylene Acrylic Acid (EAA)

  • Characterized by the presence of an acid group that significantly influences properties:
    • Better adhesion and clarity compared to other types, such as LDPE.
  • Applications: Commonly used in packaging for meats, cheese, and medical products due to its strong bonding capabilities.

Ionomers

  • Result from neutralization of PE copolymers with various cations (e.g., Ca²⁺, Li⁺), creating ionic bonds that enhance performance.

  • Properties: Superior transparency, toughness, and reliable seals; however, generally poor barrier properties.

  • Applications: Skin packaging for electronics and food packaging (frozen foods, bacon).

Polypropylene (PP)

  • Comparison with PE highlights PP's unique structure with methyl side groups, enhancing its properties:
    • Properties include better heat resistance, medium transparency, low density, and higher stiffness.

Tacticity in Polypropylene

  • Different forms of PP based on stereochemistry:
    • Isotactic: Highest crystallinity, excellent thermal resistance.
    • Syndiotactic: Regular alternating point of side groups.
    • Atactic: Random placement of side groups results in amorphous structure.

Applications of Polypropylene

  • Commonly used forms and their applications include:
    • Stretch film, containers for sterilization, and consumer products. Process adjustments improve optical and mechanical properties significantly.