Polypropylene (PP): The Engineer’s Choice

Technical Specification: Why Polypropylene (PP) Wins

Polypropylene (PP) is often called the “steel” of the plastics industry. It offers a unique balance of properties that no other commodity plastic can match: high melting point, high tensile strength, and excellent chemical resistance. At Golden Soar, we leverage these properties to create packaging that performs under pressure.

1. Heat Resistance & Hot Filling

One of PP’s defining characteristics is its melting point, which ranges from 160°C to 170°C. This makes it the only commodity plastic suitable for hot-filling processes (filling liquid at 85°C-95°C) and autoclaving (steam sterilization). For food products like jams, sauces, or baby food, PP jars are the industry standard because they can withstand the pasteurization process without deforming. In the cosmetic sector, this allows for the filling of hot waxes and balms directly into the final container.

2. Injection Molding Precision

While PE is blown, PP is predominantly Injection Molded. This process involves injecting molten plastic into a precision-machined steel mold under high pressure. This allows for:

• Complex Geometries: We can mold internal threads, snap-fits, and intricate mechanisms (like pump engines) with tolerances as tight as +/- 0.05mm.
• Living Hinges: PP’s fatigue resistance allows us to create flip-top caps where the hinge is molded as a thin web of plastic that can flex millions of times without breaking.
• Double-Wall Structures: For luxury creams, we often mold a PP inner jar (for chemical compatibility) and nest it inside a PS or PMMA outer jar (for clarity), or a PP outer jar for a mono-material solution.

3. Chemical Compatibility

PP is highly resistant to a wide range of chemicals, including acids, alkalis, alcohols, and oils. It is superior to PET for products with high pH (alkaline) or those containing aggressive solvents. Unlike some plastics that may stress-crack or haze upon contact with essential oils, PP maintains its integrity, making it a safe choice for natural and organic skincare formulations.

4. Decoration & Finishing

PP has a natural semi-matte, translucent appearance. However, we can modify this through:

• Clarified PP: Using nucleating agents to improve transparency, approaching the look of PET but with higher heat resistance.
• In-Mold Labeling (IML): Fusing the label with the container during molding for a seamless, scratch-resistant finish.
• Surface Textures: From high-gloss polish to EDM-eroded matte textures directly from the mold surface.