1. Key Plastic Materials for Blow Molding
The most commonly used thermoplastics in blow molding include:
HDPE (High-Density Polyethylene)
LDPE (Low-Density Polyethylene)
PP (Polypropylene)
PET (Polyethylene Terephthalate)
PVC (Polyvinyl Chloride)
PC (Polycarbonate)
ABS (Acrylonitrile Butadiene Styrene)
2. Methods to Distinguish Between Them
(A) Physical & Mechanical Properties
| Property | HDPE | LDPE | PP | PET | PVC | PC | ABS |
|---|---|---|---|---|---|---|---|
| Rigidity | High | Low | High | High | Medium | Very High | High |
| Flexibility | Semi-flex | Very flexible | Semi-flex | Rigid | Flexible | Rigid | Semi-rigid |
| Density (g/cm³) | 0.94-0.97 | 0.91-0.93 | 0.90-0.91 | 1.38-1.40 | 1.3-1.45 | 1.2-1.22 | 1.04-1.06 |
| Impact Strength | Good | Good | Moderate | High | Brittle | Excellent | High |
| Clarity | Opaque | Translucent | Opaque | Clear | Transparent | Clear | Opaque |
(B) Chemical & Thermal Resistance
| Material | Chemical Resistance | Max Temp (°C) | Common Uses |
|---|---|---|---|
| HDPE | Resistant to acids, alcohols | 80-100 | Bottles, fuel tanks |
| LDPE | Poor vs. oils, good vs. water | 70-80 | Squeeze bottles |
| PP | Resistant to solvents, acids | 100-120 | Food containers, automotive |
| PET | Poor vs. alkalis, good barrier | 70-85 | Beverage bottles |
| PVC | Resists oils, acids (varies) | 60-80 | Pipes, medical tubing |
| PC | Resists alcohols, weak vs. solvents | 120-135 | Water jugs, medical devices |
| ABS | Resists oils, weak vs. acetone | 80-100 | Automotive parts, toys |
(C) Processing & Appearance
HDPE: Opaque, waxy surface, floats in water.
LDPE: Soft, flexible, milky translucent.
PP: Lightweight, floats, high gloss (used for living hinges).
PET: Crystal-clear (when amorphous), sinks in water.
PVC: Can be rigid or flexible, may have plasticizer smell.
PC: Glass-like clarity, high heat resistance.
ABS: Smooth finish, slightly glossy, tough.
(D) Burn Test (Caution: Use in Ventilated Area)
| Material | Flame Behavior | Smell | Residue |
|---|---|---|---|
| HDPE | Blue base, drips | Paraffin-like | Hard, melted blob |
| LDPE | Same as HDPE | Waxy smell | Soft drips |
| PP | Blue-yellow, drips | Diesel-like | Hard, stringy |
| PET | Yellow, sooty | Sweet, acrid | Black, brittle |
| PVC | Green flame (chlorine) | Pungent, HCl | Black, hard |
| PC | Yellow, sooty | Phenolic (burnt hair) | Black char |
| ABS | Yellow, smoky | Acrylic/rubber | Black soot |
3. Common Applications in Blow Molding
HDPE: Milk jugs, detergent bottles, fuel tanks.
LDPE: Squeeze bottles, tubing.
PP: Pharmaceutical bottles, automotive ducts.
PET: Soda/water bottles, food packaging.
PVC: Clear bottles (oil, shampoo), medical containers.
PC: Large water coolers, impact-resistant containers.
ABS: Tool cases, automotive components.
4. Advanced Identification Methods
Density Test: Float/sink in water (e.g., PP/HDPE float, PET sinks).
Solubility Test: ABS dissolves in acetone, PC in chloroform.
FTIR Spectroscopy: Lab technique for precise polymer ID.
Summary
For rigid, chemical-resistant parts → HDPE, PP, PET.
For clarity & high heat → PET, PC.
For flexibility → LDPE, PVC (plasticized).
For toughness & impact → ABS, PC.
