I. Material Properties of PP Shopping Bags
PP shopping bags are made of polypropylene (PP) a thermoplastic resin with low density good toughness and strong chemical stability. Physically PP has a smooth surface and moderate friction coefficient so it is not easy to stick to items; it also has good tensile strength and is not easy to break when pulled by external forces. PP has certain chemical resistance and can resist most acids alkalis salt solutions and common organic solvents (such as alcohol and cooking oil) so it will not deteriorate or be damaged due to contact with these substances in daily use.
II. Comparison with Ordinary Plastic Bags
1. Load-Bearing Capacity
Ordinary plastic bags are mostly made of polyethylene (PE which is divided into high-density HDPE and low-density LDPE). Low-density polyethylene bags (common thin supermarket shopping bags) have weak load-bearing capacity and can usually only hold 1-3 kg of items and exceeding this load will easily cause the bag body to stretch and deform or the handle to break. High-density polyethylene bags have slightly stronger load-bearing capacity but they are generally only limited to 3-5 kg.
PP shopping bags have significantly better tensile strength and impact strength than ordinary PE bags because their molecular structure is more regular and their crystallinity is higher. PP shopping bags with regular thickness (0.03-0.05 mm) can bear 5-8 kg of weight; if the thickness is increased to 0.06-0.1 mm (such as thickened shopping bags) the load-bearing capacity can be increased to 10-15 kg. When carrying heavy objects the PP bag body will not stretch significantly and the handle is not easy to break making it more suitable for carrying heavy items such as rice flour bottled water and books.
2. Temperature Resistance
Ordinary PE plastic bags have a narrow temperature resistance range. Low-density polyethylene plastic bags have a heat resistance upper limit of about 60-70°C and high-density polyethylene plastic bags have a heat resistance upper limit of about 80-90°C. When they come into contact with freshly cooked food (usually at about 100°C) or are close to heat sources (such as rice cookers and kettles) they are easy to soften and deform and may even release trace harmful substances due to high temperature. PE plastic bags also have poor low-temperature resistance and they will become brittle and crack in an environment below -10°C which affects their use.
PP shopping bags have much better temperature resistance than ordinary PE plastic bags. The upper limit of heat resistance of ordinary PP shopping bags can reach 100-120°C and some modified PP materials (such as PP with heat-resistant additives) can have a heat resistance upper limit of up to 130°C. They can hold freshly cooked food hot soup and other items (when the temperature does not exceed 120°C) without softening deformation or releasing harmful substances. In addition PP has good low-temperature resistance and can still maintain good toughness in an environment below -20°C without being brittle and cracked making it suitable for use in low-temperature environments (such as outdoor in winter and refrigerated scenarios).
