The disadvantages of using PP (polypropylene) boxes or bags for packaging mooncakes
1. Limited Temperature Resistance
The continuous heat resistance temperature of PP material is generally 80–100℃, with a short-term peak heat resistance of approximately 120℃. However, the core temperature of freshly baked mooncakes can reach 90–100℃ and remain dissipating heat for a period. Direct heat-sealing or loading of hot mooncakes will easily cause deformation and edge warping of the boxes or bags. High temperatures can also accelerate the migration of trace additives in the material to the surface of mooncakes, posing potential food safety risks. In addition, in microwave heating scenarios, unmarked "microwave-safe" PP packaging may experience local melting and decomposition due to uneven heating.
2. Insufficient Barrier Performance
As a non-polar polymer, PP has a loose molecular structure, with an oxygen barrier coefficient of about 30–50 cm³·mm/(m²·d·atm) and a water vapor barrier coefficient of approximately 10–20 g·mm/(m²·d), which is far lower than that of high-barrier materials such as PET and EVOH. The abundant oils and sugars in mooncakes are highly susceptible to oxidation when exposed to oxygen, leading to rancidity and discoloration. Meanwhile, water vapor in the air can easily penetrate the packaging, causing the mooncake crust to soften and the filling to absorb moisture and mold. Under normal temperature storage conditions, the shelf life of mooncakes packaged in PP will be shortened by 2–3 days, which is much shorter than the 7–15 day preservation period achieved with composite film packaging.
3. Significant Low-Temperature Brittleness
The glass transition temperature of PP is around -10℃. When the ambient temperature drops below 0℃, the mobility of molecular chains decreases sharply, resulting in a dramatic reduction in material toughness and a significant increase in brittleness. During cold chain transportation or winter storage in northern regions, slight extrusion or collision can cause cracks or even brittle fracture of the packaging. Damaged packaging will accelerate the oxidative deterioration of mooncakes and increase transportation loss rates. According to industry data, the damage rate of PP packaging at low temperatures is 3–5 times higher than that at room temperature.
4. Poor Printability
PP material features low surface tension (approximately 29 mN/m), making it difficult for inks to form a stable adhesive layer. Direct printing tends to result in blurry patterns, color fading, and indistinct edges. To improve printing quality, processes such as corona treatment or primer coating are required, which will increase processing costs by 20%–30%. Even after such treatments, printed patterns are still prone to peeling and lifting under high-temperature and high-humidity conditions, failing to meet the exquisite appearance requirements of high-end mooncake gift boxes and hindering the effective display of brand logos.
