What heat deformation temperature (HDT) and Vicat softening point should the plastic of the soup spoon reach for soups at different temperatures

1. Industry Standards for Heat Resistance: HDT and Vicat Softening Point

In the manufacturing of disposable tableware, especially plastic soup spoons, heat resistance is a core indicator that determines product functionality and safety. The plastic material used in soup spoons must be precisely matched to the heat loads of soups at different temperatures. The two main parameters used to measure plastic heat resistance are heat deflection temperature (HDT) and Vicat softening temperature (VST).

HDT, also known as heat deflection temperature, is the temperature at which a specimen undergoes a specified deformation under a specific load (usually 0.45 MPa or 1.82 MPa). It simulates the ability of a plastic product to withstand short-term thermal loads under load. For a soup spoon, this simulates the stress experienced at the connection between the handle and the spoon head when scooping hot soup.

VST, the Vicat softening point, is the temperature at which a standard indenter penetrates a plastic specimen to a depth of 1 mm under a specified load and heating rate. It more closely reflects the temperature at which a plastic material begins to soften rapidly under no or light load. For relatively thin spoon heads, VST provides a crucial guide for maintaining shape stability in hot liquids.

These two parameters together form the scientific basis for selecting plastic soup spoon materials and are directly related to user safety, comfort, and product lifespan.

II. For low-temperature soups (cold drinks/desserts): HDT ≈ 60°C to 80°C

Target temperature range: 0°C to 40°C (e.g., ice cream, yogurt, cold drinks, room-temperature salads).

For plastic soup spoons primarily used for cold and room-temperature dishes, heat resistance requirements are relatively low. Commonly used materials include polystyrene (PS) and polypropylene (PP).

PS (general-purpose polystyrene): This material offers high transparency and rigidity, but offers average heat resistance. Its HDT typically ranges from 75°C to 95°C, while its VST is approximately 90°C to 100°C. Although this value is lower than boiling water, PS is more than adequate for cold dishes up to 40°C, and offers significant cost advantages.

PP (Polypropylene): PP's HDT and VST are generally slightly higher than those of PS, especially homopolymer PP. However, since soup spoons are subjected to less force at low temperatures, their mechanical strength only needs to be guaranteed to prevent brittle cracking at low temperatures.

Professional Requirements: Select materials with an HDT of at least 60°C to ensure they will not stick or deform during high-temperature summer transportation or storage.

III. For Medium-Temperature Soups (Rice Porridge/Warm Noodles): HDT ≈ 80°C to 100°C

Target Temperature Range: 50°C to 85°C (e.g., coffee, tea, hot milk, and warm rice porridge at normal drinking temperatures).

This temperature range is common in most takeout food service scenarios. If a material with an HDT below 85°C is used, consumers may experience noticeable "soft feet" or handle bending when using hot liquids.

High-heat PP or Copolymer PP: By controlling the molecular weight distribution and adding nucleating agents, the crystallinity of PP can be increased, bringing its HDT close to 100°C.

Crystallized Polystyrene (CPLA): This material, made by crystallizing PLA through a special process, significantly improves its heat resistance, achieving an HDT and VST exceeding 90°C, making it suitable for medium-temperature soups while also meeting market demand for biodegradability.

Professional Requirements: The HDT of soup spoon materials should be set slightly above the maximum operating temperature by 5°C to 10°C, meaning at least 90°C.

IV. For High-Temperature Soups (Boiling Hot Soup/Hot Pot): HDT ≥ 110°C

Target Temperature Range: 90°C to 100°C (e.g., freshly cooked broth, hot pot, instant noodles in boiling water).

This scenario presents the greatest challenges to the heat resistance of plastic soup spoons. In this case, an HDT below 100°C will cause the spoon to soften immediately, rendering it unusable and potentially posing a safety risk.

Heat-Resistant Modified PP: Highly crystalline PP specifically designed for the food and beverage industry. Modification by adding high-performance glass fiber or mineral fillers significantly improves the material's rigidity and heat resistance, enabling HDTs to easily exceed 110°C and VSTs to reach over 150°C.

PLA modified blends or specialized engineered plastics: When considering reusable or high-end markets, polycarbonate (PC) or specialized thermoplastic polyesters can be used. However, these are typically used for durable products rather than disposable spoons due to their high cost.

Professional requirements: For spoons intended for prolonged contact with boiling water, the material's HDT must be greater than 110°C. This ensures the spoon's geometry and mechanical strength remain stable during scooping, stirring, or prolonged soaking, preventing the risk of burns or chemical release due to softening.