Are PLA Small Take-Out Containers a Type of Plastic?

I. Definition and Characteristics of Traditional Plastics

1.1 Authoritative Definition of Traditional Plastics

1.2 Main Types and Classification of Traditional Plastics

1.3 Chemical Structural Characteristics of Traditional Plastics

• Carbon chain structure as the main component: The main molecular chain of most traditional plastics is composed of carbon atoms, such as polyethylene, polypropylene, and polystyrene. This carbon chain structure gives the materials excellent chemical stability and mechanical properties.
• Strong regularity of repeating units: The molecular structure of traditional plastics is formed by the repeated connection of simple monomer units, such as the repeating unit of polyethylene being -CH₂-CH₂-, and that of polypropylene being -CH(CH₃)-CH₂-. This highly regular structure is the basis for the excellent performance of plastics.
• Wide molecular weight distribution: The molecular weight of traditional plastics is usually between tens of thousands and millions, and has a relatively wide molecular weight distribution. The size of the molecular weight directly affects the mechanical strength, melting point, viscosity, and other properties of the material.
• Significant differences in crystallinity: Different traditional plastics have different degrees of crystallinity, which mainly depend on the regularity and symmetry of the molecular chain. For example, HDPE has a higher degree of crystallinity, while LDPE has a relatively lower degree of crystallinity.

1.4 Performance Characteristics of Traditional Plastics

• Excellent mechanical properties: Traditional plastics possess high strength, rigidity, and toughness. For example, high-density polyethylene has excellent rigidity and strength, and polypropylene has superior strength, rigidity, and hardness compared to PE, with excellent resistance to bending fatigue.
• Good chemical stability: Traditional plastics have good resistance to most chemicals, including acids, bases, and salt solutions. For example, polyethylene has excellent chemical stability and is resistant to most acids and bases, and is insoluble in common solvents at room temperature.
• Excellent electrical insulation properties: Traditional plastics have a volume resistivity as high as 10¹⁶ Ω・cm, making them excellent insulators. At the same time, their thermal conductivity is only 0.1-0.5 W/(m・K), providing good thermal insulation.
• Good processing performance: Traditional plastics have excellent plasticity and can be processed through various methods such as injection molding, extrusion, blow molding, and thermoforming. Thermoplastics can be repeatedly heated and molded, which makes recycling possible.
• Significant differences in temperature resistance: The heat resistance of different traditional plastics varies significantly. General-purpose plastics such as PE and PP have a temperature range of approximately 80-120℃, while engineering plastics such as polyether ether ketone (PEEK) and polyimide (PI) can withstand high temperatures above 200℃.

1.5 Environmental Impact of Traditional Plastics

• Difficulty in biodegradation: Traditional plastics are difficult to degrade in the natural environment and may take hundreds or even thousands of years to decompose. This characteristic leads to serious "white pollution" problems.
• Microplastic pollution: Traditional plastics gradually decompose into tiny particles during use, forming microplastics. These microplastics have been found in the ocean, soil, and even the human body, posing a potential threat to the ecological environment and human health.
• High carbon footprint: The production process of traditional plastics requires the consumption of a large amount of fossil fuels, resulting in significant carbon dioxide emissions. According to statistics, the production process of traditional plastics is extremely energy-intensive, contributing significantly to greenhouse gas emissions, global warming, and the depletion of non-renewable resources.
• Recycling difficulties: Although some traditional plastics are recyclable, the actual recycling rate remains low due to difficulties in sorting, high recycling costs, and decreased performance of recycled products.

 

II. Chemical Structure and Properties of Polylactic Acid (PLA)

2.1 Chemical Structure and Molecular Characteristics of PLA

• Diversity of stereoisomers: Due to the presence of an asymmetric carbon atom in the lactic acid molecule, there are two enantiomers: L-type (levorotatory) and D-type (dextrorotatory). Based on different stereoconfigurations, PLA can be divided into poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), and poly-DL-lactic acid (PDLLA). Among them, PLLA and PDLA have opposite helical structures, and mixing the two can form a stereocomplex type PLA (SC-PLA), significantly improving heat resistance.
• Crystallinity characteristics: PLA has good crystallization ability. Its α phase is the most stable isomorphic structure, corresponding to an orthorhombic unit cell, in which the helices are arranged in a hexagonal packing manner, with each unit cell containing two antiparallel chains. The degree of crystallinity directly affects the mechanical properties, heat resistance, and degradation rate of PLA.
• Controllable molecular weight: The molecular weight of PLA can be precisely controlled through polymerization conditions. Polymers with a molecular weight of up to 130 kDa can be obtained through direct polycondensation, while higher molecular weight products can be obtained through lactide ring-opening polymerization.

2.2 Production Raw Materials and Preparation Process of PLA

• Starch-based crops: Corn is the most commonly used raw material, with corn starch being primarily used in North America. In addition, cassava and potatoes are also important sources of starch.
• Sugar-based crops: Sugar extracted from sugarcane and sugar beets is also an important raw material for PLA production and is widely used in other parts of the world.
• Cellulose-based raw materials: Materials containing cellulose, such as crop straw and forestry waste, can also be used as raw materials for PLA production, providing a new way to address agricultural waste disposal problems.

• Raw material extraction and saccharification: Starch is extracted from plants such as corn and cassava, or sugar is extracted from sugarcane and sugar beets. Starch needs to be enzymatically hydrolyzed to obtain glucose.
• Lactic acid fermentation: Glucose is fermented under the action of lactic acid bacteria to produce high-purity lactic acid. This step is a key link in PLA production, and the control of fermentation conditions directly affects the yield and purity of lactic acid.
• Lactic acid polymerization: Lactic acid can be polymerized into PLA through two main methods: direct polycondensation and lactide ring-opening polymerization. Direct polycondensation involves directly polymerizing lactic acid monomers, but the molecular weight is relatively low; ring-opening polymerization involves first dehydrating and cyclizing lactic acid to form lactide, and then performing ring-opening polymerization under the action of a catalyst to obtain high-molecular-weight PLA.

2.3 Physical Properties of PLA

• Density and appearance: The density of PLA is 1.21-1.43 g/cm³, and its appearance is white or light yellow transparent granules, with good transparency and a light transmittance of 90%-95%.
• Thermal properties: The melting point of PLA is 150-175℃, and the glass transition temperature is 45-65℃. Compared to traditional plastics, PLA has relatively low heat resistance, typically not exceeding 60°C, which limits its use in high-temperature applications.
• Mechanical properties: PLA has an elastic modulus of 3000-4000 MPa, a tensile strength of 50-70 MPa, an elongation at break of 1.5%-380% (varying with molecular weight and crystallinity), and a notched impact strength of 20-30 J/m. These performance parameters indicate that PLA has good mechanical strength and rigidity, but relatively low toughness.
• Processing performance: PLA has good thermal processing properties and can be processed through various processes such as melt extrusion, film casting, blow molding, and spinning. This characteristic allows PLA to be produced using existing plastic processing equipment, lowering the technical threshold for industrialization.

2.4 Biodegradability Characteristics of PLA

• Hydrolysis stage: The ester bonds (-CO-O-) in the PLA molecular chain break under the action of water, gradually decomposing into oligomers and lactic acid monomers. This process is significantly affected by environmental conditions such as temperature and humidity.
• Microbial decomposition stage: The oligomers and lactic acid monomers produced by hydrolysis are metabolized by microorganisms (such as bacteria and fungi) in the environment as a carbon source, and finally converted into CO₂ and H₂O. This is a key step in the complete mineralization of PLA.

• Temperature influence: Under industrial composting conditions (50-60°C), the degradation rate of PLA is the fastest. According to international standards (such as ISO 13432, ASTM D6400), PLA can usually achieve more than 90% degradation within 6-12 months under industrial composting conditions.
• Environmental conditions: The degradation rate of PLA varies greatly in different environments. Under industrial composting conditions (temperature 58℃, humidity 98%), PLA can be completely decomposed within 3-6 months; in natural environments, it takes 1-2 years; and in soil or water, it can remain stable for several months to a year. However, in home composting, landfills, or marine environments, due to the lack of specific conditions, degradation may take decades.
• Autocatalytic effect: The terminal carboxyl groups of PLA catalyze its hydrolysis. As degradation proceeds, the amount of terminal carboxyl groups increases, accelerating the degradation rate, thus producing an autocatalytic phenomenon. This characteristic causes the degradation process of PLA to exhibit an accelerating trend.

2.5 Current Status of PLA Production and Application

• Rapid capacity growth: PLA is currently the second-highest-produced bioplastic, second only to starch-based bioplastics. In 2010, PLA ranked second in consumption among all bioplastics globally. In recent years, with increasing environmental awareness and technological advancements, PLA production capacity has grown rapidly.
• Wide range of applications: PLA is used in various fields, including packaging materials, disposable tableware, textiles, 3D printing materials, agricultural films, and medical devices. Especially in the packaging sector, PLA is considered an ideal substitute for traditional petroleum-based plastics.
• Gradually decreasing costs: With the expansion of production scale and the maturity of technology, the production cost of PLA is gradually decreasing. It is reported that in 2024, the average price of PLA is between 17,000 and 20,000 RMB/ton, and the price gap with traditional plastics is narrowing.
• Increased market awareness: Consumer awareness and acceptance of PLA products are increasing. Surveys show that 67% of EU consumers are willing to pay a higher price for biodegradable packaging, which provides favorable conditions for the market promotion of PLA products.

 

III. Comparison of PLA and Traditional Plastics

• Raw material source: Primarily derived from fossil fuels such as petroleum and natural gas; approximately 99% of traditional plastics are derived from petroleum or natural gas.
• Resource attributes: Non-renewable resources with limited reserves; the extraction process causes serious environmental damage.
• Production process: Requires complex cracking and refining processes, resulting in extremely high energy consumption and large carbon emissions.
• Cost structure: Significantly affected by fluctuations in international oil prices.

• Raw material source: Primarily derived from renewable plant resources such as corn, cassava, sugarcane, and sugar beets.
• Resource attributes: Renewable resources that can be continuously obtained through cultivation, without relying on fossil fuels.
• Production process: Produced through fermentation processes, resulting in relatively low energy consumption and a significantly reduced carbon footprint.
• Cost structure: Affected by agricultural product prices and climate conditions.
• Comparative analysis: From the perspective of raw material sources, the fundamental difference between PLA and traditional plastics lies in the fact that the former is bio-based, while the latter is petroleum-based. This difference is not only reflected in the renewability of resources, but more importantly, it reflects two completely different development models: traditional plastics rely on limited fossil resources, while PLA relies on sustainable biomass resources. According to statistics, PLA's carbon footprint is up to 75% lower than that of traditional plastics.

• Consumer awareness: Surveys show that only 45% of international respondents can accurately distinguish between the concepts of bio-based and biodegradable plastics.
• Price sensitivity: 67% of EU consumers are willing to pay a higher price for biodegradable packaging.
• Brand impact: Consumers view PLA products as a "more environmentally friendly" option, which helps to enhance brand image.
• Promotion challenges: The phenomenon of "greenwashing" exists, and some consumers have misconceptions about the environmental benefits of PLA.

IV. Comprehensive Judgment on Whether PLA Belongs to Traditional Plastics