The raw materials of biodegradable bags include PLA, PBAT, starch, synthetic polymers, plasticizers, starch structure breakers, and other additives. Starch used in the raw materials does not require prior drying or water addition. Synthetic polymers employed in the formulation include polyvinyl alcohol (PVA), ethylene/vinyl alcohol (EVOH) copolymer, and ethylene/acrylic acid (EAA) copolymer. PVA has a molecular weight of 50,000–120,000, a melting point of 160–200°C, and a degree of hydrolysis of 75%–98%, available in granular, flocculent, or powdered forms.

To enhance biodegradability, 10%–50% (by mass) of modified PVA is incorporated into the formulation. Modification methods include:

• Substitution of hydroxyl functional groups with oxo groups (O==) or alkylcarbonyl groups (CR, where R = C1–C4) via reactions of PVA with hydrogen peroxide and persulfate, or with hypochlorite and acetic acid;
• Etherification with ethylene oxide or silane;
• Esterification with sulfate, nitrate, aliphatic, or aromatic acids;
• Reaction with saturated or unsaturated aldehydes to form acetal functional groups.

For ethylene/vinyl alcohol (EVOH) copolymer: ethylene content is 10%–40% (by mass) [30%–45% (by mole)]; melt flow rate is 5–26 g/10 min at 210°C and 0.216 MPa; melting point is 160–170°C. It can be modified using the same methods as PVA. Ethylene/acrylic acid (EAA) copolymer contains up to 30% acrylic acid and is modifiable via identical processes to PVA.

To adjust the water resistance of raw material products, a small amount (2%–3% by mass of total plastic) of hydrophobic polymers such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) may be added.

Plasticizers are added during raw material production to improve the fluidity of high-melting-point synthetic polymers and achieve complete interpenetration between starch and synthetic polymer molecules. Key plasticizers include aliphatic polyols and their mixtures, such as ethylene glycol, polyethylene glycol (molecular weight 200–4000), propylene glycol, polypropylene glycol, glycerol, sorbitol acetate, and sorbitol ethoxylate. Requirements for plasticizers: good compatibility with starch and synthetic polymers, boiling point above 150°C, lower vapor pressure than glycerol at ambient temperature (25°C), water solubility, and dosage of 5%–25% (by mass) of total plastic.

Starch structure breakers are required to gelatinize starch. Common options include water, urea [(NH₂)₂CO], alkali metal hydroxides, or alkaline earth metal hydroxides. When starch is heated above its glass transition temperature and melting point in the presence of water and plasticizers, gelatinization occurs—its structure is disrupted, becoming amorphous and enabling excellent blending with synthetic polymers. Urea, when used as a structure breaker, is added at 2%–5% (by mass) of total plastic.

Other additives in the raw material formulation include:

• Boron-containing compounds (boric acid, metaboric acid and its alkali metal salts, borax and its derivatives): added to improve compatibility between starch and synthetic polymers, as well as the mechanical properties and transparency of products; dosage ≤ 0.4% (by mass).
• Lithium chloride or sodium chloride: serves the same function as boron-containing compounds; dosage 0.5%–3% (by mass).
• Aldehydes, acetals, and ketones: act as crosslinking agents, added as needed.
• Fungicides, mildew inhibitors, flame retardants, herbicides, etc.: incorporated based on specific requirements.

The raw materials of biodegradable bags are produced using masterbatch technology, with equipment including a vented co-rotating twin-screw extruder. Starch, synthetic polymers, plasticizers, starch structure breakers, and other additives are mixed and granulated to form masterbatches, which are then processed into desired products using various molding machines.

Article Title: Introduction to the Raw Material Formulation of Biodegradable Bags URL: https://en.szxylp.com/technical-data/introduction-to-the-raw-material-formulation-of-biodegradable-bags.html