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Research process of polylactic acid double drawn and blown films

2022-08-25 Page view : 19 views

PLA occupies an irreplaceable position in green degradable packaging materials, and the film-forming properties and modification methods of PLA have been studied by various countries since the early 20th century. PLA is a new degradable plastic made from lactic acid by fermentation and chemical polymerization with corn starch as the main raw material of terrestrial plants. PLA has good biocompatibility and biodegradability, and various products made from it can be completely degraded in soil, and its final degradation products are water and carbon dioxide.We have PLA sheet extrusion line, which can directly extrude PLA..In addition to the PLA sheet extrusion line, we also have pvc plastic trunk line.

Preparation of polylactic acid films

Modified PLA particles can be made into PLA films that meet production requirements through plastic film molding methods such as cast, extrusion blow molding, biaxial stretching and calendering. There are two main methods of PLA film preparation in the market: one is biaxial stretching (Qingdao InnoPack) and the other is blow molding (Shandong Starck).

Bi-directional stretch film has a series of advantages, such as tensile, impact and bending strength increase significantly, the film weather resistance is also greatly improved compared with ordinary film, the surface gloss and transparency greatly improved; in addition, after bi-directional stretch, the crystallinity of the film increases, the width increases, the thickness decreases and the utilization rate of the material increases. By blow molding, the thickness of the film can be blown thinner, with better flexibility, which is convenient for making various types of packaging film bags.
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PLA film uses in packaging

PLA is most widely used in the packaging field. It has excellent transparency and is suitable for use as packaging material. Soft PLA films can be processed as bags and packaging films for various food products, while rigid PLA sheets can be processed as packaging containers and disposable tableware, such as cold drink cups, lunch boxes and dinner plates. Research shows that PLA packaging film has better freshness than other packaging films such as PE, and because it is a hydrophobic crystalline polymer, it has good resistance to water, alcohol and oil, making it possible to store foods such as fruits and vegetables for longer periods of time.

PLA foams are also slowly replacing foamed PS materials in cushioning materials for appliances and frozen packaging for fish. This foamed PLA is prepared from foamed pellets and has better biodegradability compared to other foamed materials and does not cause environmental pollution.

Advantages and disadvantages of polylactic acid films

In recent years, PLA is a very popular polymer material. PLA is biodegradable and can be used in direct contact with acidic and oily food products, etc. PLA has higher hardness, higher tensile and flexural modulus than traditional general-purpose resins, good biocompatibility and biodegradability, the end product of degradation is water and carbon dioxide, no secondary pollution, making it one of the most promising polymers to replace traditional plastics. This makes it one of the most promising polymers to replace traditional plastics. However, PLA itself has some disadvantages that limit its application scope. Its flexibility is poor, and its impact strength, elongation at break and barrier properties are lower than those of commonly used resins.

From the structure of PLA, it can be seen that the carbonyl group in the PLA molecular chain is co-planar with the neighboring oxygen atoms, and is close to the neighboring carbon atoms, so it is not easy to rotate.

In addition, PLA is susceptible to degradation in the presence of acids, bases, alcohols and water when melted, and has poor heat resistance. In order to better improve the flexibility of PLA and meet the special packaging requirements, PLA needs to be modified to ensure the safety and integrity during transportation and storage. Many domestic and international experts have studied the modification of PLA to improve its flexibility and heat resistance through the regulation of PLA raw material formulation and modification of its film to enhance its competitiveness with petroleum-derived plastic products.

Polylactic acid film reinforced modification

The best way to enhance the modification is to add high modulus fibers to the polymer matrix for composite modification to improve the disadvantages of low modulus and low strength of plastics. Natural plant fiber has the advantages of high specific strength, extensive resources, low cost, renewable and degradable, etc. It is one of the most widely used fibers in polymer composites at present.

Polylactic acid film toughening modification

PLA is a glassy polymer with a very low elongation at break (<10%), which greatly hinders its application in many fields. In recent years, the toughening modification of PLA has become a hot topic of many researches. To improve the toughness of PLA, scholars have investigated many methods, such as melt blending and cross-linking with plasticizers, bio-based toughness polymers, thermoplastic elastomers, and inorganic fillers. Citrate is a green plasticizer approved by FDA as a food additive.The polar reaction between the ester group of PLA chain and citrate makes PLA and citrate have better compatibility and improves the brittleness of PLA by improving the motility of PLA chain segments. Polyethylene glycol (PEG) is a non-toxic, water-soluble crystalline polymer. Low molecular weight PEGS is more compatible with PLA and can effectively lower the glass transition temperature of PLA at lower concentrations, which significantly improves the toughness and impact resistance of PLA. If you need our products, please contact Sheet plate extrusion machine manufacturer.

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