PHA and PLA materials differ from traditional plastics such as polypropylene (PP) and polyethylene terephthalate (PET). They have different physical and chemical properties that can influence the extrusion and blowing process.

To achieve optimal results, it is necessary to experiment with different combinations of extrusion and blowing parameters. This includes feed temperature, extrusion speed, blow pressure, cooling time, and blend composition.

PHA is a biopolymer produced by bacteria, while PLA is a biodegradable material derived from renewable resources such as corn or sugarcane. PHA is stronger and harder than PLA, while PLA is more flexible and transparent. PHA has a higher melting temperature than PLA and is more soluble in water.

The percentage of PHA in the blend affects the physical and chemical properties of the material. A higher percentage of PHA in the blend will make it stronger and harder but also more challenging to extrude. It is important to choose the PHA percentage based on the specific needs of the product.

In this article, we will provide details on the parameters to consider for an excellent extrusion and blowing process for PLA and PHA polymers.

Extrusion of PLA and PHA: Temperatures and Parameters

Extrusion involves heating the mixture and transforming it into a continuous form, usually in the form of filaments or granules. To achieve a quality blend of PHA and PLA during the extrusion process, it is essential to carefully consider the optimal temperatures and parameters, as well as suitable extruder configurations for these blends.

Melting Temperature

In general, it is advisable to have a temperature that allows complete melting of the materials without compromising their properties. Usually, it ranges between 160°C and 200°C for PLA and between 140°C and 180°C for PHA.

Extrusion Speed

The speed at which the mixture is extruded affects the quality of the final product. The extrusion speed should be slower for PHA/PLA compared to other plastic materials. Too high a speed can compromise material uniformity and distribution, while too low a speed may cause cooling and solidification issues.

Pressure and Flow

Controlling the pressure and material flow during extrusion is crucial to ensure a uniform blend distribution. These parameters are regulated based on material viscosity and the type of extruder used.

Extruder Configurations

Single and twin-screw extruders are commonly used for PHA and PLA blend extrusion. Twin-screw extruders offer better material mixing and blend distribution.

Temperature Zone Controls

Modern extruders come with zonal temperature controls along the extruder barrel, allowing precise temperature regulation in different sections for uniform material melting.

Extruder Design and Length

Extruder design and length can vary. Some extruders have specific sections for more accurate material mixing or to optimize the melting process.

Mixing Accessories

Some extruders can be equipped with additional accessories to further improve material mixing during extrusion, ensuring a uniform distribution of the PHA and PLA blend.

After extrusion, the material is ready for the mold blowing process.

Mold Blowing

Mold blowing involves forming objects, such as bottles or containers, using compressed air inside a mold. Obtaining the right temperature and material viscosity is essential for effective blowing.

Cooling and Solidification Phases

Cooling and solidification are crucial during the blowing process of PHA and PLA blends.

Cooling of the Blown Object

After being formed inside the mold, the blown object comes out still hot. It is essential to start the cooling process immediately to preserve the desired shape and characteristics.

Temperature Control

Accurate temperature control during the cooling phase is fundamental. Excessively rapid or slow cooling can compromise material properties such as strength and structure.

Use of Air or Cooling Liquids

Usually, air or cooling liquids are used to accelerate the cooling of the blown object. Air can be blown onto the object to aid solidification and ensure uniform cooling.

Cooling Speed Control

The speed at which the material is cooled affects the molecular structure and strength of the final product. Too rapid cooling might cause internal tensions, while too slow cooling could compromise the shape.

Complete Solidification

The material must completely solidify to maintain the desired shape and properties. This process is critical to ensure that the object retains its structure and strength once removed from the mold.

Shrinkage Control

During solidification, PHA and PLA blends may experience shrinkage. Accurate shrinkage control is essential to prevent defects such as deformation of the finished object.

Optimal Cooling Times

Finding the right balance between rapid cooling for solidification and the time needed to preserve the shape and characteristics of the product is crucial.

Careful management of these phases is fundamental to obtaining high-quality finished products with desired properties such as strength, shape, and durability. The mechanical properties and strength of finished products depend on the proper execution of both processes.

Additives can be used to enhance the properties of PHA/PLA, particularly thermal stability, tensile strength, and flexibility.

Advantages of PHA and PLA Blends

The PHA and PLA blend can offer ecological advantages, reducing environmental impact compared to conventional plastic materials. The final material is intended to meet the needs of sectors such as packaging, providing more sustainable solutions in the plastics industry.