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When it comes to thermoplastics, it's essential to understand that most of these kinds of materials are initially wet before they undergo processing, molding, and forming. While some thermoplastics may exhibit surface moisture, others can absorb moisture at the molecular level, which is often invisible to the naked eye. In this article, we will explore the significance of pre-drying thermoplastics, shedding light on the vocabulary and basic principles of which processors should be aware. By properly drying thermoplastics, manufacturers can help eliminate aesthetic defects, prevent chemical attacks, and ensure the overall quality of their products.

Addressing Moisture-Related Challenges:

Correctly drying thermoplastics plays a crucial role in the efforts to avoid aesthetic defects caused by the presence of water. Moisture can originate from within the pellet or condense on the surface of non-hygroscopic resins, leading to potential issues during processing. By implementing proper drying techniques, manufacturers can help prevent cosmetic problems and even chemical reactions, such as hydrolysis, where water molecules break chemical bonds within the polymer. It is important to note that some non-hygroscopic materials may still require drying due to the presence of additives. For instance, impact-modified Polyoxymethylene (POM) typically does not require drying, but when an impact modifier (e.g., polyurethane derivatives) is added, pre-drying becomes necessary.

In Nexeo Plastics' extensive product line card, approximately 90% of the materials offered require proper drying before processing. This statistic highlights both the widespread relevance and the importance of understanding the drying process for thermoplastics.

Key Elements in the Drying Process:

The drying process involves four key elements: heat, airflow, dew point, and drying time. Each element plays a fundamental role in achieving effective drying of the material and in helping to maintain product quality.

1. Heat: Heat is the primary element in reducing moisture in thermoplastics. Whether dealing with hygroscopic or non-hygroscopic resins, the introduction of heat enables water molecules to move more easily and weakens the forces that attract water to hygroscopic polymer chains.
2. Airflow: Proper airflow is critical in the drying process. Proper airflow ensures that the dried air is carried to the hopper unit and that used air that has picked up moisture after passing through a resin-rich environment is recycled. For hygroscopic materials, hot air with a low dew point (-40°C target) is necessary to remove water molecules from the plastic. In the case of non-hygroscopic materials, hot air is introduced to evaporate condensed moisture on the pellet's surface.
3. Dew Point: The dew point refers to the temperature at which moisture in the air starts to condense. Introducing low dew point dry air to the material causes moisture molecules within the chemical structure to migrate to the surface. Forced airflow then transfers the surface moisture to a desiccant, where it is trapped. It's important to monitor desiccants as they become saturated over time and require replacement. Signs that desiccants need replacement include the dryer not holding a dew point between -20°C and -50°C or if the desiccant beads crumble when pinched.
4. Drying Time: Drying thermoplastic resins requires patience, as it is not an immediate process. The type of material and its initial moisture content determine the required drying time. Resin suppliers typically provide suggested drying times of 2 to 4 hours, while emphasizing cumulative drying times should not exceed 8 to 12 hours. Excessive drying can lead to the degradation of small molecular weight constituents within the formulation. Drying time is generally shorter for non-hygroscopic materials.

By following proper drying procedures for thermoplastics, manufacturers can often enjoy several key benefits:

1. Maximizing Efficiency: Proper drying minimizes potential production delays caused by moisture-related defects. By eliminating issues upfront, manufacturers can help streamline their processes and maintain efficient production lines.
2. Maintaining Consistency: Consistency is crucial for producing high-quality products. Proper drying helps ensure that the material properties remain consistent throughout the manufacturing process, leading to consistent end products.
3. Eliminating Issues Downstream: By addressing moisture-related challenges early on, manufacturers can also help prevent issues downstream, such as defective parts or compromised product performance, saving time and resources while maintaining customer satisfaction.

Properly drying thermoplastics is essential for helping to maintain product quality, prevent defects, and maximize efficiency in manufacturing processes. By understanding the principles of drying thermoplastics and implementing the necessary steps, manufacturers can help eliminate potential issues caused by moisture and be better positioned to ensure the overall success of their thermoplastic projects.