Low Melting Polyester Particles for Energy-Efficient Extrusion
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Solution Overview
Problem
Polyester polymer particles with high crystallinity and melting points require excessive energy for extrusion, leading to increased acetaldehyde production and deformation in molded products, while conventional drying temperatures can cause yellowing and energy inefficiency.
Innovation Solution
Developing polyester polymer particles with a lower degree of crystallinity and a specific melting point profile, comprising at least 75% virgin polyester, an intrinsic viscosity of 0.72 dL/g, and residual acetaldehyde content of 10 ppm or less, which allows for efficient extrusion and reduced energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyester particles are crystallized at high temperatures (140-180°C) for extended periods (40 min to 1 hour) followed by solid state polymerization at 200-220°C for 8-12 hours, then the molecular weight and crystallinity of the polymer are increased, but the melting point increases to above 220°C and the degree of crystallinity exceeds 50%, requiring excessive energy for extrusion
Solution Approach 1:
The patent applies parameter changes by controlling crystallization temperature (80-120°C) and time (5-30 minutes) to achieve a specific degree of crystallinity (20-40%) and melting point (200-220°C). This optimization balances molecular weight development with extrusion energy requirements, avoiding excessive crystallinity that would increase melting energy while still achieving sufficient strength.
Solution Approach 2:
The patent uses partial action by performing limited crystallization (20-40% degree of crystallinity) rather than complete crystallization (>50%). This partial crystallization provides enough structural strength while leaving sufficient amorphous content to reduce the energy required for melting during extrusion, thereby resolving the contradiction between strength and energy consumption.
2Loss of time
If drying temperature is increased to shorten drying time, then drying efficiency is improved, but the polyester particles must first be crystallized to prevent sticking at glass transition temperature (about 80°C)
Solution Approach 1:
The patent applies preliminary action by performing low-temperature crystallization (80-120°C) before drying. This preliminary crystallization creates a stable structure that prevents particle sticking during subsequent high-temperature drying, enabling faster drying times without requiring additional anti-sticking measures or equipment modifications.
Solution Approach 2:
The patent changes the crystallization temperature parameter to a lower range (80-120°C) that is sufficient to prevent sticking but does not overly increase crystallinity. This parameter optimization allows extended drying temperatures to be used safely, reducing drying time while maintaining process simplicity.
3Temperature
If high crystallinity and high melting point pellets are used, then the temperature applied in the dryer can be increased, but more energy is required to melt the polymer particles in the extrusion zone and the production rate of acetaldehyde increases
Solution Approach 1:
The patent optimizes the degree of crystallinity to a specific range (20-40%) and melting point (200-220°C) that allows effective drying at elevated temperatures while minimizing the energy required for melting during extrusion. This parameter control also reduces thermal degradation and acetaldehyde formation, resolving the contradiction between drying temperature capability and harmful emissions.
4Stability of the object's composition
If the degree of crystallinity is increased to improve particle stability, then the melting point increases, but the energy required to melt the particles increases and cycle time increases
Solution Approach 1:
The patent applies partial crystallization (20-40% degree of crystallinity) rather than complete crystallization. This provides sufficient particle stability and structural integrity while maintaining a lower melting point that reduces melting time during extrusion, thereby shortening the overall cycle time and improving productivity without sacrificing necessary stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables energy-efficient extrusion with reduced acetaldehyde generation and improved product quality by lowering the melting point and crystallinity of polyester polymer particles, thereby reducing energy costs and processing time.
Implementation Method 1
the energy required to melt the particles. Accordingly, it would be desirable to melt extrude particles with a lower degree of crystallinity to save energy costs.
Implementation Method 2
the amount of energy applied to the crystallized pellets will depend on the nature of the polymer since each polymer has a different latent heat of fusion, and the degree of crystallinity in any given pellet.
Implementation Method 3
To increase the drying temperature, the polyester particles must first be crystallized to prevent the pellets from sticking at their glass transition temperature (about 80° C.).
Implementation Method 4
then solid state polymerized at about 200-220° C. for about 8 to 12 hours to increase their molecular weight in the solid state.
Implementation Method 5
This crystallization process combined with the annealing or perfecting of the crystals during the long hot solid-stating process imparts to the pellets high melting points of about 220° C. and more.
Data Source
AI summary
A bulk of polyester polymer particles comprising polyester polymer comprising greater than 75% virgin polyester polymer, the particles having:A) an It.V. of at least 0.72 dl/g, andB) 10 ppm or less of residual acetaldehyde; andC) at least two melting peaks, wherein one of said at least two melting peaks is a low peak melting point within a range of 140° C. to 220° C. and having a melting endotherm area of at least the absolute value of 1 J/g.The particles may also have a degree of crystallinity within a range of 20% and a maximum degree of crystallinity Tcmax defined by the equation:Tcmax=50%−CA−OHwhere CA is the total mole % of all carboxylic acid residues other than terephthalic acid residues, based on 100 mole % of carboxylic acid residues, and OH is the total mole % of all hydroxyl functional compound residues other than ethylene glycol residues, based on 100 mole % of hydroxyl functional compounds residues. The preforms and bottles made from these particles can be obtained by melt processing these particles at either lower overall power, faster screw speeds, lower residence time, or lower overall cycle time to thereby reduce the level of residual acetaldehyde generated in the melt.