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 PET Crystallization

 
PET based products are replacing more and more materials like glass, PVC, PP or PS. The advantageous properties are food grade admission, high clearity, high impact properties as well as its low specific weight. PET is mainly used for all kinds of packing with the consequences that a large amount of post-consumer PET needs recycling to a valuable raw material. These advantageous properties of PET are due to its special material 
structure and cause some extended treatment for the reprocessing. PET will appear in two different structures, amorphous or crystalline resp. part-crystalline. Amorphous PET is mostly crystal clear, crystallized materials are opak or white (nontransparent). Like all thermoplastic materials which are available in amorphous or crystalline conditions, a 100% of crystallization is not possible. Only a part of the structure can be orientated, that means crystallized. Crystalline and amorphous sections are alternating. The correct expression would be a part-crystallization. PET can be crystallized up to 50%.With the meaning that half of the mole structure is orientated parallel to each other or positioned circular (spherulite).
Consequently will the alternating changing cause a influence on the mole structure. The chains are causing a gravity towards each other and are filling the gaps between the chains.
The molecule structure of PET can be destroyed by destined factores. One of these factores is the thermal degradation. The link of the mole structure will be destroyed through extensive heat introduction. For this reason processing time and temperature are of eminent importance for the production of high quality.
Secondary reduction of material properties is due to the possible hydrolysis of the process. PET has a hygroscopic structure, that means PET is absorbing moisture. This will be packed into intermoleculare gaps of the chains.
Reprocessing of PET requires energy (heat). Too high contence of moisture will destroy the polymer chains and a chemical reaction will separate the PET partly into the original sources of terephtalic acid and ethylen glycol. For this reason the moisture needs to be extracted before the plastification in the extrusion line. Additionally causes amorphous PET a sticking together at a point of heat introduction.
This appearance requires a special process of recycling of PET and forced new recycling technology. Plastmachines recycling systems have been extended in their use for a gentle and economic reprocessing of PET. One makes oneself the advantages of densifying to the appropriate use of drying and crystallization.
A hopper screw feeds the freeflowing flakes or pellets into the crystallizer. Appropriate heating and friction elements in the process chamber and an exact supply of energy enable the optimized conditions for the crystallization process.
Through the high speed rotation of the agitation element an extended agglomeration is protected.
Moisture is evaporated through the corresponding extraction system and the reduction of intermolecular spaces in the basic material. Crystallization and drying is effected in an integrated and combined process. This results in an enormous time saving and a very high efficiency.
The crystallization and drying time is minimized to 60 – 90 seconds and enable on inline operation shortest reaction time on production changings.
The material will be automatically continuously densified and enables a freeflowing pellet production. As the operation temperature is considerable under the softening point, a extremely sensitive preparation is gained without alteration of the IV-value with unsurpassed economic viability.

The Foliolux-Crystallizer of Plastmachines International – the solution for economic recycling of PET.

 
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