Mechanical recycling of thermoplastics for high value applications is directly associated with restabilization. The state of the art of processing-, long term heat-and light stabilization of recyclates in different polymers (e.g. PP, PPEPDM, HDPE, LDPE, PS, PVC and various blends) with examples from packaging, distribution, automotive and construction industry is shown. Because of predamage and impurities, recyclates degrade faster and differently compared with virgin polymers and, therefore, specially designed stabilizer systems are required according to the previous damage, subsequent application and type of polymer.Recommendations for restabilization include combinations of phenolic antioxidants and phosphites as well as HALS compounds or "Recyclostab" stabilizer systems.

The role of additives in creating tailor-made plastics and in generating innovative products is commonly accepted. Stabilizers, pigments, lubricants, impact modifiers and other additives enable safe and effective processing and guarantee, for example, mechanical properties and appearance appropriate for the required service time. Recycled plastics still suffer from the imputation of being of low value and, consequently, acceptable only for "second-hand'' applications. The concept of restabilization and repair has been introduced in order to provide recyclates with properties similar to those in their original use ("closed loop") or to upgrade them to high-value applications, thus providing a potential substitute for virgin materials. Supplying the necessary processing and long-term stability of the recyclate including elimination of the negative influence of prodegradants and of impurities are the key factors of this idea. The concept presented here comprises the development of an appropriate formulation for recyclates taking into consideration both the materials source and the targeted application. It may be classified into four scenarios:-Closed-loop applications from clearly defined sources (e.g., bottle crates, waste bins, automotive parts) require a carefully adjusted restabilization system with sufficient amounts of processing, light, and heat stabilizers. At least the part of stabilizers used up in the first life has to be compensated.-The formulation of recyclates in applications different from the original ones depends clearly on the requirements. For instance, a recyclate from packaging applications utilized in long-term applications is only attainable by means of the addition of heat andlor light stabilizers. The type and amount of the suitable stabilizer system have to be defined according to the material (e.g., PP, HDPE, blends), the targeted lifetime and the application area (e.g. outdoor), above all, however, the final product itself (e.g., thick posts or thin films).-If impurities such as paint residues, printing inks or a heavily degraded material cause severe problems with respect to processing and material properties, the addition of reactive compounds can compensate their negative contribution. For example, selected oxirane key compounds are able to eliminate to a great extent the detrimental influence of paint residues in PPIEPDM bumper materials on the mechanical and long-term heat properties of the material.-Recyclates of condensation polymers such as polyamides and polyesters as well as their blends are degraded mainly by hydrolytic cleavage of the polymer chains. The reduced molecular weight can result in inferior properties rendering certain applications impossible. However, difunctional oxirane compounds in combination with catalytically active accelerators can entirely repair the predegradation through a chain-extension process. The concept of restabilization and of repair molecules has been translated into a proprietary product line ('Recyclostab, 'Recyclossorb, aRecycloblend) special...

A remelting-restabilization technique was applied for the recycling of postused, yellow-pigmented high-density polyethylene (HDPE) bottle crates. Multiple extrusion cycles procedure, at different reprocessing temperatures, was performed for monitoring the processing stability of the restabilized and nonrestabilized material as reference. In addition, mechanical properties measurements were carried out, to study further the effect of restabilization on the performance of the recycled material. Finally, repigmentation was used to investigate the role of new pigments on the final recycled product. The results illustrate that restabilization of postused crates leads to careful reprocessing without severe degradation, which is an essential prerequisite for reuse in the original application.

Oven aging was applied for about 8800 hours (more than one year) to evaluate the long‐term thermal stability of post‐used HDPE material recycled from bottle crates. For recycling, the remelting‐restabilization technique was applied. To study the effect of restabilization, crystallinity and melt flow rate were monitored during heat aging. Furthermore, tensile strength and tensile impact strength were followed together with the time until embrittlement. These data were enriched with microphotographs of the specimens' surfaces. Finally, repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The results illustrate that restabilization is mandatory for improving the long‐term thermal stability of the post‐used crate material, enabling its reuse in the original application.

Artificial weathering was applied for about 8000 h to evaluate the light stability of postconsumer high‐density polyethylene (HDPE) material recycled from bottle crates. For recycling the remelting‐restabilization technique was applied. To study the effect of the restabilization, the tensile impact strength was monitored during the artificial weathering exposure. The data were compared with microphotographs of the specimens' surface. Repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The repigmented grades were further studied by colorimetric determinations of the color difference (ΔE) during artificial weathering. The results illustrate that the restabilization is mandatory for improving the light stability of the postconsumer crate material, ensuring its re‐use in the original application. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1118–1127, 2000