Compatibilized Recycled Polymer Blends

Binary req cled polymer blends, such as recycled polyolefin-polystyrene or polyolefin-polyamides, have poor mechanical properties. It is found in these cases that to introduce styrene-hydrogenated butadiene-styrene block copolymer or maleated polyolefins, respectively, as compatibilizing agents has great benefits. These both produce finer morphologies and enhanced mechanical properties. Other additives [55 to 69] should also be included into recycled polymer blends. We describe this in detail in Section 8.4.3. 

---

Recyclable polymer blends. Here, the recyclability is conditional on re-generation of morphology, by means of re-compatibilization, re-stabilization, and re-compounding. 

In the following text examples of recycled polymer blends will be given, first for the commodity, then for the engineering and specialty resin blends. Whenever possible, the methods of compatibilization and re-compatibilization should be the same. In particular, when recycling is to reproduce the original blends performance, the same compatibilization method is essential. For this reason, support of the blends manufacturer should be ascertained. 

To recycle polymer blends it is important to regenerate the morphology and to restabilize the ingredients. Thus, it is necessary to provide adequate mixing, re-compatibilize and restabilize the blend. Frequently, the recycled blends should be impact modified. There are two reasons for this (i) contamination of the composition by other polymers and (ii) degradation of the usually less stable compatibilizers and impact modifiers. 

When the heterogeneous recycled polymer blends are to be used for applications without a downcycling, the materials must show improved mechanical properties. These can be generated ascertaining fine phase dispersion and intensive interactions between the phases. The method that leads to such improvement of properties is known in polymer blends industry as compatibilization. 

Blends of PET and HDPE have been suggested to exploit the availability of these clean recycled polymers. The blends could combine the inherent chemical resistance of HDPE with the processing characteristics of PET. Since the two polymers are mutually immiscible, about 5% compatibilizer must be added to the molten mixture (41). The properties of polymer blends containing 80—90% PET/20—10% HDPE have been reported (42). Use of 5—15% compatbilizer produces polymers more suitable for extmsion blow molding than pure PET. 

Much effort is being expended on polymer blends to reduce the need for separation and to improve the properties of the recycled materials. Because most polymers are incompatible with one another, this usually requires the addition of a compatibilizer,151 or the preparation of one in situ. (Com-... 

Compatibilization and upgrading of commingled plastics for reprocessing, and (3) Recycling of polymer blends [Akovali et al., 1998]. 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process, viz. reactive injection molding (RIM). However, most often the term refers to reactive extrusion, and in particular, to the reactive compatibilization of immiscible polymer blends, usually conducted in a TSE. During the last 50 years, the latter machines have been used as chemical reactors for the polymerization, depolymerization (chemical recycling), polymer modification and compatibilization [Brown, 1992, Xanthos, 1992 Utracki, 1989, 1991, 1994, 1997]. 

Figures 16.8 and 16.9 illustrate the extend to which the judicious stabilization is able to protect polyolefin resins and their blends from the thermo- (Figure 16.8) or photo-degradation (Figure 16.9). As the data indicate, the recyclates even after five extrusions show performance within 10% approximating that of a virgin material. Similar behavior is expected for strongly immiscible polymer blends, under the condition that the recyclates will be re-compatibilized to recover the original morphology.

Bio-based and recycled polymers often have short-lifecycles compared to oil-based virgin resins. We studied bio-based (PAX) and recycled (PA6) polyamide (PA) blends [LOU 13]. Scanning electron microscopy (Figure 12.4) shows that the formulations are composed of 75% PA6 and 25% PAX by mass (denoted PA6/PAX (25/75)) and PAX nodules appear in the PA6 matrix. To refine the morphology and improve PA6/PAX interfaces, we conducted reactive compatibilization to couple the... 

These materials, known as polymer blends or polymer alloys (see Table 1.3), are generally prepared by mixing two or more thermoplastics. They combine, in an advantageous manner, the properties of the thermoplastic components, and in some cases, the properties of the blends are superior to those of the individual components. (Polymer mixtures also result from the recycling of mixed plastics which have to be identified before they can be reused.) Because of the large number of possible blend components, and the fact that usually so-called compatibilizers of often rather complicated chemical composition are present, a complete analysis of polymer blends is not possible with simple methods. However, by means of some screening tests and selected special tests, one can at least obtain qualitative information about the main components of such systems. 

In some cases, lack of noticeable influence of electron beam radiation on the values of tensile and Charpy impact strengths of 24-23-21-15-17 LDPE-HDPE-PP-PS-PET blends (based on recycled polymers) compatibilized with 1% trimethylol propane trimethylacrylate (TMPTMA) were found. Zenkiewicz et al. ° explained this lack of influence by the protective action of aromatic rings of PS and PET that hindered cross-linking. In the same article, the addition of 10% of styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS-g-MA) led to the great increase of both tensile and Charpy impact strengths. 

Applications of these reactive polymers to the compatibilization of various polymer blends are made to improve the impact strength, tensile strength, permeability, heat resistance, crystallization, morphology, and other properties of polymers and recycled plastics. 

Polymers from carpet waste produced by melt processing may be used to make products in a molding process, either alone or blended with virgin polymers. The recycled polymers may also be used as matrices in glass fiber reinforced composites. For such applications, the properties of the composites are dominated by the reinforcement (glass fibers), and therefore even recycled polymers without compatibilization could provide the composites with satisfactory mechanical properties. ... 

---