Compatibilizers trends

Pospisil, J., Nespurek, S., Pfaendner R. and Zweifel, H., (1997) Material Recycling of Plastics Waste for Demanding Applications Upgrading by Restabilization and Compatibilization, Trends Polym. ScL, 5(9), 194. 

The agro-based composites industry has an opportunity to follow this trend and greatly expand markets for new materials based on blends and alloys with other materials. Most of the research going on today is focused on agrofiber/plastic-compatibilized blends in an attempt to produce materials with consistent, uniform, continuous, predictable, and reproducible properties. 

The third trend is the growing interest in functionalization of polyolefin blends in their melt by means of reactive extrusion. Particular attention has been paid to blended systems PP/PE, PP/EPR, PE/ethylene-octene copolymer (EOC), PP/EOC, PE/PS, and PP/PS functionalized in melt by reactive extrusion. The major field for application of functionalized polyolefin blends is compatibilization of blends of condensation polymers, where they can be used in place of homopolyolefins. 

Although a sizable number of books on polyolefins and general polymer blends are available, only a few chapters address polyolefin blends. Currently, there is no single book that focuses exclusively on the fundamental aspects and applications of polyolefin blends. This is the primary source of motivation behind this book. The second motivation stems from the fact that new research trends in polyolefin blends such as in situ reactor blending and compatibilization/functionalization in the melt have emerged that need to be covered in a book format. 

This book is stmctured as follows Chapter 1 serves as a guide to polyolefin blends introducing this important class of materials, why they are important, typical systems studied, issues of fundamental and applied interest, and current trends. The contributed chapters are divided into two main categories polyolefin/polyolefin blends (Chapters 2-16) and polyolefin/nonpolyolefin blends (Chapters 17-21). Issues covered in these chapters include miscibility, phase behavior, functionalization, compatibilization, microstructure, crystallization, hierarchical morphology, and physical and mechanical properties. Most of the chapters are in the form of review articles. Some original articles are included to capture the latest development in polyolefin blends research. 

The change in volume of the copolymer as the system goes from a miscible to an immiscible state has been utilized as a qualitative measure of its ability to compatibilize a biphasic blend. This can be quantified by using the difference between the volume of the copolymer in the miscible system and the volume of the copolymer in the phase separated system at its deepest quench as a measure of the effectiveness of the copolymer as a compatibilizer. This value is plotted vs. the sequence distribution, Px in Figure 2. This data quantifies the trend that is described above the alternating and diblock copolymers are the best compatibilizers, however within the random structures, the more blocky structures is a more effective interfacial modifier than the statistically random copolymer which is more effective than an alternating-random structure. 

Sarazin et al. reported that the molecular weight of the compatibilizer also has some influence over the dispersion of clay platelets [28]. Their study reveals that composite produced with 330 kg/mol PP-g-MA shows the presence of very small size clay particles when compared to composites produced with low molecular weight PP-g-MA (9 kg/mol). However, the presence of the same compatibilizer in master batch shows a different trend. 

The reverse could be observed in a compatibilized blend. Because in these blends a serious decrease of the spheruhte size was observed, the authors concluded that the compatibihzer acted as a nucleating agent for the PP phase. However, due to the increase of the melt viscosity upon compatibilization, the overall crystallization kinetics was retarded. Additionally, they observed experimentally that AF (free energy for the formation of a nucleus of critical size) and (surface free energy of folding) in compatibilized blends were larger than in PA-6 homopolymer. An opposite trend was observed for the physical PA-6/EPR blends. No further investigations have been dmie to elucidate this phenomenon. 

The maximum apparent shear viscosity was observed at a loading level of 5% w/w for both compatibilizers used. This trend of apparent shear viscosity was found to be the same as the apparent shear stress. 

The results of normalized strength and modulus as a function of monomer content (%) in compatibilized composites are shown in Figure 7. The strength first increased in pre-grafted LLDPE composite due to the improvement at the interface of the matrix and bamboo-fiber and then showed no trend with the addition of compatibilizer. It was clear that the p-grafted composites held good strength with the addition of 1.5%... 

The molecular dynamics of ternary polymer blends of PP/PA6/acrylonitrile butadiene styrene copolymer (ABS) in the presence of compatibilizers and multiwall carbon nanotubes (MWNTs) was investigated using DRS [69]. The relaxation time of the PA6 chains was found to have increased significantly when small amounts of compatibilizers (PP-g-MA) or styrene maleic anhydride (SMA) were added. The variation in relaxation time was found to depend heavily on the com-patibilizer efficiency. The variation in relaxation time for PA6 in the presence of 1 wt% MWNTs in the respective ternary blends also followed a similar trend however, the extent of mobility of the PA6 phase was influenced by the state of dispersion of MWNTs in the corresponding blends. 

According to the actual trends in additive use in polymers, a system composed of starch and a prooxidant such as manganese stearate with a styrene-butadiene copolymer as compatibilizing agent was developed [70, 73]. 

Future development will see two competing trends. On the one hand, major polymer producers will develop and sell standard grades of compatibilizers for major polyblend markets. On the other hand, with growing understanding and experience in compatibilization, increasing numbers of polyblend processors will develop their own proprietary ingredients and techniques for compatibilizing the polyblends they sell. 

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