Commercial LCP blends

This section contains a description of commercial activity in LCP blends. In addition, a discussion of patent activity on the topic is provided. 

Much of the early publication in this field was in the form of patents. There was a flurry of patent activity in the early 1980s in the area of LCP/thermo-plastic polymer blends, starting withTakayanagi at Asahi Early 

Celanese remained active in this area and produced some interesting technology in the mid-1990s. Many of these involved blends in which both components were anisotropic (Section 5.4), but Makhija et al. describe a technique for LCP/isotropic thermoplastic blends in which components are fed sequentially into a mixing die to give additional control over the morphology. Either the LCP or the isotropic polymer can be first, followed by the other component. In some cases solid polymer is fed into an extruded stream of melt. The patent gives numerous examples of PET first vs. LCP first vs. simultaneous feed, and shows improved mechanical properties. 

A relatively recent patent from Foster-Miller describes a multiaxially oriented film in which the LCP component of the blend provides barrier properties and controls CTE, while allowing operations such as heat-sealing 

Some descriptions from the trade literature of the 1990s indicated that commercial products were being launched. Although some of the blends described were development projects, a few sound as if they were commercial at the time. Hoechst-Celanese (actually its Polyplastics joint venture with Daicel in Japan) had two Vectra grades X037 and X039 which were PC/ LCP blends, neither of which have survived. 

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Liquid crystalline polyesters (LCP s) are interesting polymers, exhibiting inherently high mechanical strength and modulus due to a high degree of selforientation very few commercial blends of LCP are commercial. LCP blends... 

The commercial LCP/PPS blend is designed for injection molding complex electronic parts, chip carriers, sockets and cod bobbins. It is very likely that due to its low melt viscosity, LCP still forms the continuous phase, while PPS may simply be present as a dispersed filler along with the glass fibers. Very httle information about this blend has been pubhshed. 

Table 19.38 Typical properties of commercial LCP/PPS blend (GF-reinforced)...

Recently, several researchers (8,10-12) have reported that compatibilized LCP blends exhibit much enhanced mechanical properties, and they have attributed it to the improved interface adhesion between LCP and matrix phases. In this study, an isotropic polymer was incorporated to the binary LCP blends as a third component to solve the problems caused by interface instabilities and poor deformation of LCP domains. The third component was selected from the commercially available block copolymers on the experimental basis, or prepared by synthesizing block copolymers by molecular design. 

The focus of this chapter is more specifically blends in which the reinforcing species is a thermotropic LCP which is blended in a rather conventional way with isotropic thermoplastics (TP). This exploits the inherent strength and low viscosity of the LCP in a way which leads to maximum benefit at minimum processing complexity. This has been an actively studied area of polymer engineering for 40 years and continues to be of interest. We note that though much work has been done on the science of LCP blends, there is also a need to review the exploitation aspects in terms of cost considerations, patents and commercial products. 

The rule of thumb ( ... the reinforcing effect is directly related to the viscosity decrease of the blends compared to the neat thermoplastics ) stated by Fekete et alP is intriguing but of course too simple and limited. There is a need for a more general theory or predictive model of LCP blends which would allow input of rheological parameters, parameters related to adhesion, orientability, degradation temperature, etc. and of course the cost of the components, and allow one to compare the expected material to commercially available grades of glass-filled thermoplastics, etc. 

We feel confident that given the dual benefit of reinforcement and processability improvement, there are high value niches which would be best filled by an LCP blend, particularly a relatively low-cost variant. The potential low cost and unusual rheology of HIQ polymers opens up interesting scientific and commercial possibilities. It would give an opportunity to control viscosity ratio in a novel way. It could be used either alone, or blended with Vectra, since the two seem to be miscible. We would like to see a resurgence of interest in LCP blends and the introduction of commercially successful in situ composite products after all these years. 

The widespread use of LCPs is hindered by their high cost, promoting the study of their blends with conventional thermoplastic polymers. However, commercial LCPs are immiscible with many thermoplastic polymers. The challenge in the processing of thermoplastic/LCP blends is to increase the interfacial adhesion between the blend components while preserving the in-situ fiber formation. An optimum amount of compatibilization is necessary to fully utilize these blends [2,4]. 

Various researchers have attempted to compatibilize blends of commercial LCPs with thermoplastics [2, 4-6], Among the methods they used are the addition of blockcopolymers, catalysts, and acids into the blends as well as prolonged annealing. In the case of polyester/LCP blends, transesterification in the melt state after prolonged annealing creates copolymers with molecular affinity to both phases of the blends [2,4]. 

The study of the ultrasonic treatment of polyester/LCP blends is of particular interest as the continuous compatibilization of these blends is of great commercial value [9]. In this article, we study the effects of high power ultrasound on the rheology, morphology, and mechanical properties of pure PET, LCP and their blends. 

In this research, commercially available PHB/PET copolyester LCP, PEN and PET were mechanically blended to form the LC phase of the blends. The critical composition of PHB in the PEN and PET forming an LC ternary blend was investigated, and the miscibility and thermal behavior were studied using thermal analysis. The PHB content in the ternary blend was controlled by the amount of PHB/PET copolyester, as a high-molecular-weight PHB homopolyester does... 

Most of the work to date concerns the area with the greatest potential for commercial exploitation, the blending of LCPs with conventional polymers. While a few studies of solution blending with Kevlar do exist [57-61], most of the work has centered on melt blending thermotropic copolyesters (Vectra, Xydar) with engineering thermoplastics (PET, PC, PEI, etc.). For convenience, this work may be separated into three blend regions based on LCP content, namely ... 

Polyaryletherketones (PAEK) are aromatic polymers with ether and ketone linkages in the chain, viz. PEK, PEEK, PEEKK, etc. Polyetheretherketone (Victrex PEEK), [-( )-C0-( )-0-( )-0-]jj, was commercialized in 1980 (Tg = 143°C, T = 334°C). Commercial blends of PEEK include, Sumiploy PEEK/PES/PTFE, PEEK/LCP, Cortem PEEK/ LTG, etc. Evolution of PEEK blends technology is outlined in Table 1.73. 

These polyesters, [-0-(t)-C(CH3)2-(t)-C02-(t)-C0-]jj (Tg = 188°C, and HDT = 120-175°C), were introduced in 1974. The commercial resins include U-polymer , Ardel , Durel , and Arylon . Their advantages include transparency, good weatherability and high HDT. PAr has been blended with nearly all resins, including ABS, EPDM, lonomers, LCP, PA, PB, PBI, PBT, PC, PEI, PEK, PET, Phenoxy, PMB, PS, PPE, PPS, etc. Three types of PAr blends are of particular importance — those with polyesters, PEST, polyamides, PA, and with polyphenylenesulhde, PPS. A summary of PAr blends is provided in Table 1.76. 

Table 9.23 lists examples of the compatibili-zation studies conducted in laboratory TSE s, whereas Table 9.24 provides examples from the commercial patent literature. It is noteworthy that about 90% of patents on polymer blends published during the last few years, specify a TSE as the preferred compounder. Exceptions are blends formulated for oriented fibers and films e.g., with LCP) that require high die pressure and thus are usually prepared in a SSE. Similarly, elastomeric blends of either PO or PVC are preferably prepared using one of the older methods, viz. roll mill or Banbury mixer. 

The crystalline polymers such as PPS, LCP, PEEK offer the additional advantages of high solvent resistance. Due to the inherently high cost of the specialty polymers, very few blends have been developed for commercial applications. The only driving force for the development of even the few blends of specialty polymers has been the desire to reduce the cost of the base resins by blending with lower cost engineering plastics, although this invariably results in a lower DTUL. Nevertheless, a few commercial blends of specialty polymers exist and their properties will be discussed below ... 

Recently a PPS blend with liquid crystalline polyesters (LCP) has also been offered commercially in 40% glass tilled form (Vectra V140, Hoechst-Celanese). The liquid crystalline polyester used in this blend is a copolyester of p-hydroxybenzoic acid and 2-hydroxy-6-naph-thoic acid. The melting point of this LCP and of PPS closely match, i.e., T = 285 to 290°C. Since there is no compatibility or reaction between the two components, LCP/PPS blend is considered to be a simple mechanical blend. 

The last several decades have seen an exponential increase in the activity of engineering polymer blends. While this activity will continue, the area that will probably show the most future increase in commercial activity will be in high temperature systems. These blends include LCP and molecular composites as subsections that will be discussed separately. The activity in high temperature polymer blends has been primarily in the patent and published literature. Several examples of developmental and specialty commercial blends have emerged and many more are expected to follow in the future. 

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