PEN copolyesters

Figure 9.5 DSC transitions and crystallizability data for PET and PEN copolyesters and blends m, crystallizable copolyesters , amorphous copolyesters M, crystallizable PET/PEN blends -----------, Tg ., Tm...

Figure 9.5 DSC transitions and crystallizability data for PET and PEN copolyesters and blends crystallizable copolyesters , amorphous copolyesters ...

When the full improved property potential of PEN compared to PET is not needed for an end-use application, copolyesters may be considered. Common available comonomers which may be used include terephthalic acid and isoph-thalic acid (IPA), DEG and cyclohexane dimethanol glycols. 

Many evaluations have led to the commercial utilization of PEN, its copolyesters and blends in some commercial applications. The cost effectiveness is especially apparent in retumable-refillable applications, which take advantage of PEN s chemical resistance in commercial washing operations, so ensuring an increased number of re-fill trips [26], Other applications benefit from PEN s increased gaseous barrier, UV absorption, thinner and lower weight potential. Considerable effort is underway to enable utilization of PEN, its copolyesters and blends for beer, higher hot-fill and heat-pasteurizable containers [27],... 

Chuah et al. [107] prepared a series of PTT/poly(trimethylene napthalate) (PTN) copolyesters by copolymerizing PDO with dimethyl terephthalate and dimethyl naphthalate. The PTN homopolymer has a 7 g of 75 °C and a Tm of 245 °C. Despite the more rigid napthalate moiety, the PTN Tg and Tm were much lower than the Tg of poly(ethylene naphthalate) (PEN), indicating the strong influence of the flexible trimethylene units. 

The modification of PET with naphthalene-2,6-dicarboxylic acid and other additional comonomers is a common measure in bottle manufacturing. Copolyesters based on this compound show excellent barrier properties. Such materials can be produced by addition of the desired amount of comonomer during polymer processing or by blending PET with poly(ethylene naphthalate) (PEN). Additionally, PEN can also be modified by other comonomers such as isophthalic acid (IPA) to improve the flow properties and reduce the melting point. The high price of naphthalene dicarboxylic acid is the reason for its limited application. The overall cost may be reduced by using TPA or IPA as comonomers. 

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... 

Polarized optical photographs of the blends are shown in Figure 20.3. The spherical LCP domains are irregularly dispersed in the PEN and PET phases below 20 mol % PHB content (Figure 20.3(a)). The results observed from 30 mol % PHB reveal a continuous co-existence of the PHB phase and the PEN/PET matrix in the blended polymers (Figure 20.3(b)). However, the blend with 40 mol % PHB shows a nematic LC phase. This result is similar to that found for the copolyesters synthesized by Chen and Zachmann [26], who found... 

The kinetics of crystallization of polyethylene-naphthalene-2,6-dicarboxylate (PEN) and of copolyesters of this material with p-hydroxybenzoic acid (PHB) was studied by Wiswe, Gehrke, and Zachmann. PEN crystallizes in two different crystal modifications. One modification is obtained by crystallization at comparatively low temperatures, the other one is obtained sometimes when the material is crystallized near the melting point. Fig. 55 shows the change in the wide angle scattering during isothermal crystallization at 167 °C and 245 °C. 

Rate [7-18] and temperature [ 16-26] effects on the EWF parameters have been investigated by many authors on several different polymeric materials, like PET [7,18,22,24], PBT [12,21,2.5] PBT/PC blend [8], PEN [11, 26], amorphous copolyester [9], iPP [10,23], sPP [15], UHMWPE 113], LDPE, LLDPE and LDPE/LLDPE blends [19], ABS [13], POM [14] uPVC [16], and PC [17. 20]. The results are not indicating a clear and general trend showing that rate and temperature effects on the fracture parameters strictly depend on the material under investigation. 

One may ask at this stage, why does H then gradually decrease with increasing tm if the molecular weight and the viscosity remain practically constant as shown by additional measurements One possible explanation is that at the beginning of the transesterification process the copolyester has a rather block-like character. Only after longer times does it become a statistical copolymer as found for other similar blends (Fakirov Denchev, 1999). The results, therefore, indicate that the microhardness of the block copolyester is larger than that of the statistical copolymer. The existence of blocks may lead to a microphase separation between PEN and PET blocks. It seems, then, reasonable to assume that parallel packed sequences of blocks with the same chemical compositions would yield mechanically less easily than parallel copolymer sequences of statistical composition. 

Mechanical studies have also been performed on another non-LCP system -copolyesters of PET and PEN, where both copolymer units having flexible chain segments and lack a liquid-crystalline behaviour (Santa Cruz et al, 1992). The whole range of PET/PEN copolymers can therefore be prepared in the amorphous state. 

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