Effect of compatibilizer on the morphology and properties of blends containing polypropylene and nylon-6

207 Journal of Chemistry, Vol. 45 (5A), P. 207 - 213, 2007 EFFECT OF COMPATIBILIZER ON THE MORPHOLOGY AND PROPERTIES OF BLENDS CONTAINING POLYPROPYLENE AND NYLON-6 Received 16 August 2007 Ta thi Phuong Hoa, Vu Minh Duc, Vu Van Khiem Polymer Center, Hanoi University of Technology summary Polymer blends containing nylon-6 and polypropylene (PP) were prepared by using a single screw extruder. Three different types of maleic anhydride modified PP (PPMA06, PPMA1and PPMA05) were used as compabilizers to examine their effects. The properties included tensile strength, Izod impact strength, torque rheometry and extent of water absorption of the resulting blends were measured and the morphology was characterized by using scanning electron microscope (SEM). The crystallization behavior of blends was analyzed by monitoring differential scanning calorimetry (DSC), X-ray diffraction. It seemed that blends compatibilized with PPMA06 exhibited the most homogeneous phase morphology and superior properties among the three. I - Introduction Blending of polyamides (PA) with polypropylene (PP) has found many applications due to its cost-effective and balanced barrier and mechanical properties. The nylon phase offers high strength and excellent resistance to organic liquids, heat, abrasion and wear. However, its tendency to absorb moisture in equilibrium with the environment usually leads to lowering of modulus and reductions in both dimension stability and impact strength. Polypropylene is characterized by its moisture resistance, high elongation-to-break, and low costs, but it suffers from relatively low strength and poor chemical and heat resistance. The incompatible nature of the two polymers usually is indicated by a two-phase morphology of poor bonding between the consisting polymers and a very wide range of dispersed particle size. In order to induce compatibility between polyamides and polypropylene, the approach of introducing a reactive component, such as acrylic acid or maleic anhydride modified polypropylene, as the compatibilizer into the system seems to have received the most attention. [2 - 4] have been reported the chemical modification of PP to contain pendant carboxylic groups, which are potentially reactive with polyamides, improvements of phase morphology and mechanical properties. The purpose of this study is to examine effect of compatibilizers on the phase morphology and properties of PP/PA-6 blends. In particular, the influences of different compatibilizers are explored. II - Experimental 1. Materials and blend preparation All polymers used in this work were commercial PP, PA6, and compatibilizers 208 (PPMA06, PPMA1, and PPMA05). The blends were prepared using a Brabender laboratory extruder (D = 19 mm, L/D = 25). PP, PA6 and compatibilizers were dried in an oven at 100oC for over 8h. The granules were dry- mixed in appropriate ratios and extruded at screw speed of 50 rpm and then granulated and injection-molded into the test specimens. Mechanical properties Tensile properties were obtained using an Istron model 5582 at a crosshead speed of 20mm/min, following ISO 527. Impact strength was determined using a Radmana ITR-2000 (Australia) in Izod mode. All results were the average of at least ten measurements. Specimens for the water absorption measurement had dimensions of about 25 × 10 × 3 mm and were dried prior to measurements. The thermal analysis was carried out using a BAHR DSC 301L (Germany). The melting temperatures were determined at a heating rate of 10oC/min. The percent crystallinity was calculated using the following equation: 1000 * ×   = f H f H  Where  is the % crystallinity, H*f is the heat of fusion for PP or PA6 in the corresponding blend and H0f is the heat of fusion of 100% crystalline PP or PA6 and was taken as H0f (PA6) = 230.1 J/g and H0f (PP) = 207.1 J/g. A scanning electron microscope (JEOL JSM 5300) was used to examine the morphology of the blends. The diffractograms were obtained from sample prepared at 220oC and a pressure of 5 bar, using a VNU-HN-SIEMEN D5005 diffractometer with Cu anode generator, registered between 2 = 50 – 350. Table 1: Physicochemical Properties of the Raw Materials Sample Code Commercial name Supplier Melt index (g/10 min) Function group (%) PP PPJ700 Japan 8.00 - PA6 Nylon UBE Thailand 8.39 - PPMA06 - Aldrich - 0.6 PPMA1 - Austria - 1 PPMA05 - Polymer Center, Hanoi, Vietnam - 0.5 III - Results and discussion 1. Torque and Morphological observation 0 2 4 6 8 1 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 To rq ue (N m ) w t% o f P P M A P P M A 0 5 P P M A 0 6 P P M A 1 Figure 1: Torque vs. wt% compatibilizers for 70PA/30PP blends Figure 1 compares the torque between the non-compatibilized blends and the compatibilized systems. It can be inferred that all the blends containing the compatibilizer have higher torque level than non-compatibilized blends. The increase in torque level can be attributed to the higher reactivity of maleic anhydride resulting in formation of new covalent bonds between these groups and the terminal amine groups of the polyamide. For all three kinds of PPMA, the compatibilizer concentration of 4 wt% shows a higher increase in torque values than that of 2 and 6 wt% compatibilized systems, emphasizing the optimum concentration of the compatibilizer in 209 the blends. From figure 1, it can be seen that the PPMA06 compatibilized blend demonstrates the highest torque level. SEM micrographs of fractured surfaces prepared at a liquid nitrogen temperature show lack of interfacial adhesion in the binary blends of PA/PP (70:30) as shown in figure 2. The dispersed phase particles are large and irregularly shaped and have relatively smaller contact areas with the matrix. Figure 2: SEM micrograph of blend containing 70PA/30PP Many voids suggest that the PP dispersed particles are pulled out during the cryogenic fracture because of the poor adhesion between the two phases. For PP/PA/PPMA05 (2 wt %) blends, a drastic reduction in particle size of the PP dispersed phase was observed (Fig 4b) that shows increased adhesion between the PP and Nylon-6 phases. Homogeneity of dispersion and decreased size of the PP dispersed phase in compatibilized blends increases the surface area in contact with the matrix, resulting in better adhesion of the dispersed phase and the PA matrix. In the blends containing 4 and 6 wt % PPMA05, dispersed particles and voids are not seen (Figs. 4c, d). This phenomenon was also observed in the blends containing 2, 4 and 6 wt % PPMA1 or PPMA06 (Figs. 3 a, b, c, d, e, and f)]. The morphology of these compatibilized blends looks very homogeneous, indicating the strong interaction and adhesion between the PP and PA due to the presence of reactive maleic anhydride groups. Mechanical Properties Yield stress, elongation at break and impact strength values are plotted as functions of compatibilizer concentrations in figure 5. It was observed that the performance of non- compatibilized blend is strongly influenced by the addition of PPMA. The mechanical Figure 3: SEM micrographs of 70PA/30PP compatibilized with (a) 2%; (b) 4%; (c) 6% PPMA06 and (d) 2%; (e) 4%; (f) 6 % PPMA1 a b c d e f 210 0 20 40 60 80 100 120 -2 0 2 4 6 8 PP PA Im pa ct St re ng th ,k J/ m 2 wt. % Compatibilizer -2 0 20 40 60 80 100 0 2 4 6 8 PP PA Y ie ld St re ss ,M PA wt. % Compatibilizer 0 200 400 600 800 1000 0 2 4 6 8 PA PP E lo ng at io n at B re ak ,% wt. % Compatibilizer PPMA06 PPMA1 PPMA05 Figure 5: Tensile and Impact properties of blends (70PA/30PP) versus weight percentage of compatibilizer Figure 4: SEM micrographs of 70PA/30PP compatibilized with (a) 0%; (b) 2%; (c) 4% and (d) 6% PPMA05 properties go on increasing with increasing concentration of compatibilizer up to 4wt%. On further addition of the compatibilizer (6 wt%), a slightly decrease in these properties was observed, emphasizing again the optimum concentration of the compatibilizer in the a b c d 211 blends, as shown in the torque level and SEM. The blends with PPMA1 or PPMA06 show an improvement of all the mechanical properties. However the blends with PPMA05 only show an increase in tensile properties whereas impact strength slightly decreases. So, PPMA1 and PPMA06 work better than PPMA05. The interest is that the impact strengths of the blends compatibilized with PPMA1 or PPMA06 are higher than not only those of corresponding non-compatibilized blends but also those of both neat PA and PP. It was observed from figure 5 that tensile elongations at break of all the compatibilized blends are considerably higher than the non- compatibilized one. That indicates an increase in toughness, which is defined as the area beneath the stress-strain curve. The above observation may be ascribed to the fact that in the PP/PA blends without compatibilizer the components are incompatible, with almost no mutual adhesion. Furthermore, the large size of dispersed PP particles probably hiders cold drawing of PA matrix, causing the premature rupture of the material and lowering of the elongation values. That can be explained on the basis of formation of PP-graft-PA copolymer during melt blending, which is mostly located at the interface of PP/PA, acting as an interfacial agent. Thus higher homogeneity probably contributes to a decrease of the high stress concentration around the dispersed PP particles by local plastic deformation and by making the system more efficient for cold drawing Water Absorption PA are very sensitive to the humidity. Blending PA with PP can reduce water absorption. Figure 6 shows that all the compatibilized blends have lower percentage water absorption than PA and non- compatibilized blends. Water susceptibility of PA is mainly due to the presence of amide/amine groups. In 70PA/30PP, the addition of PP may be resulting in a decrease in the number of amide groups, leading to a significant drop in the percentage of water absorption. In compatibilized blends, the maleic anhydride groups may interact with the amide/amine groups of PA causing the reduction of number of free amide in the blends and therefore can reduces the water susceptibility. It can be seen that the 70PA/30PP with 4% PPMA06 has the lowest percentage water absorption. A combination of several results above can show that PPMA06 seems to be the most efficient compatibilizer among the three systems studied. 0 10 20 30 40 50 60 70 -2 0 2 4 6 8 10 12 W at er ab so rp tio n, % Time, day Polyamide PA 70PA/30PP 70PA/30PP with 4% PPMA05 70PA/30PP with 4% PPMA1 70PA/30PP with 4% PPMA06 Figure 6: Water absorption versus time Thermal Analysis The melting and cooling characteristics of the blends and the pure components were recorded using differential scanning calorimetry 212 (DSC). The pure PP and PA show single Tm around 162 and 218oC, respectively, whereas the endotherms of the blends show two separate Tm, each corresponding to the individual components. Similarly the pure PP and PA show single TC around 111 and 152 oC, respectively, whereas the exotherms of the blends show two TC: 118 oC for PP phase and 186 for PA phase. No significant differences in both endotherms and exotherms between compatibilized and uncompatibilized blends were found from DSC data in table 2. Table 2: DSC Exotherms and Endotherms Data of PP, PA and PP/PA blends PP Phase PA Phase Specimens Tc, oC Tm, oC Hm, J/g , % Tc, oC Tm, oC Hm, J/g , % PP 111.5 162.3 73.8 35.6 - - - PA - - - 152.3 218.5 45.6 19.8 70PA/30PP 118.5 163.4 17.0 8.2 186.1 219.8 30.9 13.4 70PA/30PP/4PPMA06 118.1 162.2 30.1 14.9 185.6 219.0 32.0 14.0 The percent crystallinity of PP and PA phases in the blend is given in table 2. This suggests that the presence of the PA component has considerably reduced the degree of crystallinity of PP in the blend, whereas the presence of PP, which is in molten state during the crystallization of PA 6, has slightly decreased the overall degree of crystallinity of the PA in the blend. X-ray Diffraction Figure 7: X-ray diffraction diagrams of the blends and the pure PP, PA As shown in Fig 7, the X-ray diffraction spectrum (XRD) of the neat PA showed a characteristic  crystalline form, corresponding to reflection (2) at 210. The neat PP exhibited a mainly -crystalline form as the major reflections appeared at 2 = 14.0, 16.6, 18.3, 21.0 and 21.70, corresponding to the (110), (040), (130), (111), and (  1 31) plane of -PP, respectively. At 2 = 15.90, a reflection is found, corresponding to the (300) plane of the -PP. In fact, the -PP has another reflection at 2 = 21.00, which corresponds to the (311) plane of the -PP. This reflection is relatively weak compared with the (300) plane of the - PP and overlapped with the (111) plane of - PP. Thus, the -PP reflection mentioned in this article refers to the typical (300) plane reflection peak at 2=15.90. XRD of profiles of the 70PA/30PP and the 70PA/30PP/4PPMA06 blends showed similar results to that of PP. However, for these blends, the -crystalline reflection at 2=15.90 becomes much weaker. It is noteworthy that the reflection peaks of the crystalline PA in these blends can not be easily identified from XRD patterns (Fig. 7). This may be explained by the fact that the PA crystalline reflection ( form at 2 = 210) may be masked by the (111) and (  1 31) reflections of -PP. 213 IV - Conclusions In this study it was observed that blending PP and PA with small amounts of PPMA as compatibilizer remarkably influences on the tensile properties, impact strength and water absorption of the blends. The morphology of compatibilized blends indicates no phase separation and finer dispersion and good adhesion. This resulted in higher torque level and water absorption properties of the blend. Among three different types of PPMA, PPMA06 provided the most homogeneous phase morphology, superior mechanical properties, the highest torque level and the lowest water absorption of the blend. The 4 wt % PPMA was observed to be the optimal concentration for these 70PA/30PP blend system. References 1. Jeng-yue Wu, Wan-chung Lee, Wen-faa Kuo and Hsin-Ching Kao. Advances in Polymer Technology, Vol 14, No. 1, 47 - 58 (1995). 2. Sachin N. Sathe, Surekha Devi, G. S. Srinivasa Rao and K. V. Rao. J. Appl. Polym. Sci., Vol. 61, 97 - 107 (1996). 3. J. Duvall, C. Sellitti, C, Myers, A. Hiltner and E. Baer, J. Appl. Polym. Sci., Vol. 52, 195 - 206 (1994). 4. F. P. La Mantia, Advances in Polymer Technology, Vol. 12, No. 1, 47 - 59 (1993).