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

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 207 (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 Table 1: Physicochemical Properties of the Raw Materials Sample Commercial Supplier index Function min) (%) PP PPJ700 Japan 8.00 -PA6 Nylon UBE Thailand 8.39 - PPMA06 - Aldrich - 0.6 PPMA1 - Austria - 1 Tensile properties were obtained using an Istron model 5582 at a crosshead speed of PPMA05 -20mm/min, following ISO 527. Impact strength was determined using a Polymer Center, Hanoi, Vietnam - 0.5 Radmana ITR-2000 (Australia) in Izod mode. All results were the average of at least ten III - Results and discussion measurements. 1. Torque and Morphological observation Specimens for the water absorption measurement had dimensions of about 25 × 10 × 40 3 mm and were dried prior to measurements. 35 30 The thermal analysis was carried out using a 25 BAHR DSC 301L (Germany). The melting 20 temperatures were determined at a heating rate 15 of 10oC/min. The percent crystallinity was 10 calculated using the following equation: 5 P PM A05 P PM A06 P PM A1 H * = ´ 100 H f 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. 208 0 0 2 4 6 8 10 w t% of PPM A 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 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 a b c d e f Figure 3: SEM micrographs of 70PA/30PP compatibilized with (a) 2%; (b) 4%; (c) 6% PPMA06 and (d) 2%; (e) 4%; (f) 6 % PPMA1 209 a b c d Figure 4: SEM micrographs of 70PA/30PP compatibilized with (a) 0%; (b) 2%; (c) 4% and (d) 6% PPMA05 100 1000 80 800 PA 60 600 40 400 PA PP 20 200 PP 0 0 -2 0 2 4 6 8 wt. % Compatibilizer 0 2 4 6 8 wt. % Compatibilizer 120 100 80 PPMA06 60 PPMA1 40 PA 20 PP PPMA05 0 -2 0 2 4 6 8 wt. % Compatibilizer Figure 5: Tensile and Impact properties of blends (70PA/30PP) versus weight percentage of compatibilizer properties go on increasing with increasing concentration of compatibilizer up to 4wt%. On further addition of the compatibilizer (6 wt%), a 210 slightly decrease in these properties was observed, emphasizing again the optimum concentration of the compatibilizer in the 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. 12 10 8 6 4 2 0 -2 Polyamide PA 70PA/30PP 70PA/30PP with 4% PPMA05 70PA/30PP with 4% PPMA1 70PA/30PP with 4% PPMA06 0 10 20 30 40 50 60 70 Time, day 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 211 ... - tailieumienphi.vn