Reactor-produced TPOs

There are two methods used to blend polypropylene and EPDM rubber to make a TPO. The original method, still used extensively, is to simply mechanically blend the two polymers together with high shear mixing at an elevated temperature. However, a newer procedure employs new catalyst technology to blend EPDM and PP in the polymer reactor itself. This newer technique lowers the TPO production costs however, this type of TPO can only be obtained from the polymer manufacturers themselves. Reactor-produced TPOs can also be made softer than the mechanically blended TPO types. Some TPOs are also based on polyethylene as well (such as metallocene-catalyzed polyethylene), see Figure 6.7. 

TPO can be prepared either by melt mixing PP and elastomer in an extruder or by copolymerization of olefins in a series of reactors to give a blocklike structure. The reactor-made TPO produces a fine and stable morphology due to controlled reaction parameters however, they have an elastomer composition fixed by the polymerization process. On the other hand, extruder-made TPOs provide wide flexibility in... 

An in-reactor TPO may be defined as a reactor-produced polypropylene copolymer (PP-b-E/P), containing between 22 % and 55 % ethylene-propylene copolymer blocks. Small amounts of other comonomers, such as octene-1 or butene-1, may also be present so as to provide unique functionality. In-reactor propylene block copolymers containing less than 20 % ethylene are fairly hard and are usually classified as impact polypropylenes. Reactor-made polymers containing >50 % ethylene are soft and also have relatively poor elastomeric properties - these are classified as plastomers. 

As compounders developed and refined TPO blend technology, PP manufacturers pursued an alternate approach to PP impact modification by developing PP impact copolymers (ICPs). These products are produced in a series of reactors. The first reactor produces PP homopolymer, followed by one or two gas phase reactors in which ethylene is introduced to produce EPR. The gas phase reactor can be either a vertical fluidized bed or a horizontal stirred bed design (6). Because of different reactivity of propylene and ethylene inside the gas phase reactor, complex mixtures of PP with ethylene-propylene copolymers and linear low-density polyethylene (LLDPE) are produced. 

TPOs, comprising TPEs with a polyolefin matrix and an unvulcanized rubber. They can be produced by blending or by block copolymerization of polypropylene and EPDM (reactor TPOs). Sometimes TPVs are included in TPOs. 

Figure 3. TPO (a) and ESR (b) evidence of carbonaceous deposits produced on Si02-Al20, (25%) during cyclohexene hydrogenation while fluidised in the reactor [7] at 296-393K with (—) and without (——) Pt/alumina pellets. In TPO the samples were heated in (VN2 at 5K.min l.

Figure 4. Relationship of aedvity in cyclohexene hydrogenation at 343K of carbonaceous deposits produced on SiC -A C (25%) in the reactor [7] to TPO intensity (and hence number of unpaired electrons seen by ESR).

Temperature programmed oxidation (TPO/MS) was performed with 50 mg of the deactivated samples in a microreactor with 1% 02/He, flowing at 30 ml/min (heating rate 5 K/min). The reactor effluent was monitored by a Balzers QMS200 quadrupole mass spectrometer. Carbon monoxide was not detected in the effluent gas. Thus, the profiles of O2 consumed and CO2 produced represent the complete oxidation. 

Coke was characterized by Temperature-Programmed-Oxidation (TPO). These experiments were carried out using a modified unit. The CO2 produced during the coke burning is converted to CBU, in a methanator reactor. A H2 stream is fed to this reactor, which is loaded with a Ni catalyst, in order to quantitatively convert CO2 into CH4. This compound is then continously monitored by a flame ionization detector (FID). With this configuration the sensitivity and resolution of the classical TPO technique is greatly improved. Typically, 10 mg... 

Figure 4 shows the TPO profiles of catalysts in the four sections under 1%02/He A small amount of carbon is oxidized before 400 <>C. Host of the coke is removed between 400 and 600 °C. The TPO spectra above 400 °C composed of three different peaks. The first is represented by the low temperature shoulder (label A), and the third one by the high tempeature shoulder (label C). The temperature of the main peak (label B) shifted to lower temperature from section 1 to 4, being 566, 553, 543, and 540 °C respectively. The coke percentage as a function of percent of bed is presented in Table 1. The greatest change in the coke profile is produced in the beginning of the reactor. 

Advanced reactor polymerization processes Single-site metallocene catalyzed POs reportedly can produce PP with a fine, homogeneous dispersion of rubber regions and a soft, saatch-resistant surface. For example, LyondellBasell s Catalloy process and its Softell PP is said to provide improved saatch resistance and lower gloss, compared with standard TPO, and it can be compounded with glass fiber rather than talc [17-7]. 

Ziegler-Natta catalyst makes it possible to polymerize a-olefins into elastomers with controlled degree of crystallinity and cross-likability. The first EPR s were manufactured in 1960, 3 years later, the first EPDM. It is advantageous to produce block copolymers with PP being the rigid and PE the soft block. A direct sequential polymerization of propylene and ethylene-propylene mixture leads to the reactor blends (R-TPO) (Cecchin and Guglielmi 1990). 

However, in situ TPOs with high elastomer content are difficult to produce, and high levels of other additives, such as fillers and especially colorants such as carbon black, must still be done by compounding. In-reactor TPOs are used to reduce cost and increase the end-use value in those cases where the TPO does not need to be compounded prior to fabrication. In-reactor TPOs are mostly used in the automotive applications such as bumpers, interior impact trim, under-the-hood cladding, wire harness, weather strip, etc. 

Due to cost reduction needs of late, these blends have been substituted by reactor blends using stepwise propylene- and ethylene-propylene copolymerization techniques in the gas phase. Thus the rubber elastifier is introduced in a low-cost one-step process. Rubber contents as high as 50 percent can be provided. It was quickly seen that TPO produced by this manufacturing method gave more problems with paint adhesion than that seen in traditional PP-EPDM compounds. 

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