RO132386A2 - Process for preparing shock-proof composites of recovered polypropylene - Google Patents

Abstract

The invention relates to a process for preparing recovered polypropylene composites of improved impact strength. According to the invention, the process consists in modifying, by melt-alloying, the polypropylene recovered on the roller, at a friction coefficient of 1.18...1.20, at a temperature of 185...190°C, for 15 min, with 5...95% mixture of two styrene-isoprene block-copolymers in a ratio of 25:75, with a melt flow index of 8.2...13.9 g/10 min, to result in a composite which has an impact strength of 4.8...6.4 kJ/mat 20°C and of 3.2...4.2 kJ/mat -20°C.

Description

DESCRIPTION OF THE INVENTION

PROCESS FOR OBTAINING ANTI-SHOCK COMPOSITIONS OF RECOVERED POLYPROPYLENE

The invention relates to obtaining composites of recovered polypropylene modified by melting alloy with styrene-isoprene block copolymers (SIS), which have the highest values of shock resistance, a property that allows the plastics industry to produce a wide range. of landmarks used in non-food fields.

Polypropylene is one of the most used polyolefms in the production of industrial parts (containers, pipes, packaging) due to the good melt processing (injection, extrusion, filming) and high-value physical-mechanical indicators, except for shock resistance. Shock resistance is even more deficient in the case of recovered polypropylene, especially at negative temperatures.

It is known that the modification in melting with styrene-diene block copolymers is the most advantageous method both technically and economically, especially when alloying is performed during normal processing by extrusion or injection for the manufacture of various objects and parts. technical.

The melting modification of polypropylene with styrene-dienic block copolymers follows the disturbance of the crystalline network and the elasticity of the amorphous phase, which ensures an improved workability, allowing to obtain polypropylene films with superior tensile strength. The non-correlation of melt flow rates of the two components is a disadvantage, as it does not ensure a significant increase in shock resistance (U.S. Patent 5034449, 8071681).

The use of hydrogenated SIS (SEPS) as a shock modifier ensures a significant increase in the shock resistance of the composites. The melt flow rate of SEPS assortments varies very little, which is a disadvantage in maximizing the increase in shock resistance of polypropylene composites (U.S. Patent 5492967, Hl, 518).

Thermal processing studies of polyolefins have established that the maximum effect of modification by alloying is achieved when the viscosity of the components has values as close as possible, in

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The viscosity in the melt as close as possible to the components of the compound allows the optimal dispersion of the minority polymer (SIS) in the form of uniform elastic domains in the polyolefin matrix. Thus, when the composite is subjected to shocks, the destructive force is more effectively cushioned by the elastic domains by more uniform energy absorption and dispersion and by preventing the growth of microfissures that appear in the composite material when it is struck.

Because recovered polypropylene has a viscosity in the melt that varies depending on the origin of the collected objects and their degree of degradation, complying with this criterion of optimum alloying in the melt requires the use of a very wide assortment of styrene-isoprene block-copolymers, which will ensure the entire range. of viscosities of the various batches of recovered polypropylene, which is obviously impossible to achieve.

This variation of the melt viscosity of the recovered polypropylene constitutes a major disadvantage and its composites with styrene-isoprene block copolymers do not exhibit the optimum values of shock resistance.

The present invention removes this disadvantage, the technical solution consisting in obtaining a mixture of styrene-isoprene block-copolymers having a viscosity similar to or as close to that of the recovered polypropylene batch, thus ensuring the optimum modification of the obtained polyolefin with some compounds. with the highest values of shock resistance.

The process according to the invention consists in the use of two styrene-isoprene block copolymers with different melt viscosities, which by mixing in the melt lead to obtain an elastomeric modifier with a melt rheological behavior as close as possible to the recovered polypropylene lot. The melt viscosity regulation of the styreneoprene block-copolymer mixture is achieved by varying the composition ratio of the two thermoplastic elastomers.

The process according to the invention has the advantage of optimizing the modification by melting alloy of the recovered polypropylene, ensuring the obtaining of composites with maximum values of shock resistance.

To exemplify the invention, two types of recovered polypropylene (PP 1, PP 2) and two styrene-isoprene block-coplimers whose properties are presented in tables 1 and

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Table 1: Properties of recovered polypropylene

No. crt. Property PP 1 PP2 1. Crystallinity,% 74.5 70 2. Hardness, Sh D ^u 72 72 3. Tensile strength, MPa 36.4 26.3 4. Elongation at break,% 40 166 5. Shock resistance Izod at +20 ^υ C, Kg / m ² 4.8 6.4 6. Shock resistance Izod at - 20 ^υ C, Kg / m ² 3.2 4.2 7. Melt flow rate at 190 ^υ C load 5 kg, g / l 0 min 8.1 14

The styrene-isoprene block copolymers were synthesized by sequential anionic polymerization of the monomers in cyclohexane solution, initiated with n-BuLi. The molecular mass determined by gel permeation chromatography (GPC) and the physical-mechanical characteristics are presented in Table 2. The physical-mechanical indicators were determined on films obtained by centrifugal casting from toluene solution.

Table 2: Properties of styrene-isoprene block copolymers

No. crt. Property SIS1 SIS 2 1. Polystyrene content,% 20.2 29.8 2. Total mass, g / mol 133 800 76400 3. Mass polystyrene block, g / mol 13500 11400 4. Polyisoprene block mass, g / mol 106 800 53600 5. Tensile strength, MPa 8.7 11.4 6. Elongation at break,% 1580 1320 7. Hardness, ° Sh D 34 42 8. Melt flow rate at 190 ^υ C load 5 kg, g / l0 min 4.4 20.6

The melt modification of the polypropylene recovered with styreneoprene block copolymers was performed on the roller at a temperature of 185-190 ⁰ C, using a friction coefficient of 1.18-1.20. The composites were obtained using 200 g of recovered polypropylene which was alloyed with 20 - 40 g of block copolymers, not exceeding the maximum loading level of the 300 g roll.

In the first stage, it is introduced on polypropylene roll recovered and after melting and catching

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01/08/2016 incorporates polypropylene (2-4 min). Next, the mixing operations are carried out by successive cuts (4-6 min) and, finally, the material is removed from the roll in the form of foil with a thickness of 2-3 mm. From these sheets, 1 and 4 mm thick plates are obtained by pressing at 190 ⁰ C for 15 minutes at a pressure of 200 N / m ² . Thick plates of 1 mm were used to determine the physical-mechanical properties by traction at a speed of 50 mm / min. From the 4 mm thick plates, we have machined crimped specimens necessary to determine the Izod shock resistance carried out at + 20 ⁰ C and -20 ⁰ C.

The following are examples of embodiments of the invention:

Example 1:

According to the modification procedure described above, 200 g of recovered polypropylene PP 1 was alloyed in melt with 10% styrene-isoprene block copolymers with respect to polyolefin, as follows:

- 1 A with 20 g SIS 1

- 1 B with 20 g SIS 2

C with 20 g mixture of the two styrene-isoprene block copolymers in a SIS 1 / SIS 2 ratio of 25:75%, which has a melt flow rate of 8.2 g / 10 min.

The shear strengths of the composites were determined according to the methodology described above and are presented in Table 3.

Table 3: Shock strengths of recovered PP 1 polypropylene composites obtained according to example 1

No. crt. Property \ Z PP1 TAKES 1B IC 1. Shock resistance Izod at + 20 ° C, kJ / m ² 4.8 9.4 9.0 11.2 2. Shock resistance Izod at - 20 ° C, kJ / m ² 3.2 7.8 7.1 8.7

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Example 2:

Proceed as in Example 1, 200 g of recovered polypropylene PP1 is modified by melting alloy with styrene-isoprene block copolymer at a ratio of 20% to polyolefin, as follows:

- 2 A with 40 g SIS 1

- 2 B with 40 g SIS 2

- 2 C with 40 g of mixture of the two styrene-isoprene block-copolymers in a SIS 1 / SIS 2 ratio of 25:75%, which has a melt flow rate of 8.2 g / 10 min.

The values of the shock resistance of the composites obtained are presented in table 4.

Table 4: Shock strengths of PP1 recovered polypropylene composites obtained according to example 2

No. crt. Property PP1 2 A. 2B 2C 1. Izod shock resistance at +20 ° C, kJ / m ² 4.8 24.4 23.6 27.6 2. Shock resistance Izod at - 20 ° C, kJ / m ² 3.2 19.2 17.5 24.8

Example 3:

Proceed as in Example 1, 200 g of recovered polypropylene PP 2 is modified by melting with 10% styrene-isoprene block-copolymer with respect to polyolefin, as follows:

- 3 A with 20 g SIS 1

- 3 B with 20 g SIS 2

- 3 C with 20 g of mixture of the two styrene-isoprene block copolymers in a SIS 1 / SIS 2 ratio of 60:40%, which has a melt flow rate of 13.9 g / 10 min.

The values of the shock resistance of the composites obtained are presented in table 5.

Table 5: Shock strengths of recovered polypropylene composites obtained according to Example 3

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No. crt. Property and / PP2 3A 3B 3C 1. Izod shock resistance at +20 ° C, kJ / m ² 6.4 14.3 16.6 20.2 2. Shock resistance Izod at - 20 ° C, kJ / m ² 4.2 11.0 12.3 15.6

Example 4:

Proceed as in Example 1, 200 g of recovered polypropylene PP 2 is modified by melting with 20% styrene-isoprene block-copolymer with respect to the polyolefin, as follows:

- 4 A with 40 g SIS 1

- 4 B with 40 g SIS 2

- 4 C with 40 g of mixture of the two styrene-isoprene block copolymers in a SIS 1 / SIS 2 ratio of 60:40%, which has a melt flow rate of 13.9 g / 10 min.

The values of the shock resistance of the composites obtained are presented in table 6.

Table 6: Shock strengths of recovered polypropylene composites obtained according to Example 4

No. crt. Property J PP2 4A 4B 4C 1. Izod shock resistance at +20 ° C, kJ / m ² 6.4 26.2 29.6 36.4 2. Shock resistance Izod at - 20 ° C, kJ / m ² 4.2 19.5 25.1 32.3

From the data presented in tables 3-6 there is a significant increase of the shock resistance of the recovered polypropylene composites modified with the styreneoprene block-copolymer mixture according to the invention.

In the case of the recovered polypropylene composites modified by 10% mixture of SIS 1 / SIS 2, according to the invention, the shock resistance at +20 ⁰ C increases by a maximum of 22% and the shock resistance at -20 ° C with a maximum of 27%, compared to the highest values of this physical-mechanical indicator of the composites obtained on the basis of SIS 1 or SIS 2.

in the case of the recovered polypropylene composites modified with 20% mixture of SIS 1 / SIS 2, the shock resistance at +20 ⁰ C increases by a maximum of 23% and the shock resistance at -20 ⁰ C with a maximum of 29%, compared to the third range ^ the highest of this physico-mechanical indicator of the composites obtained on its NIS 2 zaJoffi ^.

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This confirms the advantage of using a mixture of styrene-isoprene block copolymers according to the invention, which has a melting viscosity close to that of the recovered polypropylene for the optimum modification of the polyolefin, leading to the obtaining of polypropylene composites with maximum resistance values and .

The recovered polypropylene composites obtained according to the invention, due to the maximum shock resistance values that ensure a longer operating time of the manufactured parts and products, produce important economic advantages for the users.

Claims (1)

The process of obtaining the shock-resistant composites of the recovered polypropylene with maximum values of the shock resistance, characterized in that the melting modification of the recovered polypropylene is carried out on the roll, using a friction coefficient of 1.18 - 1.20, at the temperature from 185 to 190 ° C, for a maximum of 15 minutes with a mixture of two styrene-isoprene block copolymers, one with lower melting viscosity and the other with higher melting viscosity of the recovered polypropylene, in the range 5 -95%, so that the block-copolymer mixture has a viscosity in melt equal to or as close to that of the recovered polypropylene.