RO132386B1 - Process for preparing shock-proof composites of recovered polypropylene - Google Patents

Description

The invention relates to a process for obtaining a recovered polypropylene composite, modified by melt alloying with styrene-isoprene block copolymers (SIS), which has the highest values of shock resistance, a property that allows the plastics industry to produce a wide range of parts used in non-food fields.

Polypropylene is one of the most used polyolefins in the production of industrial parts (containers, pipes, packaging) due to the good machinability in melting (injection, extrusion, filming) and physical-mechanical indicators with high values, except for shock resistance. Shock resistance is even poorer in the case of recovered polypropylene, especially at negative temperatures.

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

The melt alloying of polypropylene with styrene-diene block copolymers aims to disrupt the crystal lattice and elasticize the amorphous phase, which ensures improved machinability, allowing to obtain polypropylene films with superior tensile strength. The non-correlation of the melt flow indices of the two components is a disadvantage, because it does not ensure a significant increase in shock resistance (US 5034449, US 8071681).

The use of hydrogenated SIS (SEPS) as a shock modifier ensures a significant increase in the shock resistance of composites. The melt flow index of SEPS assortments varies very little, constituting a disadvantage in maximizing the increase in shock resistance of polypropylene composites (US 5492967, H1, 518).

in the article Modification of Waste Polypropylene by Styrene-isoprene Block-copolymers, PLASTIC MATERIALS | 50 | No. 1 | 2013, by Paul Ghioca et. al., the changes of the mechanical properties of the polypropylene recovered by the styrene-isoprene block polymers are treated. This article describes a process for melting the recovered polypropylene, which takes place on a roller, at a temperature of 185 ... 190 ° C, a coefficient of friction of 1.18 ... 1.20, for 15 min. The initial PP has an Izod shock resistance (+ 20 ° C) of 6.4 Kj / m ² , and at 3.20 Kj (-20 ° C). This PP is then mixed with a styrene-isoprene block copolymer with a polystyrene (%) content of 19 or 20. The composite obtained from mixing the PP with the block copolymer with 20% polystyrene content has the best impact resistance, having a similar viscosity PP used. CN 103756142 Discloses the mixing of styrene elastomers with polypropylene, in order to improve its mechanical properties, the impact strength being improved to values equal to or greater than 15 Kj / m ² .

The studies of thermal processing of polyolefins have established that the maximum effect of modification by alloying is achieved when the viscosity of the components presents values as close as possible, in ideally identical cases, leading to obtaining composites with the highest values of shock resistance.

The melt viscosity 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 damped more efficiently by the elastic domains, by more uniform absorption and dispersion of energy, and by preventing the growth of microcracks that appear in the composite material when hit.

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

RO 132386 Β1

This variation in the melt viscosity of the recovered polypropylene is a major disadvantage, and its composites with styrene-isoprene block copolymers do not have the optimal values of shock resistance.

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

The technical problem solved by the invention consists in the realization of a polymeric compound based on recovered polypropylene, with high values of shock resistance.

The process for obtaining an anti-shock composite with maximum shock resistance values in the range of 8.7 ... 36.4 kJ / m ² , according to the invention, consists in the modification by melt alloying on a roller, of a recovered polypropylene mixture. with a melt viscosity of 240 ... 1600 Pa-s, with a coefficient of friction of 1.18 ... 1.20, at a temperature of 185 ... 190 ° C, for a maximum of 15 min, with an amount of 5 ... 40%, preferably 10 ... 20%, mixture of two block-styrene-isoprene copolymers, mixture in a proportion of 5 ... 95%, which is calculated so that their mixture presents a melt viscosity equal to or close to that of the sort used of the recovered polypropylene.

Anti-shock polymeric composite, based on recovered polypropylene, with a shock resistance of 11.2 ... 36.4 kJ / m ² at 20 ° C, and 8.7 ... 32.3 at -20 ° C , directly obtained by the process according to the invention, consists of a mixture of recovered polypropylene and 5 ... 40%, preferably 10 ... 20%, based on the amount of recovered polypropylene, a mixture of two block-styrene-isoprene copolymers having a polystyrene content of 20.2 ... 29.8%.

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

To exemplify the invention, two sorts of recovered polypropylene (PP 1, PP 2) and two styrene-isoprene block-coplymers were used, the properties of which are shown in tables 1 and 2.

Table 1

Properties of recovered polypropylene

Nr. crt. Property PP1 PP2 1 Crystallinity,% 745 70 2 Hardness, ° Sh D 72 72 3 Tensile strength, MPa 364 263 4 Elongation at break,% 40 166 5 Shock strength Izod at + 20 ° C, kJ / m ² 48 64 6 Izod shock resistance at -20 ° C, kJ / m ² 32 42 7 Melt flow rate at 190 ° C, load 5 kg, g / 10 min 81 14

Styrene-isoprene block copolymers were synthesized by sequential anionic polymerization of monomers in cyclohexane solution, initiated with n-BuLi. Molecular mass determined by gel permeation chromatography (GPC) and physico-mechanical properties are shown in Table 2. Physico-mechanical indicators were determined on films obtained by centrifugal casting from toluene solution.

RO 132386 Β1

Table 2

Properties of block-styrene-isoprene copolymers

Nr. crt. Property SIS1 SIS 2 1 Polystyrene content,% 202 298 2 Total mass, g / mol 133 800 76400 3 Polystyrene block mass, g / mol 13500 11400 4 Polyisoprene block mass, g / mol 106 800 53600 5 Tensile strength, MPa 87 114 6 Elongation at break,% 1580 1320 7 Hardness, ° Sh D 34 42 8 Melt flow rate at 190 ° C, load 5 kg, g / 10 min 44 206

The modification by melt alloying of the recovered polypropylene with styrene-isoprene block copolymers was performed on the roller temperature of 185 ... 190 ° C, using a coefficient of friction 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 degree of roll loading of 300 g of mixture.

In the first stage, recovered polypropylene is introduced on the roller and, after melting and gripping it on the roller cylinder (3 ... 5 min), the block-styrene-isoprenic copolymer is added and incorporated into the polypropylene (2 ... 4 min). then the homogenization of the mixture is carried out, by successive cuts (4 ... 6 min) and, finally, the material is removed from the roller in the form of a foil with a thickness of 2 ... 3 mm. From these foils thick plates of 1 and 4 mm are obtained by pressing at 190 ° C, for 15 min, at a pressure of 200 N / m ² . The 1 mm thick plates were used to determine the physical-mechanical properties by traction at a speed of 50 mm / min. Notched specimens were machined from 4 mm thick plates, necessary to determine the Izod shock resistance performed at + 20 ° C and -20 ° C.

The following are embodiments of the invention.

Example 1

According to the modification process described above, 200 g of recovered PP1 polypropylene was alloyed in melt with styrene-isoprene block copolymers in a proportion of 10% compared to polyolefin, as follows:

-1 Acu20gSIS1;

- 1 B with 20 g SIS 2;

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

The impact 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

Nr. crt. Property PP1 0042 1B 1C 1 Izod shock resistance at + 20 ° C, kJ / m ² 48 94 90 112 2 Izod shock resistance at -20 ° C, kJ / m ² 32 78 71 87

RO 132386 Β1

Example 21

Proceed as in Example 1, 200 g of recovered PPI polypropylene is modified by melt alloying with styrene-isoprene block copolymer in a proportion of 20% compared to polyol-3-fine, as follows:

- 2 A with 40 g SIS 1; 5

- 2 B with 40 g SIS 2;

- 2 C with 40 g of a mixture of the two styrene-isoprene block copolymers in the proportion of SIS 7

1 / SIS 2 of 25: 75%, which has a melt flow index of 8.2 g / 10 min. The shock resistance values of the obtained composites are presented in table 4.9

Table 411

Shock strengths of PPI recovered polypropylene composites obtained according to Example 2 13

Nr. crt. Property PPI .0833 2B 2C 1 Shock strength Izod at + 20 ° C, kJ / m ² 48 244 236 276 2 Izod shock resistance at -20 ° C, kJ / m ² 32 192 175 248

Example 3

Proceed as in example 1,200 g of recovered polypropylene PP 2 is modified 19 by melt alloying with styrene-isoprene block copolymer in a proportion of 10% relative to polyolefin, as follows: 21

- 3 A with 20 g SIS 1;

- 3 B with 20 g SIS 2; 2. 3

- 3 C with 20 g of a mixture of the two styrene-isoprene block copolymers in the ratio SIS 1 / SIS 2 of 60: 40%, which has a melt flow index of 13.9 g / 10 min. The values of the impact strengths of the composites obtained are shown in Table 5.

Table 5

Shock strengths of recovered polypropylene composites29 obtained according to Example 3

Nr. crt. Property PP2 0125 3B 3C 1 Shock strength Izod at + 20 ° C, kJ / m ² 64 143 166 202 2 Izod shock resistance at -20 ° C, kJ / m ² 42 110 123 156

Example 435

It is proceeded that in the example 1,200 g of recovered polypropylene PP 2 is modified by melting in alloy with styrene-isoprene block copolymer in a proportion of 20% in relation to 37 polyolefin, as follows:

- 4 A with 40 g SIS 1; 39

- 4 B with 40 g SIS 2;

- 4 C with 40 g of a mixture of the two styrene-isoprene block copolymers in the proportion of SIS41

1 / SIS 2 of 60:40%, which has a melt flow index of 13.9 g / 10 min. The shock resistance values of the obtained composites are presented in table 6.43

RO 132386 Β1

Table 6

Shock strengths of recovered polypropylene composites obtained according to Example 4

Nr. crt. Property PP2 .1667 4B 4C 1 Shock strength Izod at + 20 ° C, kJ / m ² 64 262 296 364 2 Izod shock resistance at -20 ° C, kJ / m ² 42 195 251 323

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

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

in the case of recovered polypropylene composites modified by 20% mixture of SIS 1 / SIS 2, the shock resistance at + 20 ° C increases by a maximum of 23%, and the shock resistance at -20 ° C by a maximum of 29%, compared to the values higher levels of this physical-mechanical indicator of composites obtained on the basis of SIS 1 or SIS 2.

This confirms the advantage of using a mixture of block-copolymer styrenisoprene, according to the invention, which has a melt viscosity close to that of recovered polypropylene for optimal modification of polyolefin, leading to polypropylene composites with maximum values of shock resistance.

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

Claims (2)

1. Process for obtaining an anti-shock composite with maximum values of resistance to 3 shocks in the range of 8,7 ... 36,4 kJ / m ² , characterized in that a polypropylene mixture is modified by melt alloying on a roller recovered, with a melt viscosity of 5 240 ... 1600 Pa-s, with a coefficient of friction of 1.18 ... 1.20, at a temperature of 185 ... 190 ° C, for a maximum of 15 min, with an amount of 5 ... 40%, preferably 10 ... 20%, mixture of two 7 block-styrene-isoprene copolymers, mixture in a proportion of 5 ... 95%, which is calculated so that their mixture has a melt viscosity equal to or close to that of the recovered polypropylene type used. 2. Shockproof polymeric composite, based on recovered polypropylene, with an impact resistance 11 of 11.2 ... 36.4 kJ / m ² at 20 ° C, and 8.7 ... 32.3 at - 20 ° C, directly obtained by the process defined in claim 1, characterized in that it consists of a mixture of recovered polypropylene and 5 ... 40%, preferably 10 ... 20%, based on the amount of recovered polypropylene, a mixture of two styrene-isoprene block copolymers having a polystyrene 15 content of 20.2 ... 29.8%.