High density polyethylene

Abstract

The invention is directed to HDPE having a quotient of melt strength according to ISO 16790:2005 and apparent viscosity according to ISO 11443:2014 (melt strength/apparent viscosity)>2 cN/k.Math.Pa.Math.s and 30 cN/k.Math.Pa.Math.s. In a preferred embodiment, HDPE with an Ml in the range between 0.1 and 10 a density in the range between 935 and 970 kg/m.sup.3 a gel fraction less than 5% and an elasticity (ratio of G/G at 0.1 rad/sec) between 0.6 and 10 is obtained by chain branching HDPE with an Ml in the range between 10 and 100 a density in the range between 935 and 970 kg/m.sup.3 and an elasticity (ratio of G/G at 0.1 rad/sec) between 0.01 and 0.2.

Claims

1. HDPE having a melt strength/apparent viscosity >2 cN/k.Math.Pa.Math.s and 30 cN/k.Math.Pa.Math.s wherein the melt strength is determined as described in the Procedure section of ISO 16790:2005 and the apparent viscosity is determined as described in ISO 11443:2014, wherein the HDPE has melt index in the range between 0.1 and 10 density in the range between 935 and 970 kg/m.sup.3 a gel fraction less than 5% and an elasticity, ratio of G/G at 0.1 rad/sec, between 0.6 and 10 is obtained by chain branching HDPE with characteristics melt index in the range between 10 and 100 density in the range between 935 and 970 kg/m.sup.3 and an elasticity, ratio of G/G at 0.1 rad/sec, between 0.01 and 0.2.

2. HDPE according to claim 1 characterised in that the melt strength of HDPE 9 cN.

3. HDPE according to claim 1 characterized in that HDPE with characteristics the density in the range between 940 and 970 kg/m.sup.3 the gel fraction of less than 3% and the elasticity, ratio of G/G at 0.1 rad/sec, between 0.7 and 2 is obtained by chain branching HDPE with characteristics the MI in the range between 12 and 30 the density in the range between 940 and 970 kg/m.sup.3 and the elasticity, ratio of G/G at 0.1 rad/sec, between 0.01 and 0.2.

4. HDPE according to claim 3 characterized in that HDPE with characteristics melt index in the range between 0.1 and 5 density in the range between 945 and 965 kg/m.sup.3 a gel fraction less than 2% and an elasticity, ratio of G/G at 0.1 rad/sec, between 0.8 and 1.3 is obtained by chain branching HDPE with characteristics melt index in the range between 12 and 30 density in the range between 945 and 965 kg/m.sup.3 and an elasticity, ratio of G/G at 0.1 rad/sec, between 0.01 and 0.1.

5. HDPE according to claim 1 characterized in that the chain branching of HDPE takes place by irradiation.

6. A foam composition comprising HDPE according to claim 1 and a blowing agent characterized in that the density of the resulting HDPE foam ranges between 100 and 500 kg/m.sup.3.

7. A foam composition according to claim 6 characterised in that the HDPE foam is obtained with a physically foaming process at a temperature between 120 C. and 140 C. with use of isobutane, isobutane with CO.sub.2, nitrogen or pure CO.sub.2 as the physical blowing agent.

8. An article prepared from the composition according to claim 1.

Description

EXAMPLES

(1) Electron beam irradiation of HDPE was carried out at Beta-Gamma-Service GmbH (BGS, Germany) in their facility in Bruchsal (10 MeV). In order to improve homogeneity of irradiation dose, HDPE bags were repacked into thinner bags (600450100 mm3) containing 12.5 kg HDPE granules. The 100 mm thick bags were radiated with the target irradiation dose on two sides in order to further improve the homogeneity of the irradiation dose.

(2) HDPE was treated with 3000 ppm peroxide (Triganox 101) using a twin-screw extruder with a temperature of 210 C. A nitrogen atmosphere is maintained during reactive extrusion.

(3) The HDPE was characterized by the following measurements:

(4) The melt strength was measured according ISO 16790:2005 using a Gttfert Rheograph 6000 in combination with a Rheotens 71.97. The equipment specifications are:

(5) Oven diameter of 12 mm.

(6) Capillary 40/2 (l/d), length 40 mm, diameter 2 mm, entrance angle 180 (flat).

(7) Pressure transducer: max 200 bar.

(8) The test conditions were as follows: the rheograph was filled in less than one minute and the sample preheating time was 300 seconds. The measuring temperature was 190 C. The speed of the piston was 0.049 mm/s corresponding to a throughput of 5.5 mm.sup.3/s and apparent shear-rate of 7 s.sup.1. The drawing device (Rheotens 71.97) was operated at an acceleration of 1.2 mm/s.sup.2 and a velocity of 1.8 mm/s. The melt strength is expressed in cN.

(9) The apparent viscosity was measured according ISO11443:2014 using the Gttfert Rheograph 6000 and the test conditions being described for the determination of the melt strength. The apparent viscosity is defined as the quotient of the apparent shear stress and the apparent shear rate being 7 s.sup.1. The apparent shear stress is calculated from pressure drop in kPa times the capillary diameter in mm divided by 4 times the length of the capillary in mm. The apparent viscosity is usually expressed in kPa.Math.s.

(10) The melt index was measured according ISO1133-1:2011 at a temperature of 190 C. and at 2.16 kg.

(11) The density of the compression molded HDPE disks was measured at a temperature of 23 C. according ISO1183-1:2012 after at least one day of conditioning.

(12) Dynamic mechanical spectroscopy (DMS) frequency sweep measurements were performed on 2 mm disks at a temperature of 190 C. in a nitrogen environment using a parallel plate set-up. The frequency range is 100-0.01 rad/s and the strain was varied between 0.5 and 20% in order to stay in the linear regime. This technique is used to determine the elasticity which is the ratio between the loss modulus and the storage modulus at a frequency of 0.1 rad/s.

(13) The gel content was determined according to ASTM D2765-11. The samples were extracted for 12 hours in o-xylene with 1% anti-oxidant. The xylene insoluble fraction was determined gravimetrically.

(14) Density of the foam samples (around 33 cm.sup.2 section) was determined by the geometric method according to the ASTM standard D1622-14.

(15) Closed cellular characteristic value. In water in a vessel having water volume sufficient to sink sample in water and a function to be sealed is sunk an expanded product sample of 5040 mm.sup.2 (V.sub.sample=surface area times thickness; weight: W1) to be held therein, followed by sealing of the vessel. Subsequently, the inner pressure in the vessel is reduced to 0.5 bar and left to stand for 10 minutes. Then, the inner pressure in the vessel is restored to atmospheric and the sample is taken out. The sample is calmly dipped in pure methanol for about 2 seconds, followed by wipe-off of the moisture adhered on the surface, dried in a drier at 60 C. for 5 minutes and thereafter its weight (W2) is measured. Closed cellular characteristic value is calculated by the following formula:

(16) $\mathrm{Open}\mathrm{cell}\left(\%\right)=\frac{p\mathrm{ambient}}{p\mathrm{vacuum}}\frac{\mathrm{volume}\mathrm{of}\mathrm{absorbed}\mathrm{water}}{\mathrm{volume}\mathrm{sample}}$
P ambient=1 bar; P vacuum=0.5 bar

(17) $\mathrm{Volume}\mathrm{of}\mathrm{absorbed}\mathrm{water}=\frac{W2-W1}{\mathrm{density}\mathrm{of}\mathrm{water}}$
in which W1: specimen mass before immersion and W2: specimen mass after immersion

(18) The cell size was determined using image analysis of scanning electron micrographs. For scanning electron microscopy, each sample was frozen with liquid nitrogen and fractured. The fractured surface was made conductive by sputtering deposition of gold and observed using a Jeol JSM-820 operating at 20 kV. The microstructure of the materials has been studied in one plane (machine direction, thickness direction). Three micrographs are taken with a magnification of 30. Analysis of the micrographs has been performed using an image processing tool based on the software Image J. Cell.

(19) Table 1 gives an overview of the HDPE granulate used in the following examples (HDPE I and II and comparative Examples HDPE III and IV).

(20) TABLE-US-00001 TABLE 1 Melt index (190 C., HDPE resin Catalyst Co-monomer 2.16 kg) HDPE I Ziegler Natta C4 19.6 HDPE II Ziegler Natta C4 27.5 HDPE III Ziegler Natta 9 HDPE IV Ziegler Natta C4 2.1 HDPE I is SABIC grade HDPE CC2056. HDPE II is SABIC grade HDPE CC3054. HDPE III is SABIC grade HDPE M80064 HDPE IV is SABIC grade HDPE 3H671
Table 2 shows the melt index, density and gel fraction of electron beam irradiated HDPE materials. The melt index decreases with increasing dose.

(21) TABLE-US-00002 TABLE 2 Melt index, density and gel fraction HDPE Irirradiation dose Melt index Density Gel fraction resin kGy (190 C., 2.16 kg) kg/m.sup.3 % HDPE I 0 19.6 956 0.7 HDPE I 30 0.6 953 1.2 HDPE I 40 0.1 953 1.5 HDPE II 0 30 953 0.7 HDPE II 30 1.4 950 0.8 HDPE II 40 0.4 950 1.0 HDPE I 3000 ppm 0.5 950 0 peroxide
Table 3 shows the mechanical shear of electron beam irradiated HDPE materials.

(22) TABLE-US-00003 TABLE 3 Dynamic mechanical shear Viscosity at Viscosity at Elasticity at HDPE Irirradiation dose 0.1 rad/sec 100 rad/sec 0.1 rad/sec resin kGy kPa .Math. s kPa .Math. s (G/G) HDPE I 0 0.5 0.27 0.02 HDPE I 30 18.7 0.6 0.8 HDPE I 40 45.2 0.7 1.2 HDPE II 0 0.3 0.2 0.02 HDPE II 30 9.7 0.45 0.6 HDPE II 40 20.6 0.50 0.9 HDPE I 3000 ppm 44.9 1.11 0.8 peroxide
Table 4 shows the data for melt strength and apparent viscosity of both unmodified and irradiated HPDE. The melt strength is directly related to the force when the strand breaks. The apparent viscosity is the apparent wall shear stress divided by apparent shear rate.

(23) TABLE-US-00004 TABLE 4 Melt strength and apparent viscosity Ratio between melt Irirradiation Melt Apparent strength and apparent dosis strength viscosity viscosity HDPE resin kGy cN kPa .Math. s cN/kPa .Math. s HDPE I 0 0.3 0.42 0.72 HDPE I 30 21.7 3.29 6.6 HDPE I 40 22.4 5.76 4.0 HDPE II 0 0.2 0.32 0.6 HDPE II 30 15.4 2.87 5.4 HDPE II 40 13.9 2.47 5.6 HDPE I 3000 ppm 6.8 4.7 1.5 peroxide

(24) The foam extrusion line was a 60 mm direct gassed single screw extruder with fluid cooled extension barrel and with a metering unit for liquid and gaseous blowing agents, fluid cooled static mixer and melt pump. A 50 mm annular die with tempered die lips and a cooling mandrel (expansion 1:2) were used.

(25) In order to form and stabilize the cells, master batches of various additives were added via a separate feeder (see Table 5 for details on additives). The physical blowing agent was isobutane. The machine settings for extrusion foaming are given in Table 6.

(26) TABLE-US-00005 TABLE 5 Additives for extrusion foaming Commercial name Chemical name Master batch Role Schulman PBHFPE50T Talcum 50% in LDPE Nucleator Atmer 7300 PL GMS 50% in LDPE Cell stabilizer

(27) TABLE-US-00006 TABLE 6 Machine settings for extrusion foaming. Parameter Unit Values foaming Throughput kg/h 16 Screw speed extruder rpm 8 Extrusion temperatures C. 190 Temperatures in cooling zone C. 134 to 140 Temperatures in mixer and die C. 132 to 140 Take off speed m/min 1.7 to 2.6

(28) TABLE-US-00007 TABLE 7 Process conditions for foaming with isobutane and talcum as additive in % by weight. All examples have 1.0% by weight GMS Die Die pressure temperature Talcum HDPE bar C. Isobutane % % A HDPE III 22 127 1.9 1.5 B HDPE IV 23 132 2.0 1.5 C HDPE I - 3000 ppm 41 130 2.4 1.0 peroxide I HDPE I - 30 kGy 32 129 1.7 1.0 II HDPE I - 30 kGy 32 129 2.4 1.0 III HDPE I - 40 kGy 53 129 2.3 1.0 IV HDPE II - 40 kGy 31 133 2.3 1.0

(29) TABLE-US-00008 TABLE 8 Foam characteristics Density Cell size HDPE kg/m.sup.3 Open Cell % m A HDPE III 222 10.2 679 B HDPE IV 275 2.4 602 C HDPE I - 264 20.7 n.d. 3000 ppm peroxide I HDPE I - 30 kGy 228 0.2 684 II HDPE I - 30 kGy 129 1.6 837 III HDPE I - 40 kGy 192 0.2 728 IV HDPE II - 40 kGy 156 1.8 831