WATER-SOLUBLE POLYMER AND POLYMER INTERNAL LUBRICANT

Abstract

A melt-processable water soluble polymer composition having a high Melt Flow Index comprising a blend of a water soluble polymer with at least 15% by weight of the total composition of a hygroscopic salt to act as a lubricant to render the polymer extrudable and/or mouldable, wherein the water content of the salt is of less than 10% by weight, and optionally a solvent polymer plasticizer in a lower amount by weight percent than the hygroscopic salt.

Claims

1. A melt-processable water soluble polymer composition comprising a blend of a water soluble polymer with at least 15% by weight of the total weight of the composition of a hygroscopic salt to act as a lubricant to render the polymer extrudable and/or mouldable, wherein the water content of the composition is of less than 10% by weight.

2. A melt-processable water soluble polymer composition as claimed in claim 1, wherein at least 20% by weight of the hygroscopic salt is provided.

3. A melt-processable water soluble polymer as claimed in claim 1, wherein the polymer comprises a polyvinyl alcohol polymer.

4. A melt-processable water soluble polymer composition as claimed in claim 1, wherein the hygroscopic salt is an anhydrous or hydrated salt selected from an alkaline or alkaline earth metal salt.

5. A melt-processable water soluble polymer composition as claimed in claim 4, wherein the salt is selected from the group consisting of sodium chloride, sodium citrate and magnesium chloride.

6. A melt-processable water soluble polymer composition as claimed in claim 1, wherein the salt has a water content of less than 10% by weight.

7. A melt-processable water soluble polymer composition as claimed in claim 6, wherein the salt is in the anhydrous form.

8. A melt-processable water soluble polymer composition as claimed in claim 1, wherein the salt is included in the composition in an amount up to 75% by weight of the total weight of the composition.

9. A melt-processable water soluble polymer composition as claimed in claim 8, wherein the salt is included in an amount of at least 40% by weight of the total weight of the composition.

10. A melt-processable water soluble polymer composition as claimed in claim 9, wherein the salt is included in an amount of at least 50% by weight of the total weight of the composition.

11. A melt-processable water soluble polymer composition as claimed in claim 1, further comprising a solvent polymer plasticizer.

12. A melt-processable water soluble polymer composition as claimed in claim 11, wherein the solvent polymer plasticizer is selected from glycerine and or propylene glycol.

13. A melt-processable water soluble polymer composition as claimed in claim 11, wherein the salt is provided in a higher amount by weight percent than the solvent polymer plasticizer.

14. A melt-processable water soluble polymer composition as claimed in claim 13, wherein the ratio of salt to solvent polymer plasticizer is 1.25-12:1.

15. A melt-processable water soluble polymer as claimed in claim 14, wherein the ratio of salt to solvent polymer plasticizer is 1.25-7:1.

16. (canceled)

17. A melt-processable water soluble polymer composition as claimed in claim 1, having a Melt Flow Index of at least 20 g (10 mins/190° C./2.16 kg, under ISO 1133).

18. A melt-processable water soluble polymer composition as claimed in claim 1 provided in the form of any one of a powder, pellet, tablet or extruded filament.

19. (canceled)

20. A soluble polymer internal lubricant comprising a blend of a hygroscopic salt and a solvent polymer plasticizer of the salt.

21-25. (canceled)

26. A method of making a water soluble polymer composition comprising blending a water soluble polymer with at least 15% by weight of the total weight of the composition of a hygroscopic salt to act as a lubricant to render the polymer extrudable and/or mouldable, wherein the water content of the composition is of less than 10% by weight.

27. A method according to claim 26, further including adding a solvent polymer plasticizer.

28-30. (canceled)

Description

EXAMPLE 1

[0048] Formulations were made according to the method above having the ingredients shown in Table 1 below mixed in the given percentage by weight. 88% hydrolysed PVA was used in each formulation and the thermal stabiliser was calcium stearate. The Melt Flow Index (MFI) was determined according to the analysis given above.

TABLE-US-00002 TABLE 1 Thermal PVA Glycerin NaCl stabilizers MFI/g (% by (% by (% by (% by Ratio of 10 Formulation weight) weight) weight) weight) salt:glycerin minutes 1 84.7 10.0 5.0 0.3 0.5:1 7.0 2 39.7 8.0 52.0 0.3 6.5:1 44.0 3 38.7 10.0 51.0 0.3 5.1:1 56.0 4 36.7 12.0 51.0 0.3 4.25:1  77.0 5 25.7 14.0 60.0 0.3 4.28:1  78.0

[0049] Formulation 2 shown in Table 1 above was found to have a white/cream colour with the following properties:

TABLE-US-00003 Density 1.68 g/cm Melt density 1.52 g/cm at 200° C. (under ISO 1183).

[0050] These results illustrate the importance of having a high ratio of salt to plasticizer in the formulation to achieve the desired high MFI but that peak MFI values are obtained in the above formulations where the salt to plasticizer ratio is 3.5-5:1, more preferably 4-4.4:1.

EXAMPLE 2

[0051] Formulations were made according to the method above having the ingredients shown in Table 2 below mixed in the given percents by weight. 88% hydrolysed PVA was used in each formulation. The Melt Flow Index (MFI) was determined according to the analysis given above. The part wall section of the moulded formulations was measured from 600 microns to 100 microns.

TABLE-US-00004 TABLE 2 Propylene Thermal PVA glycol NaCl stabilizers Ratio of (% by (% by (% by (% by salt:propylene Formulation weight) weight) weight) weight) glycol MFI/g 6 84.7 10.0 5.0 0.3 0.5:1 9.0 7 39.7 8.0 52.0 0.3 6.5:1 40.0 8 36.7 10.0 51.0 0.3 5.1:1 51.0 9 38.7 12.0 51.0 0.3 4.25:1  75.0

[0052] Table 2 demonstrates that the type of plasticizer does not have a significant effect on the MFI achieved

EXAMPLE 3

[0053] Formulations were made according to the method above having the ingredients mixed in the percent by weights shown in Table 3 below. 98% hydrolysed PVA was used in formulation 10-13 and 80% hydrolysed PVA was used in formulations 14-16. The formulations were moulded using a Boy 50 tonne moulding process in automatic mode with a cycle time of 20 seconds using a mould with a cold runner system. The screw temperature profile (in ° C.) from the hopper to tip was 160, 170, 180, 180, 220. The part wall section was measured from 600 to 2000 microns.

TABLE-US-00005 TABLE 3 Thermal PVA Glycerin NaCl stabilizers (% by (% by (% by (% by Ratio of Formulation weight) weight) weight) weight) salt:glycerin MFI/g 10 89.0 10.0 0.0 0.3 0:1 1.9 11 84.5 9.5 5.0 0.3 0.52:1   3.48 12 80.1 9.0 10.0 0.3 1.1:1.sup.  2.75 13 67.2 7.5 25.0 0.3 3.33:1   1.91 14 20.0 15.7 64.0 0.3 4:1 73.5 15 15.0 11.7 73.0 0.3 6:1 1.9 16 12.0 9.3 78.4 0.3 8:1 0.00

EXAMPLE 4

[0054] Formulation 17 was prepared as a blend in a similar way to Formulation 2 of Example 1 but having sodium citrate in place of sodium chloride, as follows:

TABLE-US-00006 PVA (88% hydrolysed) 39.0% by wt. Sodium citrate 51.0% by wt. Glycerol 9.70% by wt. Calcium stearate  0.3% by wt

[0055] This formulation was found to have the following properties:

TABLE-US-00007 Density 1.67 g/cm Melt density 1.40-1.42 g/cm at 190° C. (under ISO 1183) MFI 38 g.

[0056] Processing temperature was 190-200° C. with a residence time of up to 30 minutes. Drying time was 4 hours at 90° C. The MFI is again substantially higher with the salt included in the composition.

[0057] This formulation and that of Formulation 2 were examined for their extrudability in injection moulding machines made by Boy, Demag and Arburg. Extrusion processing was carried out using a single full flight screw with constant pitch. The barrel temperature had a profile of 160-200° C. and the screw speed varied typically between 20-150 rpm. Shut down of the apparatus was carried out by maintaining the temperature at 100° C. with screw rotation stopped. Complete shutdown was then carried out by switching off the machine.

[0058] Formulations 2 and 17 were capable of being moulded into a range of containers of various sizes and colours and were suitable for injection moulding. The use of sodium citrate as the polymer lubricant provides additional advantages if it is used for packaging laundry products as it acts as a water softener.

EXAMPLE 5

[0059] A study was carried out to investigate the requirement to have a low water content in the formulations of the present invention.

[0060] Table 4 below sets out the composition of the formulations, together with their MFI and drying time.

TABLE-US-00008 TABLE 4 Thermal Moisture Moisture PVA Glycerin NaCl Stabilizers Water content content Drying (% by (% by (% by (% by (% by pre- post time/hr at Formulation weight) weight) weight) weight) weight) drying drying 90° C. MFI/g A 73.0 11.7 15.0 0.3 0.00 2.4 0.9 5.0 22.0 B 37.0 11.7 51.0 0.3 0.00 2.0 0.9 3.0 77.0 C 71.3 10.2 5.2 0.3 13.0 24 0.9 9.0 10.0 D 60.5 9.7 12.5 0.3 17.0 23 0.9 13.0 7.0

[0061] Table 4 clearly shows the importance of the amount of salt and water contained within the formulation on drying time and on MFI. The formulation has a higher percentage of salt (of at least 15%, preferably at least 20%, and more preferably at least 40%) with minimal or no water content. Formulations C and D which contained 13 and 17% water respectively were very sticky formulations that were not free-flowing making them unsuitable for compounding. Additionally, the excess drying times resulted in undesirable glycerine vapour loss.

[0062] The compositions of the present invention thus provide a melt-processable PVA containing polymer typically having a flexural modulus similar to other extrudable polymers. This enables a soluble and biodegradable polymer to be used for the processing of a wide variety of articles without the processing problems experienced in the prior art, such as thermal degradation and high temperature cross-linking. The known advantageous properties of PVA, such as its high tensile strength and good barrier characteristics, are retained in the melt-processable composition, which may be extruded on current extrusion lines, blow-moulders and injection moulders without modification.