DK201700367A1

DK201700367A1 - A hydrophilic polymer material

Info

Publication number: DK201700367A1
Application number: DKPA201700367A
Authority: DK
Inventors: Jonsman Jacques
Original assignee: Jonsman Innovation Aps
Priority date: 2017-06-21
Filing date: 2017-06-21
Publication date: 2019-01-30
Also published as: WO2018233793A1; EP3642022A4; EP3642022A1

Abstract

The invention relates to a hydrophilic polymer material, that is hydrophilic directly after thermoforming processes such as injection molding and extrusion. The invented material is a compound material based on polyamide (PA) and polyvinylpyrrolidone (PVP). What makes the invented material very hydrophilic and thermoformable; is the type, grade and concentration of polyamide (PA) and polyvinylpyrrolidone (PVP). The patent description specify; type, grade and concentration, and provide experimental data to support these.

Description

A hydrophilic polymer material

TECHNICAL FIELD

The present invention relates to a polymer material with intrinsic hydrophilic properties.

BACKGROUND ART

Hydrophilic materials

Hydrophilic means “water loving”. A hydrophilic material likes to be in contact with water. This means that a water droplet placed on the surface of the hydrophilic material will spread over the surface, and capillary flow will occur in enclosed geometries.

The hydrophilic property of a material is determined by three surface tensions; 1. The surface tension between the solid material and air, 2. The surface tension between the solid material and water, and 3. The surface tension between water and air. For practical reasons this is very often condensed into the Contact angle. The Contact angle is measured on a water droplet placed on the surface of the solid material being tested. The Contact angle is the angle between the water-air surface, and the solid material being tested, at the point where the droplet contacts the solid material. This is the standard definition of Contact angle.

Materials with contact angles above 90° are defined as being hydrophobic, meaning “water fearing”.

Materials with contact angles less than 90° are defined as being hydrophilic.

Materials with contact angles around 90° are neutral, meaning it is neither hydrophilic or hydrophobic.

Approximate ranges of contact angle

90° Neutral surface

75° - 89° Hydrophilic by definition, but for practical purposes the surface is neutral, ie. a water droplet will not spread on the surface, and no capillary flow will occur.

40° - 74° Mildly hydrophilic, slow capillary flow will occur, and a droplet will spread a little on the surface.

° - 39° Very hydrophilic, fast capillary flow and droplets will spread over the surface. 0° Superhydrophilic or wetting surface. A water droplet will completely spread over the surface and form a thin water film.

Applications of hydrophilic materials

Devices that are used in contact with water, generally benefit from being hydrophilic. The hydrophilic property means the device will interact better with water, and the device thus performs its function better and is more reliable. Some applications even depend on the device being hydrophilic, for example for capillary filling of a device with water or a water based solution.

Hydrophilic materials are of particular interest for medical devices, because these very often are in contact with biological samples such as blood, and pharmaceutical solutions.

Polymer materials

Most liquid handling devices are made from polymer materials; this is for reasons of cost and speed of production. The manufacturing processes are often injection molding and extrusion. Many standard materials are available for these processes, and are manufactured in million tons per year. Table 1 lists the most hydrophilic of the standard materials. It is noteworthy

DK 2017 00367 A1 that even these most hydrophilic polymer materials, are either neutral or mildly hydrophilic, none are very hydrophilic.

Standard material	Contact angle
Polyamide 6 (PA6) (Polycaprolactum, Nylon 6)	63°
Nylon 6-6	68°
Nylon 7,7	70°
Polysulfone	71°
Nylon 6,10	71°
Acrylic (PMMA)	73°
PET	74°
Polyimide	75°
POM	77°
Polycarbonate (PC)	82°
Polystyrene (PS)	87°

Table 1. Standard materials for injection molding and extrusion with contact angles listed. Only the materials with the lowest contact angles are listed.

Devices molded in these mildly hydrophilic materials must be given a post-molding process to make them very hydrophilic. These processes include; hydrophilic coatings, plasma treatments and surfactant treatments. Such post-molding processes generally work well, but they make the production more complex, cost more and give extra failure and degradation modes.

A select few polymers exist that are very hydrophilic. These are listed in table 2 with their contact angles.

Hydrophilic material	Contact angle
Polyvinylpyrrolidone (PVP)	10°
Polypropylen glycol (PPG)	42°
Polyvinyl alcohol (PVOH)	51°
Polyvinyl acetate (PVA)	61°

Table 2. Special hydrophilic polymers with contact angles listed.

Unfortunately, these hydrophilic polymers have properties that make them unsuitable for molded devices. The 4 materials are all water soluble, and devices made of the materials will thus dissolve over time when in use. None of the materials work well with injection molding (PPG is a liquid polymer at room temperature, PVA is a thermoset, and PVOH is most difficult to melt). PVP is prone to both crosslinking and degradation at elevated temperatures, and are therefore difficult to injection mold and extrude.

Compound polymers

Thermomechanical mixing different polymers together, produce a polymer that is called a Compound polymer.

To a person skilled in the art, it is normal to compound polymers with different properties, properties that are all needed in the resulting compound polymer material.

To get a polymer that is both hydrophilic and can be injection molded, it is intuitive to compound a standard polymer from table 1 and a hydrophilic polymer from table 2. To

DK 2017 00367 A1 maximize the hydrophilic property, it is apparent to compound the most hydrophilic polymers in table 1 and table 2, these are Polyamide 6 (PA6) and Polyvinylpyrrolidone (PVP).

Compounding PA6 and PVP have been done before, as described in the patents and publication listed in table 3.

Ref.	PVP type	PVP cone.	Intended use
EP0802268A1	K-Value 20 to 70	3% to 15%	Hygroscopic textile fibers
CN101735608A	1000 to 100000 g/mol	0.1% to 10%	Hygroscopic textile fibers
PCT/EP2011/ 070814	2500 to 2500000 g/mol K-Value 20 to 100	0.01% to 7%	Catheter material
Publication *	7500 to 12500 g/mol	1% to 10%	Hygroscopic textile fibers
US5543465 A	Above 8000 g/mol	0.5% to 20%	Hydrophilic membrane

Table 3. Patents and publications describing mixtures of PA6 and PVP.

★Functional materials based on PA6/PVP blends, A. Gnatowski*, O. Suberlak, P. Postawa. Journal of Achievements in Materials and Manufacturing Engineering, Vol. 18, Issue 1-2, September-October 2006.

Unfortunately, none of these PA6/PVP compounds have been adopted in industry and replaced post-molding hydrophilic treatments.

In the cause of our extensive research, we have learned the complications and pitfalls of PA6/PVP compounding. The complications are significant and the solution is not obvious. We assume the significant complications is the reason PA6/PVP compounds so far have been unsuccessful in gaining widespread use. Our solution to the complications of PA6/PVP compounding, is the object of this invention as detailed in the description of the invention.

Polyvinylpyrrolidone nomenclature

Polyvinylpyrrolidone is used extensively in a number of different fields and applications: Food thickener (E1201), paint additive, glue, coating on pharmaceutical tablets, blood plasma substitute etc. Due to the wide range of use, PVP is specified by several different parameters. The most common way to describe a batch of PVP is by the Fikentscher’s K-value. The Kvalue is calculated from the viscosity of a water solution containing PVP. The higher the viscosity the higher the K-value.

A batch of PVP contain a range of molecular weights from short to long. The viscosity of a PVP solution depends on the molecular weight of PVP (long polymer chains give higher viscosity). The K-value thus give an indication of the distribution of molecular weights in a batch of PVP. A high K-value indicate a high average PVP molecular weight.

Table 4, lists the K-Value range and Molecular weight range, for different grades of PVP.

PVP Polymer grade	K-Value range	Molecular weight range [g/mol]
K-12	10-14	2500 - 6000
K-15	13-19	6000- 15000
K-17	15-22	9000- 17000
K-30	26-35	40000 - 80000
K-60	50-62	390000 - 470000
K-90	88-100	1000000-1700000

Table 4. Data obtained from three manufacturers of PVP; BASF, Ashland and Hefei Trendchem.

DK 2017 00367 A1

OBJECTIVE OF THE INVENTION

The primary objective of the invention is to obtain a polymer material with intrinsic hydrophilic properties. The material must be thermoformable by standard processes such as injection molding and extrusion, and must be very hydrophilic directly from the molding machine without extra processes.

Secondary objectives are; 1. The material should be transparent or at least translucent, and

2. The material should be stable when in contact with water.

These objectives have been achieved by the invention as it is defined in the claims.

DESCRIPTION OF THE INVENTION

Our R&D effort in developing the material described in this patent, we have tested many combinations of standard and hydrophilic polymers. We have also tested the hydrophilic property for different concentrations of the hydrophilic polymer. Unlike the prior art previously listed, we have optimized PA6/PVP compounds for low contact angle of injection molded test devices.

In our R&D we have tested more than 100 different compounds, some of these are summarised in table 5.

Compound material	Result / Contact angle
PS + PVP K30 (2%, 10%, 20%, 35%)	Lowest contact angle =69°
PET + 30% PVP K30	46° degree contact angle
LDPE + 25% PVP K17	86.6 degree contact angle, a very low reduction in contact angle.
ABS + 20% PVP K30	53° degree contact angle
PMMA + PVP K30 (10%, 20%, 30%, 35%, 40%, 45%)	Lowest contact angle =48°
PP + 10% PVP K30	64.7 degree contact angle, a significant reduction in contact angle.
PC + PVP K30 & K17	Dark brown and semi-degraded compound due to high process temperature.
PCL + 1% PPG	25.4 degree contact angle, a significant reduction in contact angle. PPG continuously leached out of the compound.
PA6 + PVP (K90, K60, K30, K17, K15, K12)	Lowest contact angle =18°
PA6 + PVOH	No reduction in contact angle.
TOPAS 8007 + 25% PVP K17	No reduction in contact angle.

Table 5. Summary results of compounding different standard polymers with hydrophilic polymers. PA6 with low K-Value PVP give a much lower contact angle than any other tested compound.

As is apparent in table 5, PA6 compounded with PVP is far better than any of the other tested compounds.

Based on the initial good results with PA6/PVP compounds, a detailed study was conducted. During this study, we have learned how to make a very hydrophilic PA6/PVP compound.

DK 2017 00367 A1

PA6 + PVP compounds

We have compounded and measured contact angles, on all commercially available grades of PVP (K12, K15, K17, K30, K60, K90), in concentrations from 0% PVP to 35% PVP. The results are displayed in figures 1 and 2.

Figure 1 show plots of contact angle vs. the PVP concentration, for each grade of PVP. Figure 2 show the lowest consistently measured contact angle for each grade of PVP.

Several conclusions can be made from the data in figures 1 & 2:

1. Optimum PVP concentration. A molded PA6/PVP compound is most hydrophilic when the PVP concentration is 25% to 30%.

2. Low K-Value PVP is good. Low PVP K-Values give more hydrophilic compounds, but below a certain threshold between K-Value 17 and 30, the contact angle doesn’t get lower by lowering the K-Value. This indicates that the K-Value should be below a certain threshold (17-30) to give maximum reduction of the contact angle. Even at the optimum PVP concentration (25-30%), PVP K30, K60 and K90 reduce the contact angle too little to make a significant change in hydrophilicity.

For low PVP concentrations, adding more PVP will reduce the contact angle. This is as intuitively expected. For PVP concentrations above the optimum (25-30%), adding more PVP will increase the contact angle. The reason is that the molded compound will react strongly with water and swell the material very quickly. The swelling pins the flow front of the spreading test droplet, and the contact angle thus remain high. This effect is the reason for the minimum contact angle between 25% and 30% PVP.

PA6 + PVP thermal compatibility

Despite being chemically the same polymer, the different grades of PVP have significantly different thermal properties. We have measured several thermal properties of relevance to compounding and injection molding. Two properties are of particular interest; 1. The minimum process temperature for compounding and injection molding, and 2. The thermal degradation temperature for PVP.

Minimum process temperature

To successfully compound different polymers, the compounding must be done at a temperature where both polymers have a viscosity low enough to allow intermixing. This means that the compounding temperature must be well above the glass transition temperature for both polymers; PA6 and PVP. For practical reasons, such as compounding speed, this is at least 50°C above the glass transition temperatures.

Figure 3 show the minimum process temperature for the different PVP grades (black curve), and the standard compounding and molding process temperature range for PA6 (grey shading). Compounding PA6 and PVP thus require that the temperature is above the black curve and in the grey zone. The minimum process temperature is therefore 210°C for all grades of PVP.

DK 2017 00367 A1

Thermal degradation of PVP

At elevated temperatures, PVP will thermally degrade. Above a specific degradation temperature, the PVP will discolor in orange or green tones, lose weight, crosslink the PVP polymer chains and produce small undefined molecules from the degrading PVP. The result is a brittle and non-moldable material, with discoloration and reduced & non-reproducible hydrophilic properties. Degradation of the PVP is unacceptable, and the process temperature must thus be below the degradation temperature.

We have measured the degradation temperature of the different PVP grades. The measurement is done by a combination of weight loss and discoloration. The red curve in figure 3 shows the lowest temperature where degradation occurs. Processing PVP at a temperature below the red curve will not cause degradation of the PVP.

It is both surprising and unexpected that there is a significant variation in degradation temperature between the different PVP grades. PVP K12 and K15 degrades at a significantly higher temperature than PVP K17, K30, K60 and K90. The mechanism behind this difference is unclear.

PVP K17, K30, K60 and K90 can be compounded with PA6, but only above the degradation temperature. Degradation of the PVP is thus inevitable.

Only PVP K12 and K15 have a non-degrading process temperature window, as indicated by the green bars in figure 3.

The unexpected and highly beneficial effect, is that it is possible to process (compound, extrude and mold), PVP K12 and K15 with PA6 without any degradation. This results in molded and extruded parts being reproducibly highly hydrophilic, without crosslinking, discoloration or degradation.

Leaching of PVP

PVP is a water soluble polymer, and some of the PVP in the compound will leach into water in contact with the material. Leaching of the PVP into a contacting water solution, is undesired because it will contaminate the solution, and will swell and deform the molded device. Table 6 shows the dry weight loss of a molded device (PA6+25% PVP) after 60 days in contact with water.

The lower K-Values show the highest dry weight loss. While 4.35% weight loss for PVP K12 is significant, it should be considered that this weight loss is over 60 days. The weight loss is thus quite slow.

However, the higher leaching for the lowest K-Values, means that compounds shouldn’t simply be made with the lowest possible K-Value. PVP K12 is the lowest K-Value PVP grade available commercially, but if PVP with lower K-Value were available it wouldn’t be good for compounding. This because it would likely be as hydrophilic as PVP K12, K15 and K17, but leach much faster than these grades. For this reason, the K-Value shouldn’t be less than 10.

DK 2017 00367 A1

PVP Polymer grade	Dry weight loss [%]
K-12	4.35%
K-15	2.24%
K-17	1.34%
K-30	0.73%
K-60	0.23%
K-90	0.31%

Table 6. Dry weight loss of test devices molded from a 25% PVP compound. The lower K-Values show the highest dry weight loss.

Heat treating molded devices

During our research, we have learned that exposing a molded PA6/PVP device to elevated temperatures, will further decrease the contact angle. After considerable experimentation, we concluded that this is caused by two effects:

1. At elevated temperature, the small PVP molecules will diffuse through the PA6 matrix. Over time PVP will accumulate at the surface of the molded device, and this will decrease the contact angle toward the 10 degree contact angle of pure PVP.

2. Water molecules located in the material, have a passivating effect on the hydrophilic property of PVP. At elevated temperature, the material will become dryer over time, thereby de-passivating the PVP and thus further reducing the contact angle.

For PA6/PVP (K12, K15, K17) the contact angle is reduced the most by heat treating the molded device at temperatures between 130°C and 170°C, for 30 to 60 minutes.

The present invention

Based on the summarized results of our R&D on PA6+PVP compounds, we conclude that for a compound to be;

1. Thermoformable by standard processes such as injection molding and extrusion.

2. Very hydrophilic directly from the molding machine without extra processes.

3. Transparent or translucent (meaning no discoloration by degradation).

4. Stable when in contact with water.

The compound should:

1. Contain between 20% and 35% PVP. This is significantly more than in prior art. Optimum hydrophilicity is obtained with 25% to 30% PVP.

2. Be made with PVP with low K-Value (ie. low molecular weight). Less than 20 for optimum hydrophilicity, and less than 17 to avoid PVP degradation.

3. Be made with PVP with K-Value no less than 10, this for water stability.

These findings form the basis of the claims.

DK 2017 00367 A1

DESCRIPTION OF THE DRAWINGS

Figure 1. Graphs of water contact angle vs. the PVP concentration in the compound. Data are included for PA6 compounded with PVP K12, K15, K17, K30, K60 and K90.

Several conclusions can be made from the graphs.

1. A molded PA6/PVP compound is most hydrophilic when the PVP concentration is 25% to 30%.

2. Low K-Values give more hydrophilic compounds, but K12, K15 and K17 give nearly the same results.

3. Even at the optimum PVP concentration, PVP K90, K60 and K30 reduce the contact angle too little to make a significant change in hydrophilicity.

Figure 2. A graph of the contact angle obtained at the optimum PVP concentration, for PVP K12, K15, K17, K30, K60 and K90.

Low K-Values give more hydrophilic compounds, but below a certain threshold between KValue 17 and 30, the contact angle doesn’t get lower by lowering K-Value. This indicates that the K-Value should be below a certain level, to give maximum reduction of the contact angle.

Figure 3. A graph illustrating the thermal compatibility of PA6 and PVP with different KValues. The black curve is the minimum compounding temperature for the PVP grade (50°C above the glass transition temperature). The grey shading is the compounding and molding process temperature range for PA6; 210°C to 280°C. Compounding PA6 and PVP thus require that the temperature is above the black curve and in the grey zone. The minimum process temperature is therefore 210°C for all grades of PVP.

The red curve is the temperature where the PVP will start to thermally degrade. Degradation of the PVP is unacceptable, and the process temperature must thus be below the red curve. Only PVP K12 and K15 have a non-degrading process window as indicated by the green bars. PVP K17, K30, K60 and K90 can be compounded with PA6, but not without some degradation of the PVP.

Claims

1. A polymer material comprising at least 60% (by weight) polyamide (PA), and at least 20% polyvinylpyrrolidone (PVP).

2. A polymer material as in claim 1, wherein the polyamide is polycaprolactam also known as PA6 and Nylon 6.

3. A polymer material as in any of the preceding claims, wherein the PVP concentration by weight is between 20% and 35%, such as between 25% and 30%.

4. A polymer material as in any of the preceding claims, wherein the PA and PVP polymers have been thermomechanically mixed to form a compound polymer.

5. A polymer material as in any of the preceding claims, wherein the PVP is largely composed of PVP with a K-Value less than 20.

6. A polymer material as in any of the preceding claims, wherein the PVP is composed of at least 50% (by weight) molecules with a molecular weight less than 20000 g/mol.

7. A polymer material as in any of the preceding claims, wherein the PVP have a K-Value between 10 and 20, such as between 12 and 17.

8. A polymer material as in any of the preceding claims, wherein the PVP is composed of one of, or a mixture of, the following PVP grades; K12, K15, K17.

9. A polymer material as in any of the preceding claims, wherein the PVP source is a copolymer consisting of at least 50% vinylpyrrolidone monomer.

10. A device molded in a polymer material as in any of the preceding claims, wherein the molded device have been heat treated at minimum 120°C for at least 10 minutes.