Polymer Blends

This example teaches the general method for preparing copolymers of methyl methacrylate and methacrylic acid. A copolymer comprising 15 weight percent methacrylic acid (MAA), and the remainder methyl methacrylate (MMA) was prepared by an emulsion polymerization technique as follows: A monomer mixture was prepared, which contained 1122 grams of MMA, 198 grams of MAA, 10.56 grams of n-dodecyl mercaptan, 782.71 grams of deionized water and 24.75 grams of a 10% aqueous sodium dodecylbenzene sulfonate solution. To an appropriate glass vessel equipped with stirrer, heater, a reflux condenser, and nitrogen sparge tube, was added 1753.26 grams of deionized water, and 0.59 grams of sodium carbonate. The mixture was sparged for one hour with nitrogen while heating to 70.degree. C. The sparge rate was then changed to a sweep and 74.25 grams of a 10% aqueous solution of sodium dodecylbenzene sulfonate was added to the mixture. The temperature of the reaction vessel was then raised to 85.degree. C. At this temperature, 29.343 grams of the initiator mixture, which consisted of 1.32 grams of sodium persulfate and 380.08 grams of deionized water, was added to the reaction vessel, along with 31.42 mL of rinse water. The monomer mixture was then fed into the reaction vessel over a three-hour period.

As the polymerization proceeded, the initiator mixture was added to the reaction vessel at the rate of 29.34 mL every 15 minutes. The accumulation of solids was measured every 30 minutes just before the addition of the initiator mixture. At the completion of the initiator and monomer addition, followed by a 31.42 mL water rinse of each feed line, the mixture was held at 85.degree. C. for one hour. The mixture was then cooled, filtered and the polymer isolated by freeze-drying. The polymer was dried in a vacuum oven prior to blending experiments. The molecular weight of this polymer was about 80,000.

In a similar manner, other polymers of controlled molecular weight of alkyl (meth)acrylates and unsaturated acids may be prepared.

The ASTM test methods employed are as follows: Specific Gravity-D792-66 (re-approved 1979); Tensile-Yield, Elongation and Tensile Elastic Modulus-D638-84; Tensile Impact Strength ASTM D1822; Izod Impact-D256-84; Charpy Impact ASTM D256; Heat Deflection Temperature D648-72; Clash-Berg Torsional Modulus-D-1043; Oxygen Permeability ASTM D-3985.

The following solvent fractionation scheme was prepared to calculate the percent of graft links and grafting efficiency of the (MMA-MAA) acrylic copolymers: ##STR1##

The percent grafted PVOH and grafting efficiency of the acrylic copolymer (MMA-MAA), calculated from the above scheme and listed in TABLE IV, are supported qualitatively by FTIR spectra. The FTIR spectra show increasing evidence of the presence of an ester carbonyl stretching frequency within the frequency range of 1726-1735 cm-1. It is noteworthy to mention that evidence of this ester is not discernible in either the FTIR spectrum of the acrylic terpolymer nor that of the poly(vinyl alcohol). Hence, we may conclude that this ester functionality may have resulted from the esterification reaction between the --OH of PVOH and the --COOH of the acrylic polymer containing acid groups.

Another evidence of grafting is discernible from the increase in tensile-modulus with increasing percent graft.

These examples disclose typical blend conditions for blends reported in Table I.

PVOH and a copolymer of methyl methacrylate-methacrylic acid were dry blended in a polyethylene bag to form a mixture in a 80:20%, weight ratio of PVOH to methyl methacrylate-co-MAA copolymer. For Airvol.RTM. 205-based blends (Table I), the mixture was fed into the hopper of a single screw Killion extruder in which the mixture was melt compounded and extruded at the following extrusion conditions: extruder zone-1, 180.degree. C.; zone 2, 193.degree. C.; zone 3, 193.degree. C.; die-1 and die-2, 193.degree. C.; screw speed 80 rpm. The pelletized samples were dried in a forced air oven and then molded in an Arburg injection molding machine equipped with a heated ASTM family mold for the formation of test pieces. The molding conditions were: nozzle: 199.degree. C.; zones 1, 2, and 3: 200.degree. C.; injection pressure 6.2 MPa; back pressure 1.4 MPa; mold temperature 24.degree. C.

For Airvol.RTM. 107-based blends (Table I), the mixture was fed into the hopper of a single screw Killion extruder in which the mixture was melt compounded and extruded at the following extrusion conditions: extruder zone-1, 199.degree. C.; zone 2, 216.degree. C.; zone 3, 216.degree. C.; die-1 and die-2, 210.degree. C.; screw speed 80 rpm. The pelletized samples were dried in a forced air oven and then molded in an Arburg injection molding machine equipped with a heated ASTM family mold for the formation of test pieces. The molding conditions were: nozzle: 226.degree. C.; zones 1, 2, and 3: 235.degree.-240.degree. C.; injection pressure 6.6 MPa; back pressure 1.4 MPa; mold temperature 35.degree. C.

Other conditions may be used, depending on the viscosity of the blend. Tg, and % crystallinity (% Crys.) are measured by differential scanning calorimetry.

Tables II and III summarize the physical properties of the blends. Table IV describes the extent of grafting in one blend thoroughly analyzed.

The following table identifies starting materials and blends for which data are presented in the subsequent tables.

The data in Table I indicates that for the PVOH homopolymer, the addition of the additive polymers only slightly lowers the crystalline melting point, and only slightly decreases the glass temperature, while a lowered, but still high degree of crystallinity is maintained. For the PVOH/PVAc copolymer, the addition of the additive polymers raises the crystalline melting point and the glass temperature, while the degree of crystallinity is enhanced.

In the following table are summarized the properties of the blends with the partially hydrolyzed PVOH (Airvol.RTM.-205) with several of the additive copolymers of poly(methyl methacrylate-methacrylic acid). In general, tensile modulus is improved with increasing the amount of acid supplied by the copolymer in the blend, while tensile impact strength is decreased.

In the specific examples which follow presenting blend data, the following poly(vinyl alcohol) polymers and processing conditions are used.

The particular PVOH materials used in the EXAMPLES were obtained from Air Products. They are as follows: AIRVOL-107, is a fully hydrolyzed (98.0-98.8 mol %) resin having a solution viscosity of 5.4-6.5 cPs determined on a 4% aqueous solution at 20.degree. C. The Mw of this PVOH is 31,000-50,000. Another PVOH resin employed is Air Products AIRVOL-205 which is a partially hydrolyzed (87-89 mol %) resin possessing a solution viscosity of 5-6 cPs when determined on a 4% aqueous solution at 20.degree. C. AIRVOL-205 has Mw of 31,000-50,000. Two other PVOH polymers referred to are AIRVOL-103 and AIRVOL-325. AIRVOL-103 is a fully hydrolyzed (98.0-98.8 MOL %) resin having a solution viscosity of 3.2-4.2 cPs(Mw=13-23 k) determined on a 4% aqueous solution at 20.degree. C. AIRVOL-325 is also a fully hydrolyzed PVOH resin, Mw=85-146 k.

The PVOH (AIRVOL-205) specified above and the acrylic or styrenic copolymers were dry blended in a polyethylene bag to yield well homogenized mixtures. The mixtures were fed into the hopper of a single screw Killion extruder in which the mixtures were melt compounded and extruded at the following extrusion conditions:

EXTRUDER BARREL TEMPERATURES:

ZONE-1: 180.degree. C.

ZONE-2: 193.degree. C.

ZONE-3: 193.degree. C.

DIE TEMPERATURES:

DIE-1: 193.degree. C.

DIE-2: 193.degree. C.

SCREW SPEED:

80 RPM

The mechanical properties of the alloy were evaluated with the aid of parts which were prepared by injection molding by the following procedure:

The pelletized extrudates were dried in a forced air oven prior to injection molding in an ARBURG injection molding machine equipped with a heated ASTM family mold. The molding conditions were as follows:

INJECTION MOLDER TEMPERATURES:

NOZZLE: 199.degree. C.

ZONE-1: 200.degree. C.

ZONE-2: 200.degree. C.

ZONE-3: 200.degree. C.

INJECTION PRESSURE:

6.2 MPa

BACK PRESSURE:

1.4 MPa

MOLD TEMPERATURE:

24.degree. C.

The PVOH (AIRVOL-107) specified above and the acrylic or styrenic copolymers were dry blended to yield homogeneous mixtures. The mixtures were fed into the hopper of a single screw Killion Extruder where the dry powder was melt compounded, extruded and pelletized at temperatures ranging from 199.degree.-216.degree. C. and screw speed of 80 RPM.

EXTRUDER BARREL TEMPERATURES:

ZONE-1: 199.degree. C.

ZONE-2: 216.degree. C.

ZONE-3: 216.degree. C.

DIE TEMPERATURES:

DIE-1: 210.degree. C.

DIE-2: 210.degree. C.

SCREW SPEED:

80 RPM

The mechanical properties of the alloy were evaluated with the aid of parts which were prepared by injection molding by the following procedure:

The pelletized extrudates were dried in a forced air oven prior to injection molding in an ARBURG injection molding machine equipped with a heated ASTM family mold. The molding conditions were as follows:

INJECTION MOLDER TEMPERATURES:

NOZZLE: 226.degree. C.

ZONE-1: 235.degree. C.

ZONE-2: 240.degree. C.

ZONE-3: 240.degree. C.

INJECTION PRESSURE:

6.6 MPa

BACK PRESSURE:

1.4 MPa

MOLD TEMPERATURE:

35.degree. C.

When processed by themselves, the Airvol-107, -205, and -325 produced a yellow, unstable melt, and were unsuitable for melt-processing. Airvol 103 was not tested by itself in this series.

The following examples illustrate thermal and physical properties of blends with specific poly(vinyl alcohol) polymers of a polymer of methyl methacrylate containing glutaric anhydride (MMA-GAH) units or with a styrene/maleic anhydride (St-MAH) copolymer. The latter polymer is sold commercially as Dylark (R) 232, and is believed to contain ca. 8 mol % of units derived from maleic anhydride. The former polymer is prepared by the method of Hallden-Abberton et al., U.S. Pat. No. 4,874,824 from a poly(methyl methacrylate) homopolymer of MW ca. 150,000.

These examples demonstrate that grafts of styrene polymers containing acid groups when grafted to a polyolefin trunk are ineffective in modifying the poly(vinyl alcohol) to improve its melt processing, as are direct grafts of acrylic acid to a polyolefin trunk.

The styrene/(meth)acrylic graft copolymers were prepared by polymerization of the appropriate monomer mixture in the presence of preformed polypropylene, mfr=4 in the absence of solvent, swelling of the polypropylene being conducted prior to initiation. The graft of MMA/N-VP (N-vinylpyrrolidone) was prepared in a similar manner.

The thermal properties of blends in the system graft polymer (polypropylene/styrene/(meth)acrylic acid)//PVOH were investigated by melt mixing in a single screw Killion extruder. The homopolymers and alloys listed in Table VII were extruded and pelletized at temperatures ranging from 180.degree. to 200.degree. C. for partially hydrolyzed PVOH (AIRVOL-205) and 200.degree. to 216.degree. C. for fully hydrolyzed PVOH (AIRVOL-107 and AIRVOL-325). All compositions, listed in Table VII, are given in weight percent. Examples C.sub.1 -C.sub.3 are controls of the unmodified poly(vinylalcohols). As can be seen from the data listed in Table VII, the melt compounding of the graft terpolymers with the several poly(vinyl alcohol)s resulted in alloys which exhibited varying degrees of melt instability. The term `UNSTABLE MELT` (Table VII) refers to the appearance of the melted PVOH or PVOH/graft terpolymer blends. `Unstable Melt` indicates a combination of degradation, phase separation and cross linking during the melt compounding and extrusion processes. The thermal stability of the alloys, in the molten state, may qualitatively be determined from the surface texture of the extrudates. The extrudates derived from the compositions listed in Table VII range in color from pale yellow to yellowish white. The former color was observed for those compositions in which the weight percent of -MAA or AA in the graft terpolymer was less than five weight percent. Particularly, it should be noted that the absence of acid and or anhydride in the graft terpolymer, PP-g-MMA-NVP, EX. 70 of Table VII, may have contributed to the blend being of a darker hue than those blends which contain acid functionalized polypropylene graft copolymers. It was observed that all of the alloys exhibited significant amounts of melt fracture. The inhomogeneous nature of the melt was also reflected in the form of low melt viscosity which led to decrease in the extruder torque during melt processing. This decrease, in torque, may be attributed to poor mixing between the blend components. Similar observations, shown in Table VIII, were encountered when the graft copolymer (polypropylene-g-acrylic acid) (PP-g-AA) was melt compounded with PVOH (AIRVOL-107 and AIRVOL-325). The graft copolymers are a commercial product; the exact nature of the trunk polymer or of the length of the acrylic acid grafted chains is not known.

These examples illustrate the utility of a multistage polymer with a butyl acrylate/acrylic acid first stage and a styrene or a styrene/methyl methacrylate second stage in improving the melt processability of poly(vinyl alcohol).

The composition delineated by Ex. 85, Table IX, represents a ternary blend comprising of a medium molecular weight (Mw=85-146 k) PVOH (AIRVOL-325), the impact modifier of Example 82, and the acrylic terpolymer, P(MMA-NVP-MAA=73/25/02). The impact modifier of Example 82 is a multistage polymer prepared by first emulsion polymerizing butyl acrylate/ethyl acrylate/methacrylic acid (60/16/4) and then polymerizing styrene/divinylbenzene (9/1) and then styrene (10) with a low level of dodecyl mercaptan. The polymer is isolated by coagulation from emulsion. The preparation of the acrylic terpolymer in emulsion is by a process very similar to that described in Example 1.

This alloy, in addition to being `melt stable`, was found to exhibit a greater degree of toughness than a similarly prepared alloy in which the impact modifier of Example 82 is absent. The thermal properties of the alloy, Tg, Tm and percent crystallinity are comparable to that of the matrix polymer, AIRVOL-325. This suggests that the combined effect of the impact modifier and P(MMA-NVP-MAA=73/25/02) is the improvement of the mechanical properties of the PVOH alloy without significantly altering the thermodynamic properties of the PVOH.

Impact modifier Example 86 is somewhat similar to the impact modifier of Example 82. It is prepared by first polymerizing 80 parts of butyl acrylate/ethyl acrylate/diallyl maleate/butylene glycol diacrylate/methacrylic acid (74.5/20/0.4/0.1/5.0) then polymerizing 20 parts of methyl methacrylate/styrene/divinylbenzene/butylene glycol diacrylate (69/30/0.7/0.3), and isolating by coagulation.

The mechanical properties of binary and ternary blends in the system: PVOH/P(MMA-NVP-MAA)/Ex. 86 are presented in TABLE X. It should be noted from a comparison of Examples 87 and 88 in Table X that the incorporation of the impact modifier of Example 86 into the binary blend of AIRVOL-107 and P(MMA-NVP-MAA) terpolymer leads to an improvement in the tensile yield strength of the final blend composition. Slight improvement is also seen in the impact property of the blend. The blend designated as Ex. 89 also shows marginal improvement in mechanical properties over that measured for blends without the impact modifier of Example 86. The blend of the low molecular weight (Mw=13-23 k) fully hydrolyzed PVOH (AIRVOL-103) with the impact modifier of Example 86, surprisingly exhibited poor overall mechanical properties.