WO1996038494A1

WO1996038494A1 - Degradable polymers and polymer products

Info

Publication number: WO1996038494A1
Application number: PCT/US1996/008208
Authority: WO
Inventors: Pierre Bono; Dorel Feldman; Dorina Banu; Jairo H. Lora; Jiashu Wang; Chih Fae Wu
Original assignee: Alcell Technologies Inc.
Priority date: 1995-05-31
Filing date: 1996-05-31
Publication date: 1996-12-05
Also published as: CA2220191A1; EP0851888A1; AU5960696A; MX9606224A; EP0851888A4

Abstract

This invention provides for degradable plastic polymeric blends and methods of making same. The blends comprise a polymeric material and an organosolv lignin. The invention also provides for articles of manufacture.

Description

DEGRADABLE POLYMERS AND POLYMER PRODUCTS

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of International Application No. PCT/US95/06397, filed May 31, 1995, which is a continuation-in-part of U.S. Application Serial No. 08/258,280 filed June 10, 1994 which is a continuation of U.S. Application Serial No. 07/867,718 filed July 9, 1992, now U.S. Patent No. 5,321,065 issued June 14, 1994.

BACKGROUND OF THE INVENTION

Polymer blending has become one of the most commercially important and inexpensive ways of developing new materials from readily available base polymers. The main aim of polyblending is the production of good performance materials at a reduced cost or the modification of some specific properties of polymers. This is achieved through the infinite blending possibilities, the ability to use existing flexible processing equipment, and the capacity to combine expensive polymers with ordinary and abundant ones.

Polyethylene is produced by polymerizing ethylene gas and the result is a joining together of the ethylene molecules into long polymer chains. The most common additives are heat and light stabilizers, slip, antibloc and antistatic agents, flame retardants and pigments. To protect against thermal oxidation which can be a problem during processing, antioxidants are usually added. Photo or light oxidation that occurs when natural PE is exposed to UV radiation is most often inhibited by the addition of carbon black and/or UV stabilizers.

PE is classified as either low and medium density (LDPE and LLDPE) or high density (linear) PE (HDPE) based on ASTM designation. LDPE and LLDPE have been used in several applications: film and sheeting, housewares, closures and containers, packaging materials, wire and cable coating, rotational molding, powder coating, pipe extrusion, refuse or garbage bags and extrusion coating. The primary processing techniques used to convert HDPE into end products are blow and injection molding for containers and lid closures, films and large containers.

Ethylene(vinyl) acetate (EVA) copolymer is generally obtained by adding vinyl acetate to PE. EVA is tougher, more flexible, softer and less heat resistant then LDPE. Being softer and more flexible than PE, the copolymers are often competitive with rubbers and plasticized PVC. At higher levels of comonomer incorporation, the EVA's are used as wax additives and as components in other formulations for hot melt coatings and adhesives. In these applications, the copolymers provide strength, improved barrier properties and better processing characteristics.

Polypropylene (PP) in its natural form is particularly vulnerable to degradative attack by oxygen and sunlight. Stabilizers have been developed which allow PP to retain its balance of good mechanical properties at low cost, and to do so in severe environments. Phenolic antioxidants have the primary function of reacting with the polymer peroxy radicals to form more stable radicals, and thus stop the chain oxidative attack. To protect the polymer against long periods of outdoor exposure to UV radiation, UV absorbers are added before processing. These absorbers are colorless and transform UV radiation into harmless longer wavelength light. Common classes of UV additives include the benzophenones, benzotriazoles, salicylates, and phenyltriazines. Certain nickel salts also provide some degree of UV absorption and act as free radical scavengers, preventing the propagation of the photo-chain degradation process. PP finds applications in molded products for automotive and appliance uses, packaging, fibers and fibrillated films, microporous filters and desalinization equipments, spun fibers, film and sheet and nonwovens.

Styrene is used primarily for the manufacture of thermoplastic resins, of which polystyrene (PS) and polystyrene copolymers are the most important. Polystyrene is the third most widely used thermoplastic resin, surpassed only by PVC and PE. Most polystyrene is processed by rotational and injection molding, extrusion and thermoforming. Two types of polystyrene are currently used: crystal and impact polystyrene. Both types find uses in houseware applications, packaging, appliances, wall coverings and many specialty applications.

PVC is the most highly modifiable plastic known. Products can be formed with a broad range of mechanical properties. Being self-extinguishing, PVC also has inherent flame resistance. Plasticizers such as phthalates and adipates contribute to its flexibility. The feel of PVC is controlled by the amount of plasticizers and/or filler material, as well as the type of resin. Impact modifiers can be included to increase breakage resistance.

Under UV irradiation, and in the presence of oxygen and moisture, PVC undergoes a very fast dehydrochlorination and peroxidation process with the formation of polyenes and subsequent scission and/or crosslinking of the chains. Additives which have UV stabilization effect can be included to prevent degradation in sunlight. One such stabilizer is titanium dioxide (Ti0₂) which provides adequate protection for most purposes and is most often introduced at levels up to 10 to 12 phr. At these levels, Ti02 can enhance the weathering properties of PVC products because of its ability to absorb to a certain degree UV radiation falling on the polymer. Ti0₂ is widely used in white and light color formulations. Ti0₂ is approximately 50% more costly than unplasticized PVC used for outdoor service and PVC producers are looking for ways to reduce their Ti0₂ consumption.

Current thermoplastic polymeric materials are generally disposed of by incineration. They can also be disposed of by recycling which can be achieved by increasing their oxidation temperature. Increasing the oxidation temperature can be achieved through the use of additives. Such additives have generally been known to have certain other drawbacks as when such materials must be incinerated, such additives generate toxic fumes necessitating an additional treatment step which increases the overall cost of disposal. In any event, with PVC, additional treatment for effluent gases is necessary.

Certain thermoplastic polymeric materials can either photodegrade or biodegrade. Generally, photodegradable thermoplastic polymeric materials are obtained by introducing photoactive additives into a base material such as for example polyolefin. These additives consist of molecules containing oxygen and/or heavy metals which play a role in the initiation and formation of free radicals under the action of ultraviolet (UV) radiation. The free radicals cause a rupture of the chains of the polymer and therefore make the polymer fragile and mechanically degradable.

Although frequently in use, such photoactive additives are generally strongly oxidizing which can cause the degradation of the plastic material to begin immediately after the manufacture of the material thus reducing the shelf life of the thermoplastic polymeric materials.

Generally, biodegradable plastic materials can be obtained by the introduction of a biopolymer such as starch. As starch can be attacked by microorganisms, the material becomes susceptible to degradation.

However, the incorporation of starch in such material can have drawbacks as it can be partially decomposed during the processing and it is highly sensitive to water. Furthermore, starch is not compatible with most polymers, and its incorporation during polymer manufacture can render the final product brittle. Furthermore, in polymeric films with a particularly small thickness, the particle size of starch can be a limiting factor on the overall manufacturing process and the cost becomes prohibitive.

A number of biopolymers in addition to starch can also be used such as for example other carbohydrates with one major drawback that upon blending with the polymeric material, the biopolymer can undergo various alterations such as oxidation and polycondensation. Such alteration to the biopolymer can have a negative effect on the mechanical properties of the polymeric materials.

As an alternative to the foregoing, a biopolymer such as organosolv lignin can be incorporated with thermoplastic polymeric materials.

SUMMARY OF THE INVENTION

This invention provides for degradable polymers and polymer products having incorporated therein an organosolv lignin. It also provides novel formulations and processing techniques for their manufacture. The incorporation of the lignin enhances the mechanical properties of the polymers while causing them to degrade under certain conditions. Additionally, and if desirable, the properties of the blends of the present invention, including the lignin, can be formulated to allow timed and/or controlled release of a desired active ingredient. The polymers of this invention can be disposed of without incineration or recycled, resulting in a savings in energy and minimal pollution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The biopolymer employed in this invention is a lignin which is separated from plant biomass by a novel chemical delignification technology based on organic solvents, for example ethanol; see e.g., U.S. Patent No. 4,764,596. Generally referred to as organosolv lignin, it is a free-flowing, non-toxic powder. It is soluble in aqueous alkali and in selected organic solvents. It is generally characterized by its hydrophobicity, purity, melt flow properties and a low level of carbohydrates and inorganic contaminants.

The lignins of this invention can be incorporated into various polymeric materials and can have various effects on the polymeric blend such as for example they can function as an antioxidant, as a stabilizer against ultraviolet radiation, as a compatibalizer, and can enhance the mechanical properties of these materials.

The lignins of this invention can stimulate degradation of the polymeric materials when photoadditives are added to the blend. The products can degrade by photodegradation of the polymeric materials and the lignin, or alternatively, by biodegradation of the lignin under composting conditions.

The lignins of this invention can be blended and compounded with polymers such as for example polyethylene, polypropylene, poly(vinyl) chloride and polystyrene in a weight ratio of from about 0.5% to about 50% with the polymer of choice. Alternatively, the lignin can be blended with a copolymer such as for example ethylene(vinyl) acetate or styrene-butadiene copolymers. The resulting blends are master batches which can be diluted by further blending with polymers such as for example polyethylene, polypropylene, poly(vinyl) chloride and polystyrene. The blends can be then processed by extrusion, calendaring, injection or known processes in the art to yield articles of manufacture having different utilities such as for example, film and molded products.

Preferably, the polymer blends and/or master batches are formulated to allow them to be processed with simple extrusion equipment. Various polymer and copolymer blends and formulations together with desirable processing parameters are selected to not only enhance ease of mixture and/or blending, but also the resultant properties of the overall formulations and final products.

One factor which is believed to be important to ensure enhanced properties of the blend and/or master batch is controlling the integrity of the lignin constituent throughout processing, namely, to prevent or mitigate against lignin degradation. For example, it is believed that the untreated organosolv lignin constituent of the present invention can begin to degrade and/or decompose during blending and/or processing at temperatures of about 220°C and higher. Accordingly, it is generally preferred to select the polymer and/or copolymer systems and processing parameters to enable the effective blending and/or compounding of the formulations under conditions where the lignin component is exposed to temperatures of no more than about 200°C.

On the other hand, it is believed that the organosolv lignin can be treated chemically or otherwise in a manner consistent with maintenance of its unique characteristics and purity to stabilize the lignin against degradation. Without limiting the scope of potential mechanisms and/or processes for stabilizing the lignin, it is believed that stability can be achieved through chemical pretreatment of the lignin using, for example, peroxide treatments and/or etherification and/or acetylation, or by controlling temperatures to which the lignin is exposed either directly or indirectly, through selection of ingredients or processing techniques which shield the lignin from such temperatures. Some specific examples of such techniques are set forth in the detailed description of the preferred embodiments which follows.

Other anticipated benefits of the foregoing are to increase the amount of lignin that can be incorporated into the blends, thereby reducing the overall cost of the final product, and increasing the degradability rate.

In one preferred embodiment, blends can be prepared by mixing about 0.5 to 50% by weight of organosolv lignin with a polymer or polymer blend of choice known to have a softening temperature in the same range as that of the lignin. The blends can be prepared by mixing all ingredients directly or in successive stages. The blends may be used as produced to make a product, or as master batches.

In another preferred embodiment, a master batch can be prepared by mixing organosolv lignin of from about 35% to 85% on a weight basis with the copolymer of choice such as EVA, SBS or any other polymer which is known to have a glass transition temperature in the same range as that of the lignin. The master batch can be prepared by mixing all ingredients directly or in successive stages.

In a further embodiment, the use of additives is contemplated to improve the compatibility between the lignin and the selected polymer(s) to be blended. The additives or compatibilizers are selected from those materials which are chemically compatible or formulated to not only be chemically compatible with the lignin and the selected polymer, but also to cause no deterioration of the overall properties of the polymeric system blend and/or master batch and their resultant articles of manufacture. Preferred compatibilizers include additives such as EVA, SBS, and maleic anhydride copolymers such as poly(ethylene-maleic anhydride) . Examples II and III illustrate the effects of both SBS and poly(ethylene-maleic anhydride) compatibilizers, each of which resulted in substantial improvements of strength properties when the blends were used for dumbbells made by injection molding and/or for film.

For specific applications, the master batch can also be coextruded with a polymer of choice depending on the desired final product. Pellets can be produced with a core and a sheath with a variable composition. The core of the pellet can have the composition of the master batch while the sheath can have the polymer composition of the intended final product. The pellets can generally be obtained by granulating the filaments coming out of the extruder.

The core of the pellet can^" be manufactured by considering the nature of the biopolymer to be incorporated therein. When organosolv lignin is used, the pellet can be manufactured without causing any chemical or physical deterioration by mixing the lignin or a master batch polymer of particular interest such as for example EVA or SBS or any other master batch polymer which is known to have a glass transition temperature in the same range as that of the lignin.

The core, which comprises of from about 35% to about 85% lignin and 65% to 15% master batch polymer, can be extruded at a temperature of from about 115°C to about 145°C to form a polymer sheath having a similar composition as the final product. It is believed that extrusion at the foregoing temperature will result in no damage to the lignin. Extrusion of the sheath generally requires a temperature of from about 170° to about 230°C. As a target, the overall composition of the coextruded compound is preferably equivalent to the composition of the finished product. The thickness of the sheath can be adjusted according to the diameter of the core, which corresponds to the diameter of the central filament, such that the level of lignin in the final coextruded product is of from about 0.5% to about 50%. In a preferred embodiment, for a core diameter of from about 1 mm to about 2 mm, the sheath thickness is of from about 4 mm to about 5 mm such that every individual pellet of compound comprises from about 4% to about 25% of lignin.

An advantage of using coextrusion at the compounding temperature of polyethylenes and polypropylenes is that the problem associated with the thermal decomposition and oxidation of the biopolymer is alleviated. In this particular instance, the coextruded compound upon extrusion, takes on the appearance of pellets which are heterogeneous under the microscope but still are more homogeneous overall by contrast to the appearance of pellets which result from the mechanical mixing of two different pellet compositions.

The master batch of this invention can be processed by extrusion, blowing, injection or other processes known in the art. The machinery generally used requires adaptation to the processes of this invention to meet the shorter residence times which are required at critical temperatures such as for example the oxidation temperature. It is also believed that the processes of the invention can operate at a lower temperature mainly because of the additional heat protection from the sheath to the lignin-rich core which is easier to melt and the viscosity of which is not as sensitive to the temperature as the PE or PP.

In certain specific applications of this invention, organosolv lignin powder with a median particle size of from about 0.1 micron to about 100 microns and in a quantity of from about 0.5% to about 50% can be mixed with polyethylene or more generally an ethylene copolymer to manufacture homogeneous films having a thickness of from about 5 microns to about 100 microns. The polyethylene blends can be prepared by direct mixing or by using a master batch preparation. It has been observed that the resulting films can photodegrade, particularly when iron stearate or any other photoactive and/or oxidizing additives such as cerium salt is added in a range dependent on the target film shelf life and the conditions under which the film will be used. A preferred range is of from about 0.1% to about 0.5% of salt based on total weight of polymer blend. The plastic films thus obtained can be used for many agricultural applications, as well as for the manufacture of plastic bags for refuse, shopping baskets, etc. In agricultural applications, in which the stiffness of the film is essential, the lignin containing polyethylene film of the present invention appears particularly interesting to use since the degradation of the film over time is total, both for the surfaces which are outside the ground and for those which are buried inside the ground. Furthermore, in the agricultural applications field, the adsorption and absorption capacities of lignin, of essential oils, insecticides and the like, will permit then a use of lignin as an additive for the new fungicidal, rat- killing or other properties.

The films of the present invention can be multi- layered films, prepared by processes known in the art. These films can have as many layers as desired, and the layers may be arranged in any desired fashion. For example, a three- layered film could be made, having a polyethylene layer in the middle, surrounded by a layer of lignin-containing polymer blend above and below the middle polyethylene layer. Alternatively, if the film is to be placed on a substance that may react deleteriously with the lignin, the film can be structured so that one layer, such as polyethylene, which will not react with the substance being covered, is placed on an outermost layer of the film. The film would then be placed on the substance to be covered, such as food for example, with the polyethylene layer facing the substance, to act as a barrier or buffer, shielding the substance to be covered from the lignin. Obviously, there are many applications where, by varying the layers, different results can be achieved as desired.

Accordingly, the products and formulations of the present invention allow one to control the speed and manner in which the lignin-containing products degrade, which when coupled with the adsorption properties of the lignin, thereby allow production of a variety of controlled release products for various industrial, agricultural and other applications. These products may be provided with an active ingredient which is activated upon degradation of the product. As used herein, the term "active ingredient" designates matter such as herbicides, fungicides, insecticides, etc., which produce the desired effect or property to be achieved by the blend and/or the final product.

Likewise, the adsorption properties of lignin can be utilized so that the lignin can be incorporated into the photoactive products prior to its mixture with the copolymers, which has the advantage of increasing the homogeneity and the degradability of the film. On the other hand, this lignin- containing plastic film can be coextruded, and can therefore be a part of a composite film.

It should further be noted that the initial mechanical properties of the lignin-containing degradable film of the present invention are comparable to those of a film which does not contain any lignin.

Generally and highly dependent on the process of preparation, the lignin thermally behaves by partially condensing with apparent fusion and without oxidizing in a temperature range of from about 125°C to about 200°C and on the other hand by oxidizing without condensation at about 160°C. The properties of the lignin are material to the processes of this invention. When the lignin condenses, it is believed that it is capable of generating water to approximately from about 1% to about 6% of its weight. Therefore, special attention must be given to eliminating water produced during the manufacture of the thermoplastic polymeric material.

The lignin and polymer can be mixed in an extruder which can be either a single or double screw. The mixing is preferably performed in a vented extruder such that any water vapor formed from the lignin is eliminated. The extrusion conditions are dependent on the scale of the process, the polymer system being utilized, nature of the ultimate product and other factors, as are known in the art. In view of the unexpected results attributable to the use of lignin in the present invention (e.g., its addition does not cause the embrittlement of the product and can improve resilience to degradation, such as increase the initial resilience to ultraviolet radiation when the lignin biopolymer is added to polyethylene) however, it has been found that by more intimately mixing the blends of the present invention, significantly improved dumbbell properties and blown film properties are obtained; see Example IV. It is further believed that the amount and intensity of the mixing of these blends can be adjusted to permit the incorporation of higher amounts of lignin into the blend. While Example IV illustrates the advantage of utilizing "double" and thus multiple extrusions to accomplish the foregoing, it is contemplated that single extrusions with longer mixing intervals and/or adjustment of other compounding conditions such as manner and timing of the additions of the ingredients of the blends, the screw element profiles, screw speeds, extruder temperatures and/or combinations thereof, will also have these beneficial effects, e.g. see Examples V and VI.

The temperature profile is also an important element of the success of a good mix since the lignin must be protected from oxidation and thermal degradation. This can be accomplished by adding the lignin to the already molten polymer or by using the master batch described herein. Upon mixing with the lignin, the lignin behaves as a thermal antioxidant which results in an increase in the oxidation temperature of the polymer. An increase in the oxidation temperature of the mixture enables the recycling of such material thus permitting it to be melted again for reuse without degradation. In the case where the material can no longer be recycled and it may prove necessary to effectively incinerate the material, addition of the lignin is beneficial as the heating value of the lignin is equivalent to that of the polymer used, thus allowing its destruction by incineration.

For example, when the polymer used is pure polyethylene, its oxidation temperature is about from 150°C to about 160°C. By contrast with about 10% lignin, the oxidation temperature is from about 185°C to about 195°C and with about 25% lignin, the oxidation temperature is from about 195°C to about 205°C. In another example, when the polymer used is polypropylene, the oxidation temperature is from about 210°C to about 220°C. By contrast with about 10% lignin, the oxidation temperature is from about 255°C to about 265°C.

The thermoplastic polymeric material of this invention can be used in applications known in the art for example in extrusion/blowing applications, calendaring, injection molding to form films, plates, sheets, tubes, bottle caps, wrapping paper, car parts and the like.

In order to improve the machining of the thermoplastic polymeric materials of this invention, plasticizers such as styrene butadiene rubber, zinc stearate, soybean oil to name a few can be added during fabrication.

Generally, as thermoplastic polymeric materials cannot be perfumed, the invention provides for the addition of perfume material because of the presence of lignin or any other biopolymer which can absorb such scent additives. In one embodiment of this invention, lignin can be mixed hot or cold either alone or in conjunction with the thermoplastic polymeric material. In this embodiment, the lignin can be treated by maceration in solvents containing essential oils before it is blended with the polymeric materials. In another embodiment, a mixture of scents, such as for example, terpenes and citronella can be directly injected in one of the sections of the extruder during the manufacturing of the mixture.

It is to be noted that unexpectedly for polymers such as polyethylene, the addition of a biopolymer such as lignin to a polymeric material can lead to an improvement in the material's resilience to ultraviolet radiation. This is unexpected as one does not add an additive which would enable the resistance to photodegradation but rather the lignin plays a role in stabilizing the thermoplastic polymeric material to degradation by ultraviolet radiation as shown in Table 1. It is also to be noted that without the lignin, an increase in the length of exposure to ultraviolet radiation causes an important fragmentation of the polymer and a sudden and significant variation in the molecular weight of the polymer. Table 1 Molecular Weight

Length Of Exposure To Polyethylene + 10% UV Radiation (hours ) Polyethylene Liσnin 0 320,000 300,000 30 240,000 242,000 200 35,000 120,000

In a preferred embodiment of this invention, PVC can be blended on a weight basis with from about 0.5 to about 50% organosolv lignin with a specific gravity of about 1.27 and a median particle size of from about 0.1 micron to about 100 microns. The final PVC/lignin blends have stronger mechanical properties and can degrade under the effect of light. The PVC blends can be used in medical, food, fashion and home applications.

The following sets forth one particular embodiment for the blending of PVC with organosolv lignin. The PVC used is a commercial unplasticized resin (Geon 85862 from BF Goodrich Technical Center, Avon Lake, Ohio, USA) as a suspension polymer of high molecular weight (k = 67) and has the following formulation: PVC resin, 100 phr; stabilizer, 2 phr; processing aid, 1.5 phr; impact modifier, 6 phr; lubricants, 3.75 phr; Ti0₂, variable from 0 to 10 phr. With 10 phr Ti02, the PVC resin has a specific gravity of about 1.48.

PVC blends were prepared with the composition set forth in Table 2. Table 2

Blend # Ti02 (%) Orσanosolv Liσnin (

1 9.09 0

2 6.81 2.27

3 4.54 4.54

4 2.27 6.82

5 0 0

6 0 4.54

7 0 6.82

8 0 9.09

9 0 13.63

10 0 18.18

The blends were prepared by melt compounding in a Haake Rheomix 600 equipped with roller blades at a temperature of about 195°C. The time of mixing was about 8 minutes at a speed of roller blades of about 65 rpm. PVC was added first and the lignin second after about 30 seconds. Several batches were prepared for each formulation and after melt mixing the obtained blends were ground to a particle size of from about 3 to about 5 mm. Sheets with a thickness of about 2 mm were molded by compression at about 195°C. After cooling with air and under pressure, the sheets were cut with a cutting die in shoulder shaped specimens for mechanical testing.

The mechanical properties, tensile strength and elongation at break were measured before and after 5 days and 20 days of artificial weathering and were correlated with the properties of PVC controls. They were measured in accordance with ASTM D 638 using an Instron universal testing machine.

The weathering of the samples was carried out using equipment known in the art such as a Q-Panel QUV. In this tester rain and dew are simulated by a condensation system and it contains a series of UV-A lamps with a peak emission at 343 nm and a spectral power distribution of from 295 to about 400 nm. All the specimens were subjected to several cycles of 4 hours each of UV exposure at an equilibrium temperature of about 50°C alternating with condensation exposure at an equilibrium temperature of about 40°C. The number of days of accelerated weathering was 5 and 20.

Table 3 shows the influence of lignin on the fusion characteristics of the blends. The processability or the fusion characteristics of PVC blends is generally influenced by the type of resin and additives present. A change in formulation especially in the case of rigid PVC composition can affect the fusion characteristics of PVC blends and consequently their processability. Improper processability can have a negative effect on the mechanical properties of PVC and its weatherability. It has been found that the fusion characteristics of blends of PVC with lignin formulated with or without Ti0₂ present almost the same characteristics as PVC controls. One may conclude that the fusion characteristics of PVC-lignin blends in comparison with PVC controls are very close and the presence of lignin does not have a negative effect on the processability of PVC- lignin blends. The specimens of PVC lignin blends with Ti0₂ were colored from beige to tan and PVC lignin blends without Ti0₂ were dark brown.

Table 3

Blend Average Average Torque Valluuee AAvveerraaggee

Type Fusion Temperature of the

Time melt (°C) (S)

Max. At the end At max At the end

(fusion) of 3 min. torque of 8 min.

1 75 2500 1575 184 205

2 80 2530 1600 180 204

3 85 2570 1600 183 204

4 88 2425 1475 182 204

5 165 1960 1430 182 204

6 100 2280 1430 186 204

7 105 2350 1420 189 203

8 78 2370 1400 181 202

Table 4 shows the strain-stress data for PVC controls and PVC-lignin blends before and after 5 and 20 days. The lack of correlation between the values of the tensile stress-strain data predicted by the theoretical model elaborated by Nielsen (J. Appl. Poly . Sci., Vol. 10, 97-103 (1966)) particularly in the case of perfect adhesion between filler (in this case lignin) and polymer (in this case PVC) and the experimental values shown in Table 4 suggest a certain degree of interaction between the two polymers in the blend. Moreover, up to a certain level of about 6.81% lignin acts as a reinforcing agent without having a negative impact on the elongation. As can be seen after weathering, all the blends show a higher tensile strength value than PVC controls, and the increased values can be correlated with lignin loading and weathering period. The elongation at break decreasing can be also correlated with weathering period and lignin loading. It can also be seen that after 20 days weathering period, all the blends regardless of their Ti0₂ level show a high degree of embrittlement and an increase in tensile strength with an almost lack in elongation. It is believed that the effect observed can be due to crosslinking.

Table 4

Blend Tensile Strength Elongation at Break Type (MPA) (%)

Initial 5 Davs 20 Days Initial 5 Days 20 Days

5 42.30 48.36 50.52 280 289 47

1 40.15 45.76 49.73 332 292 269

2 43.85 48.30 49.86 281 193 61

3 44.14 49.40 50.58 326 110 45

4 47.05 50.41 51.60 312 91 30

8 48.66 50.26 51.67 182 51 29

In addition, after the weathering period the PVC blends without Ti02 and the PVC blends comprising lignin are characterized by a change in color observed only on the exposed side to UV light. In the case of PVC blends without Ti02, the color changed from white-gray to reddish yellow and in the case of the PVC blends comprising lignin the color changed to lighter tones . In the case of the PVC blends comprising 9.09% Ti02, the change in color after weathering is barely perceptible which is believed to be due to the effect of Ti0₂ on the weathering of PVC.

It is believed that the embrittlement and color change due to artificial weathering show the susceptibility of both interacting polymers to UV radiation. It is believed that the lignin photodegrades as a result of the formation of free radicals, mainly phenoxy radicals.

The PVC blends of this invention can be formulated to achieve good weatherability by blending synergistic levels of Ti02 and lignin.

The invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various modifications and changes can be made without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the specific materials, procedures and example hereinbefore described being merely preferred embodiments.

For example, by blending different kinds of PVC compounds with lignin, other types of blends can be formulated which would have the advantage of a lower processing temperature and milder weatherability conditions. Suitable UV absorbers and/or light-thermal stabilizer systems can also be included in the formulations in order to achieve suitable mechanical properties before weathering and suitable shades of colors in the final blend.

In another example, the lignin and Ti0₂ can be formulated together to further optimize the photochemical reaction of the lignin and Ti0₂ thus affecting the final photodegradability of the formulation.

The following additional examples will further illustrate various aspects of the present invention.

Example I

Polyethylene films that incorporate bio-degradable materials such as starch are typically very weak and brittle. Surprisingly, the use of lignin to make polyethylene films actually increases the tensile strength and elongation properties as compared with films made from polyethylene alone as well as with SBS and calcium stearate. As set forth below, in Table 5, three different compounds were extruded into films using a single screw extruder with a 24 L/D ratio (1 inch screw diameter) at extruder temperatures of about 175°C at a run rate of 50 rpm. The extruder utilized a two inch spiral blown film die with a die temperature of about 200°C and a blown-up ratio of approximately 2. The film was tested pursuant to ASTM 882-91, Standard Test Method for Tensile Properties of Thin Plastic Sheeting.

Table 5

Compound Tensile, MPa Elonσation, %

Machine Cross Machine Cross Direction Direction Direction Direction

LDPE (100%) 15.5 7.9 67 105

LDPE (93.7%) 21.9 9.5 241 440 6% SBS +

0.3% Calcium stearate

LDPE (80.7%)+ 21.9 18.6 182 300

13% lignin

6% SBS +

0.3% Calcium stearate

LDPE is Dow LDPE 681, from Dow Chemical Company, Midland, Michigan. SBS is Kraton D1102, from Shell Canada Chemical Company, Calgary, Alberta. Calcium stearate 114-36 is from Synthetic Products Company, Cleveland, Ohio. The lignin is ALCELL lignin from Alcell Technologies Inc., New Castle, New Brunswick,Canada.

The compounds fed to the above extruder were pelletized by compounding them in a twin screw extruder with a 40 L/D ratio (50 mm diameter) . Initially, in stage 1, the extruder is run at about 200°C to melt the polymer. Thereafter, in stage 2, the average barrel temperature is 170°C, and the lignin is introduced at this point in the compounding process. At the end of stage 2, the melt temperature is measured, and is generally about 190°C. The extruder was run at 300 rpm.

Example II

The three compounds referenced in Table 6 were pelletized in the compounding extruder in the same manner and using the same ingredients as described in Example I, above. The pelletized compounds were then extruded into film in the same manner set forth in Example I and dumbbells manufactured and tested according to ASTM D638-91 Standard Test Method for Tensile Properties of Plastics. Table 6 illustrates the effect of the presence of different levels of SBS in dumbbells and blown film.

Table 6

Dow LDE SBS Content Dumbbell Film Properties

681 %wt Properties

%wt

Tensile Elong¬ Tensile Elong¬ MPa ation MPa ation (%) (%)

83.7 3 10.0 484 15.4 140

80.7 6 13.3 820 19.5 137

77.7 9 13.5 840 25.0 112

The above blends include 13% ALCELL lignin, low density polyethylene (LDPE), and 0.3% calcium stearate. As can be seen, when the SBS content increased, strength properties in general increased for both film and dumbbell. This example supports the use of SBS as a compatibilizer, namely an ingredient added directly to the blend during compounding, which improves the compatibility between the polyethylene and the lignin, as distinct from a system wherein the SBS is utilized as a second ingredient in a lignin master batch which is then diluted with, e.g., a polymer such as polyethylene.

Example III

Table 7 illustrates the use of poly(ethylene- maleic anhydride) as a compatibilizer for the polyethylene and lignin blend, which results in a strength improvement in physical properties of up to about 20% over the lignin-LDPE blend without compatibilizer.

Table 7

% compatibilizer Dumbbell tensile, based on lignin MPa

0 9.1

10 10.1

20 11.2

In the above formulations, 80% LDPE-LOOOOl polyethylene from Federal Plastics Corporation, Cranford, New Jersey is utilized, with the balance constituting ALCELL lignin and compatibilizer. The polyethylene co-maleic anhydride 18.805- 0 is from Aldrich Chemical Company, Milwaukee, Wisconsin. The materials were manually blended and extruded directly into a dumbbell machine as per the ASTM Standard D 638-91. Example IV

Table 8 illustrates the effect of improving the compounding of lignin-polymer blends. The indicated lignin- polymer blend denoted "single" extrusion was compounded as set forth in Examples I and II. The properties of the dumbbells and films for the single extrusion, also manufactured as previously set forth, is compared with a "double" extrusion of the same compound; the single extruded blend was compounded/extruded again prior to manufacturing the dumbbells and films. Multiple extrusion of the lignin- polymer blends resulted in stronger products, which presumably, will also lead to the incorporation of larger amounts of lignin into the blends with the resultant beneficial effects as outlined herein.

Table 8

Extrusion Dumbbell Blown film type properties properties

Tensile Elongation Tensile Elongation MPa (%) MPa (%)

Single 11.0 660 18.1 104

Double 13.3 820 22.5 109

Compounds were made with 13% ALCELL lignin, 80.7% Dow LDPE, 6% SBS Kraton D1102 and 0.3% calcium stearate.

Example V

Table 9 illustrates the effect of increased extruder screw speed on dumbbells manufactured from 80.7% Dowlex LLDPE 2045 (Dow Chemical Company) , 6% SBS Kraton D1102, 13% ALCELL lignin and 0.3% calcium stearate. In this example, the average barrel temperature was about 170°C upon introduction of the lignin, the melt temperature at the end of stage 2 was about 188°C, and the screw speed was varied as set forth below. As can be seen, the strength of the dumbbells increased as the rotational speed increased. Since certain polymers may degrade with shear, there are practical limits to how much shear can be applied. These limits are dictated by the nature of the components of the polymer blend.

Table 9

Screw speed, Dumbbells properties rpm

Tensile, MPa Elongation, %

100 7 300

200 11 590

300 13 730

Example VI

Table 10 shows the effect of increasing extrusion barrel and melt temperatures on strength properties of dumbbells and films manufactured in the manner set forth in the previous Examples. The blend has the same formulation as that in Example V. The compounding extruder screws were set at 300 rpm for all cases.

Table 10

Extruder Melt Dumbbell Blown film tensile, MPa barrel temperature tensile, MPa temperature °C °C

Machine Cross direction direct¬ ion

160 176 12.1 14.4 6.7

170 190 12.8 21.3 8.7

180 199 12.1 19.5 8.5

This example shows that for both compounds and films, a maximum strength was obtained at a barrel temperature of 170°C (wherein the lignin is introduced) and a melt ^■ temperature at the end of Stage 2 of 190°C. The superior strength was more obvious in the blown film properties than in the dumbbell test results.

Claims

We claim:

1. A method of making a degradable thermoplastic polymeric blend comprising the step of mixing a polymeric material with an organosolv lignin in a weight ratio of from about 0.5 to about 50% on weight basis with said polymeric material, and an effective amount of a compatibilizer.

2. The method of claim 1, wherein said polymeric material is polyethylene, and said compatibilizer is selected from the group consisting of poly(ethylene-maleic anhydride) , styrene butadiene copolymers and mixtures thereof.

3. A method of making a degradable thermoplastic polymeric blend comprising the step of mixing a polymeric material with an active ingredient and an organosolv lignin in a weight ratio of from about 0.5 to about 50% on a weight basis with said polymeric material.

4. The method of claim 3, wherein said active ingredient is adsorbed by said organosolv lignin.

5. The method of claim 4, wherein said active ingredient is mixed with said organosolv lignin prior to mixing with said polymeric material.

6. The method of claim 3, further including the step of fabricating a product from said thermoplastic polymer blend, whereby said active ingredient is activated upon degradation of said product.

7. A method of making a degradable thermoplastic polymeric blend comprising the step of mixing a polymeric material with an organosolv lignin in a weight ratio of from about 0.5 to about 50% on a weight basis with said polymeric material, wherein said polymeric material is compounded until it is molten, and said polymeric material and said organosolv lignin are mixed by adding said organosolv lignin to said molten polymeric material.