RENEWABLE, BIODEGRADABLE POLY(LACTIC ACID) COMPOSITES WITH IMPROVED THERMAL PROPERTIES BACKGROUND OF THE INVENTION

Field of the Invention

This invention generally concerns a poly(lactic acid) composite that has improved thermal properties, is biodegradable and is made from renewable materials.

Description of Related Art

Poly(lactic acid) (PLA) is a thermoplastic aliphatic polyester derived from renewable resources such as corn starch in the United States or sugarcane in much of the rest of the world. PLA can also be used as a compostable packaging material, either cast, injection molded, or spun. Cups and bags have been made of this material although their use is limited to cold applications because of the low heat deflection temperature (HDT) it exhibits (see for example D. Garlotta, /. of Polymers and the Environment 9(2), April 2001).

Many attempts have been made to improve the low HDT with varying degrees of success. It has been reported by M. S. Huda, et al. {Mechanical and Thermo-mechanical Studies of Poly (lactic acid) PLA Talc/Recycled Newspaper Fiber Hybrid Composites, SPE's Global Plastics Environmental Conference, March 2005) that the use of shredded newspaper resulted in a moderate increase in the HDT of a PLA-based composite.

However, this moderate increase was still significantly below the point where the composite could be considered efficacious for hot food and drink applications.

Further, the US government funded efforts to incorporate various cellulosic nano- whiskers (CNW) into PLA during polymerization (see

http://cfpub.epa.gov/ncer abstracts/index.cim/fuseactiori/'dispiav.abstractDetail/abst ract/794 8 and

http://cfpub.epa.gov/ncer abstracts/index. cfm/fuseaction/displav.abstractDetail/abs ract/838 4). These products were brittle and the process was not cost-effective.

There are methods by which PLA's HDT can be increased through physical blending with Poly-D-Lactic Acid (PDLA). However this D-stereoisomer is much more expensive to produce than Poly-L- Lactic Acid (PLLA) and is not proving to be

economically viable for commercial uses. Further, the use of PDLA dramatically increases the time required for the composite to biodegrade.

Other techniques that introduce nucleating agents such as talc have also been reported to increase PLA's HDT but talc is not a sustainable or biodegradable component (e.g., US Patent Appln. 2003/0038405 Al).

US Patent 8,222,320 discloses the use of poly(lactic acid), an aliphatic polyester, and an organically coated calcium carbonate. The latter is likely functioning as the nucleating agent. The HDT provided by this composition is at least 165°F up to 180°F, but exemplified to only 165°F. This polymer composite is not entirely biodegradable or sustainable.

US Published Appln. 2009/0226655 teaches the use of poly(L-lactic acid) with high crystallinity and a functional filler of D-lactic acid to form a resin with heat resistance for blow molding. This resin is used for bottles.

Further, PLA blends with other plastics have yielded high HDT composites but again, they suffer from high cost, reduced sustainability and reduced biodegradability. Some of these PLA blends were discussed by J.H. Schut, in "Bio-resins Tackle Durable Applications", Plastics Technology, Thursday, January 1 , 2009.

Clearly, a PLA-based biocomposite made from renewable materials that is biodegradable and possesses an increased HDT, increased modulus via a commercial process at a lower cost when compared to PLA is still needed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a composite comprising PLA and microground cellulosic forming a PLA/cellulosic composite having a HDT greater than or equal to about 85°C at 66 PSI. This PLA/cellulosic composite is about 100% compostable and biosourced. The microground cellulosic size is from about 10 to about 250 μ, preferably from about 20 to about 50 μ. The PLA/cellulosic composite contains from about 5 to about 70% of microground cellulosic, preferably from about 5 to about 50%, especially from about 5 to about 30%. The moisture is removed from both the PLA and cellulosic prior to forming the composite and then the composite is annealed. PLA/cellulosic composite characteristics are that it does not block (whether annealed or not) has good dimensional stability, and is cost- effective compared with PLA. DETAILED DESCRIPTION OF THE INVENTION

It is understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in this specification, the singular forms "a", "an", and "the" include plural referents unless the content clearly indicates otherwise. The following terms in the Glossary as used in this application are to be defined as stated below and for these terms, the singular includes the plural.

Various headings are present to aid the reader, but are not the exclusive location of all aspects of that referenced subject matter and are not to be construed as limiting the location of such discussion.

Also, certain US patents and PCT published applications have been incorporated by reference. However, the text of such patents is only incorporated by reference to the extent that no conflict exists between such text and other statements set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference US patent or PCT application is specifically not so incorporated in this patent.

Glossary

% means weight percent, unless stated otherwise

CFHA means conveyorized forced hot air

DSC means differential scanning calorimetry

DTUL means deflection temperature under load

GPC means Gel Permeation Chromatography

h(s). means hour(s)

HDT means heat deflection temperature

IR means infrared

in. means inch(s)

min(s). means minute(s)

psi means pounds per square inch

PDI means polydispersity index PLA means poly(lactic acid)

PDLA means poly-D-lactic acid

PLLA means poly-L-lactic acid

PSI means pounds per square inch

μ means micron or μιη for micrometer and are equivalent terms

Discussion

Biobased materials, as a renewable source of a PLA/cellulosic composite, are desired to eliminate the use of oil-based alternatives and to provide environmentally friendly solutions. This invention describes how a cost-effective, high HDT PLA biocomposite is formed by compounding with microground cellulosic. The present invention produces a PLA-based biocomposite, or PLA/cellulosic composite, with increased HDT, increased modulus, as a commercial process, and all at a lower cost when compared to PLA. These present PLA/cellulosic composites are formed as pellets, directly injection molded or extruded into sheet and thermoformed or otherwise used in a variety of applications, such as food packaging and other uses, while being made from sustainable, biodegradable, renewable resources.

PLA is a thermoplastic, aliphatic polyester derived from renewable resources and can be used as a compostable packaging material, either cast, injection molded, or spun. However, because of its low HDT only cold applications are presently possible in commercial applications. Typical literature values for PLA properties are shown in Table A below.

Table A

Literature Values for PLA

Most typically 55-65°C unless additives are used.

The data in Table A was compiled from: Polylactic Acid (PLA ) Typical Properties,

IDES: The Plastic Web, http://www.ides.com/generics/PLA PLA typical properties.htm; J.S. Dugan, Novel Properties of PLA Fibers, Fiber Innovation Technology, Inc.,

http : //www . f itfiber s . com/files/PLA%2()Fibers . doc ; Engineering Properties of PLA - NatureWorks PLA Engineering Properties, http://www.nat.ureworksllc.com/pK)duct-and- applications/mgeo-biopolvmer/ echnical-reso

biopolymer/technical-resources/processing- guides/processingguides en gineeringproperties pdf . ashx ; and Material Properties of Polylactic Acid (PLA ), Agro Based Polymers,

http://www.matbase.com/materiaypolym Cellulose

Cellulose biocomposites in general are widely used in industry as low-cost engineering materials with plant fiber reinforcement. However, the chemical and microstructural inhomogeneity that results from the difficulty to mix these components was discussed by M.R. Levit, et al. in Proceedings ofANTEC '96, 1996, 1387-1390. Such mixing issues may cause low strength, low strain-to-failure, high moisture sensitivity, and odor and discoloration problems in forming the composite.

Nanopaper and polymer matrix nanocomposites based on cellulose nanofiber networks have been reported by D.R. Witzke (Introduction to Properties, Engineering and Prospects of Polylactide Polymers, Dissertation, Michigan State University, 1997) that shows enhanced strength, high work-of-fracture, low moisture adsorption, low thermal expansion, high thermal stability, high thermal conductivity and superior barrier properties.

Microground cellulosic may be obtained from cotton, hemp, switchgrass, flax, ramie, sisal, hardwood, softwood, mixed woods, paper, paper pulp, wood flour, rice hulls, coconut shell, coconut fiber, or corn stover. Most plant cellulosic materials or other cellulosic sources may be used so long as the HDT of about 85°C at 66 PSI or more is met. The present use of microground paper or paper pulp as the biosourced filler also addresses these processing concerns. The present paper can be virgin cellulosic, pulp, by-products, or recycle products. Newspaper can be used but is less desirable for some applications because of the metals use in the inks for printing and cheap fillers used in newspaper make it less cost-effective to microgrind. The size of the present microground cellulosic is from about 10 to about 250 μ, preferably from about 20 to about 50 μ with narrow size distribution.

Biosource PLA/cellulosic Composite

The present invention is a composite of PLA and microground cellulosic, used as a filler, having high HDT. The present PLA/cellulosic composite is predominantly biosourced and biodegradable as is PLA alone. It should be noted that even though PLA does not meet the specifications of ASTM D6868, it fails only by a specified arbitrary time and does biodegrade. The present PLA/cellulosic composite should, at least at some cellulosic loadings, still be classified in a manner similar to that of the base PLA. The organic part of paper when used as the cellulosic (cellulose, hemi-cellulose and lignin - all plant materials) is biodegradable.

Inorganic fillers such as china clay, calcium carbonate, latex, and others that are present in paper at low loadings, however, are not biodegradable but should not detrimentally effect the overall classification of the biocomposite. Usually paper that has been printed such as newspaper is not desired because of the metals in the ink for printing, especially when the PLA/paper composite is used for food packaging applications. The use of pulp alternatives or other cellulosic, not containing these inorganic fillers, would further negate this concern.

Properties of the Present PLA/Cellulosic Composite

There are several advantages to the processing of the present PLA/cellulosic composite. No coupling agent is required. No additives are required unless special properties are sought where they are needed. Such additives include, but are not limited to, mold releases, nucleating agents (such as sorbitals, ZnO), plasticizers, compatibalizers, mineral oil, polyglycols, silica, impact modifiers, processing aids, anti-oxidants, and flame retardants (such as phosphorus-containing, aluminum hydroxide, silicon-containing or carbon-containing materials; and expanded graphite) (e.g. Jingjing Wang, et al., Ind. Eng. Chem. Res. 2014, 53, 1422 - 1430). The entire process can be performed using standard equipment. In contrast, when natural fiber fillers are used that are typically 1 mm to 1 cm in length, the composites that result are very difficult to injection mold and do not work well for thermoforming applications.

The present PLA/cellulosic composite comprising microground pulp is 100% compostable (ASTM D6400 and possibly ASTM D 6002) and biosourced (ASTM D6866). In contrast, paper can have clays and talcs present which are not biodegradable or compostable. If 100% biodegradable or compostable PLA/cellulosic composite is desired, then using a microground cellulosic that does not have these additives is required. Such paper as the cellulosic has been previously mentioned above under the "Cellulose" heading.

The present PLA/cellulosic composite exhibits excellent high HDT when annealed; does not block even unannealed, has good dimensional stability in as much as there is no discernible change in dimensions on either x, y, or z axis of the finished part, and is cost effective compared with PLA. In contrast, PLA often deforms when annealed. If certain properties are desired, such as enhanced impact or tensile properties, then various additives may be added to the composition. Such additives include, but are not limited to impact modifiers (such as DuPont's Hytrel™ 4056), processing aids (such as mineral oils), flame retardants (such as ammonium polyphosphate), rubbery polymers such as butadiene, di- and tri-block copolymer emulsion particles, ParaloidsTM, and polyolefins.

Process to Prepare PLA/cellulosic Composite

The PLA is dried prior to use to below about 250 ppm of water present and is crystallizable; it is semicrystalline in form. The cellulosic is dried prior to use so that it has less than about 0.5% of water, preferably less than about 0.4%.

The cellulosic is dispersed in the PLA in concentration that is from about 5 to about 70%, preferably about 5 to about 50%, more preferably about 5 to about 30%, and annealed. The size and size distribution of cellulosic is important to obtaining good dispersion through the polymer and subsequent ease of processing; the microground cellulosic is about 10 to about 250 μ. While not wishing to be bound by theory, it is believed that the cellulosic serves in part as a nucleating agent in forming the composite. The annealing method used is any commercial method such as batch annealing, CFHA annealing or IR annealing.

The PLA/cellulosic composite is prepared by:

a. drying the PLA to about 250 ppm moisture prior to making the PLA/paper composite;

b. drying the cellulosic to less than 0.5% moisture before or after microgrinding but prior to making the PLA paper composite;

c. dispersing the microground cellulosic throughout the PLA;

d. forming pellets of the PLA/cellulosic composite; and

e. optionally annealing or drying the pellets; or

f. using the PLA/cellulosic composite by thermoforming, extrusion, injection molding, or sheet casting to make the desired material; and

annealing the PLA/cellulosic composite product.

The present PLA/cellulosic composite can be processed by extrusion, injection molding, thermoforming, or sheet casting from these pellets or can be used to directly make the desired product without making pellets. The cellulosic in the composite provides an aid in blocking such that the pellets do not clump together. However, these pellets should be further dried before shipping or use.

PLA composites having cellulosic filler that are fibers results in a product that is even less ductile than PLA without cellulosic filler. PLA without cellulosic filler is already not particularly ductile. Thus the present microground cellulosic material size makes this processing possible while attaining the desired HDT.

The present PLA/cellulosic composite has an HDT of greater than or equal to about 85 °C, which is the HDT value needed for hot food service products and packaging. When a mixture of DPLA and PPLA is used to make the composite, HDT of about 143°C can be achieved.

The cost of materials and process to produce the composite is comparable to that of PLA and is cost-effective for commercial use.

Utility

Many applications where PLA is used can be available for the present

PLA/cellulosic composite. Some of these applications are for making articles by thermoforming, extrusion, injection molding or sheet casting or can be used to directly make the desired product without making pellets. Such methods are well known in the art (e.g., Modern Plastics Encyclopedia, pub. McGraw-Hill, Inc., edition Oct. 1991). The various products which can be formed from the present PLA/cellulosic composite, include but are not limited to: cups, disposable flatware, food packaging, items for food service industry, loose fill packaging (such as packing peanuts), trays, boxes (replacing cardboard boxes), 3D printing feedstock, consumer electronics covers, drinking straws, sheets, packaging and other durable and non-durable goods.

The invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the invention. The letter examples are starting materials and the numbered examples are of this invention. Materials and Equipment:

PLA was obtained from Nature Works ^® , LLC, Minnetonka, MN.

An Arburg All-Rounder ^® 320M injection molding machine was used on the pellets to injection mold test coupons.

A Tinius-Olsen DTUL was used to test the HDT of the samples.

The dehumidified dryer was by Conair ^® .

The moisture analyzer used was an Arizona Instruments ^® CompuTrac Vapor Pro moisture analyzer.

Moisture content was determined using a Cenco ^® moisture balance.

The extruder used was a Werner-Pfleiderer 30 mm twin screw extruder using the 5/31/12 PP/Talc screw design (Midland Compounding and Consulting screw design).

The pelletizer was a Conair- Jetro ^® rotary knife pelletizer.

The vacuum oven was a Cole-Parmer ^® vacuum oven.

DSC analyses were done on DSC Q 2000 from TA Instruments ^® .

All compounding was done by Midland Compounding and Consulting, Midland,

MI.

General Procedure

Example A: HDT of PLA Samples

A variety of commercial PLA samples were obtained from Nature Works ^® , LLC. The pellets were then placed into hoppers on a dehumidified dryer at 55 °C and maintained in a dry atmosphere until they were injection molded. The PLA resins were injection molded into test bars.

Sixteen 6 x 0.5 x 0.125 in. HDT testing samples were produced conforming to ASTM D648. The unannealed bars were tested in a DTUL tester. The DTUL bars were placed on a wax paper lined tray and dried in a dehumidified dryer overnight (about 18-22 h.) at 55°C. The temperature was then increased to 110°C for 1 h. to anneal the bars. The bars were tested in the same DTUL tester. The HDT results of various PLA resins are reported in Table B below. Table B

HDT of Various Commercial PLA Resins

Amorphous materials were not tested when annealed

Example B : Crystallinity of PLA Samples

The crystallinity of the PLA samples was not provided with the material data sheets.

Crystallinity is a function of processing and molecular architecture and has been established as an important consideration for PLA strength, impact resistance and heat resistance. It also may influence biodegradability (see for example, L.A. Berglund and T. Peijs,

Wallenberg Wood Science Centre, Royal Institute of Technology, Stockholm, Swedish Materials Research Society Bulletin 2010, 35(3), pp. 201-207).

The lactic acid produced in nature is optically pure, L-lactic acid. However, in the Nature Works polymerization process, lactic acid is first dimerized to lactide using a tin- based catalyst and then polymerized via ring-opening polymerization using the same tin- based catalyst. Each exposure to the tin-based catalyst causes a small amount of racemization of the lactic acid. Therefore, polymers of various D-level isomer present can be produced. These isomer ratios and molecular weight of polymers influence the crystallinity and heat resistance of the polymer (and its resulting composites). It is the level of D isomer present which controls the ultimate level of crystallinity as the higher the D level, the lower the ultimate crystallinity. The level of D-isomer present was assessed by ¹³ C Nuclear Magnetic Resonance (NMR) and is reported in Table C below. The degree of crystallinity is of importance as higher ultimate crystallinity achieved after annealing has been reported to lead to higher HDT values (R.A. Auras, et al., Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications, Wiley and Sons, Danvers, MA, 2010). Table C

Composition of PLA Samples

from different shipments

Example C: Annealed Methods

It is known that when PLA is heated, it expands; when cooled, it will contract. Most plastics are poor conductors of heat and uneven or rapid heating and cooling can introduce stresses into the material. Annealing is performed to allow polymer chains to recoil, induce secondary crystallization (when applicable), and relieve internal stresses. Generally, the annealing process includes heating a plastic to a temperature just below its softening point (above the glass transition temperature, Tg, but below the melting temperature, Tm), keeping it at the high temperature for a period of time, then cooling it very slowly until it returns to room temperature (G.S.Y. Yeh, et al., "Annealing Effects of Polymers and their Underlying Molecular Mechanisms." Polymer, 1976, 17, 309-318).

There are numerous methods by which plastic parts are annealed on a commercial level (e.g., D. Kopeliovich, Annealing of Plastics

http://www. substech.com/dokuwiki/doku.php?id=annealing_of_plastics). Such methods that could be used in the present process include, but are not limited to:

• Batch annealing. This is the most common annealing method and the one used in the present examples. The process is performed in a batch oven with forced convection. The plastic parts are placed on the shelves/racks. The main disadvantages of this method are: batch type (non-continuous) process and a longer annealing operation due to the restricted air flow.

• CFHA Annealing. CFHA is a continuous annealing process in which the plastic parts are placed on the conveyor belt moving through a long tube like oven with forced hot air convection. The heating process is much faster than in a batch oven.

Additionally the continuous character of the technique is preferable for industrial implementation. • IR annealing. IR annealing also utilizes a continuous oven but the heating method uses the energy transmitted by infrared radiation. This process is the fastest heating method. However IR heating is not always uniform as shadowed portions of the part heat up slower.

Example 1 : PLA/Paper Compounding

Preliminary experiments were performed to evaluate the compounding conditions required for composites comprising 30% and 70% microground paper in PLA. Compounds comprising up to 70% paper were made but found difficult to process and mold so that 50% microground paper content in PLA were produced and tested. PLA without microground paper was also extruded to evaluate the degree of degradation resulting from the process. The materials used in the evaluation are recorded in Table 1 below.

Table 1

Compositions of PLA/paper Compounds (weight % basis)

Maintenance of minimal moisture content is critical when processing PLA. PLA drying and processing conditions were supplied by NatureWorks ^® and adhered to during these experiments. Two hoppers were filled with semi-crystalline PLA, one with Ingeo™ 4043D and one with Ingeo™ 4032D and the dryer was set at 80°C. A starting moisture test was taken for each material using a moisture analyzer to approximate the amount of drying required to reach the drying point of less than 250 ppm of moisture content. The initial moisture content for both PLA purchased materials was 400 ppm. The oven was also attached to the dehumidifying dryer to allow tray drying of the microground paper. The moisture content of the microground paper was tested before compounding on moisture balance; Sample A was 0.70%, Sample B was 0.36%, and Sample C was 0.36%, Sample D was 0.36%, and Samples E and F were 0.39%.

Preliminary dispersions achieved at 50% paper content in Ingeo™ 4043 PLA. Dispersion is dramatically enhanced as volatile content is reduced. Dispersion at 0.36% volatiles was evaluated as being very good.

The moisture regain rate of the dried paper is less than 5 mins. The paper powder with moisture content less than 0.4% disperses better. The Ingeo™ 4060 (amorphous) PLA had to be dried at 50°C to prevent it from blocking. Results indicated that it had an initial moisture content of 700 ppm and was dried for 12 hs. before processing.

All samples were compounded on a twin screw extruder. Strands were cast onto a stainless steel cooling belt (cooled by running water) and pelletized.

Example 2: PLA/Paper Stability during Compounding

The molecular weights of the compounds prepared were determined by GPC. Prime (as-received), dried and extruded samples of the PLA were assessed along with composites containing 30% paper under ambient and dried conditions. PLA assessment was performed without issue. However, composites were difficult to assess because the microground paper was difficult to filter completely thereby plugging the guard columns so only one sample was fully analyzed. Results are reported in Table 2 below. Further, the reduction in molecular weight in this one sample was used to evaluate molecular weight loss by melt flow rate in future samples. The precision on these values was reported to be approximately ±5,000. It is evident from the results that the experimental process used to incorporate paper into PLA reduces the molecular weight of PLA 4032 D by -20%. Although significant, the resulting molecular weight should be adequate to produce PLA/paper composites with useful thermal and mechanical properties. Table 2

Effect of Processing on Molecular Weight of PLA and PLA Composites

Example 3 : Microground Paper Increases PLA HDT

PLA/Paper compounding was performed as described in Example 1. The pellets were then placed into hoppers on a dehumidified dryer at 130°F and maintained in a dry atmosphere until they were injection molded. Sixteen 6 x 0.5 x 0.125 in. HDT testing samples were produced conforming to ASTM D648. The unannealed bars were tested in a DTUL tester. The DTUL bars were placed on a wax paper lined tray and dried in a dehumidified dryer overnight (about 18-22 h.) at 55°C. The temperature was then increased to 110°C for 1 h. to anneal the bars. The bars were tested in the same DTUL tester. The results are reported in Table 3 below. Table 3

HDT of Various PLA/paper Composites

Amorphous materials were not tested when annealed

Based on these results Ingeo™ 4032D was selected for further development as that PLA benefited most by the addition of paper, was described by the resin manufacturer as having utility for high temperature applications and is readily available. Paper loadings up to 30% were focused upon to ensure good dispersion throughout.

A second analysis of the 4032 PLA with 30% paper composite revealed a different HDT when repeated. There is some variation in results under identical conditions. Two HDT evaluations are presented in Table 4 below.

Table 4

Variations in HDT of 30% Paper in Ingeo™ PLA 4032 D

During heating, it was observed that unfilled PLA was "blocky" in nature; the pellets stuck together after heating. A brief evaluation was performed to understand whether the filled PLA materials would block during drying. A vacuum oven was preheated to 100°C. Approximately 25 grams of two filled samples and two unfilled samples were placed in aluminum foil pans. These pans were placed in the oven with the vacuum engaged for 1 h. and then held without vacuum for another 12 hs. Each sample was stirred to determine whether the pellets blocked together. The unfilled pellets were -95% blocked together, but the samples filled with paper showed no evidence of observable blocking. It became apparent that the incorporation of paper into PLA offers the additional benefit of acting as an anti-blocking agent for the resin. PLA pellets sold commercially are typically annealed to prevent blocking; a requirement that is negated by the inclusion of microground paper.

Example 4: Effect of Injection Molding Rate on HDT

Experiments were performed to determine if the processing conditions could be used to modify the thermal properties of PLA/paper composites and/or eliminate the need for an annealing step. The results are reported in Table 5 below.

Table 5

HDT of 30% Paper in Ingeo™ PLA 4032 D Injection Molded under

Different Conditions

Modified injection molding conditions.

There is evidently little difference between the samples produced under the different molding conditions employed during these evaluations. In addition to not changing the HDT properties, the lower stress conditions did not eliminate the need for an annealing step to achieve higher HDT values. Example 5 : Amount of Paper in PLA Required to Enhance HDT

A comparison of the effect on the HDT of PLA compounds comprising 0, 5 and 30% microground paper was performed. Composites comprising 5% paper recorded similar HDT values to the base PLA so a minimum amount of paper content appears to be required to efficiently enhance the HDT. This quantity is between 5% and 30% of paper.

During annealing, only the PLA/paper compounds with 30% microground paper eliminated blockiness. Further, during annealing, the injection molded PLA test pieces (0% paper) dimensionally distorted on all axes. Neither 5% nor 30% paper content composites observably distorted thereby demonstrating a significant improvement in dimensional stability. Table 6 below shows the comparison of HDT of the PLA/paper composites.

Table 6

HDT of Various Loadings of Microground Paper in Ingeo™ PLA 4032 D

Modified injection molding conditions.

Example 6: Annealing Step

30% Paper was compounded into PLA 4032D. The composite was injection molded into DTUL bars and placed on a wax paper lined tray and dried in the Conair dehumidified dryer overnight (18-22 hs.) at 55°C. The temperature was then increased to 110°C to anneal the bars. The samples were subjected to annealing times of 0, 5, 10, 15, 20, 25, 30, 45 and 60 mins. The bars were tested in the Tinius-Olsen Deflection Temperature Under Load Tester. The results are shown in Table 7 below. Table 7

Varying Annealing Time for HDT Effect on 30% Paper-content PLA at 110°C

The full effect on HDT of annealing is exhibited in composites submitted to as little as 5 mins. of annealing treatment time but some level of annealing is always required.

There is no evidence that the annealing step can be eliminated through compounding configuration changes, additive changes or changes in injection molding. However, the increase in HDT is seen with as little as 5 mins. of annealing.

An increase in the degree of crystallinity is observed with the addition of as little as 5% natural filler. However, 5% natural filler does not increase the HDT. At 30% natural filler, the degree of crystallinity is often no longer improved above the 5% level, but HDT increases significantly.

Example 7: Paper Size and Distribution

Earlier work by Drzal's group (M. S. Huda, et al., Mechanical and Thermo- mechanical Studies of Poly (lactic acid) PLA Talc/Recycled Newspaper Fiber Hybrid Composites, SPE's Global Plastics Environmental Conference, March 2005) resulted in minimal HDT increase with the addition of ground recycled newspaper. Consequently, it showed that the addition of scrap paper had an effect on the thermal properties of PLA. However, the observed increase in HDT was minimal and the ability to process the composite was greatly reduced, resulting in composites that offered little commercial benefit. However, in contrast this invention has found that by using microground cellulosics, HDT is greatly increased (about 80°C with annealing) without significant detriment to the ability to process the composite.

Paper of larger size and wider size distribution than standard was tested to establish which particle sizes were efficacious in enhancing the HDT of PLA. The standard paper used in this study had an average particle size of about 24 μ with 97% below 100 μ with an aspect ratio of about 10-15:1. The ground recycled paper obtained from the printing industry had an average particle size of 32 μ with 20% above 100 μ with an aspect ratio of about 2:1. The effects on HDT are shown in Table 8 below.

Table 8

HDT of Paper of Different Size and Size Distributions Dispersed in Ingeo™ PLA 4032 D

The recycled printing industry sourced paper showed the same enhancement of HDT at 66 PSI that was seen with the standard microground paper. However, there was only a negligible improvement of HDT at 264 PSI. These differences are measurable but the mechanism behind these differences has not been established. HDT enhancement is improved the most with paper of particle size range of from about 10 to about 250 μ and with no particles larger than 500 μ.

The source of the pulp and paper was also determined for any differences. The microground paper from Japan was derived from pulp from eucalyptus. The paper from the printing industry was derived from mixed cellulosics but principally hardwoods from North America. Thus cellulosics from different sources are efficacious in improving HDT. All cellulosics when microground and compounded into PLA in sufficient quantities may enhance the HDT of PLA. The source of the cellulosics may have an effect on the degree to which the PLA HDT is enhanced. Further, both virgin and recycled cellulosic sources enhance the HDT of PLA.

Example 8: HDT Natural Fillers vs. Mineral Fillers

0, 5 and 30% Paper, talc and mica were each compounded into PLA 4032D. The talc, IMI Fabi's Talc HTPultra5c, has an average particle size of 2.5 μ with nothing above 10 μ in size. The mica, IMERYS Suzorite® 200-HK phlogopite, has an average particle size of 60 μ with the majority below 100 μ. Note that these are w/w comparisons and that: the density of talc is -2.8 g cm ^"3 ; the density of mica is 2.73 g cm ^"3 ; and the density of compounded paper is -1.2 g cm ^"3 . Further, mixtures comprising (i) 5% paper with 2% mica and (ii) 30% paper with 2% mica were also compounded. These results are shown in Table 9 below.

Table 9

Effect on HDT by Natural or Mineral Fillers

Similar results were seen when using paper, mica and talc at the same

concentrations. The increases in HDT seen with paper in PLA were also observed with both mica and talc. Mixtures of paper with mica exhibited no added benefit in terms of HDT increase. The talc appears to enhance HDT at low concentrations somewhat better than paper or mica, but this would be expected given the particle size differences. Smaller sized particle additives provide for higher net surface areas at the same concentrations. Higher surface area provides more nucleation sites which should increase the crystallization rate. At 30 % loading, however, there was no significant difference in the HDT of composites comprised of any of the fillers.

Example 9: Mechanical Properties

The mechanical properties of PLA composites comprising different fillers were also assessed in addition to HDT. It was anticipated that impact and tensile properties would be reduced with the addition of cellulosics or talc fillers whereas modulus would be increased as is typical in systems comprising rigid additives. Table 10 below compares the properties of both annealed and unannealed base PLA resin with those with 30% of talc and microground paper.

Table 10

Mechanical Properties of Annealed and Unannealed Ingeo™ PLA 4032 D

and Various Composites

There were no unexpected mechanical benefits gained by using the present microground paper (or talc) in PLA. Strain at break was lower in composites comprising talc than with microground paper. However, the modulus was higher in composites containing talc compared to those containing microground paper (believed due to the relative moduli and coefficients of thermal expansion of the additive components).

There was no significant detriment in using microground paper over talc and all anticipated trends were followed; modulus increased, strain at break decreased, peak stress decreased, peak load decreased and impact strength decreased. Annealing has only a modest effect on the mechanical properties of composites comprising microground paper but had a more significant detrimental effect when talc was used. Peak load, peak stress, strain at break and impact strength were all reduced by annealing composites comprising talc. From these results, there were no apparent reasons that would preclude using microground paper to replace talc in filled PLA applications.

Example 10: Crystallinity

Correlation of the observed enhancement in HDT with PLA resin to both the thermal properties and the crystallinity of PLA and its composites were done. DSC analyses were performed to establish the isothermal crystallization behavior of the samples. The samples (6-8 mg) were encapsulated in standard aluminum DSC pans and an empty pan was used as reference. Typically, a sample was heated from about 25 to about 200°C at a rate of 10°C/min. and then held at 200°C for 5 mins. The sample was then cooled rapidly at a rate of 50°C/min. to the isothermal evaluation temperature (7ί) of 110°C and held at that temperature for 60 mins., allowing crystallization.

TA Universal Analysis software was used to plot the heat flow [W/g] against time [min] at T. The same software was used to determine the melting temperatures, T _m . The kinetic parameters of crystallization (reaction order, n and rate constant, k (1/s)) have been obtained after fitting the Avrami equation [see M. Avrami, "Kinetics of Phase Change. I. General Theory", Journal of Chemical Physics, 7 (12) 1939, pp 1103-1112; M. Avrami, "Kinetics of Phase Change. II. Transformation-Time Relations for Random Distribution of Nuclei", Journal of Chemical Physics, 8 (2) 1940, pp 212-224; M. Avrami, "Kinetics of Phase Change. III. Granulation, Phase Change, and Microstructure", Journal of Chemical Physics, 9 (2) 1941, pp 177-184]. The Avrami equation describes how solids transform from one phase (state of matter) to another at constant temperature. It can specifically describe the kinetics of crystallization and can be applied generally to other changes of phase in materials. Results from these analyses are presented in Table 11 below. Table 11

Melting Temperature, Reaction Order, and Rate Constant of Ingeo™ PLA 4032 D and

Various Composites

Crystallization not symmetrical so a different model was used to estimate the equivalent value.

** Isothermal crystallization for sample with talc was conducted at 120°C whereas the other samples where performed at 110°C.

The melting temperature for the Ingeo™ 4032D PLA and all of its composites made containing paper from different sources or talc surprisingly had identical melting temperatures (T _m ). The variations in the HDTs of the composites were not mirrored in the T _m .

The reaction order for all of the systems had an n value of approximately 3. Models derived from the Avrami equation with n=3 are consistent with systems that undergo heterogeneous crystallization and subsequent spherulitic crystal growth (see, for example, B. Wunderlich, Macromolecular Physics, Volume 2. Crystal Nucleation, Growth and Annealing, P147, Academic Press, New York, 1976). The addition of paper and talc did not change the model but did change the rate at which the crystals grew. The presence of any cellulosic increased the rate of crystallization. Further, an increased quantity of cellulosic filler led to an increased rate of crystallization. The smaller particle sized fillers offered the greatest improvement in the rate of crystallization. However, the smaller sized inorganic fillers did not appear to further improve HDT above that of the annealed composites of PLA/paper.

Percent crystallinity was assessed for the samples and the data is presented in Table 12 below. The crystallinity (χ) of PLA and composites were calculated using equation 1

ΔΗ

% wt filler

AH'

Ϊ00 *

Equation 1

wherein ΔΗ = AH _m - AH _CC

Equation 2

wherein

AH _m is the specific melting enthalpy of the sample,

AH _cc is the specific cold crystallization enthalpy of the sample),

AH° _m is the melting enthalpy of the 100% crystalline polymer matrix (93.0 J/g for PLA) and

% filler is the total weight percentage of filler.

DSC was used to evaluate the crystallization rate of the compounded materials. The samples were heated to 200°C and held for 2, 5 and 10 mins. and then rapidly quenched to 100°C to assess the crystallization rate. These results are shown in Table 12 below.

Table 12

Crystallinity of Ingeo™ PLA 4032 D and Various Composites Table 12 Cont'd

Not tested but anticipated values.

Annealing typically raised the crystallinity from about 10-15% to about 30-40%. Some unannealed samples also recorded higher degrees of crystallinity (for example, the sample containing 5% paper which, however, did not improve HDT so HDT is not just dependent upon the increase in crystallinity). The Ingeo™ 4032D pellets appear to have undergone an annealing treatment at the producer prior to shipping to prevent the pellets from blocking. The crystallization rate does not appear to be strongly influenced by the paper concentration within the range tested, just by its presence or absence (paper concentration did significantly influence the effect on HDT). The degree of crystallinity increased slightly by increasing the time at which the samples were annealed. This increase was more evident with composites comprising 30% paper than with 5% paper.

While not wishing to be bound by theory, it is believed that the microground paper is acting as a nucleating agent. Differences in the localized order of the crystalline lamellae were not established during this study.

Example 11 : PLA/paper vs. Larger Sized Filler

30% paper of different sizes was compounded into PLA 4032D. The two sizes used were 20 μ (standard EBPM) and a 250 μ (60 mesh) wood flour product supplied by American Forest Products. Somewhat surprisingly, the well dispersed, larger cellulosic particles increased the HDT of PLA to 134°C at 264 PSI which was one of the highest values obtained. These results are shown in Table 13 below.

Table 13

HDT of paper of different size and size distributions dispersed in

Ingeo™ PLA 4032 D

In contrast Example 7 shows that the paper of larger size and wider size distribution than standard showed the same enhancement of HDT at 66 PSI that was seen with the smaller microground paper. However, there was only a negligible improvement of HDT at 264 PSI.

The differences are measurable but the mechanism behind these differences has not been established. HDT enhancement is improved greatest with the smaller additives of narrow size distribution. Therefore, it is perhaps the size distribution rather than the actual size itself, within a specific size range, which is of more importance in enhancing HDT performance.

Example 12: PLA/paper vs. Natural Fillers

Various natural fillers were compounded into PLA 4032D at 30% loading. The natural fillers available were paper, rice, flax, coconut and wood flour. The natural fillers were all microground using EBPM grinding capabilities under the same processing conditions used to produce microground paper (time is the only variable that can be controlled in the EBPM grinder). The chemistries of these materials vary to a certain degree such that confirmation that the increased HDT effect is seen with all of these additives indicates that it would be seen with most natural fillers. HDT was only measured at 264 PSI in this study because of material constraints. The results are shown in Table 14 below.

Table 14

Effect on HDT of Different Natural Fillers

The relatively large 32 μ paper, but with 20% above 100 μ with an aspect ratio of approximately 2:1, did not show the enhancement in HDT that all of the narrowly distributed samples showed. Also, none of the natural fillers tested increased the HDT of PLA at the 5% loading concentration. However, all of the natural fillers tested increased the HDT of PLA at the 30% loading concentration. Flax and wood flour appeared to offer the greatest improvement in the HDT. While not wishing to be bound by theory, it is believed that the mechanism for HDT improvement requires that: (i) the filler content is above a minimum of 5%; (ii) the filler must enhance crystallinity; (iii) the filler be well dispersed in the PLA; (iv) the filler must be of a particle size range of from about 10 to about 250 μ and with no particles larger than 500 μ; and (iv) the composite must be subjected to a heat-treatment to anneal the formed part post-formation.

Although the invention has been described with reference to its preferred embodiments, those of ordinary skill in the art may, upon reading and understanding this disclosure, appreciate changes and modifications which may be made which do not depart from the scope and spirit of the invention as described above or claimed hereafter.

Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention.