Methods of making composites containing cellulosic pulp fibers

Details Methods of making composites containing cellulosic pulp fibers Methods of making composites containing cellulosic pulp fibers

2001-02-15

2004-05-04

Eashoo, Mark (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With severing, removing material from preform mechanically,...

To form particulate product

C264S176100, C264S328100, C428S292100

Reexamination Certificate

active

06730249

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved composite materials containing cellulosic pulp fibers dispersed in a polymeric matrix material. The invention also relates to melt-blending and extrusion methods of making these composites and methods of using the same in injection molding applications.
2. Description of the Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
In the plastics industry, fillers and reinforcement materials are typically used to improve the properties of plastics. The addition of such materials can improve properties such as conductivity, strength, modulus values, notched impact resistance, etc.
Glass fibers are the most used reinforcement material for thermosets and thermoplastics. Glass fibers impart high strength, dimensional stability, and heat resistance to a plastic composite. Although glass fibers achieve desirable reinforcing properties, glass fibers are costly, abrade processing equipment and increase the density of the plastic systems. In certain applications, these disadvantages outweigh the advantages of using glass fibers as a reinforcement additive.
Cellulosic pulp materials have been evaluated as fillers for plastics in the past. Klason, et al., “Cellulosic Fillers for Thermoplastics”,
Polymer Composites,
(1986); Klason, et al., “The Efficiency of Cellulosic Fillers in Common Thermoplastics. Part 1. Filling without processing aids or coupling agents”,
Intern. J. Polymeric Mater.,
Volume 10, pgs. 159-187 (1984); Snijder, et al., “Polyolefins and Engineering Plastics Reinforced with Annual Plant Fibers”,
The Fourth International Conference on Wood Fiber-Plastic Composites,
pg. 181-191.
Cellulosic pulp materials have relatively low densities (approximately 1500 kg/m
3
) and result in reduced wear on the processing equipment compared to glass and mineral materials [e.g., the density of wollastonite, a mineral fiber, is 2900 kg/m
3
; the density of E(electrical) glass fiber is 2500 kg/m
3
]. However, prior investigations of the use of wood cellulosic pulps or raw lignocellulosic resources (e.g., wood flour, bagasse) in polymeric materials such as thermoplastics found that a pronounced discoloration of the composite material occurred with the use of these materials at temperatures above 200° C. Furthermore, the use of such pulps were found to cause significant off-gasing and disadvantageous odors, principally due to impurities such as lignin. Moreover, previous studies have also found that at temperatures above 200° C. the cellulosic fibers themselves had poor reinforcing properties compared even to ground wood and cellulose flours [Klason, et al.,
Intern. J. Polymeric Mater.,
Volume 10, p. 175 (1984)]. These disadvantageous results directed previous research efforts to the use of cellulosic materials in polymers having melting temperatures below 200° C. such as polypropylene and polyethylene (melting temperatures below 180° C.), and away from higher melting temperature materials.
It would be desirable to provide an improved reinforcement filler for use in polymeric materials such as thermoplastics where the filler has a lower cost, lower density, increased reinforcing characteristics, reduced abrasiveness, and the ability to be processed at high temperatures (e.g., above 200° C.).
OBJECTS OF THE INVENTION
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide an improved composite containing cellulosic pulp materials and methods of making and using the same.
It is a further object of the invention to provide improved composites containing cellulosic pulp materials having reduced discoloration and lower densities.
It is a still further object of the invention to provide extrusion/injection molded products made from the improved composites and methods of making and using the same.
The foregoing and other objects and advantages of the invention will be set forth in or are apparent from the following description.
SUMMARY OF THE INVENTION
The inventors of the present application have surprisingly and unexpectedly discovered improved composite materials containing a cellulosic pulp as a reinforcing material. The cellulosic pulp fibers used according to the invention have an alpha-cellulose purity greater than 80% by weight. The use of such cellulosic pulp materials not only provides improved structural characteristics to the composite at a reduced cost and with only a modest increase in the density of the plastic system, but also do not significantly abrade the processing equipment, generate malodors, or result in unacceptable discoloration of the composite. Additionally, the use of the cellulosic pulp materials according to the invention allows for the blending of the components and shaping of the resultant composite material at lower processing temperatures. Surprisingly, the composite materials may be injection molded using processing temperatures below those used with conventional composites, even below the melting point of the polymeric matrix material itself.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One aspect of the invention relates to improved composites containing cellulosic pulp fibers dispersed in a matrix, wherein the matrix comprises a polymeric material and said cellulosic pulp fibers have an alpha-cellulose purity greater than 80% by weight. Preferably, the composite comprises greater than 1% and less than 60% by weight cellulosic pulp fibers, more preferably less than 50% by weight cellulosic pulp fibers, even more preferably, less than 40% by weight and most preferred around 30% or less by weight. Preferably, the fibers are substantially dispersed throughout the composite.
According to one embodiment, the cellulosic pulp fibers have an alpha-cellulose purity greater than 90% by weight, preferably greater than 95% by weight, more preferably greater than 96% by weight, even more preferably greater than 98%.
According to another embodiment, the cellulosic pulp fibers have a lignin content less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight.
Suitable purified cellulosic pulps include Ultranier-J, Rayfloc-J-LD, Porosanier-J-HP, Ethenier-F-UHV, Sulfatate-H-J-HD and Placetate-F, each of which are available from Rayonier, Specialty Pulp Products (Jesup, Ga. and Fernandina Beach, Fla.). All of these pulps have an alpha-cellulose purity of 95% or greater with the exception of Rayfloc-J (about 86% alpha-cellulose content). All are softwood pulps with the exception of Sulfatate-H-J which is manufactured from hardwood fibers. The Placetate and Ethenier grades are sulfite pulps whereas the others are kraft pulps. Such pulps are readily available commercially. Other suitable cellulosic pulp materials from other manufacturers include Estercell and Viscocell (International Paper—Natchez, Miss.), Supersoft (International Paper—Texarkana, Tex.), Borregaard UHV-S (Borregaard, Sarpsborg, Norway), Saiccor Acetate and Saiccor Viscose (Saiccor-Umkomass, South Africa), Weyerhaeuser MAC II (Weyerhaeuser, Cosmopolis, Wash.), Buckeye A-5 and Buckeye Cotton Linters (Buckeye Technologies—Perry, Fla. and Memphis, Tenn., respectively).
The cellulosic pulp fibers may be derived from a softwood pulp source with starting materials such as various pines (Southern pine, White pine, Caribbean pine), Western hemlock, various spruces, (e.g., Sitka Spruce), Douglas fir or mixtures of same and/or from a hardwood pulp source with starting materials such as gum, maple, oak, eucalyptus, poplar, beech, or aspen or mixtures thereof.
Commercial pulps are typically available in sheet form. In order to facilitate the blending of the fibers with the polymeric material, the fiber sheets may be broken down to individual fibers or small aggregates of fibers. According to one embodiment, the cellulosic pulp fibers are granulated so that the fibers can be re

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