Process for making thermoplastic-biofiber composite materials and articles including a poly(vinylchloride) component

A continuous process for making a dense thermoplastic-biofiber composite, the process comprising the steps of:

• (a) introducing biofiber into a processor comprising a plurality of isolated zones, each zone including means for independently controlling temperature and pressure therein, a first zone including a vent, a first and second zones respectively including first and second feed ports, and separate zones respectively including a first, a second, and a third vacuum port, said biofiber having a moisture content and further comprising cells with an interior volume, into said first zone through said first feed port, and retaining biofiber within said first zone at a temperature greater than 100° C. for sufficient time to vaporize and vent said moisture to form partially dried biofiber;
• (b) introducing thermoplastic resin including poly(vinylchloride), into said second zone through said second feed port;
• (c) heating, shearing, and compressing resin to form fluxed resin;
• (d) conveying fluxed resin to a subsequent zone to remove impurities and decomposition products through said first vacuum port forming a purified fluxed resin;
• (e) transferring said purified fluxed resin from said subsequent zone and said partially dried biofiber from said first zone into a fourth processor zone;
• (f) compressing and shearing fluxed resin and dried biofiber at first conditions of temperature, pressure, and shear rate sufficient to introduce fluxed resin into said cell interior volume to form a first compressed composite including first volatile products;
• (g) conveying first compressed composite to a fifth processor zone, and therein expanding and evaporatively cooling said first compressed composite by evacuating said first volatile products through said second vacuum port, to form a first expanded composite;
• (h) conveying first expanded composite to a sixth processor zone and therein mixing, recompressing, and re-heating said first expanded composite at second conditions of temperature, pressure, and shear rate sufficient to re-homogenize and re-compress first expanded composite to form a second compressed composite including second volatile products;
• (i) conveying second compressed composite to a seventh processor zone, and therein expanding and evaporatively cooling said second compressed composite by evacuating said second volatile products through said third vacuum port, to form a second expanded composite;
• and
• (j) conveying second expanded composite to an eighth processor zone and therein mixing and simultaneously compacting said second expanded composite to form a dense thermoplastic biofiber composite material;
• wherein the composite comprises less than about 8000 ppm moisture, the ratio of composite density to the theoretical maximum density exceeds 0.7 and polymer occupies greater than 50% of the interior volume of said biofiber cells.

A process for making a thermoplastic biofiber composite, the process comprising the steps of:

• (a) introducing a biofiber into a processor having a first and second zones including a first and second feed port, said biofiber having a moisture content and further comprising cells with an interior volume, into said first feed port into said first zone at a temperature greater than 100° C. to remove water from the biofiber;
• (b) introducing thermoplastic resin comprising poly(vinylchloride) into said second zone through second feed port;
• and
• (c) combining the resin and biofiber in a subsequent zone or zones such that the resin and biofiber are compressed and sheared to introduce the resin into the cell interior at conditions of temperature and pressure to form a composite while removing volatile materials from the composite;
• wherein the processor having two or more vacuum devolatilization stations that remove water and decomposition products from the biofiber, the processor having at least one zone that exceeds 205° C. for at least 2 seconds during the processing of the composite, the processor applying a specific mechanical energy of about 300 to 400 Kj-kg−1 to the composite wherein the ratio of composite density to theoretical maximum density exceeds 0.7 and the resin occupies greater than 50% of the interior volume of said biofiber cells.

A continuous process for making dense, thermoplastic-biofiber composite, the process comprising the steps of:

• (a) providing a first extruder comprising at least a biofiber drying zone having a biofiber feed port and vent, a blending one with resin feed port, a compression zone, a shear zone, an isolated first devolatilization zone having a first vacuum port, an isolated recompression zone, and transition box having second vacuum port;
• further providing a second extruder including compression zone and feed port communicating with said first extruder transition box;
• (b) introducing biofiber, having a moisture content and cells with an interior volume, into said biofiber drying zone maintained at a temperature of greater than 100° C. through said biofiber feed port, retaining said biofiber in said drying zone for sufficient time to vaporize and vent said moisture to form partially dried biofiber;
• (c) conveying partially dried biofiber into said blending zone and simultaneously introducing thermoplastic resin including poly(vinylchloride) through said resin feed port into said blending zone and therein mixing biofiber with resin to form a blend;
• (d) conveying biofiber-resin blend to said compression zone, and therein fluxing said resin, and mixing biofiber with fluxed thermoplastic polymer, shearing said fluxed polymer and biofiber under first conditions of temperature, pressure, and shear rate sufficient to introduce fluxed polymer into said cell interior volume to form a first compressed composite including first volatile products;
• (e) expanding an evaporatively cooling first compressed composite in said isolated devolatilization zone, while evacuating first volatile products through said first vacuum port to form a first expanded composite;
• (f) mixing, re-compressing, and re-heating first expanded composite in said isolated recompression zone under second conditions of temperature, pressure, and shear rate sufficient to re-homogenize and re-compresses said first expanded composite to form a second compressed composite including second volatile products;
• (g) expanding and evaporatively cooling second compressed composite in said transition box while evacuating second volatile products through said second vacuum port to form a second expanded composite;
• (h) introducing second expanded composite to said second extruder compression zone through said second extruder feed port, and therein mixing and simultaneously compacting said second expanded composite to form a dense thermoplastic biofiber composite material;
• wherein the ratio of composite density to the theoretical maximum density exceeds 0.7, polymer occupies greater than 50% of the interior volume of said biofiber cells, and the relative screw speed exceeds 0.35 and the relative through put exceeds 0.3.