SE2330258A1

SE2330258A1 - Cellulosic composite

Info

Publication number: SE2330258A1
Application number: SE2330258A
Authority: SE
Inventors: Carl Ternström; Roger Bergström; Tobias Moberg
Original assignee: Woodcomposite Sweden Ab
Priority date: 2023-06-02
Filing date: 2023-06-02
Publication date: 2024-12-03
Also published as: SE547316C2

Abstract

A cellulosic composite comprises cellulose and/or lignocellulose fibers, at least one thermoplastic elastomer and at least one thermoplastic polymer. The cellulose and/or lignocellulose fibers are a mixture of elongated cellulose and/or lignocellulose fibers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose fibers having an average elongation equal to or higher than 0.325. The cellulosic composite is an environmentally friendlier substitute for fossilbased plastics that is adapted for production of articles (30) by injection molding.

Description

TECHNICAL FIELD The present invention generally relates to cellulosic composites, composite granulates and articles, and methods of producing cellulosic composites and composite articles, and in particular to such cellulosic composites having improved impact and elongation properties.

BACKGROUND With growing awareness for the environment and humanly induced climate change, the use of plastic items and products, and in particular single use plastic items and products, has come more and more into question. However, despite this concern the use of these items and products has grown vastly with new trends in lifestyles and consumer habits of the last decade. There is therefore a need to provide cost-effective replacement to the plastic items and products. Examples of such replacements would be to use composite materials that are derived from renewable feedstock. Cellulosic composites based on chemically processed pulp have been under development a long time and recently commercialized. Chemically processed pulp is cellulosic material produced using chemical pulping processes, such as kraft or sulﬁte processes, that involve chemical treatment and high temperatures. These chemical pulping processes remove much of the hemicelluloses and lignin from the pulp, so the resulting chemical pulp contains little or no residual lignin.

From an environmental point of view, the content of cellulose in such cellulosic composites should be as high as possible to thereby lower the content of the polymer matrix in the cellulosic composite. However, a high cellulosic content in the cellulosic composite may not be suitable for all applications as the resulting composite articles produced from the cellulosic composite might not have desired mechanical properties including, for instance, impact strength and elongation at break.

WO 2022/084059 discloses a composite material comprising at least one matrix polymer and a mass fraction of at most 80 % of a mixture of cellulose short fibers having a ﬁber length of less than 500 pm and cellulose long ﬁbers having a ﬁber length of more than 1 mm. The cellulose short ﬁbers constitute at least 50 % of the mixture of cellulose short ﬁbers and cellulose long fibers.

There is therefore a need for cellulosic composites having desired mechanical properties including impact strength, elongation at break, and ﬂexural elongation.

SUMMARY lt is a general objective to provide cellulosic composites having desired mechanical properties including impact strength, elongation at break, and ﬂexurai elongation.

This and other objectives are met by the embodiments of the present invention.

The present invention is defined in the independent claims. Further embodiments of the invention are defined in the dependent claims.

An aspect of the invention re|ates to a cellulosic composite comprising cellulose and/or lignocellulose ﬁbers, at least one thermoplastic elastomer and at least one thermoplastic polymer. The cellulose and/or lignocellulose ﬁbers are a mixture of elongated cellulose and/or lignocellulose ﬁbers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose fibers having an average elongation equal to or higher than 0.325.

Other aspects of the invention relate to a composite granulate made of a cellulosic composite according to the above and a composite article obtainable by injection molding composite granulates according to theinvenüon.

Another aspect of the invention re|ates to a method of producing a composite article. The method comprises injection molding composite granulates of the invention to produce a composite article.

A further aspect of the invention re|ates to a method of producing a cellulosic composite comprising cellulose and/or lignocellulose ﬁbers, at least one thermoplastic elastomer, and at least one thermoplastic polymer, the method comprises melt processing a mixture comprising the at least one thermoplastic elastomer, the at least one thermoplastic polymer and a mixture of elongated cellulose and/or lignocellulose ﬁbers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose fibers having an average elongation higher than 0.325.

The cellulosic composite of the invention can be used as an environmentally friendlier alternative to fossil-based plastics in injection molding applications for the production of various articles. The cellulose and/or lignocellulose ﬁbers in the cellulosic composite are tailored to obtain desired mechanical properties of the cellulosic composite and articles produced therefrom while improving the processibility of the cellulosic composite during injection molding to lower injection molding pressure and reduce the risk of thermal degradation of the cellulosic composite during injection molding. The cellulosic composite have desired impact and elongation properties due to the presence of a combination of thermop|astic po|ymer(s) and thermop|astic e|astomer(s).

BRIEF DESCRIPTION OF THE DRAWINGS The embodiments, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which: Fig. 1 is a schematic illustration of a cellulose and/or Iignocellulose fiber; Fig. 2 is a schematic illustration of a compounding machine; and Fig. 3 is a schematic illustration of an injection molding machine.

DETAILED DESCRIPTION The present invention generally relates to cellulosic composites, composite granulates and articles, and methods of producing cellulosic composites and composite articles, and in particular to such cellulosic composites having improved impact and elongation properties.

There is a large demand for biocomposites, such as cellulosic composites, to at least partially replace fossil-based plastics in injection molding applications of various articles, such as caps, jars, lids, cutlery and housings. The cellulosic composites and the articles produced therefrom should have desired mechanical properties in terms of, for instance, impact and elongation properties. Cellulosic composites may have comparatively inferior elongation properties, such as elongation at break and ﬂexural elongation. This could thereby reduce the utilization of such cellulosic composite as more environmental replacements to fossil-based plastics when there is a need for higher elongation properties. The present invention is based on the discovery that the elongation properties, such as elongation at break and flexural elongation, can be improved by replacing a portion of thermop|astic polymers in the cellulosic composite with thermop|astic elastomers.

Furthermore, the cellulosic composite comprises a mixture of different forms of cellulose and/or Iignocellulose fibers. In more detail, less elongated, i.e., rounded, cellulose and/or Iignocellulose ﬁbers are included together with elongated cellulose and/or Iignocellulose fibers in the cellulosic composite. This mixture of elongated and rounded cellulose and/or Iignocellulose fibers enables achieving desired strength properties for composite articles produced from the cellulosic composite. A further advantageous effect achieved by using a mixture of different forms of cellulose and/or lignocellulose ﬁbers is that the cellulosic composite is easy to process during injection molding.

An aspect of the invention re|ates to a cellulosic composite comprising cellulose and/or lignocellulose ﬁbers, at least one thermop|astic e|astomer and at least one thermop|astic polymer. The cellulose and/or lignocellulose ﬁbers comprise a mixture of elongated cellulose and/or lignocellulose fibers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose ﬁbers having an average elongation equal to or higher than 0.325.

The cellulosic composite of the invention thereby comprises at least one thermop|astic polymer and at least one thermop|astic e|astomer. The at least one thermop|astic polymer and the at least one e|astomer typically form a thermop|astic matrix. This matrix formed by the thermop|astic polymer(s) and elastomer(s) in turn comprises cellulose and/or lignocellulose ﬁbers as an environmentally friendly replacement of part of the thermop|astic material in the cellulosic composite. As a consequence, the cellulosic composite comprises less fossil-based plastics as compared to a material solely consisting of the thermop|astic material, i.e., without any cellulose and/or lignocellulose ﬁbers.

The cellulose and/or lignocellulose fibers included in the cellulosic composite are preferably intermixed with the at least one thermop|astic polymer and the at least one thermop|astic e|astomer and thereby preferably contained within the thermop|astic matrix. ln such a case, the matrix is a mixture of thermop|astic polymers, thermop|astic elastomers and the cellulose and/or lignocellulose ﬁbers.

The cellulosic composite could comprise a single thermop|astic e|astomer or multiple, i.e., at least two, different thermop|astic elastomers. Correspondingly, the cellulosic composite could comprise a single thermop|astic polymer or multiple different thermop|astic polymers. Various embodiments of the cellulosic composite thereby comprise cellulose and/or lignocellulose ﬁbers, one thermop|astic e|astomer and one thermop|astic polymer; cellulose and/or lignocellulose ﬁbers, multiple different thermop|astic elastomers and one thermop|astic polymer; cellulose and/or lignocellulose fibers, one thermop|astic e|astomer and multiple different thermop|astic polymers; or cellulose and/or lignocellulose ﬁbers, multiple different thermop|astic elastomers and multiple different thermop|astic polymers.

According to the invention, the cellulose and/or lignocellulose ﬁbers comprises a mixture of elongated cellulose and/or lignocellulose fibers and rounded cellulose and/or lignocellulose ﬁbers. ln an embodiment, the elongated cellulose and/or Iignocellulose ﬁbers preferably constitute the main component of the cellulose and/or Iignocellulose ﬁbers and with the rounded cellulose and/or Iignocellulose ﬁbers as an additive. Hence, a mass fraction of the elongated cellulose and/or Iignocellulose fibers in the mixture is larger than a mass fraction of the rounded cellulose and/or Iignocellulose fibers in the mixture. ln a particular embodiment, the mass fraction of the elongated cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 55 up to 95 % of the mixture of cellulose and/or Iignocellulose ﬁbers. For instance, the mass fraction of the elongated cellulose and/or Iignocellulose fibers is selected within an interval of from 60 up to 90 % of the mixture, such as within an interval of from 70 up to 90 % of the mixture, or within an interval of from 75 up to 87.5 % of the mixture.

Correspondingly, in a particular embodiment, the mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 5 up to 45 % of the mixture. For instance, the mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 10 up to 40 % of the mixture, such as within an interval of from 10 up to 30 % of the mixture, or within an interval of from 12.5 up to 25 % of the mixture. ln another embodiment, the rounded cellulose and/or Iignocellulose fibers preferably constitute the main component of the cellulose and/or Iignocellulose ﬁbers and with the elongated cellulose and/or Iignocellulose ﬁbers as an additive. Hence, a mass fraction of the rounded cellulose and/or Iignocellulose fibers in the mixture is larger than a mass fraction of the elongated cellulose and/or Iignocellulose fibers in the mixture. ln a particular embodiment, the mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 55 up to 95 % of the mixture. For instance, the mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 60 up to 90 % of the mixture, such as within an interval of from 70 up to 90 % of the mixture, or within an interval of from 75 up to 87.5 % of the mixture.

Correspondingly, in a particular embodiment, the mass fraction of the elongated cellulose and/or Iignocellulose ﬁbers is selected within an interval of from 5 up to 45 % of the mixture. For instance, the mass fraction of the elongated cellulose and/or Iignocellulose ﬁbers is selected within an interval of from up to 40 % of the mixture, such as within an interval of from 10 up to 30 % of the mixture, or within an interval of from 12.5 up to 25 % of the mixture. ln a further embodiment, a mass fraction of the elongated cellulose and/or Iignocellulose ﬁbers in the mixture is substantially the same as a mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers in the mixture. Hence, in such an embodiment, the mass fraction of the elongated cellulose and/or Iignocellulose fibers is about 50 % of the mixture and the mass fraction of the rounded cellulose and/or Iignocellulose ﬁbers is about 50 % of the mixture.

The elongated cellulose and/or Iignocellulose ﬁbers provide desired mechanical properties in terms of, for instance, tensile and flexural properties, such as tensile strength and modu|us and ﬂexural strength and elongation, to the ce||u|osic composite. However, these elongated cellulose and/or Iignocellulose ﬁbers require high injection mo|ding pressures and generate heat when producing articles from the ce||u|osic composite by injection mo|ding due to the comparatively high viscosity of the ce||u|osic composite comprising such elongated cellulose and/or Iignocellulose ﬁbers. As a consequence, less elongated, i.e., rounded, cellulose and/or Iignocellulose fibers are included to the elongated cellulose and/or Iignocellulose fibers in the ce||u|osic composite to improve the processability of the ce||u|osic composite during injection mo|ding, such as represented by an increase in melt flow volume rate (MVR).

Accordingly, the respective mass fraction of elongated and rounded cellulose and/or Iignocellulose ﬁbers in the ce||u|osic composite can be selected to tailor mechanical and production properties of the ce||u|osic composite and composite articles produced based on the ce||u|osic composite.

Elongation of cellulose and/or Iignocellulose ﬁbers is preferably as defined in International Standard ISO 9276-6: 2008, Representation of results of particle size analysis, Part 6: Descriptive and quantitative representation of particle shape and morphology.

Hence, in an embodiment, elongation E of a cellulose and/or Iignocellulose ﬁber is defined as: E=X|5/X|_G [1] ln equation [1], XE represents average thickness of a cellulose and/or Iignocellulose fiber and xLe represents geodesic length of the cellulose and/or Iignocellulose ﬁber. Fig. 1 illustrates a cellulose and/or lignocellulose ﬁber 10 and indicates the geodesic length XLG of the cellulose and/or lignocellulose fiber 10 and the average thickness XE of the cellulose and/or lignocellulose fiber 10.

These parameters xie, xE can be determined according to techniques well known in the art, for instance, as described in lnternational standard ISO 13322-2:2021 Particle size analysis - lmage analysis methods, Part 2: Dynamic image analysis methods; Pons et al., Particle morphology: from visualization to measurement, Powder Technology (1999) 103: 44-57; Schmid et al., Characterizing Flock Fibres using Quantitative lmage Analysis, Flock (2004) 30: 6-12.

With this deﬁnition of elongation, an elongated cellulose and/or lignocellulose ﬁber has a lower elongation as compared to a rounded cellulose and/or lignocellulose fiber. This means that the elongated cellulose and/or lignocellulose ﬁbers have a lower average elongation as compared to the rounded cellulose and/or lignocellulose ﬁbers. There is, though, generally a distribution of elongations around the average elongation for the cellulose and/or lignocellulose ﬁbers. As a consequence, individual elongated or rounded cellulose and/or lignocellulose fibers may have an elongation different from the average elongation of the elongated or rounded cellulose and/or lignocellulose ﬁbers. However, the average elongation for the elongated cellulose and/or lignocellulose ﬁbers in the cellulosic composite is equal to or lower than 0.300 and the average elongation for the rounded cellulose and/or lignocellulose fibers is equal to or higher than 0.325.

"Elongated" and "rounded" as used herein for the two different forms or fractions of cellulose and/or lignocellulose ﬁbers in the cellulosic composite are used to indicate that the two forms or fractions of cellulose and/or lignocellulose fibers have different elongations as defined in equation [1]. This means that the elongated cellulose and/or lignocellulose ﬁbers have a lower average value of the quotient in equation [1] as compared to the rounded cellulose and/or lignocellulose fibers. The elongated cellulose and/or lignocellulose ﬁbers are also referred to herein as ﬁrst form or fraction of cellulose and/or lignocellulose fibers having an average elongation equal to or lower than 0.300 and the rounded cellulose and/or lignocellulose fibers are referred to as second form or fraction of cellulose and/or lignocellulose fibers having an average elongation equal to or higher than 0.325. ln a preferred embodiment, when determining the average elongation of cellulose and/or lignocellulose ﬁbers, the elongation is determined only for cellulose and/or lignocellulose ﬁbers having a geodesic length above a minimum length, preferably 50 pm. ln such an approach, very small cellulose and/or lignocellulose particles, sometimes referred to as fines, dust, etc. are excluded from the elongation determination of the cellulose and/or lignocellulose ﬁbers. ln an embodiment, average elongation as used herein for the cellulose and/or lignocellulose ﬁbers could be defined as: 1 3 2 E1- [21 OFQS [31 OFQS [41 ln equation [2], [3] and [4], the parameter N represents the number of cellulose and/or lignocellulose ﬁbers, E,- represents the elongation of a cellulose and/or lignocellulose ﬁber no. i, whereas A,- and V1 represent the area and the volume of the cellulose and/or lignocellulose ﬁber no. i, respectively. Equation [2] represents the number average of the elongation, equation [3] represents the area- weighted average elongation, and equation [4] represents the volume-weighted average elongation. ln a preferred embodiment, the average value of the elongation for the cellulose and/or lignocellulose ﬁbers is an area-based average value as defined in equation [3].

The cellulose and/or lignocellulose fibers in the cellulosic composite are typically not uniform but often display a distribution of characteristics and parameters, including elongation. This distribution in, for instance, elongation around the average elongation can be ﬁtted with various mathematical distributions, such as Gaussian distribution, Cauchy distribution, etc. When mixing elongated cellulose and/or lignocellulose ﬁbers and rounded cellulose and/or lignocellulose ﬁbers, the distributions in elongation might be at least partly overlapping for the tvvo forms of cellulose and/or lignocellulose ﬁbers. However, the different forms of cellulose and/or lignocellulose fibers included in the cellulosic composite can still be distinguished by finding the different distributions, which for Gaussian distributions, have peak positions corresponding to the respective average eiongations. ln an embodiment, the cellulosic composite comprises cellulose and/or Iignocellulose ﬁbers, at least one thermoplastic elastomer and at least one thermoplastic polymer. ln this embodiment, the cellulose and/or Iignocellulose fibers consists of a mixture of elongated cellulose and/or Iignocellulose ﬁbers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or Iignocellulose ﬁbers having an average elongation equal to or higher than 0.325. ln an embodiment, the elongated cellulose and/or Iignocellulose ﬁbers have an average elongation equal to or lower than 0.290. ln a preferred embodiment, the elongated cellulose and/or Iignocellulose ﬁbers have an average elongation equal to or lower than 0.280, such as equal to or lower than 0.275, or even lower, such as equal to or lower than 0.260. ln a particular embodiment, the elongated cellulose and/or Iignocellulose ﬁbers have an average elongation equal to or higher than 0.010, preferably equal to or higher than 0.025, and more preferably equal to or higher than 0.050. Hence, in a particular embodiment, the elongated cellulose and/or Iignocellulose fibers have an average elongation selected within an interval of from 0.010 up to 0.300, preferably selected within an interval of from 0.025 up to 0.290, and more preferably selected within an interval of from 0.050 up to 0.280. ln an embodiment, the rounded cellulose and/or Iignocellulose fibers have an average elongation equal to or higher than 0.350. ln a preferred embodiment, the rounded cellulose and/or Iignocellulose ﬁbers have an average elongation equal to or higher than 0.375, such as equal to or higher than 0.400. ln a particular embodiment, the rounded cellulose and/or Iignocellulose fibers have an average elongation equal to or below 0.800, preferably equal to or below 0.750, and more preferably equal to or below 0.700. Hence, in a particular embodiment, the rounded cellulose and/or Iignocellulose fibers have an average elongation selected within an interval of from 0.325 up to 0.980, preferably selected within an interval of from 0.350 up to 0.750, and more preferably selected within an interval of from 0.375 up to 0.700. ln the above-described embodiment, elongation of the elongated and rounded cellulose and/or Iignocellulose fibers have been presented as average elongation. Alternatively, the elongation of the cellulose and/or lignocellulose fibers could be presented as median elongation. As an example, the elongated cellulose and/or lignocellulose fibers used in the Example section had an average elongation of 0.260 and a median elongation of 0.152. Correspondingly, the rounded cellulose and/or lignocellulose ﬁbers used in the Example section had an average elongation of 0.410 and a median elongation of 0.361. ln an embodiment, the cellulosic composite comprises from 5 up to 80 wt% of the cellulose and/or lignocellulose ﬁbers. Wt% as used herein is an abbreviation for weight percent, i.e., percentage of total weight.

Reference to a range or interva| of values herein, such as from X up to Y, includes the full range of values from X to Y including the end values of the range, i.e., X and Y. ln an embodiment, the cellulosic composite comprises from 10 up to 80 wt% of the cellulose and/or lignocellulose ﬁbers. ln a preferred embodiment, the cellulosic composite comprises from 10 up to 70 wt% cellulose and/or lignocellulose ﬁbers, preferably from 20 up to 60 wt% cellulose and/or lignocellulose fibers, and more preferably from 30 up to 50 wt% cellulose and/or lignocellulose ﬁbers.

Generally, the higher the content of the cellulose and/or lignocellulose ﬁbers in the cellulosic composite the less the content of fossil-based plastics, i.e., the thermoplastic material, and thereby the cellulosic composite becomes more environmentally friendly. However, if the cellulosic composite comprises a too high content of the cellulose and/or lignocellulose fibers, i.e., above 80 wt%, then the cellulosic composite may have a tendency to decompose or fall apart. Furthermore, it is generally hard to successfully produce cellulosic articles by injection molding from a cellulosic composite comprising more than 80 wt% cellulose and/or lignocellulose ﬁber. Hence, in a preferred embodiment, the cellulose and/or lignocellulose fibers constitute from 5 up to 80 wt% of the weight percentage of the cellulosic composite.

The cellulose and/or lignocellulose ﬁbers could be in the form of cellulose ﬁbers, lignocellulose ﬁbers or a mixture of cellulose fibers and lignocellulose ﬁbers. Lignocellulose as used herein represent a mixture of cellulose, hemicellulose and lignin. ln an embodiment, the cellulose and/or lignocellulose ﬁbers are milled cellulose and/or lignocellulose ﬁbers, such as milled wood fibers or milled pulp ﬁbers. 11 ln an embodiment, the cellulose and/or lignocellulose fibers are selected from the group consisting of chemical pulp fibers, thermomechanical pulp fibers and mechanical pulp fibers. ln a preferred embodiment, the cellulose and/or lignocellulose fibers are chemical pulp fibers. ln a particular embodiment, the cellulose and/or lignocellulose ﬁbers are selected from the group consisting of sulfate pulp ﬁbers, sulﬁte pulp ﬁbers, dissolving pulp fibers, thermomechanical pulp (TMP) ﬁbers, high temperature thermomechanical pulp (HTMP) fibers, mechanical ﬁbers intended for medium density fiberboard (MDF-ﬁbers), chemi-thermomechanical pulp (CTMP) ﬁbers, high temperature chemi- thermomechanical pulp (HTCTMP) fibers, and a combination thereof.

The cellulose and/or lignocellulose ﬁbers may be bleached or unbleached.

The cellulose and/or lignocellulose ﬁbers can also be produced by other pulping methods and/or from other cellulosic or lignocellulosic raw materials, such as ﬂax, jute, hemp, kenaf, bagasse, cotton, bamboo, straw, or rice husk. lt is also possible to use cellulose and/or lignocellulose fibers that are a mixture of ﬁbers from different raw materials, such as a mixture of wood and any of the materials mentioned above. Also synthetic cellulose and/or lignocellulose fibers could be used. ln an embodiment, the cellulose and/or lignocellulose fibers have an average geodesic length below 1 mm, preferably equal to or below 750 pm. ln a particular embodiment, the cellulose and/or lignocellulose ﬁbers have an average geodesic length above 50 pm but below 1 mm, such as above 50 pm but equal to or below 750 pm. ln this embodiment, both the elongated cellulose and/or lignocellulose ﬁbers and the rounded cellulose and/or lignocellulose fibers have an average geodesic length below 1 mm, preferably equal to or below 750 pm, such as above 50 pm but below 1 mm, preferably above 50 pm but below 750 pm.

Cellulosic composites comprising cellulose and/or lignocellulose ﬁbers having an average geodesic length above 1 mm are generally harder to process and produce as the long cellulose and/or lignocellulose fibers may become entangled causing an increase in viscosity during injection molding. ln an embodiment, the at least one thermoplastic polymer is selected from the group consisting of polyethylene (PE), polypropylene (PP), polyoleﬁn copolymers, polystyrene (PS), polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinylchloride (PVC), ﬂuoropolymers, 12 polyamides (PA), polyether imides, polyphenylene sulfides, polysulfones, polylactic acid (PLA), polyacetals, polycarbonates, polyphenylene oxides, polyurethanes, polyacrylates, polyhydroxyalkanoates (PHA), polybutyrate adipate terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactones (PCL), polyglycolic acid (PGA), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), po|y(methy| methacrylate) (PMMA), polyoxymethylene (POM), po|y(p-pheny|ene oxide) (PPO), a copolymer thereof and a mixture thereof. ln a preferred embodiment, the at least one thermoplastic polymer is selected from the group consisting of PE, PP, a copolymer thereof and a mixture thereof. ln a currently preferred embodiment, the at least one thermoplastic polymer is PP or a copolymer thereof.

As mentioned in the foregoing, the cellulosic composite could comprise a single thermoplastic polymer, preferably selected among the above-presented thermoplastic polymers. ln another embodiment, the cellulosic composite comprises a mixture or copolymer of multiple thermoplastic polymers, preferably selected among the above-presented thermoplastic polymers. ln an embodiment, the cellulosic composite comprises at least 20 weight-% and up to 50 weight-% of the at least one thermoplastic polymer. ln a preferred embodiment, the cellulosic composite comprises at least 25 weight-% and up to 45 weight-% of the at least one thermoplastic polymer, preferably at least 30 weight-% and up to 40 weight-% of the at least one thermoplastic polymer, and more preferably at least 30 weight-% and up to 35 weight-% of the at least one thermoplastic polymer. ln an embodiment, the at least one thermoplastic elastomer is selected from the group consisting of styrenic block copolymers (TPS), thermoplastic polyolefin elastomers (TPO), thermoplastic vulcanizates (TPV), thermoplastic polyurethanes (TPU), thermoplastic copolyester (TPC) and thermoplastic polyamides (TPA). ln a preferred embodiment, the at least one thermoplastic elastomer is a thermoplastic polyolefin elastomer. Particular examples of thermoplastic elastomers that could be used in the cellulosic composite include an ethylene-1-octene polyoleﬁn elastomer and an oleﬁnic elastomer primarily composed of isotactic propylene repeat units with random ethylene distribution.

As mentioned in the foregoing, the cellulosic composite could comprise a single thermoplastic elastomer, preferably selected among the above-presented thermoplastic elastomers. ln another 13 embodiment, the cellulosic composite comprises a mixture of multiple thermoplastic elastomers, preferably selected among the above-presented thermoplastic elastomers. ln an embodiment, the cellulosic composite comprises at least 5 weight-% and up to 35 weight-% of the at least one thermoplastic elastomer. ln a preferred embodiment, the cellulosic composite comprises at least 10 weight-% and up to 30 weight-% of the at least one thermoplastic elastomer, preferably at least 15 weight-% and up to 25 weight-% of the at least one thermoplastic elastomer, and more preferably at least 17 weight-% and up to 23 weight-% of the at least one thermoplastic elastomer.

Thermoplastic elastomers (TPE) are a class of copolymers or a physical mixture that comprises materials with both thermoplastic and elastomeric properties. While most elastomers are thermosets, thermoplastics are in contrast relatively easy to use in manufacturing, for example, by injection molding. The principal difference betvveen thermoset elastomers and thermoplastic elastomers is the type of cross-linking bond in their structures. Thermoplastic elastomers show advantages typical of both rubbery materials and plastic materials. ln an embodiment, the at least one thermoplastic elastomer has a lower Vicat softening temperature than the at least one thermoplastic polymer. Vicat softening temperature (VST) or Vicat hardness is the determination of the softening point for materials that have no definite melting point. lt is taken as the temperature at which a specimen is penetrated to a depth of 1 mm by a ﬂat-ended needle with a 1 mm2 circular or square cross-section. For the Vicat A test, a load of 10 N is used, and for the Vicat B test, the load is 50 N. VST is determined as defined in ISO 306:2022 Plastics - Thermoplastic materials - Determination of Vicat softening temperature (VST).

The cellulosic composite comprises the cellulose and/or lignocellulose ﬁbers, the at least one thermoplastic elastomer and the at least one thermoplastic polymer. ln an embodiment, the cellulosic composite may also comprise at least one coupling agent. Such coupling agents can be used to promote chemically bonding between the thermoplastic polymers, the thermoplastic elastomers and the cellulose and/or lignocellulose fibers. ln an embodiment, the at least one coupling agent is selected from the group consisting of maleic anhydride, including maleic anhydride grafted polymers, a silane, a siloxane, and a mixture thereof. ln a preferred embodiment, the at least one coupling agent is maleic anhydride, including maleic anhydride 14 grafted polymers. For instance, if the cellulosic composite comprises PP as thermoplastic polymer then the coupling agent could be a maleic anhydride modiﬁed copo-polypropylene.

The cellulosic composite could comprise a single coupling agent or a mixture of tvvo or more coupling agents. ln an embodiment, the cellulosic composite comprises at least 0.5 weight-% and up to 5 weight-% of the at least one coupling agent. ln a preferred embodiment, the cellulosic composite comprises at least 1 weight-% and up to 5 weight-% of the at least one coupling agent, and preferably at least 1.5 weight- % and up to 3 weight-% of the at least one coupling agent.

The cellulosic composite may optionally comprise one or more additives, such as selected from the group consisting of a lubricant, a colorant, a pigment, a filler, an acid scavenger, an antioxidant, a light stabilizer, a blowing agent, a UV-stabilizer, a flame retardant, a heat stabilizer, an antistatic agent, and a foaming additive. The at least one additive could thereby be selected among additives traditionally used in cellulosic composites or in thermoplastic materials, for instance, to achieve a visual effect or a desired property to the cellulosic composite.

The cellulosic composite of the invention could be used as a composite masterbatch, from which various composite articles could be produced. ln such a case, the cellulosic composite could be in the form of composite granulates made of the cellulosic composite of the invention. Such composite granulates could then be used as a starting material in the production of the composite articles, such as by injection molding.

Fig. 2 schematically illustrates an example of a compounding machine 200 that can be used to produce composite granulates 20, also referred to as composite pellets herein, based on the cellulosic composite. Generally, the compounding machine 200 comprise a barrel 210, in which an injection ram or rotating screw 220 is arranged. The interior of the barrel 210 is in connection with a hopper 230, into which a feeding system 290, 291, 292 feeds the thermoplastic polymer(s), the elongated cellulose and/or lignocellulose ﬁbers and the rounded cellulose and/or lignocellulose ﬁbers. ln the ﬁgure, the feeding system 290, 291, 292 has been represented by a feed unit 290 for the thermoplastic polymer(s), a feed unit 291 for the thermoplastic elastomer(s) and a feed 292 for the cellulose and/or lignocellulose fibers. ln alternative embodiments, a single feed unit could feed a mixture of the thermoplastic polymer(s), the thermoplastic elastomer(s) and the cellulose and/or lignocellulose fibers or a feed unit feeds the thermoplastic po|ymer(s) and the thermoplastic e|astomer(s) and another feed unit feeds the cellulose and/or lignocellulose fibers into the hopper 230. lt is also possible to have separate feeds for the elongated cellulose and/or Iignocellulose fibers and the rounded cellulose and/or lignocellulose fibers.

At least a portion of the barrel 210 downstream of the hopper 230 may be heated to at least partly melt the thermoplastic po|ymer(s) and e|astomer(s). ln such a case, one or multiple heating elements 240 may be arranged, preferably circumferentially arranged, in connection with at least a portion of the barrel 210. The barrel 210 also comprises a nozzle 250 through which the compounded polymer and ﬁber material is pushed by the injection ram or rotating screw 220. The extrudate from the nozzle 250 is then cut into segments to form the composite granulates or pellets 20.

Fig. 3 schematically illustrates an injection molding machine 100 that could be used to produce a cellulosic article 30 based on the composite granules 20 according to the invention. Generally, the injection molding machine 100 comprises a barrel 110, in which an injection ram or rotating screw 120 is arranged. The interior of the barrel 110 is in connection with a hopper 130, into which the composite granules 20 are added. At least a portion of the barrel 110 downstream of the hopper 130 may be heated to at least partly melt the thermoplastic polymer matrix of the cellulosic composite. ln such a case, one or multiple heating elements 140 may be arranged, preferably circumferentially arranged, in connection with at least a portion of the barrel 110. The barrel 110 also comprises a nozzle 150 through which the injection molded cellulosic composite is pushed by the injection ram or rotating screw 120. The nozzle 150 is connected with a mold cavity 160 defined by matching molds 170, 180. The injection molded cellulosic composite is pushed through the nozzle 150 and into the mold cavity 160. At least one of the matching molds 170, 180 is movable to provide access to the mold cavity 160 and the cellulosic article 30 formed therein. ln operation, the composite granules 20 are poured into the hopper 130. After that composite granules 20 go down under the action of gravity into the barrel 110. The circumferential heater 140, which is located on the barrel 110, is used to melt the cellulosic composite. The injection ram or rotating screw 120 pushes the cellulosic composite fon/vard into the mold 170, 180 by applying some pressure. Molten cellulosic composite material is injected into the mold cavity 160 deﬁned by the molds 170, 180. After the whole injection molding process is done the manufactured composite article 30 is cooled sufficiently and then mold 180 is opened to allow removal of the composite article 30. 16 The present invention also relates to a composite article 30 obtainable by injection molding composite granulates 20 according to the invention. The composite article 30 could be any article that can be manufactured by injection molding using cellulosic composites. lllustrative, but non-limiting, examples of such articles include caps, jars, lids, cutlery and housings.

The present invention also relates to a method of producing a composite article 30. The method comprises injection molding composite granulates 20 according to the invention to produce the composite article 30.

The settings of the injection molding machine used to produce the composite article 30 can be selected based on the particular types of thermoplastic polymer and thermoplastic elastomer, the types and content of the cellulose and/or lignocellulose fibers in the cellulosic composite, etc. As an illustrative, but non-limiting, example the injection pressure is typically selected within an interval of from 10 up to 300 MPa, preferably from 30 up to 200 MPa, and more preferably from 40 up to 150 MPa, and the molding temperature is typically selected to be below the degradation temperature of the cellulose and/or lignocellulose ﬁbers, i.e., typically below 240°C, preferably below 210°, and more preferably below 190°C.

An aspect of the invention relates to a method of producing a cellulosic composite comprising cellulose and/or lignocellulose fibers, at least one thermoplastic elastomer and at least one thermoplastic polymer. The method comprises melt processing a mixture comprising the at least one thermoplastic elastomer, the at least one thermoplastic polymer and a mixture of elongated cellulose and/or lignocellulose fibers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose ﬁbers having an average elongation equal to or higher than 0.325. ln an embodiment, the at least one thermoplastic elastomer, the at least one thermoplastic polymer and the cellulose and/or lignocellulose ﬁbers could be mixed together and then exposed to heat to melt the at least one thermoplastic elastomer and the at least one thermoplastic polymer and form the cellulosic composite. ln this embodiment, the mixture of the at least one thermoplastic elastomer, the at least one thermoplastic polymer and the cellulose and/or lignocellulose ﬁbers is heated to a temperature above the melting point of the thermoplastic polymer and of the thermoplastic elastomer or above the highest melting point if more than one type of thermoplastic polymer and/or more than one type of thermoplastic elastomer is used. 17 ln another embodiment, the at least one thermoplastic polymer and the at least one thermoplastic elastomer are melted and the cellulose and/or Iignocellulose ﬁbers are added to the melted at least one thermoplastic polymer and the at least one thermoplastic elastomer. ln this embodiment, the at least one thermoplastic polymer and the at least one thermoplastic elastomer are heated to a temperature above the melting point of the thermoplastic polymer and of the thermoplastic elastomer or above the highest melting point if more than one type of thermoplastic polymer and/or more than one type of thermoplastic elastomer is used. The mixture of elongated and rounded cellulose and/or Iignocellulose ﬁbers is then added to the melted thermoplastic polymer(s) and elastomer(s) and then the mixture is allowed to cool to form the cellulosic composite. ln the above-described embodiments, the cellulose and/or Iignocellulose fibers preferably become distributed within a thermoplastic matrix formed by the at least one thermoplastic polymer and the at least one thermoplastic elastomer.

EXAMPLES Various cellulosic composites were made using polypropylene and different combinations of cellulose and/or Iignocellulose ﬁbers with or without TPO as shown in Table 1.

Table 1 - Composition of cellulosic composites Cellulosic _ _ Coupling _ Fiber 1 (wt%) Fiber 2 (wt%) PP (wt%) TPO (wt%) composite agent (wt%) Reference _ 40 0 58 0 2 composite 1 Reference _ 0 40 58 0 2 composite 2 Reference 20 20 58 0 2 composite 3 Composite 20 20 38 20 2 Fiber 1 - milled, bleached Kraft pulp ﬁbers with an average elongation of 0.259 and an average geodesic length below 1 mm Fiber 2 - milled spruce wood fibers with an average elongation of 0.410 and an average geodesic length below 1 mm 18 PP - polypropylene TPO - thermoplastic polyolefin elastomer Coupling agent- maleic anhydride modified copo-polypropylene The ﬁbers were analyzed using dynamic image analysis in accordance with lnternational standard ISO 13322-2:2021 Particle size analysis - lmage analysis methods, Part 2: Dynamic image analysis methods. The ﬁbers were tested in the dry state and in the form as they were fed to the compounder. Clean compressed air was used as dispersing medium. The measurements of the ﬁbers included the area A, the long linear dimension x_Fmax and the short linear dimension x_Fmin and were recorded for all imaged ﬁbers. From this data set, the geodesic length (XLG) and thickness (XE) were determined and the elongation was calculated in accordance with the standard ISO 9276-6: 2008, Representation of results of particle size analysis, Part 6: Descriptive and quantitative representation of particle shape and morphology.

The materials were compounded using a co-rotating tvvin screw extruder with a diameter of 50 mm and a L/D ratio of 36:1. Polypropylene polymer, TPE, if included, and the coupling agent were added in the main inlet and the ﬁbers were dosed through a side feeder into the melted polymer. The temperature in the melt zones was 190°C and in the compounding zones the temperatures were kept at 170°C, the rotational speed of the compounder was kept at 150 revolutions per minute (rpm). The material from the compounder was pelletized using an unden/vater pelletizer.

The ratio between polymer : ﬁber : coupling agent was selected to 58:40:2 as this led to a cellulosic composite with good mechanical properties, see Table 2.

The melt flow volume rate (MVR), which can be taken as a measurement of the processability of the cellulosic composite, was determined according to lnternational standard ISO 1133-1:2022 Plastics - Determination of the melt mass-flow rate (MFR) and melt volume-ﬂow rate (MVR) of thermoplastics, Part 1: Standard method with a temperature of 220°C and a load of 5 kg. 19 Table 2 - Mechanical properties cellulosic composite Composite 6.9 _ _ _ Flexural lmpact notched MVR Cellulosic composite Elongation at break _ _ elongation (%) (kJ/m2) (cm3/10 min) Reference composite 1 3.9 5.6 2.1 7.96 Reference composite 2 1.9 2.8 3.5 - Reference composite 3 3.1 17.1 3.3 12.51 25.2 6.2 11.85 As is shown in Table 2, mixing elongated and rounded cellulose and/or Iignocellulose ﬁbers (Reference composite 3) generally led to mechanical properties, in betvveen those of a cellulosic composite comprising only elongated cellulose and/or Iignocellulose ﬁbers (Reference composite 1) and a cellulosic composite comprising only rounded cellulose and/or Iignocellulose ﬁbers (Reference composite 2). However, including a thermoplastic elastomer in the cellulosic composite comprising a mixture of elongated and rounded cellulose and/or Iignocellulose fibers signiﬁcantly improved mechanical properties in terms of elongation at break, ﬂexural elongation and impact notched as seen by comparing Composite with Reference composite 3 in Table 2. Hence, replacing a portion of the polypropylene thermoplastic polymer with a thermoplastic elastomer signiﬁcantly improved these mechanical properties resulting in the higher values of all tested cellulosic composites.

Replacement of a portion of the polypropylene thermoplastic polymer with a thermoplastic elastomer did not signiﬁcantly affect the processability of the cellulosic composite as can be seen by comparing MVR values for Composite with Reference composite 3.

The embodiments described above are to be understood as a few illustrative examples of the present invention. lt will be understood by those skilled in the art that various modiﬁcations, combinations and changes may be made to the embodiments without departing from the scope of the present invention. ln particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible.

Claims

1. A cellulosic composite comprising: cellulose and/or lignocellulose fibers; at least one thermoplastic elastomer; and at least one thermoplastic polymer, wherein the cellulose and/or lignocellulose fibers are a mixture of elongated cellulose and/or lignocellulose fibers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or lignocellulose ﬁbers having an average elongation equal to or higher than 0.

2. The cellulosic composite of claim 1, wherein elongation of a cellulose and/or lignocellulose fiber is defined as XE / xrc, wherein XE represents average thickness of a cellulose and/or lignocellulose fiber and XLG represent geodesic length of the cellulose and/or lignocellulose fiber.

3. The cellulosic composite of claim 1 or 2, wherein the elongated cellulose and/or lignocellulose ﬁbers have an average elongation equal to or lower than 0.

4. The cellulosic composite of any one of claims 1 to 3, wherein the rounded cellulose and/or lignocellulose fibers have an average elongation equal to or higher than 0.350, preferably equal to or higher than 0.

5. The cellulosic composite of any one of claims 1 to 4, wherein the cellulosic composite comprises from 5 up to 80 weight-% of the cellulose and/or lignocellulose fibers, preferably from 10 up to 80 weight-% of the cellulose and/or lignocellulose ﬁbers, more preferably from 10 up to 70 weight-% of the cellulose and/or lignocellulose ﬁbers, even more preferably from 20 up to 60 weight-% of the cellulose and/or lignocellulose ﬁbers, and most preferably from 30 up to 50 weight-% of the cellulose and/or lignocellulose fibers.

6. The cellulosic composite of any one of claims 1 to 5, wherein the cellulose and/or lignocellulose ﬁbers are milled cellulose and/or lignocellulose ﬁbers.

7. The cellulosic composite of any one of claims 1 to 6, wherein the cellulose and/or lignocellulose ﬁbers are selected from the group consisting of chemical pulp ﬁbers, thermomechanical pulp ﬁbers and mechanical pulp ﬁbers, preferably chemical pulp ﬁbers.

8. The cellulosic composite of claim 7, wherein the cellulose and/or Iignocellulose ﬁbers are selected from the group consisting of sulfate pulp ﬁbers, sulfite pulp ﬁbers, dissolving pulp ﬁbers, thermomechanical pulp (TMP) ﬁbers, high temperature thermomechanical pulp (HTMP) ﬁbers, mechanical ﬁbers intended for medium density ﬁberboard (MDF-ﬁbers), chemi-thermomechanical pulp (CTMP) fibers, high temperature chemi-thermomechanical pulp (HTCTMP) fibers, and a combination thereof.

9. The cellulosic composite of any one of claims 1 to 8, wherein an average geodesic length of the cellulose and/or Iignocellulose fibers is below 1 mm, preferably equal to or below 750 pm.

10. The cellulosic composite of any one of claims 1 to 9, wherein the at least one thermoplastic elastomer has a lower Vicat softening temperature than the at least one thermoplastic polymer.

11. The cellulosic composite of any one of claims 1 to 10, wherein the at least one thermoplastic elastomer is selected from the group consisting of styrenic block copolymers (TPS), thermoplastic polyolefin elastomers (TPO), thermoplastic vulcanizates (TPV), thermoplastic polyurethanes (TPU), thermoplastic copolyester (TPC) and thermoplastic polyamides (TPA), preferably TPO.

12. The cellulosic composite of any one of claims 1 to 11, wherein the cellulosic composite comprises at least 5 weight-% and up to 35 weight-% of the at least one thermoplastic elastomer, preferably at least 10 weight-% and up to 30 weight-% of the at least one thermoplastic elastomer, and more preferably at least 15 weight-% and up to 25 weight-% of the at least one thermoplastic elastomer.

13. The cellulosic composite of any one of claims 1 to 12, wherein the at least one thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene, polyolefin copolymers, polystyrene, polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinylchloride, ﬂuoropolymers, polyamides, polyether imides, polyphenylene sulﬁdes, polysulfones, polylactic acid, polyacetals, polycarbonates, polyphenylene oxides, polyurethanes, polyacrylates, polyhydroxyalkanoates, polybutyrate adipate terephthalate, polybutylene succinate , polycaprolactones, polyglycolic acid, polyethylene terephthalate, acrylonitrile butadiene styrene, polycarbonate, poly(methyl methacrylate), polyoxymethylene, poly(p-phenylene oxide), a copolymer thereof and a mixture thereof.

14. The cellulosic composite of claim 13, wherein the at least one thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene, a copolymer thereof and a mixture thereof, preferably polypropylene or a copolymer thereof.

15. The cellulosic composite of any one of claims 1 to 14, wherein the cellulosic composite comprises at least 20 weight-% and up to 50 weight-% of the at least one thermoplastic polymer, preferably at least 25 weight-% and up to 45 weight-% of the at least one thermoplastic polymer, and more preferably at least 30 weight-% and up to 40 weight-% of the at least one thermoplastic polymer.

16. The cellulosic composite of any one of claims 1 to 15, further comprising at least one coupling agent, preferably selected from the group consisting of maleic anhydride, such as maleic anhydride grafted polymers, a silane, a siloxane, and a mixture thereof, more preferably maleic anhydride, such as maleic anhydride grafted polymers.

17. The cellulosic composite of claim 16, wherein the cellulosic composite comprises at least 0.5 weight-% and up to 5 weight-% of the at least one coupling agent, preferably at least 1 weight-% and up to 5 weight-% of the at least one coupling agent, and more preferably at least 1.5 weight-% and up to 3 weight-% of the at least one coupling agent.

18. The cellulosic composite of any one of claims 1 to 17, further comprising at least one additive, preferably selected from the group consisting of a lubricant, a colorant, a pigment, a filler, an acid scavenger, an antioxidant, a light stabilizer, a blowing agent, a UV-stabilizer, a flame retardant, a heat stabilizer, an antistatic agent, and a foaming additive.

19. A composite granulate (20) made of a cellulosic composite of any one of claims 1 to

20. A composite article (30) obtainable by injection molding composite granulates (20) of claim

21. A method of producing a composite article (30), the method comprising injection molding composite granulates (20) of claim 19 to produce the composite article (30).

22. A method of producing a cellulosic composite comprising cellulose and/or lignocellulose ﬁbers, at least one thermoplastic elastomer, and at least one thermoplastic polymer, the method comprises melt processing a mixture comprising the at least one thermoplastic elastomer, the at least onethermoplastic polymer and a mixture of elongated cellulose and/or Iignocellulose ﬁbers having an average elongation equal to or lower than 0.300 and rounded cellulose and/or Iignocellulose fibers having an average elongation equal to or higher than 0.

23. The method of claim 22, wherein melt processing the mixture comprises: melting the at least one thermoplastic elastomer and the at least one thermoplastic polymer; and adding the cellulose and/or Iignocellulose ﬁbers to the melted at least one thermoplastic elastomer and the melted at least one thermoplastic polymer.