3D printing, more formally known as Additive Manufacturing (AM), is already being adopted for rapid prototyping and soon rapid manufacturing. This review provides a brief discussion about AM and also the most employed AM technologies for polymers. The commonly-used ASTM and ISO mechanical test standards which have been used by various research groups to test the strength of the 3D-printed parts have been reported. Also, a summary of an exhaustive amount of literature regarding the mechanical properties of 3D-printed parts is included, specifically, properties under different loading types such as tensile, bending, compressive, fatigue, impact and others. Properties at low temperatures have also been discussed. Further, the effects of fillers as well as post-processing on the mechanical properties have also been discussed. Lastly, several important questions to consider in the standardization of mechanical test methods have been raised.

Mechanical characterization of 3D-printed polymers

Materials for additive manufacturing

The field of 3D printing is continuing its rapid development in both academic and industrial research environments. The development of 3D printing technologies has opened new implementations in rapid prototyping, tooling, dentistry, microfluidics, biomedical devices, tissue engineering, drug delivery, etc. Among different 3D printing techniques, photopolymerization-based process (such as stereolithography and digital light processing) offers flexibility over the final properties of the 3D printed materials (such as optical, chemical, and mechanical properties) using versatile polymer chemistry. The strategy behind the 3D photopolymerization is based on using monomers/oligomers in liquid state (in the presence of photoinitiators) that can be photopolymerized (via radical or cationic mechanism) upon exposure to light source of different wavelengths (depending on the photoinitiator system). An overview of recent evolutions in the field of photopolymerization-based 3D printing and highlights of novel 3D print...

Photopolymerization in 3D Printing

Isolation of thermally stable cellulose nanocrystals by phosphoric acid hydrolysis.

Mechanical and thermal properties of ABS/montmorillonite nanocomposites for fused deposition modeling 3D printing

We report on the mechanical properties of optically curable stereolithographic resins (SLRs) which were reinforced through the addition of small amounts of cellulose nanocrystals (CNCs). The resin/filler mixtures are readily accessible via simple mixing processes. A detailed rheological investigation of such mixtures and the successful processing of these materials on a commercial SLR machine show that at low filler concentrations (below 5%) the processability of the materials is barely impacted. The storage modulus, E′, increased steadily with increasing CNC content in the regimes below and above the glass transition. A remarkable modulus enhancement was observed in the rubbery regime, where E′ increased by 166, 233, and 587% for CNC/SLR nanocomposites with 0.5, 1.0, and 5.0% w/w CNC, respectively. The modulus increase was less pronounced in the glassy state, where E′ increased by 21, 32 and 57%, for the same compositions. The increase in tensile strength was of similar magnitude. In comparison to previo...

Reinforcement of Stereolithographic Resins for Rapid Prototyping with Cellulose Nanocrystals

The invention relates to moulded ophthalmic articles, especially contact lenses, which are obtainable by cross-linking a prepolymer which is the copolymerisation product of (a) at least one polyalkylene glycol of the formula (1): HO-(CH2-CH2-O)n-(CHY1-CHY2-O)m-(CHY3-CHY4-O)p-H or (1'): HO-[(CH2-CH2-CH2-CH2-O-)]q-H, (b) at least one polyhydroxy compound selected from the group consisting of (i) a linear or branched aliphatic polyhydroxy compound of the formula (2): R1-(OH-)x or a polyether polyol or polyester polyol derived therefrom, and (ii) a cycloaliphatic polyol selected from the group polyhydroxy-C5-C8-cycloalkane and unsubstituted mono- or disaccharide, (c) at least one di- or polyisocyanate of the formula (3): R2-(NCO)y, (d) at least one ethylenically unsaturated monoisocyanate of formula (4), or an ethylenically unsaturated acid halide of formula (4'), and optionally further copolymerisable monomers, wherein the variables have the significances given in the claims, in the absence or presence of an additional vinylic comonomer.

Moulded ophthalmic article

The invention relates to compounds having at least one vinyl ether group which also contain in the molecule at least one further functional group selected from acrylate, methacrylate, epoxy, alkenyl, cycloalkenyl and vinylaryl groups, to compositions, especially for stereolithography, comprising those vinyl ether compounds, and to a method of producing three-dimensional objects using those compositions.

Vinyl ether compounds having additional functional groups other than vinyl ether groups and the use thereof in the formulation of curable compositions

Liquid radiation-curable formulation, in particular for stereolithography, based on at least one compound that contains free radically polymerisable groups, and at least one photoinitiator suitable for the polymerisation, which formulation additionally contains a polyoxyalkylene-polysiloxane block copolymer that is selected from copolymers of the chemical formulae R.sup.1 --(OC.sub.c H.sub.2c).sub.d --{[T]--(C.sub.c H.sub.2c O).sub.d-1 --(C c H 2c )} g --OR 1 (I) ##STR1## wherein: R 1 is a hydrogen atom or a C 1 -C 8 alkyl group; R 2 is a methyl or phenyl group; [T] is a polysiloxane group [PS] terminated as described in the specification in more detail; [PS] is the group of formula ##STR2## and [Alk] is an alkylene group of 3 to 10 carbon atoms, as well as novel block copolymers of formulae (I) and (II). The cured formulations have, inter alia, superior impact strength.

Liquid radiation-curable formulation, in particular for use in stereolithography

A liquid, radiation-curable composition which in addition to a liquid, free-radically polymerizable component comprises at least the following additional components: (A) from 40 to 80 per cent by weight of a liquid difunctional or more highly functional epoxy resin or of a liquid mixture consisting of difunctional or more highly functional epoxy resins; (B) from 0.1 to 10 per cent by weight of a cationic photoinitiator or of a mixture of cationic photoinitiators; and (C) from 0.1 to 10 per cent by weight of a free-radical photoinitiator or of a mixture of free-radical photoinitiators; and (D) up to 40 per cent by weight of a hydroxy compound, in which composition component (D) is selected from the group consisting of: (D1) phenolic compounds having at least 2 hydroxyl groups, (D2) phenolic compounds having at least 2 hydroxyl groups, which are reacted with ethylene oxide, proplyene oxide or with ethylene oxide and propylene oxide, (D3) aliphatic hydroxy compounds having not more than 80 carbon atoms, (D4) compounds having at least one hydroxyl group and at least one epoxide group, and (D5) a mixture of at least 2 of the compounds mentioned under (D1) to (D4), and component (D) is present in the compositions in a quantity of at least 2 per cent by weight; the free-radically polymerizable component comprises at least (E) from 4 to 30 per cent by weight of at least one liquid poly(meth)acrylate having a (meth)acrylate functionality of more than 2; and at least one of components (A) and (D) comprises substances which have aromatic carbon rings in their molecule, is particularly suitable for stereolithography, a particular feature of this composition being that it leads to cured material which exhibits only a very low propensity for uptake of water.

Bettina Steinmann

Papers

Reinforcement of Stereolithographic Resins for Rapid Prototyping with Cellulose Nanocrystals

Moulded ophthalmic article

Vinyl ether compounds having additional functional groups other than vinyl ether groups and the use thereof in the formulation of curable compositions

Liquid radiation-curable formulation, in particular for use in stereolithography

Liquid, radiation-curable composition, especially for stereolithography