Poaceae fibres and building products

A dry binder mix which is ready to use after addition of water, said mix comprising at least (A) a silicon containing hydraulic binder and (B) chemically modified unpyrolyzed ageing resistant fibers selected from the group consisting of Miscanthus species, Pennisetum species, Zea species and mixtures thereof, said ageing resistant fibers having a length comprised between 2 and 100 mm, said ageing resistant fibers having a water content of less than 20% by weight, said ageing resistant fibers having a coating obtained by contacting initial fibers with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibers contacted with said treating aqueous dispersion;

• whereby said coating of said ageing resistant fibers comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibers and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibers keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibers after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K20 weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%.

A building product comprising at least a part or layer comprising a hardened silicon containing hydraulic binder containing chemically modified unpyrolyzed ageing resistant fibers selected from the group consisting of Miscanthus like species, Pennisetum species, Zea species and mixtures thereof,

• wherein said ageing resistant fibers having a length comprised between 2 mm and 100 mm, said ageing resistant fibers having a water content of less than 20% by weight, said ageing resistant fibers having a coating obtained by contacting initial fibers with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibers contacted with said treating aqueous dispersion;
• whereby said coating of said ageing resistant fibers comprises at least (a) aminosilane bound to silicon atoms present in the fibers and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of said surface treating mixture is comprised between 5:1 and 20:1, the said ageing resistant fibers keeping during a storage period for 6 months
• in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibers after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K20 weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%.

A method for the preparation of a building product, said method comprising at least the steps of:

• (1) mixing together at least
• (A) chemically modified unpyrolyzed ageing resistant fibers selected from the group consisting of Miscanthus species, Pennisetum species, Zea species and mixtures thereof, said ageing resistant fibers having a length comprised between 2 and 100 mm, said ageing resistant fibers having a water content of less than 20% by weight, said ageing resistant fibers having a coating obtained by contacting initial fibers with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibers contacted with said treating aqueous dispersion;
• whereby said coating of said ageing resistant fibers comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibers and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of said surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibers keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibers after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K2O weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%,
• (B) a hardenable calcium containing hydraulic binder, and
• (C) water,
• to form a hardenable fibers containing mixture;
• and
• (2) hardening said hardenable fibers containing mixture at a temperature greater than 20° C.

A method for preparation of chemically modified unpyrolyzed ageing resistant fibers selected from the group consisting of Miscanthus species, Pennisetum species, Zea species and mixtures thereof, said ageing resistant fibers having a length comprised of between 2 mm and 100 mm, said ageing resistant fibers having a water content of less than 20% by weight, said ageing resistant fibers having a coating obtained by contacting initial fibers with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibers contacted with said treating aqueous dispersion down to a water content of less than 20% by weight;

• whereby said coating of said ageing resistant the fibers comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibers and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibers keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibers after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K20 weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%,
• said method comprising at least the following steps:
• determining, after complete burning at 600° C., an average SiO2 content of the ash of at least one sample of fresh fibers containing plant parts from plants selected from the group consisting of Miscanthus species, Pennisetum species, Zea species and mixtures thereof, intended to be harvested,
• in case the determined average SiO2 content of said ash of said at least one sample of fresh fibers containing plant parts from plants selected from the group consisting of Miscanthus species, Pennisetum species, Zea species and mixtures thereof, is greater than 30% by weight, harvesting fresh fibers containing plant parts;
• cutting said fresh fibers containing plant parts into plant fibers with a length comprised between 2 mm and 100 mm;
• drying said cut plant fibers at a temperature of less than 75° C., so as to obtain dried plant fibers with a water content of less than 20% by weight;
• treating said dried plant fibers with an aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising OH terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, an aminosilane coupling agent, and a polyethylene glycolether, in which the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1, so as to obtain humid coated plant fibers;
• drying of said humid coated plant fibers for obtaining said ageing resistant fibers with a water content of less than 20% by weight.