木材保护与改性4woodfireretarda.ppt

Chapter 4 Chemistry of fire retardancy,4.1 Preface 4.2 The chemistry of pyrolysis and combustion 4.3 Mechanisms of fire retardancy 4.4 Fire-retardant formulations 4.5 Future researches,4.1 Preface,Wood and its products are closely related to peoples lives. More and more people like to decorate their room with wood, and woody buildings draw more and more attentions. But as we known wood are combustible materials, which not only threat to peoples lives and possessions, but also limited their application areas. With the increase of high buildings and large mansions, fire becomes the main trouble needing to be solved.,indoor decoration, building, gardening, and so on,The charming wood,in,The modern wooden building is very popular in most of the countries.,In 2000, 90 percent of the American new villa(别墅) was built up of wood. And Among the 330,000 high rise residences, 275,000 was built up of wood.,In Canada, wood industry is the mainstay industry, the techniques of manufacture and installation are quite mature.,At present, more than half of the new houses in Japan are built up of wood or wood products.,Except for wooden houses, most of the public buildings such as factory, school, hotel , gymnasium and so on are built up of wood or wood products.,will you believe that wooden building can grow up in China in the future?,The chief criminal of fire,Wood,Wood is the criminal of fire.,Wooden building should be limited or discarded.,Is it right?,Its a false and unadvisable idea. why?,Wood,Steel,cement,plastic,the extensively applied materials,the only renewable material,In fact, wood especially large scale of wooden products are fireproof material. Why? P108,In our mind, reinforced concrete is a kind of fireproof material, and strong enough to resist violent collision(猛烈撞击). But reinforced concrete has a mortal defect(致命的缺点).,Would you tell me whats the fatal defect to reinforced concrete at higher temperature ?,Reinforced concrete turns soft when undergoing high temperature. Normally, the strength of steel reduces by half when the temperature exceeded 300C, and falls down when the temperature exceeded 500C. Therefore, fire retarding is of the utmost importance.,Coffer (or safe)保险柜: 制作材料？ 金属 金属和木（竹）材 其它,1.Is it necessary to preventing wood from fire, why? 2.According to your opinion, which kind of wood (assorted by their application areas) should be protected from fire? 3.From the pictures above, please tell me the most serious threats in a fire.,Questions,4.2 The chemistry of pyrolysis and combustion,Including four stages:,(1) The temperature of wood is improved under the heat.,(2) Wood gradually degrades and pyrolyzes, the following material produces: CO2, CO, CH4, CH2=CH2, R-CHO, R-CO, and so on,Tar (including phenol(酚类),aldehyde(醛类), carbonyl chemicals(羰基化合物),Flammable gases,heat,Low molecular chemicals And flammable gases,(3) Flammable gases,heat,Catch fire and combustion,There are four necessary conditions for the flammable combustion of wood: combustible gases, heat, oxygen and radical groups。,(4) Combustion continues,Heat conducts to the adjacent wood,Combustion provide large amount of heat,Wood temperature improved,Pyrolysis begins, then ignition, combustion, fire spread, and so on,Large amount of smoke also produced during the combustion of wood, the composition of the smoke is listed in the follows:,Combustible gases: CO, CH4, H2, CH2=CH2, R-CHO, R-CO, and so on,Noncombustible gases: CO2, H2O,Tar: phenol, aldehyde(醛类), carbonyl chemicals,Charcoal: combustible residue.,Pyroligneous acid(木醋液): mainly formic acid(蚁酸) or acetic acid(乙酸),Some terms of combustion,Flame combustion(有焰燃烧)： luminous burning at the gas state. 木材进行发光的气相燃烧。,Smoulding(有焰燃烧)： nonluminous burning with smog. 木材燃烧时处于一种无可见光而有烟雾的燃烧。,Flameless combustion(红热燃烧)：aphlogistic(无焰) combustion at a solid state. 木材处于固相状态 而没有火焰的燃烧，也叫无焰燃烧。,4.3 Mechanisms of fire retardancy,Prevent the escape of volatile products by forming a glassy barrier. Prevents oxygen from reaching the substrate Insulates the wood surface from high temperatures,(1) Barrier theories(障碍理论),(2) Thermal theories(热理论),Fire-retardants may increase the thermal conductivity of wood to dissipate the heat from the surface faster than it is supplied by the igniting source; Affect chemical and physical changes so that the heat is absorbed by the chemical. For example :chemicals content crystal water.,(3) Dilution by noncombustible gases theories(不燃气体稀释理论),Noncombustible gases released by the decomposition of the fire-retardant Chemicals, which dilute the combustion gases, and form a non flammable Gaseous mixture.,(4) Free radical trap theories(自由基捕集理论),Fire-retardant chemicals release free radical inhibitors at pyrolytic temperatures that interrupt the chain propagation mechanism of flammability.,CO，CO2，H2O，HO和其它成分(1) HO十COCO2+H (2) H十O2HO十O (3) O+ H2HO+ H,(5) Increased charcoal/reduced volatiles theories(炭量增加/挥发性气体减少理论)书上P118反应式,Fire-retardant chemicals lower the temperature at which pyrolysis occurs, directing the degradation pathway toward more charcoal production and fewer volatiles.,(6) Reduce heat content of volatiles theories(挥发物热含量下降理论),This step is closely related with theories (5), that is theories (5)and (6) function together, resulting in more char, fewer volatiles and lower heat content of volatiles.,4.4 Protection of wood with fire-retardant,4.4.1 Treating methods 4.4.2 wood fire retardant,4.4.1 Treating methods,Physical methods,Reduce the ratio of combustible material by mixing wood with Noncombustible materials. For example: board made up of wood and cement, or fiberglass（玻璃纤维）, plaster（石膏） or asbestus（石棉）.,Cover the surface of wood with metal board or fireproof board.,Chemical methods:,The application of fire retardant.,Impregnate into the wood,Applied as paint or surface coatings,Two classes,Both of the two chemical methods have virtues and defects.,4.4.2 wood fire retardant,木材阻燃剂应该满足一定条件。P109,(1) Phosphors and its combinations（磷及其化合物）,Fire resistance of Phosphors and its combinations are showed in the follows:,Reduce the temperature of pyrolysis;,Increase the production of char;,Reduce the production of combustible gases；,Dilute the combustible gases,Monoammonium and diammonium phosphates(磷酸一铵盐和二铵盐) have been the most effective fire retardants. Organophosphorus and polyphosphate compounds (有机磷酸盐及聚磷酸复合物)are also effective.,X(NH4)2HPO4 (HPO3)x + 2xNH3+ xH2O,(HPO3)x is polyphosphate(聚磷酸)， which acts as a strong dehydrate agent at higher temperature. Then hastens the forming of char, which protect the inner wood from fire.,The efficiency of phosphorus compounds can be increased by the presence of other compounds such as nitrogen compounds that produce a synergistic effect（协同效应）P110.,P,N,synergistically,B,Br,抑制表面燃烧,The most effective fire retardants of phosphorus are the follows:,Phosphoric acid and urea （磷酸合尿素）,Phosphoric acid and diammonium phosphates（磷酸和磷酸氢二铵）,Phosphoric acid and melamine（磷酸和三聚氢胺）,(2) Halogen and its combinations（卤素及其化合物）,Mechanisms,halogen hydride（卤化氢） can dilute the combustible gases.,At higher temperature, halogen escaped from the wood and Cover the surface of wood for their high molecular weight.,Halogen can capture radicals from combustible materials and reduce the concentrations of radicals,Defects of halogen fire retardants: moisture absorption、二噁英,Halogen applied in fire retardants:,NH4Cl，NH4Br，AlCl36H2O，CaCl22H2O，ZnCl2,(3) Boron（硼）,Borax and boric acid（硼砂、硼酸）, the primary fire-retardant compounds, have low melting points and form glassy films on exposure to high temperature.,Borax and boric acid are always used together.,Defects of boron compounds,Lower solubility;,Easy to leach from wood and move to the surface, which influence the gluing, painting and other subsequent process.,(4) Leach-resistant fire-retardants,Insoluble metallic salt complexes(不溶的金属盐络合物),Others,Amino-resins(氨基树脂):,UDFP阻燃剂：37%甲醛溶液调pH至8，加热至80 加入尿素和双氰胺混合液溶解后冷却冷却到35 时，慢慢加入磷酸得清亮阻燃剂溶液。,DBP阻燃剂：双氰胺、磷酸、硼酸制成。,FRW阻燃剂：高纯度磷酸脒基脲（GUP）、硼酸和少量助剂制成。,Examples,4.5 Future researches,Leach-resistant compounds Improved fire-retardant treatments for panel products Effective coating systems Reduced smoke and toxicity Basic mechanisms,4.6 Test methods,概 念,点燃温度（Ignition Temperature） ： 也称燃点温度。在规定的实验条件下，从材料中释放出的可燃性气体经外火焰点燃并燃烧一定时间的最低温度及氧指数。一般木材的点燃温度为220-290； 氧指数（Critical Oxygen Index ）：在规定的实验条件下，试样在氮氧气流中，维持平稳燃烧所需最低氧气浓度。木材的氧指数为27-30%。 火焰传播指数（Flame spread index） ：指外火焰将材料一端点燃一定时间，火焰沿材料表面的蔓延速度与某种不燃材料、某种可燃材料表面或蔓延速度（标准样品）比较。 燃烧热值：材料燃烧时释放的热量。一般木材的燃烧值为17.6-20.0 MJ/kg。 发烟等级： 材料燃烧时产生的烟雾对光遮蔽或光衰减程度所分的等级。 一般木材的发言等级为1-2级。,Critical Oxygen Index (极限氧指数) Test,The oxygen index test measures the minimum concentration of oxygen in an oxygen-nitrogen mixture that will just support flaming combustion of a test specimen. Highly flammable materials have a low oxygen index, and less flammable materials have high values 。,氧指数代表材料的难燃性，其值越高，表明材料被点着所需的氧气越多，即越难点着。 测定氧指数对实验室筛选阻燃配方、初步确定材料的燃烧性能是一种简便、易行、重复性好的方法。国内标准：GB/T 2406-93。国外相同的标准有：ISO4589.3、美国材料学会标准、ASTM D2863、日本标准JIS D1201等。,There are several ways to test the efficiency of a fire retardant. The most common is to run TGA. TGA involves weighing a finely ground sample and exposing it to a heated chamber in the presence of nitrogen.,Thermogravimetric Analysis (TGA),DTA measures the amount of heat liberated or absorbed by a wood sample as it moves from one physical (transition state to another (such as melting or vaporization) or when it undergoes any chemical reaction. This heat is determined by measuring the temperature differences between the sample and an inert reference. DTA can be used to measure heat capacity (热容), provide kinetic data, and give information on transition temperatures.,Differential Thermal Analysis (DTA),Differential Scanning Calorimetry (DSC),DSC is similar to DTA, except the actual differential heat flow is measured when the sample and reference temperature are equal. I